U.S. patent application number 12/658343 was filed with the patent office on 2010-06-10 for liquid phase diffusion bonding method of metal machine part and such metal machine part.
This patent application is currently assigned to Nippon Steel Corporation. Invention is credited to Yasushi Hasegawa, Ryuichi Honma, Yutaka Takagi.
Application Number | 20100143747 12/658343 |
Document ID | / |
Family ID | 33493936 |
Filed Date | 2010-06-10 |
United States Patent
Application |
20100143747 |
Kind Code |
A1 |
Hasegawa; Yasushi ; et
al. |
June 10, 2010 |
Liquid phase diffusion bonding method of metal machine part and
such metal machine part
Abstract
A liquid phase diffusion bonding method for a metal machine part
superior in the quality of the joint and the productivity enabling
the bonding time to be shortened, achieving homogenization of the
bonding structure and improving the tensile strength, fatigue
strength, and joint quality and reliability. This liquid phase
diffusion bonding method of a metal machine part is characterized
interposing an amorphous alloy foil for liquid phase diffusion
bonding at bevel faces of metal materials, performing primary
bonding by melt bonding said amorphous alloy foil and said metal
material by resistance welding to form a joint, then performing
secondary bonding by liquid phase diffusion bonding by reheating
said joint to at least the melting point of said amorphous alloy
foil, then holding it there to complete the solidification process
of said joint.
Inventors: |
Hasegawa; Yasushi;
(Futtsu-shi, JP) ; Honma; Ryuichi; (Futtsu-shi,
JP) ; Takagi; Yutaka; (Hashima-shi, JP) |
Correspondence
Address: |
KENYON & KENYON LLP
ONE BROADWAY
NEW YORK
NY
10004
US
|
Assignee: |
Nippon Steel Corporation
Tokyo
JP
|
Family ID: |
33493936 |
Appl. No.: |
12/658343 |
Filed: |
February 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10559040 |
Nov 29, 2005 |
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PCT/JP2004/008011 |
Jun 2, 2004 |
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12658343 |
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Current U.S.
Class: |
428/680 ;
428/615; 428/681 |
Current CPC
Class: |
B23K 20/16 20130101;
B23K 20/023 20130101; C22C 14/00 20130101; F01L 2301/00 20200501;
B23K 2101/006 20180801; B23K 2101/06 20180801; F01L 1/047 20130101;
F01L 2303/00 20200501; C22C 19/03 20130101; C22C 19/058 20130101;
C22C 38/22 20130101; B23K 2103/04 20180801; Y10T 428/12951
20150115; B23K 20/24 20130101; B23K 28/02 20130101; B23K 11/0033
20130101; C22C 38/02 20130101; Y10T 428/12944 20150115; B23K 20/22
20130101; B23K 2101/04 20180801; B23K 2101/005 20180801; Y10T
428/12493 20150115; C22C 38/001 20130101; B23K 20/227 20130101;
C22C 38/12 20130101 |
Class at
Publication: |
428/680 ;
428/615; 428/681 |
International
Class: |
B32B 15/01 20060101
B32B015/01 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 2, 2003 |
JP |
2003-156602 |
Apr 13, 2004 |
JP |
2004-118069 |
May 19, 2004 |
JP |
2004-149581 |
Claims
1-14. (canceled)
15. A bonded metal material comprising a first metal material and a
second metal material, said bonded metal material being produced by
a method comprising: (a) melt bonding said first metal material to
said second metal material to form a joint, wherein a bonding face
of said first metal material forms a V-bevel which contacts a
non-beveled bonding face of said second metal material at bevel tip
through an amorphous alloy foil for liquid phase diffusion bonding,
and wherein said melt bonding comprises (i) passing an electrical
current across said first and second metal materials through said
bevel tip and said amorphous alloy foil to heat said bevel and said
amorphous alloy foil and (ii) applying a pressing stress such that
said bevel and said amorphous alloy foil are melted and said bevel
is collapsed to form said joint; and (b) reheating said joint to at
least the melting point of said amorphous alloy foil, and allowing
an isothermal solidification process of said joint to complete.
16. The bonded metal material of claim 15, wherein the composition
of said amorphous alloy foil is Ni or Fe as a base and, as
diffusion atoms, one or more of B, P, and C in amounts of 0.1 to
20.0 at % and further V in 0.1 to 10.0 at %.
17. The bonded metal material of claim 15, wherein said joint
produced in step (a) comprises an incomplete isothermal
solidification structure of an average thickness of not more than
10 .mu.m formed from said amorphous alloy foil.
18. The bonded metal material of claim 15, wherein said step (b) is
carried out without applying an external pressure to said metal
materials.
19. The bonded metal material of claim 15, wherein said melt
bonding is carried out by resistance welding.
20. A machine part produced by a method comprising interposing an
amorphous alloy foil for liquid phase diffusion bonding between a
first bonding face of a first metal material and a non-beveled
bonding face of a second metal material, wherein said first bonding
face of said first metal material forms a V-bevel which contacts
said non-beveled bonding face of said second metal material at the
tip of the bevel through said amorphous alloy foil, performing
primary bonding by melt bonding said amorphous alloy foil and said
first and second metal materials to form a joint, wherein said
primary bonding comprises (i) passing an electrical current across
said first and second metal materials through said contact bevel
tip and said amorphous alloy foil to heat said V-bevel and said
amorphous alloy foil and (ii) applying a pressing stress such that
said V-bevel and said amorphous alloy foil are melted and said
V-bevel is collapsed to form said joint, then performing secondary
bonding by reheating said joint to at least the melting point of
said amorphous alloy foil, and allowing an isothermal
solidification process of said joint to complete.
21. The machine part of claim 20, wherein the composition of said
amorphous alloy foil is Ni or Fe as a base and, as diffusion atoms,
one or more of B, P, and C in amounts of 0.1 to 20.0 at % and
further V in 0.1 to 10.0 at %.
22. The machine part of claim 20, wherein said joint produced in
said primary bonding step comprises an incomplete isothermal
solidification structure of an average thickness of not more than
10 .mu.m formed from said amorphous alloy foil.
23. The machine part of claim 20, wherein said secondary bonding is
carried out without applying an external pressure to said metal
materials.
24. The machine part of claim 20, wherein said primary bonding is
carried out by resistance welding.
25. A machine part produced by a method comprising interposing an
amorphous alloy foil for liquid phase diffusion bonding between
metal materials including at bevel faces of at least one metal
material of metal materials to be bonded, performing primary
bonding by melt bonding said amorphous alloy foil and said metal
materials by resistance welding to form a joint, wherein said
resistance welding melts said amorphous metal foil and said bevel
faces of said at least one metal material, then performing
secondary bonding by liquid phase diffusion bonding by reheating
said joint to at least the melting point of said amorphous alloy
foil, then holding it there to complete an isothermal
solidification process of said joint; wherein said at least one of
said metal materials is a cylindrical metal material and a V-bevel
is formed at an end of said cylindrical metal material so that,
when bringing the end of said cylindrical metal material into
abutment with the surface of another metal material for primary
bonding, an inner surface bevel height A and an outer surface bevel
height B of said cylindrical metal material with respect to the
abutting contact point and a distance C from said abutting contact
point to the outer circumference satisfy the following relation
(1): 0.2.ltoreq.B/A.ltoreq.1 and C/t.ltoreq.0.5 (1) where A is an
inner surface bevel height of said cylindrical metal material, B is
an outer surface bevel height of said cylindrical metal material, C
is a distance from an abutting contact point of the cylindrical
metal material to the outer circumference, and t is the thickness
of the cylindrical metal material; and wherein a maximum residual
height of the bevel ends after said primary bonding is not more
than three times the thickness of said amorphous alloy foil.
26. The machine part of claim 25, characterized in that a maximum
residual height of the bevel ends after said secondary bonding is
not more than 70 .mu.m.
27. A joint comprising a first metal material, a second metal
material, and an amorphous alloy foil, characterized in that said
amorphous alloy foil is dissolved in said first and said second
metal materials to form a homogenous mixture.
28. The joint of claim 27, wherein said amorphous alloy foil is Ni
or Fe based and, as diffusion atoms, one or more of B, P, and C in
amounts of 0.1 to 20.0 at % and further V in 0.1 to 10.0 at %.
29. The joint of claim 28, wherein said alloy foil is Ni based, and
said joint is homogenous in Ni.
30. A joint comprising a first metal material, a second metal
material, and an amorphous alloy interposed between said first and
second metal materials, wherein said amorphous alloy foil forms an
incomplete isothermal solidification structure of an average
thickness of not more than 10 .mu.m.
31. The joint of claim 29, wherein said incomplete isothermal
solidification structure has an average thickness of not more than
3 .mu.m.
32. A joint assembly for melt bonding and liquid phase diffusion
bonding, comprising a first metal material, a second metal material
forming a V-bevel, and an amorphous alloy foil, wherein said second
metal material contacts said first metal material at the tip of
said V-bevel through said amorphous alloy foil.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of production of a
metal machine part and to such a metal machine part, more
particularly relates to liquid phase diffusion bonding method of a
metal machine part used for an auto part etc. and to such a metal
machine part.
BACKGROUND ART
[0002] In the past, as the methods of bonding metal materials with
each other, welding methods had mainly been used. In recent years,
however, use of the liquid phase diffusion bonding method as new
industrial bonding technology for replacing this has been
spreading.
[0003] The liquid phase diffusion bonding method is the technology
of interposing between bonding faces of bonded materials, that is,
the bevel faces, an amorphous alloy foil with a melting point lower
than the bonded materials, specifically a multimetal alloy foil
having at least 50% of its crystal structure amorphous, containing
an element having the ability to form a bonded joint through a
diffusion-limited isothermal solidification process, for example, B
or P, and comprising a base material of Ni or Fe, then heating and
holding the joint at a temperature of at least the melting point of
this amorphous alloy foil so as to form a joint by an isothermal
solidification process.
