U.S. patent application number 14/895321 was filed with the patent office on 2016-07-07 for surface treatment method for powdered metal material.
The applicant listed for this patent is FUJI KIHAN CO., LTD.. Invention is credited to Yoshio Miyasaka.
Application Number | 20160193658 14/895321 |
Document ID | / |
Family ID | 52688884 |
Filed Date | 2016-07-07 |
United States Patent
Application |
20160193658 |
Kind Code |
A1 |
Miyasaka; Yoshio |
July 7, 2016 |
SURFACE TREATMENT METHOD FOR POWDERED METAL MATERIAL
Abstract
To provide a method for surface treatment of a powdery metal
material used for manufacture of harmonic structure metal in which
a fine grain region and a coarse grain region are harmonically
arranged. The method includes the steps of: using a blasting
machine which ejects ejection powder with a compressed gas in a
cabinet and causes the ejection powder to collide against an object
to be collided and comprises dust collecting means; and performing
blasting of causing a powdery metal material and a medium substance
having hardness equal to or higher than that of the powdery metal
material to collide with each other repeatedly, and exfoliate
surface oxides from the powdery metal material and also form the
fine grain region having a crystal grain diameter smaller than a
crystal grain diameter of a center part in the vicinity of a
surface of the powdery metal material.
Inventors: |
Miyasaka; Yoshio;
(Nagoya-shi Aichi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJI KIHAN CO., LTD. |
Aichi |
|
JP |
|
|
Family ID: |
52688884 |
Appl. No.: |
14/895321 |
Filed: |
September 14, 2014 |
PCT Filed: |
September 14, 2014 |
PCT NO: |
PCT/JP2014/074518 |
371 Date: |
December 2, 2015 |
Current U.S.
Class: |
451/38 |
Current CPC
Class: |
B24C 1/00 20130101; B22F
2207/13 20130101; B22F 1/0081 20130101; B22F 2998/10 20130101; B22F
2301/052 20130101; B22F 2301/35 20130101; C21D 8/0205 20130101;
B22F 1/0085 20130101; B22F 2009/045 20130101; B02C 19/06 20130101;
B22F 1/0003 20130101; B22F 2009/044 20130101; B22F 2301/10
20130101; B22F 2999/00 20130101; B33Y 70/00 20141201; B22F 2998/10
20130101; B22F 9/082 20130101; B22F 2009/044 20130101; B22F 2998/10
20130101; B22F 9/082 20130101; B22F 2009/045 20130101 |
International
Class: |
B22F 1/00 20060101
B22F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2013 |
JP |
2013-193254 |
Claims
1. A method for surface treatment of a powdery metal material used
for manufacture of harmonic structure metal in which a fine grain
region and a coarse grain region are harmonically arranged
comprising the steps of: using a blasting machine which ejects
ejection powder with a compressed gas in a cabinet and causes the
ejection powder to collide against an object to be collided and
comprises dust collecting means for suctioning an inside of the
cabinet and removing/collecting power dusts; and performing
blasting of causing a powdery metal material having an average
grain diameter of 10 to 200 .mu.m and a medium substance having
hardness equal to or higher than that of the powdery metal material
to collide with each other repeatedly at an ejection speed of 100
to 300 m/sec, and exfoliate surface oxides from the powdery metal
material and also form the fine grain region having a crystal grain
diameter smaller than a crystal grain diameter of a center part of
the powdery metal material in the vicinity of a surface of the
powdery metal material.
2. The method for surface treatment of a powdery metal material
according to claim 1, wherein the dust collecting means of the
blasting machine comprises a cyclone for classifying the power
dusts and the ejection powder.
3. The method for surface treatment of a powdery metal material
according to claim 1, wherein in the dust collecting means of the
blasting machine, the collected power dusts are stored with
inflammable powder.
4. The method for surface treatment of a powdery metal material
according to claim 1, wherein the blasting is performed by using
the powdery metal material as the ejection powder and the medium
substance as the object to be collided.
5. The method for surface treatment of a powdery metal material
according to claim 1, wherein the blasting is performed by using
the medium substance with a powdery shape as the ejection powder
and the powdery metal material as the object to be collided.