[0004] This liquid phase diffusion bonding method enables bonding
with lower heat input compared with ordinary welding methods, so is
characterized in that almost no residual stress of the weld occurs
along with heat expansion and contraction and no excessive buildup
of the weld such as with welding methods occurs, so the bond
surface is smooth and a precision bonded joint can be formed.
[0005] In particular, since liquid phase diffusion bonding is
facial bonding, the bonding time does not depend on the area of the
bonding faces and is constant. Further, the bonding is completed in
a relatively short time. From these viewpoints, this is bonding
technology of a concept completely different from the conventional
welding methods. Therefore, there is the advantage that if a joint
can be held for a predetermined time at a temperature of at least
the melting point of the amorphous alloy foil inserted between the
bevel faces of the bonded materials, bonding between the surfaces
can be realized without having to select the bevel shape.
[0006] The applicant has already proposed a method for producing a
metal machine part provided with a pipeline inside it using this
liquid phase diffusion bonding method in Japanese Unexamined Patent
Publication (Kokai) No. 2003-181651 and Japanese Unexamined Patent
Publication (Kokai)' No. 2001-321963.
[0007] However, the liquid phase diffusion bonding disclosed in
these patent publications enables the bonding time to be made a
relatively short time, but the isothermal solidification proceeds
limited by diffusion. In so far as this is the case, in order for
diffusion atoms in the amorphous alloy foil to diffuse and disperse
in an amount sufficient for raising the melting point of the joint,
when using an amorphous alloy foil of a thickness of 10 .mu.m, it
is necessary to isothermally hold the foil at about 900 to
1300.degree. C., corresponding to a temperature of at least the
melting point of the alloy foil, for at least about 60 seconds.
[0008] By making the amorphous alloy foil used for the liquid phase
diffusion bonding thinner, the bonding time can be shortened to a
certain extent, but the effect of the precision of working of the
bevel faces of the bonded materials on bonding defects and the
deterioration of the joint strength becomes greater, so there are
also limits to the reduction in thickness of the alloy foil. In
actuality, the concentration of the diffusion atoms is raised in
order to lower the melting point of the bonding foil or the
chemical composition of the bonded materials is relied upon to
induce melting of the parent material at the time of bonding. As a
result, the actual thickness of the bonding alloy foil quite often
exceeds 50 .mu.m.
[0009] Further, even if raising the pressing stress in liquid phase
diffusion bonding, while it is possible to shorten the bonding time
to a certain extent, raising the pressing stress makes the bonded
materials more susceptible to buckling deformation, so there are
limits to increasing the pressing stress.
[0010] Accordingly, in the methods for producing metal machine
parts using liquid phase diffusion bonding disclosed in Japanese
Unexamined Patent Publication (Kokai) No. 2003-181651 and Japanese
Unexamined Patent Publication (Kokai) No. 2001-321963, improving
the productivity of the metal machine parts and reducing the
production costs by shortening the bonding time while maintaining
the joint quality in liquid phase diffusion bonding has become an
issue in the industry.
[0011] On the other hand, electrical resistance welding is known as
a bonding technique frequently used for bonding metal machine parts
in the past.
[0012] Electrical resistance welding is a method of utilizing the
heat of resistance produced by passing a current through metal,
giving a large current to make the bevels of the bonded materials
instantaneously melt, and pressing the bevels to form a bonded
joint.
[0013] For example, when melt bonding a thermocouple to a measured
object for measurement of its temperature, bonding steel plate to a
frame member of an automobile, and in other cases where the
relative bonding area is small and a high bonding strength is not
required, spot welding, projection welding, upset welding, and
other electrical resistance welding methods are frequently used as
simplified bonding methods. Conversely, when bonding large bevels
with relatively large bonding areas, flash pad welding and
continuous electrical resistance welding able to apply a large
current and a high pressing force are utilized--such as for seam
welding of metal pipe.
[0014] However, when using these resistance welding methods to
produce metal machine parts, sometimes fluctuations in the bonding
conditions will cause for example bonding defects due to residual
oxide-based inclusions at the bonds or insufficient welding current
will cause so-called "cold welding" or welding defects due to
insufficient melting. Further, the pressing at the time of bonding
causes large deformation to occur, fine cracks occur at the welded
parts, and the bevel ends remain unbonded, which become causes of a
reduction in joint performance, particularly fatigue strength. In
particular, when at least one bonded material is a cylindrical
metal material, the drop in the joint fatigue strength tends to
become remarkable. As measures against this, in the past, for
example, changes in the material design or post-processing for
improving the shape of the weld was required and there were
problems such as the limitations on the freedom of the joint
design, increase of costs, etc.
[0015] In addition to this, in resistance welding, sometimes the
weld width is extremely narrow and bevel deformation occurs, so
quality assurance by nondestructive testing was difficult. Due to
this and other reasons, improvement of the bonding quality in
resistance welding in bonding joints where reliability is
particularly required is an issue in industrial technology.
[0016] Further, Japanese Unexamined Patent Publication (Kokai) No.
11-90619, Japanese Unexamined Patent Publication (Kokai) No.
11-90620, and Japanese Unexamined Patent Publication (Kokai) No.
11-90621 disclose a method and apparatus for bonding metal members
making joint use of liquid phase diffusion bonding and conduction
type resistance welding in the bonding of Al-based cylinder head
members and Fe-based valve seats, but in each case the technique is
just simple primary bonding resistance welding with the
interposition of a brazing material.
[0017] That is, no isothermal solidification diffusion treatment is
being performed to convert the incomplete isothermal solidification
structures of the resistance welds occurring in primary bonding in
the methods disclosed in the above patent publications to liquid
phase diffusion bonding structures, so it is difficult to
sufficient raise the quality of the bonds.
[0018] Further, in the above art, a brazing material is pressed out
until becoming extremely thin. The steps up to this are treated as
part of the production process. Therefore, homogenization of the
bond structure is not being considered. Further, these disclosed
art are technologies for forming joints for heterogeneous bonding
of nonferrous metals such as Al. There is no description at all
regarding the bonding of ferrous materials, in particular iron base
materials. Of course, ordinary welding can be used for iron base
materials and use of ordinary welding technology is difficult for
bonding heterogeneous joints. Therefore, technology for bonding
iron base materials is not described in the above patent
publications.
DISCLOSURE OF THE INVENTION
[0019] The present invention considers the problems harbored by the
above prior art and has as its object the provision of a liquid
phase diffusion bonding method for a metal machine part enabling
the bonding time to be shortened compared with the conventional
liquid phase diffusion bonding method, achieving homogenization of
the bonding structure and improvement of the tensile strength,
fatigue strength, and other aspects of joint quality and
reliability compared with the conventional resistance welding
methods, and superior in the quality of the joint and the
productivity and of a metal machine part assembled using the
same.
[0020] The present invention was made to solve the above problems
and has as its gist the following:
[0021] (1) A liquid phase diffusion bonding method of a metal
machine part characterized by interposing an amorphous alloy foil
for liquid phase diffusion bonding between bevel faces of metal
materials, performing primary bonding by melt bonding said
amorphous alloy foil and said metal material by resistance welding
to form a joint, then performing secondary bonding by liquid phase
diffusion bonding by reheating said joint to at least the melting
point of said amorphous alloy foil, then holding it there to
complete an isothermal solidification process of said joint.
[0022] (2) A liquid phase diffusion bonding method of a metal
machine part as set forth in (1), characterized in that the holding
time after said reheating is at least 30 seconds.
[0023] (3) A liquid phase diffusion bonding method of a metal
machine part as set forth in (1) or (2), characterized in that the
composition of said amorphous alloy foil is Ni or Fe as a base and,
as diffusion atoms, one or more of B, P, and C in amounts of 0.1 to
20.0 at % and further V in 0.1 to 10.0 at %.
[0024] (4) A liquid phase diffusion bonding method of a metal
machine part as set forth in any one of (1) to (3), characterized
in that said resistance welding is one type of welding method from
among conduction heating type spot welding, projection welding,
upset welding, and flash pad welding and in that a time of melt
bonding said amorphous alloy foil and said metal material by said
resistance welding is not more than 10 seconds.
[0025] (5) A liquid phase diffusion bonding method of a metal
machine part as set forth in any one of (1) to (4), characterized
in that an amount of current in said resistance welding is 100 to
100,000 A/mm.sup.2.
[0026] (6) A liquid phase diffusion bonding method of a metal
machine part as set forth in any one of (1) to (5), characterized
in that a pressing force in melt bonding of said amorphous alloy
foil and said metal material by said resistance welding is 10 to
1,000 MPa.
[0027] (7) A liquid phase diffusion bonding method of a metal
machine part as set forth in any one of (1) to (6), characterized
in that a thickness in a pressing direction of an incomplete
isothermally solidification structure in a cross-sectional
structure of a joint formed by said resistance welding ds on an
average not more than 10 .mu.m.
[0028] (8) A liquid phase diffusion bonding method of a metal
machine part as set forth in any one of (1) to (7), characterized
in that a joint efficiency of a joint formed by said resistance
welding is 0.5 to 2.0. [0029] where, the "joint efficiency" is the
ratio of the area of the bevel faces of the metal Materials to the
area of the joint after melt bonding the amorphous alloy foil and
metal materials
[0030] (9) A liquid phase diffusion bonding method of a metal
machine part as set forth in any one of (1) to (8), characterized
by cooling said joint after the end of an isothermal solidification
process by a cooling rate of 0.1 to 50.degree. C./sec to control
the joint structure.
[0031] (10) A metal machine part comprised of a joint formed by
liquid phase diffusion bonding of metal materials, said metal
machine part characterized in that a maximum grain size of prior
.gamma. phase in a metal structure of the metal machine part as
bonded is not more than 500 .mu.m.
[0032] (11) A liquid phase diffusion bonding method of a metal
machine part as set forth in any one of (1)-(9), characterized in
that at least one of said metal materials is a cylindrical metal
material and in that a V-bevel is formed at an end of said
cylindrical metal material so that, when bringing the end of said
cylindrical metal material into abutment with the surface of
another metal material for primary bonding, an inner surface bevel
height A and an outer surface bevel height B of said cylindrical
metal material with respect to the abutting contact point and a
distance C from said abutting contact point to the outer
circumference satisfy the following relation (1):
0.2.ltoreq.B/A.ltoreq.1 and C/t.ltoreq.0.5 (1) [0033] where A is an
inner surface bevel height of said cylindrical metal material, B is
an outer surface bevel height of said cylindrical metal material, C
is a distance from an abutting contact point of the cylindrical
metal material to the outer circumference, and t is the thickness
of the cylindrical metal material.
[0034] (12) A liquid phase diffusion bonding method of a metal
machine part as set forth in (11), characterized in that a maximum
residual height of the bevel ends after said primary bonding is not
more than three times the thickness of said amorphous alloy
foil.
[0035] (13) A liquid phase diffusion bonding method of a metal
machine part as set forth in (11) or (12), characterized in that a
joint efficiency after said primary bonding is at least 0.8.
[0036] (14) A liquid phase diffusion bonding method of a metal
machine part as set forth in any one of (11) to (13), characterized
in that a maximum residual height of the bevel ends after said
secondary bonding is not more than 70 .mu.m.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a view of the relationship between the thickness
of an alloy layer formed by the melting and solidification of an
amorphous alloy foil for liquid phase diffusion bonding and the
holding time until the isothermal solidification of the alloy layer
ends.
[0038] FIG. 2 is a view of the relationship between the isothermal
solidification holding time and bonded joint strength in secondary
bonding (liquid phase diffusion bonding) of the method of the
present invention.
[0039] FIG. 3 is a perspective view of an embodiment in the case of
butt bonding a cylindrical metal material and another metal
material.
[0040] FIG. 4 is a cross-sectional view of a bevel at the time of
primary bonding of a cylindrical metal material and another metal
material.
[0041] FIG. 5 is a cross-sectional view of a bevel running along a
center axis of a steel pipe and vertical to the bonding faces
before bonding metal machine parts.
[0042] FIG. 6 is a view of the relationship between a ratio (B/A)
of the outer surface bevel height B to the inner surface bevel
height A of a cylindrical metal material before primary bonding and
the maximum residual height of the bevel ends after the primary
bonding.
[0043] FIG. 7 is a view of an embodiment in the case of welding a
rectangular pipe and a branch pipe to produce a metal machine
part.
[0044] FIG. 8 is a cross-sectional perspective view of a
rectangular pipe from the inside pipeline axial direction at the
time of assembly in FIG. 7.
[0045] FIG. 9 is a cross-sectional perspective view of an
embodiment in the case of butt bonding a metal material and a
hollow metal material.
[0046] FIG. 10 is a cross-sectional view of a bevel running along a
center axis of a hollow metal material and vertical to the bonding
faces before bonding of the metal machine part.
BEST MODE FOR WORKING THE INVENTION
[0047] Below, details of the present invention will be
explained.
[0048] The method of the present invention uses metal materials as
the bonded materials, brings them into abutment while interposing
an amorphous alloy foil for liquid phase diffusion bonding between
the bevel faces formed at the end of a metal material, and performs
primary bonding by melt bonding said amorphous alloy foil and said
metal materials by resistance welding to form a joint.
[0049] In this primary bonding, for example, a resistance welding
system arranging at the bonded materials electrodes for supplying a
welding current to the bevel faces (abutting faces) of the bonded
materials to heat and melt them and using a stress applying
mechanism to apply the stress required for press bonding between
the bevel faces, for example, an oil pressure actuated Instron type
tension/compression system, is used.
[0050] In this primary bonding, the welding heat input of the
resistance welding melts the bevel faces of the bonded materials
and the liquid phase diffusion bonding alloy foil. The oxides upset
by the pressing stress and produced at the time of heating and
melting and the inclusions present at the bevel faces are
discharged from the bonding faces together with the molten
metal.
[0051] Further, in the primary bonding, the amorphous alloy foil
for liquid phase diffusion bonding inserted between the bevel faces
of the bonded materials has a lower melting point compared with the
ferrous materials of the bonded materials. An amorphous alloy foil
having a structure in which at least 50% of the volume of the foil
is amorphous is used.
[0052] By interposing between the bevel faces of the bonded
materials a liquid phase diffusion bonding alloy foil with a
melting point of about 900 to 1200.degree. C. or lower than the
bonded materials and melt bonding by resistance welding, there are
the effects that the liquid phase diffusion bonding alloy foil is
uniformly melted between the bevel faces and, at the same time, the
oxides produced at the time of heating and melting and the
inclusions which had been left at the bevel faces are discharged
from the bonding faces together with the molten metal.
[0053] Note that the amorphous alloy foil for liquid phase
diffusion bonding in the present invention is comprised of Ni or Fe
as a base material, contains as diffusion atoms one or more of B,
P, and C in amounts of 0.1 to 20.0 at % each, and further contains
V having the action of lowering the melting point of the oxides
produced between the bonding faces at the time of primary bonding
in an amount of 0.1 to 10.0 at %.
[0054] The B, P, and C in the liquid phase diffusion bonding alloy
foil are elements required as diffusion elements for realizing the
isothermal solidification required for achieving the liquid phase
diffusion bonding of the secondary bonding or for lowering the
melting point from the bonded members. To sufficiently obtain this
action, they must be contained in amounts of at least 0.1 at %, but
if excessively added, coarse borides, metal compounds, or carbides
will be produced in the crystal grains and the strength of the bond
will fall, so the upper limit is preferably made 20.0 at %.
[0055] The V in the liquid phase diffusion bonding alloy foil has
the action of reacting instantaneously with the oxide produced
between the bevel faces at the time of the resistance welding of
the primary bonding or the residual oxide (Fe.sub.2O.sub.3) and
changing them to a low melting point complex oxide
(V.sub.2O.sub.5--Fe.sub.2O.sub.3, melting point: not more than
about 800.degree. C.) and gives the effect of melting and
discharging the low melting point complex oxide along with the
molten metal by the pressing stress at the time of the resistance
welding and reducing the oxide-based inclusions of the bond. To
sufficiently obtain this action and effect, V is preferably
included in an amount of at least 0.1 at %. On the other hand, if
excessively adding V in an amount over 10.0 at %, the number of the
V-based oxide particles will increase and the residual oxide will
conversely increase. Further, the melting point of the liquid phase
diffusion bonding alloy will be raised and liquid phase diffusion
bonding of the secondary bonding will be made difficult. Therefore,
the upper limit is preferably made 10.0 at %.
[0056] Further, the resistance welding able to be used as the
primary bonding in the present invention may be any welding method
from among conduction heating type spot welding, projection
welding, upset welding, and flash pad welding. Normally, spot
welding, projection welding, and upset welding are suited for
bonding in cases where the bonding area is relatively small and a
high bonding strength is not required, while flash pad welding
enables a large current and high pressing force to be applied, so
is suited to the case of bonding bevels of relatively large bonding
areas. The selection of the resistance welding method does not
particularly have to be limited. It is preferable to suitably
select it in accordance with the features of the different welding
methods, the required properties of the bonded joint, the welding
conditions, etc. and to make the welding time not more than 10
seconds so as to improve productivity.
[0057] Further, in order for the welding heat input for the
resistance welding in the primary bonding to melt the amorphous
alloy for the liquid phase diffusion bonding between one bevel face
and the other bevel face in a short time, the current density must
be made at least 100 A/mm.sup.2. On the other hand, if the current
density is raised excessively, the molten metal of the amorphous
alloy foil will become disturbed and distributing it uniformly over
the bevel faces by a predetermined thickness will become difficult,
so the upper limit has to be made not more than 100,000 A/mm.sup.2.
Therefore, it is preferable to make the current density of the
resistance welding from 100 to 100,000 A/mm.sup.2.
[0058] Further, the pressing stress of the resistance welding in
the primary bonding has to be at least 10 MPa in order to reduce
the thickness of the bonding alloy layer formed by melting and
solidifying the amorphous alloy foil for liquid phase diffusion
bonding between the bevel faces and shorten the bonding time of the
liquid phase diffusion bonding of the secondary bonding. On the
other hand, if the pressing stress, is excessively high,
deformation of the bonded joint occurs, so it has to be made not
more than 1000 MPa. Therefore, the pressing stress of the
resistance welding is preferably made 10 to 1,000 MPa. Note that
the extent of deformation of the bonded joint differs depending on
the Young's modulus of the bonded materials at the welding
temperature, so the upper limit of the pressing stress is
preferably one adjusted by the properties of the bonded
materials.
[0059] Further, the joint efficiency of the joint formed by the
resistance welding at the primary bonding (area of bevel faces of
ferrous metal/area of joint after melt bonding amorphous alloy foil
and ferrous metal) has to be at least 0.5 taking into consideration
the joint constraint effect after bonding due to the shape of the
bevels and to secure a static tensile strength of the joint of a
tensile strength of at least the level of the parent materials.
Further, the high pressing stress at the time of resistance welding
causes the joint to swell. As a result, the joint area becomes
broader than the sectional area of the parent materials.
Considering this, to obtain good joint properties, the upper limit
is preferably made 2.0.