6. The method for surface treatment of a powdery metal material
according to claim 1, wherein the medium substance is made a
powdery metal material of the same material and the same average
grain diameter as the powdery metal material, and the ejection
powder and the object to be collided are both made into the powdery
metal material.
7. The method for surface treatment of a powdery metal material
according to claim 1, wherein a material of the medium substance is
metal having hardness equal to or higher than hardness of the
powdery metal material or ceramic having hardness equal to or
higher than hardness of the powdery metal material after the
surface treatment.
8. The method for surface treatment of a powdery metal material
according to claim 2, wherein in the dust collecting means of the
blasting machine, the collected power dusts are stored with
inflammable powder.
9. The method for surface treatment of a powdery metal material
according to claim 2, wherein the blasting is performed by using
the powdery metal material as the ejection powder and the medium
substance as the object to be collided.
10. The method for surface treatment of a powdery metal material
according to claim 3, wherein the blasting is performed by using
the powdery metal material as the ejection powder and the medium
substance as the object to be collided.
11. The method for surface treatment of a powdery metal material
according to claim 4, wherein the blasting is performed by using
the powdery metal material as the ejection powder and the medium
substance as the object to be collided.
12. The method for surface treatment of a powdery metal material
according to claim 2, wherein the blasting is performed by using
the medium substance with a powdery shape as the ejection powder
and the powdery metal material as the object to be collided.
13. The method for surface treatment of a powdery metal material
according to claim 3, wherein the blasting is performed by using
the medium substance with a powdery shape as the ejection powder
and the powdery metal material as the object to be collided.
14. The method for surface treatment of a powdery metal material
according to claim 4, wherein the blasting is performed by using
the medium substance with a powdery shape as the ejection powder
and the powdery metal material as the object to be collided.
15. The method for surface treatment of a powdery metal material
according to claim 2, wherein the medium substance is made a
powdery metal material of the same material and the same average
grain diameter as the powdery metal material, and the ejection
powder and the object to be collided are both made into the powdery
metal material.
16. The method for surface treatment of a powdery metal material
according to claim 3, wherein the medium substance is made a
powdery metal material of the same material and the same average
grain diameter as the powdery metal material, and the ejection
powder and the object to be collided are both made into the powdery
metal material.
17. The method for surface treatment of a powdery metal material
according to claim 4, wherein the medium substance is made a
powdery metal material of the same material and the same average
grain diameter as the powdery metal material, and the ejection
powder and the object to be collided are both made into the powdery
metal material.
18. The method for surface treatment of a powdery metal material
according to claim 2, wherein a material of the medium substance is
metal having hardness equal to or higher than hardness of the
powdery metal material or ceramic having hardness equal to or
higher than hardness of the powdery metal material after the
surface treatment.
19. The method for surface treatment of a powdery metal material
according to claim 3, wherein a material of the medium substance is
metal having hardness equal to or higher than hardness of the
powdery metal material or ceramic having hardness equal to or
higher than hardness of the powdery metal material after the
surface treatment.
20. The method for surface treatment of a powdery metal material
according to claim 4, wherein a material of the medium substance is
metal having hardness equal to or higher than hardness of the
powdery metal material or ceramic having hardness equal to or
higher than hardness of the powdery metal material after the
surface treatment.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for surface
treatment of a powdery metal material, and more particularly to a
method for surface treatment of a powdery metal material used as a
material in manufacture of a metal product or in formation of
coating using metal powder such as powder metallurgy such as
sintering or thermal spraying.
DESCRIPTION OF THE RELATED ARTS
[0002] The "sintering", i.e., obtaining sintered metal by heating
and solidifying an aggregate of a powdery metal material at a
temperature lower than a melting point is widely used as a type of
powder metallurgy for manufacturing various mechanical components
such as gears, and particularly recently, use of the powdery metal
material as a shaping material in a 3D printer is proposed. It is
also proposed that molding of a desired three-dimensional cubic
model directly by the metal material from shape data such as CAD by
irradiating a laser beam or an electron beam to a powdery metal
material in a predetermined pattern and then sintering it
(Non-Patent Document 1), and in the three-dimensional cubic model
manufactured by sintering of the powdery metal material as above,
unlike a resin model which has been manufactured by a prior-art 3D
printer, application not only as a model or a sample but also a
direct use as components to be incorporated in a machine or the
like are expected.
[0003] However, sintered metal obtained by sintering the powdery
metal material can easily have a density and strength lower than a
case of melt molding due to occurrence of residual pores and the
like, and it cannot be used in practice as a mechanical component
as it is in many cases.
[0004] Thus, with the purpose of removing such residual pores
leading to lower density and lower strength, treatment called
"sinter forging" for forging the obtained sintered metal has been
in practice, but as described above, if treatment of sinter forging
is further required for a component manufactured by simple
three-dimensional shaping using the 3D printer, the merit of
simplicity is lost.
[0005] Unlike the post-treatment as the aforementioned sinter
forging, researches for improving strength of the sintered metal by
devising a composition or structure of the powdery metal material
which is a raw material used for sintering have been promoted, and
as one of them, there was a report that by applying mechanical
milling treatment by stirring with a ball mill to the powdery metal
material before sintering so as to change an internal structure of
the material, sintered metal with high strength can be obtained
(Non-Patent Documents 2 and 3).
[0006] In this method, the mechanical milling treatment by a ball
mill is performed to the powdery metal material having a
predetermined crystalline structure as illustrated in FIG. 6A so as
to apply severe plastic deformation to the powdery metal material
in a concentrated manner, a region called a shell formed by
refining crystal grains (hereinafter this region shall be referred
to as a "fine grain region") is generated in the vicinity of a
surface of the powdery metal material as illustrated in FIG. 6B,
and as a result, a powdery metal material can be obtained provided
with a region at a center part called a core maintaining an
original crystal grain diameter (hereinafter this region shall be
referred to as a "coarse grain region") and the aforementioned fine
grain region covering this coarse grain region.
[0007] By sintering the powdery metal material in which the coarse
grain region and the fine grain region are formed as described
above, the obtained sintered metal is metal having a structure
called "harmonic structure" in which a network-state structure
formed of the fine grain regions of the powdery metal materials
connected to each other and the coarse grain regions arranged
harmonically in the fine grain regions as illustrated in FIG. 6C
(in the present invention, such metal is called "harmonic structure
metal") is obtained, and it has been reported that in such harmonic
structure metal, strength can be drastically improved while
ductility equal to that of sintered metal having uniform equiaxed
grain structure obtained by using a normal powdery metal material
to which the mechanical milling treatment is not applied is
maintained (Non-Patent Document 2).
[0008] In the aforementioned description, the example in which the
manufacturing method of the "harmonic structure metal" is realized
by "sintering" is described, but with regard to the powdery metal
material provided with the aforementioned fine grain region, the
formed metal coating can also be made the "harmonic structure
metal" even if the metal coating is formed on the surface of a base
material by "thermal spraying".
DOCUMENTS OF RELATED ART
Non-Patent Documents
[0009] Non-Patent Document 1: "Special Feature 2-3D Printer
`Attracting!` `Design/Manufacture Solution Exhibition` Report,
Diversification of Molding Materials" [issued by Nikkei BP, "Nikkei
Monodukuri August issue", (published on Aug. 1, 2013) pp. 64 to 58]
[0010] Non-Patent Document 2: "Creation of Innovative Structural
Material Realizing both High Strength and High Ductility by
Harmonic Structure Control" by Kei Ameyama, Tatsuya Sekiguchi
["Journals of The Japan Society for Heat Treatment" Vol. 53, No. 1
2013" issued by The Japan Society for Heat Treatment (published on
Feb. 28, 2013) pp. 1 to 2] [0011] Non-Patent Document 3: "Tripled
Renewed Brass Hardness, Chip Molding/Sintering, New Technology by
Nihon Univ. Improved Conductivity to Practice" [Nikkan Kogyo
Shimbun (Apr. 30, 2013)]
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0012] As introduced as Non-Patent Documents 2 and 3, when
sintering is to be performed by using the powdery metal material
subjected to stirring by a ball mill in advance, the sintered metal
obtained by the sintering has the "harmonic structure" so that
metal having excellent characteristics of both high ductility and
high strength is obtained.