[0060] By melt bonding by the primary bonding shown above the
amorphous alloy foil, for liquid phase diffusion bonding inserted
between the bevel faces of the bonded materials in a short time, it
is possible to form a bonding alloy layer of an extremely thin
thickness formed by the melting and solidification of the amorphous
alloy foil. The inventors conducted experiments by which they
confirmed from the results of examination of the joint
cross-sectional structure by optical microscope that the thickness
of the bonding alloy layer comprised of a structure formed by the
melting and solidification of the amorphous alloy foil obtained by
the primary bonding was a maximum of not more than 7 .mu.m and was
an average of not more than 3 .mu.m.
[0061] The bonding alloy layer formed by the melting and
solidification of the extremely thin amorphous alloy foil for
liquid phase diffusion bonding in this way substantially finishes
being isothermal solidification in the subsequent liquid phase
diffusion bonding of the secondary bonding by holding it at a
temperature of at least the melting paint of the amorphous alloy
foil for about 15 seconds. If holding it for about 30 seconds, when
using ordinary carbon steel as the bonded materials, it was
confirmed by estimation by diffusion formula and experiments that a
complete isothermal solidification structure is obtained.
[0062] FIG. 1 is a view of the relationship between the thickness
of the alloy layer formed by the melting and solidification of the
amorphous alloy foil for liquid phase diffusion bonding (in the
case of the method of the present invention, the alloy layer after
the primary bonding and in the case of the conventional method, the
alloy layer after press bonding) and the holding time until the
isothermal solidification of the alloy layer ends (holding time
until incomplete isothermal solidification structure can no longer
be observed).
[0063] In the conventional liquid phase diffusion bonding method,
the thickness of the alloy layer formed by the melting and
solidification of the amorphous alloy foil for liquid phase
diffusion bonding can be reduced to a certain extent by increasing
the pressing force, but an increase in the pressing force causes
joint deformation to occur, so as shown in FIG. 1, making the
thickness of the alloy layer thinner to not more than 10 .mu.m is
difficult. The holding time until the isothermal solidification of
the liquid phase diffusion bonding ended had to be at least 100
seconds. If making the isothermal solidification holding time in
the prior art method less than 100 seconds, the problem arose that
an incomplete isothermal solidification structure of the amorphous
alloy foil end up remaining and the strength, toughness, and other
properties of the joint ended up becoming remarkably lower compared
with the parent materials.
[0064] As opposed to this, with the method of the present
invention, primary bonding (resistance welding) enables the average
thickness of the bonding alloy layer produced by the melting and
solidification of the amorphous alloy foil for liquid phase
diffusion bonding to be reduced to not more than 7 .mu.m, while the
following secondary bonding (liquid phase diffusion bonding)
enables the holding time until the isothermal solidification of the
liquid phase diffusion bonding ends (until incomplete isothermal
solidification structure of bonding alloy layer completely
disappears) to be shortened to not more than 30 seconds.
Experiments by the inventors, as shown in the figures, confirmed
that the average thickness of the bonding alloy layer can be
reduced to 3 .mu.m by the primary bonding (resistance welding). In
this case, it is possible to expect the isothermal solidification
to be completed (incomplete isothermal solidification structure of
bonding alloy layer to completely disappear) by a holding time of
15 seconds by the secondary bonding (liquid phase diffusion
bonding). Due to the above, by the method of the present invention,
it is possible to greatly shorten the bonding time and to expect an
improvement in productivity while maintaining the joint quality at
least equal to the conventional liquid phase diffusion bonding.
[0065] FIG. 2 is a view of the relationship between the isothermal
solidification holding time in the secondary bonding (liquid phase
diffusion bonding) of the method of the present invention and the
bonded joint strength.
[0066] Note that the bonded joint strength is shown by the ratio of
the tensile strength of the bonded joint to the tensile strength of
the parent materials in the case of conducting a tensile test in
the direction pulling the joint from the bonding faces. If the
value is 1, this means that the parent material breaks, while if
less than 1, it means that the joint breaks.
[0067] In actual bonding, the thickness of the bonding alloy layer
produced by the melting and solidification of the amorphous alloy
foil for liquid phase diffusion bonding formed between the bevel
faces by the primary bonding (resistance welding) of the present
invention varies depending on the position of the bevel faces, but
from FIG. 2, by making the isothermal solidification holding time
in the secondary bonding (liquid phase diffusion bonding) at least
30 seconds, a tensile test of the joint results in the parent
material breaking and therefore a good joint strength of at least
the tensile strength of the parent material is obtained.
[0068] In the method of the present invention, based on the above
experimental findings, to secure a joint strength of at least equal
to the conventional liquid phase diffusion bonding method, it is
preferable to make the isothermal solidification holding time of
the secondary bonding (liquid phase diffusion bonding) at least 30
seconds.
[0069] Note that the isothermal solidification holding time of the
secondary bonding (liquid phase diffusion bonding) can give a
predetermined joint strength stably along with its increase, but if
the isothermal solidification holding time is excessively
increased, the old .gamma.-crystal grain size of the metal
structure of the joint will become coarser and the toughness of the
joint will fall, so the upper limit is preferably made not more
than 100 seconds.
[0070] In the present invention, after the secondary bonding, that
is, after the end of the isothermal solidification of the liquid
phase diffusion bonding, by controlling the cooling rate in
accordance with the type of the steel of the bonded materials, a
desired metal structure, for example, if a carbon steel,
ferrite+pearlite, ferrite, bainite, martensite, or other metal
structure is obtained or, if austenite steel, a bonded joint is
obtained with a good metal structure due to the action of
re-solution of precipitates and other inclusions occurring at the
time of bonding.
[0071] In the present invention, in order to secure the minimum low
temperature transformation structure (bainite or martensite) ratio
required for improving the strength and toughness of the joint
required for a machine part for an automobile, it is preferable to
make the cooling rate after the secondary bonding, that is, after
the end of the isothermal solidification of the liquid phase
diffusion bonding, at least 0.1.degree. C./sec. Excessive cooling
becomes a cause of a reduction in the toughness and ductility, so
the upper limit of the cooling rate is preferably made 50.degree.
C./sec. By controlling the cooling rate, it is possible to form a
sound, high affinity joint between ferrite steels, austenite
steels, or ferrite steel and austenite steel.
[0072] Note that in the method of the present invention, after the
above cooling and for the purpose of thermally refining the metal
structure, it is possible to reheat and perform quenching,
tempering, quenching and tempering, and other heat treatment alone
or repeated a plurality of times or in combination. In this case,
the joint structure is made more homogeneous and the effect of the
present invention can be further raised.
[0073] Note that with a material with an aversion to retained
austenite, deep cooling is also effective. Deformation due to
ageing can be suppressed.
[0074] According to the embodiments of the present invention shown
above, it is possible to reduce the amount of deformation of a
joint compared with the conventional resistance welding methods
alone. Further, when assembling metal machine parts etc., the
invention can be applied to machine parts of shapes unable to be
processed even when utilizing boring, lathing, cutting, and other
machining, machine parts including heterogeneous welded joints of
difficult to weld materials hard to combine, and machine parts
where the material cost would rise tremendously due to cutting and
therefore an improvement of productivity and further a reduction of
costs and other effects can be simultaneously achieved. Further,
according to the embodiments of the present invention, even in the
case where small cracks occur in the bonding faces after the
primary bonding (resistance welding), the subsequent secondary
bonding (liquid phase diffusion bonding) causes the unmelted
amorphous alloy foil to further melt and flow into the cracks to
thereby enable the fine cracks to be repaired. Further, the alloy
layer comprised of the incomplete isothermal solidification
structure is changed to a complete isothermal solidification
structure. Due to these effects, it is possible to obtain a joint
higher in joint strength, fatigue strength, etc. and superior in
quality compared with the conventional resistance welding
methods.
[0075] Further, according to the embodiments of the invention, it
is possible to greatly shorten the isothermal solidification
holding time of the amorphous alloy foil, that is, the time for
holding the bonded joint at a reheating temperature of at least the
melting point of the amorphous alloy foil, while maintaining a
joint quality at least the same as the conventional liquid phase
diffusion bonding method alone. As a result, the metal machine part
comprised of a joint formed by liquid phase diffusion bonding with
a ferrous metal material assembled according to the method of the
present invention can be given a maximum grain size of the prior
.gamma. phase in the metal structure as bonded of a small size of
not more than 500 .mu.m and can be improved in toughness compared
with a joint obtained by the conventional liquid phase diffusion
bonding method (where the crystal grain size is over a maximum
grain size of 1 mm).
[0076] Further, at the time of secondary bonding (liquid phase
diffusion bonding) in the embodiment of the present invention,
since it is possible not to apply pressure to the bonding faces as
required at the time of liquid phase diffusion bonding alone or to
reduce the pressing force, it becomes possible to obtain a good
liquid phase diffusion bond with just a simple pressing system.
Therefore, according to the method of the present invention, it
becomes possible to realize liquid phase diffusion bonding free
from weld defects and superior in bond quality at a low cost
without requiring sophisticated pressing technology such as
pressing the bonding faces uniformly at a high temperature.
[0077] Therefore, in metal machine parts assembled by the
conventional liquid phase diffusion bonding, it becomes possible to
simplify the QT and other heat treatment required for improving the
joint toughness and improve the productivity and reduce the
production cost.
[0078] According to the embodiments of the invention explained
above, it is possible to produce bonded joints of metal materials
at a higher quality and higher productivity compared with the
conventional bonding methods such as resistance welding methods
alone and liquid phase diffusion bonding methods. However, as shown
in FIG. 3, when at least one of the metal materials of the bonded
materials is a cylindrical metal material 11, when bringing its end
into abutment with the other metal material 12 and bonding them by
primary bonding (resistance welding), the following problems are
anticipated. Therefore, to stably achieve the effects of the
present invention and stably improve the joint quality of the
fatigue strength etc., it is preferable to use the embodiments
explained below.