[0013] However, as described in Non-Patent Documents 2 and 3, when
the powdery metal material is treated by the ball mill, treatment
efficiency is extremely poor, and treatment time is 100 hours in
Non-Patent Document 2 and 32 hours in Non-Patent Document 3 as
examples.
[0014] Moreover, the treatment of the powdery metal material by the
ball mill has a risk of powder dust explosion and is an extremely
dangerous work.
[0015] That is, since the powdery metal material used for sintering
and the like has a fine grain diameter at approximately 100 .mu.m
in general, if the powdery metal material is contained in the ball
mill, stirred under presence of air and subject to a friction force
or an impact force, discharge of static electricity generated by
friction in stirring can cause powder dust explosion.
[0016] The powder dust explosion here occurs when the following
three elements: presence of oxygen; generation of dusts at
explosion lower limit density or more; and presence of ignition
source are all satisfied and thus, if occurrence of the powder dust
explosion is to be prevented, one or more of these conditions need
to be eliminated. However, it is impossible to remove occurrence of
friction or impact, which can be the ignition source, from the ball
mill inside which the friction force and the impact force are
generated in order to apply severe plastic deformation to the
powdery metal material.
[0017] Thus, if the powder dust explosion is to be prevented, the
work should be performed in a state in which oxygen is eliminated
by filling an inside of the ball mill with an inactive gas or the
like, or an input amount of the powdery metal material should be
adjusted so as to be less than the explosion lower limit density,
or the both should be done.
[0018] However, if the treatment is performed in a state in which
the ball mill is filled with the inactive gas, a manufacturing cost
is drastically raised, and considering that the explosion lower
limit density of the powdery metal [200 mesh (opening: 74 .mu.m)
completely through] is 35 g/m.sup.3 for aluminum, 45 g/m.sup.3 for
titanium, and 120 g/m.sup.3 for iron ["Safety and Hygiene of Arc
Welding (third)" extracted from WE-COM magazine No. 6 (published in
October 2012), Japan Welding Engineering Society, General
Incorporated Association], if stirring is to be performed at the
explosion lower limit density or less, only an extremely small
amount can be treated at one time. Treatment might be possible for
small-scaled production at an experimental level in a lab, but
treatment of a large amount of the powdery metal material by a ball
mill on a commercial base is impossible.
[0019] Moreover, even if the aforementioned treatment by the ball
mill can be applied to the treatment of the powdery metal material,
surface oxides such as oxidized scale exfoliated from a surface of
the powdery metal material are mixed in the powdery metal material
treated by this method, and the oxides prevent binding between
powdery metal materials during sintering and hinder improvement of
strength.
[0020] That is, the powdery metal material used for sintering or
thermal spraying is manufactured by an atomizing method in general,
but since in this atomizing method, the powdery metal material is
manufactured by spraying/scattering molten metal for refining and
by instantaneously rapid cooling/solidifying it, the oxidized scale
adheres to the surface of the powdery metal material.
[0021] On the powdery metal materials manufactured by methods other
than the atomizing method, an oxidized film which is a surface
oxide is also formed more or less by contact with oxygen in the
air.
[0022] Even if these surface oxides such as the oxidized scale are
exfoliated from the surface of the powdery metal material by
friction or impact received during stirring in the ball mill, the
oxides exfoliated as above are not eliminated even after the
exfoliation but stay mixed in the powdery metal material due to a
structure of the ball mill.
[0023] Moreover, since the exfoliated oxides are continuously
stirred together with the powdery metal material in the ball mill,
a part of the exfoliated oxides is pressed onto the surface of the
powdery metal material by friction or impact caused by stirring and
adheres thereto again by being embedded or the like.
[0024] Thus, if the powdery metal material treated by the ball mill
is taken out as it is and used for sintering, improvement of
strength is suppressed by presence of the oxides mixed in the
powdery metal material.
[0025] On the other hand, in order to remove the oxides mixed in
the powdery metal material, the powdery metal material after the
treatment by the ball mill can be subjected to wind-power sorting
or the like, for example, but with this method, another process for
further eliminating the oxides needs to be provided in addition to
the treatment by the ball mill, whereby productivity is further
lowered.
[0026] Moreover, with this method, though the oxides mixed in the
powdery metal material can be removed to some degree, the oxides
re-adhering to the surface of the powdery metal material cannot be
separated/removed.
[0027] Thus, if surface treatment of the powdery metal material can
be performed by a method which can also remove such surface
oxidized film, further improvement of strength of the obtained
harmonic structure metal can be expected.
[0028] The present invention was made in order to overcome the
disadvantages in the aforementioned prior-art techniques and has an
object to provide a method for surface treatment of a powdery metal
material which can perform treatment of forming the aforementioned
fine grain region on a surface of the powdery metal material used
as a material for obtaining a metal product or metal coating
provided with a harmonic structure by a method such as powder
metallurgy such as sintering, thermal spraying and the like without
a concern of powder dust explosion and can perform exfoliation of
oxides from the surface and removal of the oxides after the
exfoliation easily and reliably and also efficiently in a
relatively short time.
Means for Solving the Problems
[0029] In order to achieve an objective of the invention, a method
for surface treatment of a powdery metal material according to the
present invention used for manufacture of harmonic structure metal
in which a fine grain region and a coarse grain region are
harmonically arranged comprises the steps of:
[0030] using a blasting machine which ejects a medium substance or
a powdery metal material as ejection powder with a compressed gas
in a cabinet and causes the ejection powder to collide against a
medium substance or a powdery metal material as an object to be
collided and comprises dust collecting means for suctioning an
inside of the cabinet and removing/collecting power dusts; and
[0031] performing blasting of causing the powdery metal material as
the object to be collided having an average grain diameter of 10 to
200 .mu.m and the medium substance as the ejection powder having
hardness equal to or higher than that of the powdery metal material
to collide with each other repeatedly at an ejection speed of 100
to 300 m/sec, and exfoliate surface oxides from the powdery metal
material and also form the fine grain region having a crystal grain
diameter smaller than that of a center part of the powdery metal
material in the vicinity of a surface of the powdery metal
material.
[0032] The blasting machine used in said blasting has a cyclone for
classifying the power dusts and the ejection powder.
[0033] Furthermore, in the dust collecting means of the blasting
machine, the collected power dusts are stored with inflammable
powder, such as calcium carbonate or the like.
[0034] In the method for surface treatment of a powdery metal
material, the ejection powder and the object to be collided may be
exchanged each other, i.e., the blasting may be performed by using
the powdery metal material as the ejection powder and the medium
substance as the object to be collided; and
[0035] the blasting may be performed by using the medium substance
with a powdery shape as the ejection powder and the powdery metal
material as the object to be collided.
[0036] Furthermore, the medium substance may be made a powdery
metal material of the same material and the same average grain
diameter as the powdery metal material, and the ejection powder and
the object to be collided may be both made into the powdery metal
material.
[0037] A material of the medium substance may be metal having
hardness equal to or higher than hardness of the powdery metal
material or ceramic having hardness equal to or higher than
hardness of the powdery metal material after the surface
treatment.
Effect of the Invention
[0038] According to the method for surface treatment of the powdery
metal material of the present invention, the following marked
effects can be obtained by means of the aforementioned constitution
of the present invention.
[0039] By performing blasting of causing a powdery metal material
having an average grain diameter of 10 to 200 .mu.m and a medium
substance having hardness equal to or higher than that of the
powdery metal material to be collided with each other repeatedly at
an ejection speed of 100 to 300 m/sec, surface oxides on the
powdery metal material are removed, and repetition of rapid
temperature rise and cooling occurring in the vicinity of a surface
of the powdery metal material at the collision refines crystal
grains in the vicinity of the surface of the powdery metal
material, and the powdery metal material in which a fine grain
region having a crystal grain diameter smaller than a crystal grain
diameter at a center part is formed in the vicinity of the surface
can be treated by a relatively simple method of blasting easily and
in a large quantity in a short time.
[0040] Moreover, by performing the aforementioned blasting by means
of a blasting machine with a dust collection function, mass
production is made possible while a risk of powder dust explosion
is avoided, and by removing and collecting surface oxides such as
oxidized scale exfoliated from the surface of the powdery metal
material as powder dusts by suctioning in a cabinet, a powdery
metal material without mixing of the surface oxides could be
obtained without separately providing a process of removing the
surface oxides in a post-process.