[0079] That is, when bringing the cylindrical metal material 11
into abutment with the metal material 12 and bonding them by
primary bonding (resistance welding), as shown in FIG. 4
(cross-sectional view of FIG. 3), the pressing force 14 and thermal
stress of the primary bonding cause the bevel parts of the
cylindrical metal material 11 to flare outward in the outer surface
side direction 15 and therefore a bevel end 13 of the outer surface
side of the cylindrical metal material 11 after the primary bonding
is easily left with a notch shaped groove. In the present
invention, due to the secondary bonding phase diffusion bonding)
performed after the end of the primary bonding, the unmelted
amorphous alloy foil is further melted and made to flow into the
residual notch shaped groove. However, if the maximum residual
height 17 of the bevel end becomes too large after the primary
bonding, even with subsequent secondary bonding, it becomes
difficult to obtain a flat bond. The notch tip of the residual
groove becomes a site of stress concentration and becomes a cause
of a reduction in the joint properties, in particular the fatigue
strength, so this is not preferable.
[0080] In the present invention, to solve the above problems in the
case of primary bonding (resistance welding) of at least one
cylindrical metal material and improve the joint properties more
stably, the following conditions are preferably defined.
[0081] FIG. 5 is a cross-sectional view of the bevel for explaining
the relationship among the inner surface bevel height A and outer
surface bevel height B of the cylindrical metal material with
respect to the abutting contact point, the distance C from the
abutting contact point to the outer circumference, and the
thickness t of the cylindrical metal material 11 at the time of
bringing the end of the cylindrical metal material 1 and the
surface of the other metal material into abutment. Note that the
cross-sectional direction of this figure runs along the center axis
of the cylindrical metal material 11 and is vertical to the bonding
faces.
[0082] In the present invention, to keep the bevel of the
cylindrical metal material 11 from flaring out in the outer surface
side direction 15 due to the pressing force 14 and thermal stress
as shown in FIG. 4 at the time of primary bonding of the
cylindrical metal material 11 and to reduce the metal material 12
and the maximum residual height 17 of the bevel end after the
primary bonding, it is preferable to make the relationship among
the inner surface bevel height A and outer surface bevel height B
of the cylindrical metal material with respect to the abutting
contact point 16, the distance C from the abutting contact point 16
to the outer circumference, and the thickness t of the cylindrical
metal material 11 shown in FIG. 5 a suitable condition.
[0083] FIG. 6 shows the relationship between the ratio of the outer
surface bevel height B to the inner surface bevel height A of the
cylindrical metal material before primary bonding (in the state not
pressed), that is, B/A, and the maximum residual height 17 of the
bevel end after the primary bonding. Note that the ratio of the
distance C from the abutting contact point 16 to the outer
circumference to the thickness t of the cylindrical metal material
11, that is, C/t, was made 0.5.
[0084] Under conditions where the value of B/A is 0.2 to 1, it is
learned that the maximum residual height after the primary bonding
can be sufficiently reduced. On the other hand, if the value of B/A
becomes less than 0.2, the residual height of the inner surface
bevel end of the cylindrical metal material 11 becomes larger.
Further, if the value of B/A exceeds 1, the residual height of the
outer surface bevel end of the cylindrical metal material 11 will
become larger. In both cases, the maximum residual height of the
bevel end after primary bonding will become higher than 0.1 mm. In
this case, it will become difficult to sufficiently reduce the
residual groove of the joint even by the repair action of the
residual groove by the secondary bonding (liquid phase diffusion
bonding) performed after the primary bonding, so this is not
preferred.
[0085] Further, FIG. 6 shows the results when the value of the
ratio of the distance C from the abutting contact point 16 to the
outer circumference with respect to the thickness t of the
cylindrical metal material 11, that is, C/t, is 0.5. Under
conditions where the value of C/t becomes smaller than 0.5 or less,
if a pressing force 14 is applied at the time of the primary
bonding as shown in FIG. 4, the bevel ends of the cylindrical metal
material 11 will receive stress in the outer surface direction 15
and the outer surface bevel end will more easily deform, so the
maximum residual height of the bevel end after the primary bonding
will be reduced more. However, when the value of C/t becomes larger
than 0.5, if a pressing force 14 is applied at the time of the
primary bonding, the inner surface bevel end of the cylindrical
metal material 11 will more easily deform. Even under conditions
where the value of B/A is 0.2 to 1, it will no longer be possible
to reduce the maximum residual height of the bevel end after the
primary bonding to not more than 0.1 mm, so this is not
preferable.
[0086] Based on the above discovery, in the present invention, when
at least one of said metal materials is a cylindrical metal
material, when bringing the end of said cylindrical metal material
into abutment with the surface of the other metal material for
primary bonding (resistance welding), it is preferable to form a
V-bevel at the end of the cylindrical metal material so that an
inner surface bevel height A and an outer surface bevel height B of
said cylindrical metal material with respect to the abutting
contact point and a distance C from said abutting contact point to
the outer circumference satisfy the following relation (1):
0.2.ltoreq.B/A.ltoreq.1 and C/t.ltoreq.0.5 (1)
[0087] Further, in the embodiments of the present invention, the
maximum residual height 17 of the bevel end of the cylindrical
metal material 11 after the primary bonding (resistance welding)
shown in FIG. 4 is preferably as low as possible so that the
unbonded residual part of the bevel end can be sufficiently reduced
and the fatigue strength of the joint can be more stably improved
by the melting and repair action of unmelted amorphous alloy foil
at the time of the secondary bonding (liquid phase diffusion
bonding) performed after that. When exceeding three times the
thickness of the amorphous alloy foil, it becomes difficult to more
stably improve the fatigue strength of the joint even by the
melting and repair action of the unmelted amorphous alloy foil of
the secondary bonding.
[0088] Therefore, in the above embodiments of the present
invention, considering the melting and repair action and effect of
the unmelted amorphous alloy foil of the secondary bonding, the
maximum residual height of the bevel end after the primary bonding
is preferably made not more than 3 times the thickness of the
amorphous alloy foil.
[0089] Further, in the embodiments of the present invention, when
the pressing force 14 or the welding current at the time of the
primary bonding (resistance welding) is low or the conditions are
otherwise unsuitable as shown in FIG. 4, even if the maximum
residual height of the bevel end after the primary bonding
(resistance welding) of the cylindrical metal material 11 is in the
above suitable range, it will not be possible to uniformly form a
bonding alloy layer formed by the melting and solidification of the
amorphous alloy foil between the bevel faces after the primary
bonding. Even if the area near the abutting contact point is press
bonded, the press bonding between the bevel faces will become
insufficient. Further, due to the effects of the residual stress
occurring due to the outer surface direction stress of the
cylindrical metal material 11 at the time of primary bonding
(resistance welding), there is also the possibility that the
bonding alloy layer will end up peeling off before the secondary
bonding.
[0090] To suppress these problems and form a uniform bonding alloy
layer between the bevel faces after the primary bonding and form a
bonding alloy layer with a good adhesion not peeling off before the
secondary bonding, in the embodiments of the present invention, it
is preferable to make the joint efficiency after the primary
bonding at least 0.8.
[0091] Further, in the embodiments of the present invention, the
maximum residual height of the bevel ends after secondary bonding
is preferably as low as possible so as to further improve the joint
fatigue strength without using post-processing for improving the
shape of the bevel ends.
[0092] In the embodiments of the present invention, due to the
melting and repair action of the unmelted amorphous alloy foil at
the time of the secondary bonding, the bonds can be made flat, but
to further improve the fatigue strength of the joints, it is
preferable to make the maximum residual height of the bevel ends
after secondary bonding not more than 70 .mu.m.
EXAMPLES
[0093] The effects of the present invention will be explained by
the following examples.
Example 1
[0094] Amorphous alloy foils for liquid phase diffusion bonding
having the three types of chemical compositions of the symbols A to
C and melting points shown in Table 1 and bonded materials
comprised of ferrous metals, Ni alloys, or Ti alloys having the
chemical compositions of the symbols a to f shown in Table 2 were
used to produce metal machine parts under the bonding conditions
shown in Table 3 and Table 4.
[0095] The metal machine parts obtained were subjected to tensile
tests in the direction pulling away from the bonded surfaces and
charpy impact tests of the bonds at 0.degree. C. and were evaluated
for joint strength and joint toughness. Further, the amounts of
deformation of the metal machine parts in the direction of
application of bonding stress were measured and the amounts of
deformation evaluated. The results are shown in Table 3 and Table
4.
[0096] Note that in Table 3 and Table 4, the evaluation of the
joint strength is shown by the ratio of the tensile strength of the
bonded joint with respect to the tensile strength of the parent
material. If the value is 1, this means that the parent material
breaks, while if less than 1, it means that the joint breaks.
Further, the evaluation of the joint toughness is "good" when the
absorbed energy at 0.degree. C. is 21 J or more and "poor" when it
is less than 21 J.
[0097] Note that Nos. 2 to 8 shown in Table 3 are examples of
production of metal machine parts by the following procedure. FIG.
7 and FIG. 8 are schematic views for explaining examples in the
case of bonding a branch pipe 2 to a branch opening 4 of a
rectangular pipe body 1 at the center in the longitudinal direction
of the internal pipeline 3 so as to produce an automobile use metal
machine part having a T-branch pipe inside. Note that FIG. 7 is a
perspective view of a metal machine part for an automobile, while
FIG. 8 is a cross-sectional view running along a center axis of the
passage 2 and vertical to the center axis of the internal pipeline
3.
[0098] As shown in FIG. 7, the end of the branch pipe 2 forming one
bonding face was machined in advance to give a V-bevel having an
angle of 45.degree.. The bonding faces of the bevel 9 of the branch
pipe 2 and the pipe body 1 were made to abut against each other
through a ring-shaped liquid phase diffusion bonding alloy foil 5,
then electrodes 7 and 10 brought into close contact with the branch
pipe 2 and the pipe body 1 were used to run a DC current through
the bevel parts. At the same time, a pressing stress 24 was applied
in the direction of 6. Note that the pressing stress was applied
through a stress transmitting plate (not shown) operating by oil
pressure from above the branch pipe 2. As a result, the bevel 9 of
the branch pipe 2 collapsed under the pressure and deformed to the
same thickness as the thickness 8 of the branch pipe 2. Further,
the liquid phase diffusion bonding alloy foil 5 interposed between
the bevels of the branch pipe 2 and the pipe body 1 formed an alloy
layer after melting once, then solidifying, but the bonding time wa
extremely short, so the result was an incomplete isothermal
solidification structure with an average thickness of less than 3
.mu.m, that is a so-called "brazed structure" where the
diffusion-limited isothermal solidification was not ended. Next, as
secondary bonding, the bonded joint was raised to the reheating
temperature of 150.degree. C. by an electric furnace having a high
frequency induction heating coil and resistance heat generating
element and held there for a predetermined time, whereby the
diffusion-limited isothermal solidification of the bonding alloy
layer formed in the primary bonding was ended, then the joint was
cooled.
[0099] Further, Nos. 1 and 9 shown in Table 3 are examples of
production of metal machine parts by the following procedure.
[0100] As the bonded materials, two rods of diameters of 5 mm and
lengths of 50 mm were used. The bevel end faces were made
completely I-shapes and were ground to bevel face roughnesses Rmax
of not more than 10 .mu.m. Alloy foils for liquid phase diffusion
bonding having diameters of 5 mm were interposed between these
bevels, then the bonded materials were run through with DC current
and simultaneously given a pressing stress for resistance welding
as primary bonding to form joints. The absence of any offset in
coaxiality of the rods was confirmed, then the now 100 mm long
joints were raised in temperature to the reheating temperature in
an electric furnace having a resistance heat generating element,
then held there and then cooled as secondary bonding. There was no
subsequent heat treatment at all.
[0101] Note that Nos. 10 and 11 shown in Table 4 are comparative
examples where no secondary bonding (liquid phase diffusion
bonding) was performed when producing the above metal machine
parts, while Nos. 12 and 13 are comparative examples where no
primary bonding (resistance welding) was performed when producing
the above metal machine parts. Further, No. 14 shown in Table 4 is
a comparative example where primary bonding (resistance welding)
and secondary bonding (liquid phase diffusion bonding) were
performed when producing the above metal machine part, but the
bonding conditions were outside of the scope of the present
invention.
[0102] From the results shown in Table 3, Nos. 1 to 9 of production
of metal machine parts under bonding conditions within the scope of
the present invention by the bonding method of the present
invention all had joint strengths exceeding the tensile strengths
of the parent materials and had amounts of deformation in the
direction of application of the bonding stress of not more than 5%
or satisfactory in terms of performance in use as machine parts.
Further, the holding times of the liquid phase diffusion bonding
were short, so the maximum crystal grain sizes of the joints were
fine sizes of not more than 500 .mu.m and the joint toughnesses
were also excellent.
[0103] Nos. 10 to 14 shown in Table 4 are all comparative examples
outside of the scope of the bonding conditions of the method of the
present invention. Nos. 10 and 11 are comparative examples in the
case of using only resistance welding. In this case, No. 10 had an
amorphous alloy foil for liquid phase diffusion bonding interposed,
but its structure was an incomplete isothermal solidification
structure, that is, a brazed structure, so the joint strength was
lower than the parent material strength, the value of the
evaluation was lower than the standard 1, and the joint broke. In
particular, No. 11 involved only resistance welding with no use of
any amorphous alloy foil for liquid phase diffusion bonding, so
inclusions and defects remained at the bonding interface and the
joint strength fell. With normal resistance welding, sometimes such
unstable joint strength results. These defects could not
substantially be detected.
[0104] Further, Nos. 12 and 13 are comparative examples where
bonding was performed by applying bonding stress of 5 MPa only at
the liquid phase diffusion bonding. In the comparative example of
No. 12, the holding time was a short 40 seconds. The crystal grains
of the joint could be made small, but the liquid phase diffusion
bonding was not completed at all and therefore the joint strength
fell. The comparative example of No. 13 had the holding time of the
liquid phase diffusion bonding made longer to make up for the
elimination of addition of resistance welding. Therefore, the joint
strength was improved, but the crystal grains of the metal
structure became coarser. Therefore, the absorbed energy at
0.degree. C. was less than 10 J and the toughness of the joint
fell.
[0105] Further, No. 14 is an example where the liquid phase
diffusion bonding temperature in the secondary bonding was
820.degree. C. or lower than and deviating from the conditions of
the present invention and the melting point of the amorphous alloy
foil for liquid phase diffusion bonding was not reached, so the
brazed structure formed by the resistance welding separated into
the borides and Ni base alloy and became brittle and the joint
ended up separating.
TABLE-US-00001 TABLE 1 Chemical Composition of Bonding Foil (at %)
Bonding Melting foil point symbol Base Si B P V (.degree. C.) A Ni
3.5 8 11 1073 B Fe 2.5 12 8 1122 C Ni 0.8 15 7 942
TABLE-US-00002 TABLE 2 Main Chemical Composition of Bonded
Materials (mass %) Bonded material symbol Steel type C Si Mn Fe Cr
Ni Mo Nb V N Al Ti a STPA28 0.1 0.3 0.5 bal. 9 -- 1 0.05 0.2 0.04
-- -- b SCM440 0.4 0.25 0.7 bal. 1 -- 0.2 -- -- -- -- -- c SUH11
0.5 1.8 0.2 bal. 9 -- 0.5 -- -- -- -- -- d SUH35 0.5 0.2 9 bal. 21
-- 4 -- -- 0.4 -- -- e INCONEL600 0.1 0.12 0.5 8.3 17 bal. -- -- --
-- -- -- f Ti--6Al--4V 0.05 -- -- 0.16 -- -- -- -- 4.24 -- 6.21
Bal.
TABLE-US-00003 TABLE 3 Process Conditions and Joint Properties of
Method of Present Invention Secondary bonding Primary bonding
(liquid phase diffusion bonding) (provisional attachment for liquid
phase Liquid diffusion bonding by resistance welding) phase Current
Total diffu- Maxi- value of oxide Bond- sion mum Evaluation of
joint resist- Ap- length Bond- ing Cooling bonding crystal Bond-
Joint ance plied of ing hold- rate tem- grain ing strength/ Bonded
welding pres- bonding layer Joint ing after pera- size of foil
parent Defor- Ex. material (A/ sure line width effi- time bonding
ture joint sym- material Joint mation no. symbol mm.sup.2) (MPa)
(.mu.m) (.mu.m) ciency (sec) .degree. C./s .degree. C. (.mu.m) bol
strength toughness (%) Class 1 a 180 50 0.2 4 0.8 31 5 1180 180 A
1.02 Good 3.1 Inv. ex. 2 d 1200 50 0.1 4 1.3 38 5 1170 190 A 1.1
Good 3.7 Inv. ex. 3 f 1500 80 0 6 1.2 90 5 980 250 C 1.03 Good 3.6
Inv. ex. 4 b 1200 80 0.3 3 1.5 240 5 1190 300 B 1.2 Good 4.1 Inv.
ex. 5 c 25000 40 0.1 2 1.4 35 0.3 1240 240 A 1.05 Good 3.9 Inv. ex.
6 e 40000 30 0 5 1.8 1200 14 1200 480 B 1.02 Good 4.5 Inv. ex. 7 a
1800 90 0 2 1.1 90 2 1150 140 B 1.08 Good 3.6 Inv. ex. 8 b 1200 30
0.3 6 1.9 81 1 1250 150 A 1.4 Good 3.8 Inv. ex. 9 e 600 20 0.2 7
0.7 2400 10 1280 450 A 1.2 Good 3.8 Inv. ex. Total oxide length of
bonding line = total of lengths of oxide-based inclusions present
on substantially center line of bonding layer of cross-sectional
structure of bond when observed under optical microscope/length of
bonding layer Bonding layer width = thickness of bonding layer
parallel to direction of pressure at time of resistance welding of
cross-sectional structure of bond Joint efficiency = (bevel area of
bonded materials)/(area of joint portion after bonding where
bonding metal foil is interposed) Maximum crystal grain size of
joint = diameter of largest of old .gamma.-grain sizes or ferrite
grain sizes at bonding layer and heat affected zone after bonding
Joint toughness = "good" when absorbed energy at 0.degree. C. is 21
J or more and "poor" when less than 21 J. Amount of deformation =
amount of deformation in direction of application of bonding
stress
TABLE-US-00004 TABLE 4 Process Conditions and Joint Properties of
Comparative Examples Secondary bonding Primary bonding (liquid
phase diffusion bonding) (provisional attachment for liquid phase
Liquid diffusion bonding by resistance welding) phase Current Total
Cool- diffu- Maxi- value of oxide Bond- ing sion mum Evaluation of
joint resist- Ap- length Bond- ing rate bonding crystal Bond- Joint
ance plied of ing hold- after tem- grain ing strength/ Bonded
welding pres- bonding layer Joint ing bond- pera- size of foil
parent Defor- Ex. material (A/ sure line width effi- time ing ture
joint sym- material Joint mation no. symbol mm.sup.2) (MPa) (.mu.m)
(.mu.m) ciency (sec) .degree. C./s .degree. C. (.mu.m) bol strength
toughness (%) Class 10 a 110 40 0.2 5 0.9 NA 0.6 Good 5.1 Comp. ex.
11 b 180 30 18 -- 1.1 0.4 Good 5.6 Comp. (foil ex. not inter-
posed) 12 c NA 40 0.5 1150 240 A 0.3 Good 2.8 Comp. ex. 13 e 7200
0.2 1240 1200 B 1.1 Poor 3.7 Comp. ex. 14 d 560 60 0.5 7 1.2 1500
0.7 820 450 A 0 Good 5.3 Comp. ex. Total oxide length of bonding
line = total of lengths of oxide-based inclusions present on
substantially center line of bonding layer of cross-sectional
structure of bond when observed under optical microscope/length of
bonding layer Bonding layer width = thickness of bonding layer
parallel to direction of pressure at time of resistance welding of
cross-sectional structure of bond Maximum crystal grain size of
joint = diameter of largest of old .gamma.-grain sizes or ferrite
grain sizes at bonding layer and heat affected zone after bonding
Joint toughness = "good" when absorbed energy at 0.degree. C. is 21
J or more and "poor" when less than 21 J. Amount of deformation =
amount of deformation in direction of application of bonding
stress
Example 2
[0106] Next, the same procedure as in the invention examples of
Nos. 2 to 8 shown in Table 3 of Example 1 was followed to bond
branch pipes 2 and pipe bodies 1 shown in FIG. 8. At that time, as
shown in Table 5, Table 6, and Table 7, metal machine parts bonded
under conditions changing the dimensions of the thickness t etc. of
the branch pipes 2 of the cylindrical metal materials and the bevel
conditions of the branch pipes 2 (inner surface bevel height A,
outer surface bevel height B, and distance C from abutting contact
point to outer circumference) at the time of abutting were produced
and were measured and evaluated for joint mechanical properties, in
particular the fatigue strengths. Note that the chemical
compositions of the amorphous alloy foils for liquid phase
diffusion bonding and bonded materials used were the same as in
Example 1. Further, the same procedure as in Example 1 was used for
production except for the bonding conditions shown in Tables 5 and
6.
[0107] The metal machine parts obtained were subjected to tensile
tests in the direction pulling away from the bonding faces and
fatigue impact tests and were evaluated for joint strengths and
joint fatigue strengths. The results are shown in Table 6 and Table
7.
[0108] Note that in Table 6 and Table 7, the evaluation of the
joint strength is shown by the ratio of the tensile strength of the
bonded joint with respect to the tensile strength of the parent
material. If the value is 1, this means that the parent material
breaks, while if less than 1, it means that the joint breaks.
Further, the fatigue strengths of the joints were measured and
evaluated by subjecting the metal machine parts obtained to
internal pressure fatigue tests and durability tests in a stress
range of 20 to 200 MPa and 10 million cycles (15 Hz) and judging
parts not cracking or breaking as "good" and parts cracking or
breaking as "poor".
[0109] Nos. 15 to 28 shown in Table 6 and Nos. 29 to 32 shown in
Table 7 are all examples where the primary bonding (resistance
welding) and secondary bonding (liquid phase diffusion bonding)
prescribed in the present invention are performed and where like
the invention examples shown in Example 1, the joint strength was
greater than the strength of the parent materials and superior
results were obtained in joint properties compared with the
conventional method.
[0110] Among the invention examples, Nos. 15 to 28 shown in Table 6
are invention examples of production performed by bevel conditions
of the cylindrical metal materials defined in the more preferable
embodiments of the present invention within the scope of the
present invention, while Nos. 29 to 32 shown in Table 7 are
invention examples of production performed by conditions outside
the more preferable range of the present invention.
[0111] Nos. 15 to 28 shown in Table 6 are examples where the
relations among the inner surface bevel heights A and outer surface
bevel heights B of the branch pipes 2 of the cylindrical metal
materials, the distances C from the abutting contact points to the
outer circumferences, and the thicknesses t of the branch pipes 2
satisfy the more preferable conditions of the present invention,
that is, 0.2.ltoreq.B/A.ltoreq.1 and C/t.ltoreq.0.5, so none of the
bonded joints broke after the internal pressure fatigue tests and
superior joint fatigue strengths were obtained. Further, since the
holding times of the liquid phase diffusion bonding were short, the
maximum crystal grain sizes of the joints were fine sizes of not
more than 500 .mu.m and the joint toughnesses were also excellent.
Among these, further, Nos. 16 to 22, 24, and 26 to 28 where the
conditions of the maximum residual heights of the bevel ends after
the primary bonding, the joint efficiencies after the primary
bonding, and the residual heights of the bevel ends after secondary
bonding were all in the more preferable ranges of the present
invention were further improved in results in the joint fatigue
tests compared with Nos. 15, 23, and 25 deviating from one of these
preferable conditions.
[0112] On the other hand, Nos. 29 to 32 of Table 7 are invention
examples where the relations among the inner surface bevel heights
A and outer surface bevel heights B of the branch pipes 2, the
distances C from the abutting contact points to the outer
circumferences, and the thicknesses t of the branch pipes 2 were
outside the more preferred scope of the present invention.
[0113] Nos. 29 and 30 are examples where the ratios B/A of the
heights of the bevel of the branch pipe 2 were larger than 1, that
is, the outer surface bevel heights were higher than the inner
surface sides. In this case, on top of the originally high outer
surface side, the pipe flares out slightly during the resistance
welding. Due to this deformation, a groove easily remains at the
outer surface side easily. When observing the joint cross-section
after the resistance welding, the residual height of the bevel end
became a large 100 .mu.m or more and the joint efficiency also
dropped. Further, No. 30 had an abutting contact point positioned
closer to the inner surface side, that is, C/t>0.5, so the bevel
at the inner surface side deformed preferentially and as a result
the bevel end at the outer surface side largely remained.
[0114] No. 31 is an example where the ratio B/A of the heights of
the bevel is in the scope of the invention, but when the position
of the abutting contact point is C/t>0.5, in the same way as No.
30, deformation concentrated at the inner surface side of the
bevel, so the end of the bevel at the outer surface side remained
and the residual height became a large one of at least 100
.mu.m.
[0115] As a result of the above, Nos. 29 to 31 cracked from the
ends of the bevels at the outer surface sides in internal pressure
fatigue tests and broke at numbers of cycles below the
predetermined number of cycles.
[0116] No. 32 is an example of a ratio B/A of heights of the bevel
of not more than 0.2, that is, where the height of the bevel at the
inner surface side is at least five times the height of the bevel
at the outer surface side. In this case, the bevel at the outer
side deformed during the resistance welding and closed at the end,
but much of the bevel at the inner surface side remained. The
residual height of the bevel end became a large one of at least 100
.mu.m at the inner surface side. As a result, Comparative Example
32 cracked from the bevel end at the inner surface side in the
internal pressure fatigue test and broke at a number of cycles
below the predetermined number of cycles.
TABLE-US-00005 TABLE 5 Types of Branch Pipes Branch pipe Test piece
dimensions (mm) no. Outside dia. Inside dia. Thickness i 10 6 2 ii
26 17 4.5 iii 42 32 5 iv 50 38 6
TABLE-US-00006 TABLE 6 Process Conditions and Joint Properties of
Method of Present Invention Primary bonding (provisional attachment
for liquid phase diffusion Test piece dimensions (mm) bonding by
resistance welding) Current Maximum Dimensions of bevel part value
of residual Bonded A (inner B (outer resistance Applied height of
material surface surface welding pressure bevel end Joint Ex. no.
symbol Pipe no. side) side) C B/A C/t (A/mm.sup.2) (MPa) (mm)
efficiency 15 a i 0.07 0.06 1.00 0.86 0.50 500 45 0.109 0.85 16 c i
0.06 0.06 1.00 1.00 0.50 350 50 0.066 0.93 17 e i 0.06 0.02 1.00
0.33 0.50 300 60 0.058 0.96 18 b i 0.06 0.02 0.70 0.33 0.35 350 50
0.044 0.99 19 a ii 0.04 0.02 2.25 0.50 0.50 250 60 0.074 0.95 20 c
ii 0.05 0.02 2.00 0.40 0.44 250 60 0.035 0.94 21 b ii 0.04 0.02
1.50 0.50 0.33 250 60 0.068 0.98 22 a iii 0.07 0.03 2.00 0.43 0.40
175 45 0.051 0.91 23 a iv 0.08 0.07 3.00 0.88 0.50 390 50 0.113
0.79 24 b iv 0.05 0.03 2.00 0.60 0.33 250 60 0.072 0.94 25 d iv
0.10 0.02 2.00 0.20 0.33 255 60 0.098 0.87 26 e iv 0.08 0.04 3.00
0.50 0.50 390 50 0.045 0.91 27 f iv 0.05 0.02 3.00 0.40 0.50 250 60
0.066 0.96 28 c iv 0.05 0.01 2.00 0.20 0.33 250 60 0.044 0.98
Secondary bonding (liquid phase diffusion bonding) Liquid phase
Maximum Joint evaluation Bonding diffusion residual Joint holding
Cooling rate bonding height of Bonding strength/parent Internal
time after bonding temperature bevel end foil material pressure Ex.
no. (sec) (.degree. C./s) (.degree. C.) (mm symbol strength fatigue
test Class 15 3600 10 1280 0.072 A 1.03 Good Inv. ex. 16 1800 2
1150 0.013 B 1.13 Good Inv. ex. 17 60 2 1250 0 C 1.15 Good Inv. ex.
18 360 50 1180 0 B 1.14 Good Inv. ex. 19 420 5 1200 0 A 1.1 Good
Inv. ex. 20 2400 10 1170 0 A 1.19 Good Inv. ex. 21 90 5 1240 0 C
1.08 Good Inv. ex. 22 1800 2 1150 0.011 C 1.07 Good Inv. ex. 23
1800 0.1 1160 0.081 A 1.03 Good Inv. ex. 24 400 5 1200 0.005 C 1.07
Good Inv. ex. 25 1200 5 1150 0.076 B 1.04 Good Inv. ex. 26 30 10
1250 0.023 A 1.05 Good Inv. ex. 27 600 10 1160 0 A 1.09 Good Inv.
ex. 28 400 5 1200 0 B 1.16 Good Inv. ex. Maximum residual height of
bevel end = Maximum value of cylindrical axis direction distance
between bevel end and bonded surface after primary bonding or
secondary bonding Internal pressure fatigue test = Test pieces
passing durability test comprising stress range of 20-200
MPa/10,000,000 repetitions (15 Hz) indicated as "good" and failing
test as "poor".
TABLE-US-00007 TABLE 7 Process Conditions and Joint Properties of
Comparative Examples Primary bonding (provisional attachment for
liquid phase diffusion Test piece dimensions (mm) bonding by
resistance welding) Current Maximum Dimensions of bevel part value
of residual Bonded A (inner B (outer resistance Applied height of
material surface surface welding pressure bevel end Joint Ex. no.
symbol Pipe no. side) side) C B/A C/t (A/mm.sup.2) (MPa) (mm)
efficiency 29 a i 0.07 0.10 1.00 1.43 0.50 500 50 0.176 0.72 30 c
ii 0.05 0.06 3.00 1.20 0.67 450 60 0.200 0.61 31 a iii 0.07 0.07
3.00 1.00 0.60 300 65 0.156 0.73 32 a iv 0.08 0.01 2.50 0.13 0.42
380 50 0.320 0.67 Secondary bonding (liquid phase diffusion
bonding) Liquid phase Maximum Joint evaluation Bonding diffusion
residual Joint holding Cooling rate bonding height of Bonding
strength/parent Internal time after bonding temperature bevel end
foil material pressure Ex. no. (sec) (.degree. C./s) (.degree. C.)
(mm) symbol strength fatigue test Class 29 600 10 1250 0.123 A 1.03
Poor Inv. ex. 30 360 5 1200 0.135 B 1 Poor Inv. ex. 31 400 5 1200
0.122 C 1.06 Poor Inv. ex. 32 550 2 1200 0.25 B 1.06 Poor Inv. ex.
Maximum residual height of bevel end = Maximum value of cylindrical
axis direction distance between bevel end and bonded surface after
primary bonding or secondary bonding Internal pressure fatigue test
= Test pieces passing durability test comprising stress range of
20-200 MPa/10,000,000 repetitions (15 Hz) indicated as "good" and
failing test as "poor".
Example 3
[0117] Next, an explanation will be given of an example of
application of the bonding method of the present invention when
producing hollow metal machine parts such as various types of motor
cam shafts fabricated conventionally by casting, forging and
cutting, etc. as shown in FIG. 9.
[0118] Liquid phase diffusion amorphous alloy foils having two
types of chemical compositions of the symbols A and B and melting
points shown in Table 1 and bonded materials comprised of ferrous
metals having the chemical compositions of the symbols "a" and "b"
shown in Table 2 were used to produce metal machine parts shown in
FIG. 9 by the following procedure under the bonding conditions
shown in Table 8.
[0119] That is; as shown in FIG. 9, the end of a hollow metal
material 18 forming one bonding face was machined in advance to
give a V-bevel having an angle of 45.degree.. The bonding faces of
the bevel 19 of the hollow metal material 18 and the metal material
20 were made to abut against each other through a ring-shaped
liquid phase diffusion bonding alloy foil 21, then electrodes 22
and 23 brought into close contact with the hollow metal material 18
and the metal material 20 were used to run a DC current through the
bevel 19 parts. At the same time, a pressing stress 24 was applied.
Note that the pressing Stress 24 was applied through a stress
transmitting plate (not shown) operating by oil pressure from above
the hollow metal material 18. As a result, the bevel 19 of the
hollow metal material 18 collapsed under the pressure and deformed
to the same thickness as the thickness 25 of the hollow metal
material 18. Further, the liquid phase diffusion bonding alloy foil
21 interposed between the bevels of the hollow metal material 18
and the metal material 20 formed an alloy layer after melting once,
then solidifying, but the bonding time was extremely short, so the
result was an incomplete isothermal solidification structure with
an average thickness of less than 3 .mu.m, that is a so-called
"brazed structure" where the diffusion-limited isothermal
solidification was not ended. Next, as secondary bonding, the
bonded joint was raised to the reheating temperature described in
Table 8 by an electric furnace having a high frequency induction
heating coil and resistance heat generating element and held there
for a predetermined time, whereby the diffusion-limited isothermal
solidification of the bonding alloy layer formed in the primary
bonding was ended, then the joint was cooled.
[0120] The metal machine parts obtained were subjected to tensile
tests in the direction pulling away from the bonding face and
charpy impact tests at the bonds at 0.degree. C. and were evaluated
for joint strengths and joint toughnesses. Further, the amounts of
deformation in the direction of application of bonding stress of
the metal machine parts were measured and the amounts of
deformation evaluated. The results are shown in Table 8.
[0121] Note that in Table 8, the evaluation of the joint strength
is shown by the ratio of the tensile strength of the bonded joint
with respect to the tensile strength of the parent material. If the
value is 1, this means that the parent material breaks, while if
less than 1, it means that the joint breaks. Further, the
evaluation of the joint toughness is "good" when the absorbed
energy at 0.degree. C. is 21 J or more and "poor" when it is less
than 21 J.
[0122] From the results of Table 8, Example Nos. 33 to 35 of
production of metal machine parts under bonding conditions in the
scope of the present invention by the bonding method of the present
invention all had thicknesses of the bonding layers after primary
bonding of an average of not more than 10 .mu.m and joint strengths
measured after secondary bonding of over the tensile strengths of
the parent materials at all times. Further, the amounts of
deformation in the direction of application of bonding stress were
not more than 5% or satisfactory in terms of performance in use as
metal parts. Further, since the holding times of the liquid phase
diffusion bonding were short, the maximum crystal grain sizes of
the joints were fine sizes of not more than 500 .mu.m and the joint
toughnesses were also good.
TABLE-US-00008 TABLE 8 Process Conditions and Joint Properties of
Method of Present Invention Secondary bonding Primary bonding
(liquid phase diffusion bonding) (provisional attachment for liquid
phase Liquid diffusion bonding by resistance welding) phase Current
Total diffu- Maxi- value of oxide Bond- sion mum Evaluation of
joint resist- Ap- length Bond- ing Cooling bonding crystal Bond-
Joint ance plied of ing hold- rate tem- grain ing strength/ Bonded
welding pres- bonding layer Joint ing after pera- size of foil
parent Defor- Ex. material (A/ sure line width effi- time bonding
ture joint sym- material Joint mation no. symbol mm.sup.2) (MPa)
(.mu.m) (.mu.m) ciency (sec) .degree. C./s .degree. C. (.mu.m) bol
strength toughness (%) Class 33 a 180 100 0.4 5 0.9 60 5 1200 180 A
1.09 Good 3.8 Inv. ex. 34 a 220 110 0.1 2 1.1 90 5 1200 200 B 1.04
Good 4.4 Inv. ex. 35 b 180 90 0.3 3 1.1 60 5 1250 160 B 1.01 Good
4.1 Inv. ex. Total oxide length of bonding line = total of lengths
of oxide-based inclusions present on substantially center line of
bonding layer of cross-sectional structure of bond when observed
under optical microscope/length of bonding layer Bonding layer
width = thickness of bonding layer parallel to direction of
pressure at time of resistance welding of cross-sectional structure
of bond Joint efficiency = (bevel area of bonded materials)/(area
of joint portion after bonding where bonding metal foil is
interposed) Maximum crystal grain size of joint = diameter of
largest of old .gamma.-grain sizes or ferrite grain sizes at
bonding layer and heat affected zone after bonding Amount of
deformation = amount of deformation in direction of application of
bonding stress
INDUSTRIAL APPLICABILITY
[0123] As explained above, when using liquid phase diffusion
bonding to form a joint and produce a metal machine part, the
present invention interposes an amorphous alloy foil for liquid
phase diffusion bonding at the bevels of metal materials, melt
bonds the amorphous alloy foil by resistance welding as primary
bonding to provide an extremely thin bonding alloy layer formed by
the melting and solidification of the amorphous alloy foil, then
provides an isothermal solidification process of liquid phase
diffusion bonding at a reheating temperature of at least the
melting point of the amorphous alloy foil and thereby can give a
joint with homogeneity of structure and excellent tensile strength,
toughness, fatigue strength, and other mechanical properties and
with little deformation. As a result, it is possible to produce
metal machine parts with a high joint quality and reliability with
a high productivity. Further, regarding the fatigue stress of a
bonded joint with at least one of its members comprised of a
cylindrical metal material, which was a problem in the conventional
resistance welding methods, the interaction between the primary
bonding and secondary bonding of the present invention enables the
occurrence of fine cracks in the welded part to be reduced and the
unbonded residual amount of the bevel end to be reduced and enables
a joint superior in fatigue strength and a metal machine part made
by the same to be produced.
[0124] The present invention provides a completely new welding
technique for metal machine parts enabling metal machine parts of
shapes unable to be produced in the past by ordinary machining,
grinding, and boring and further low productivity, low-material
yield, high cost metal machine parts to be produced with a high
productivity and low cost and can contribute greatly to the
improvement of functions and supply of metal machine parts able to
be achieved by the application of liquid phase diffusion bonding.
In particular, in the production of camshafts and other hollow
parts, shafts used for various types of motors, etc. which used to
be fabricated by casting, forging and cutting or metal machine
parts using just a liquid phase diffusion bonding method in the
past, application of the method of the present invention promises
the reduction of the production cost, improvement of the
productivity, improvement of the quality of the bond, and other
effects. The contribution of the present invention to industry is
therefore enormous.
* * * * *