[0041] Particularly, if means provided with a cyclone for
classifying the powder dusts from the ejected powder is to be used
as dust collecting means for the blasting, even if the powdery
metal powder and the exfoliated surface oxides are collected in the
mixed state, the surface oxides can be classified with the powder
dusts from the ejected powder and collected so that the powdery
metal material from which the surface oxides are removed with
higher accuracy could be obtained.
[0042] Moreover, in the dust collecting means of the aforementioned
blasting machine, if the removed powder dusts are stored with
inflammable powder such as calcium carbonate, a risk of powder dust
explosion not only in a processing chamber but also in the
collecting machine could be reduced.
[0043] This blasting may be so configured that the powdery metal
material as the ejection powder is ejected to the medium substance
and made to collide against said medium substance, or that the
medium substance as the ejection powder is ejected to the powdery
metal material and is made to collide against said powdery metal
material, but when it is so configured that both the ejection
powder and an object to be collided are made to be a powdery metal
material having the same average grain diameter and formed of the
same material and the powdery metal material is ejected to and is
made to collide against the powdery metal material, the surface
treatment is applied to both the powdery metal powder as the
ejection powder and the powdery metal powder as the object to be
collided, and a throughput could be doubled.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1A is schematic explanatory view of a blasting machine
of a gravity type used in a method for surface treatment of the
present invention;
[0045] FIG. 1B is schematic explanatory view of a blasting machine
of a direct pressure type used in a method for surface treatment of
the present invention;
[0046] FIG. 2 is a graph showing an X-ray diffraction result of an
untreated stainless powder (SUS304 equivalent);
[0047] FIG. 3 is a graph showing an X-ray diffraction result of a
stainless powder (SUS 304 equivalent) treated by a method in
Example 1;
[0048] FIG. 4 is a graph showing an X-ray diffraction result of an
untreated powder high-speed tool steel (SKH equivalent);
[0049] FIG. 5 is a graph showing an X-ray diffraction result of a
powder high-speed tool steel (SKH equivalent) treated by a method
in Example 2; and
[0050] FIG. 6A is an explanatory view explaining creation of a
harmonic structure in which is a schematic view of an untreated
powdery metal material;
[0051] FIG. 6B is an explanatory view explaining creation of a
harmonic structure in which is a schematic view of a powdery metal
material after treatment by a ball mill; and
[0052] FIG. 6C is an explanatory view explaining creation of a
harmonic structure in which is a schematic view of harmonic
structure metal obtained by sintering the powdery metal material in
FIG. 6B.
[0053] Subsequently, embodiments of the present invention will be
described below by referring to the attached drawings.
ENTIRE CONFIGURATION
[0054] The present invention is to remove surface oxides such as an
oxidized scale prohibiting improvement of strength in sintering or
thermal spraying from a surface of a powdery metal material and to
form a fine grain region having a crystal grain diameter smaller
than the crystal grain diameter at a center part in the vicinity of
the surface of the powdery metal material by performing blasting of
repeatedly causing the powdery metal material which is a treatment
target and a medium substance which collides against the powdery
metal material to collide against each other at a predetermined
ejection speed by means of a known blasting machine.
[0055] As described above, a metal product obtained by a method of
powder metallurgy such as sintering or metal coating manufactured
by thermal spraying by using a powdery metal material in which a
coarse grain region having a relatively large crystal grain
diameter is formed at the center part and a fine grain region with
a smaller crystal grain diameter than that of the coarse grain
region is formed in the vicinity of the surface become harmonic
structure metal having a crystalline structure [see FIG. 6C] in
which the coarse grain regions are harmonically arranged in a
network of a fine grain structure formed by binding the fine grain
regions and exhibiting an excellent characteristic that both high
ductility and high strength are realized.
Powdery Metal Material
[0056] The powdery metal material which is a treatment target in
the present invention is powdery metal having an average grain
diameter of 10 to 200 .mu.m to be used as a material in powder
metallurgy such as sintering or thermal spraying, and various
materials can be used as long as it is applicable to powder
metallurgy or thermal spraying. The material may be constituted by
either one of pure metal and an alloy.
[0057] As an example, metal used for powder metallurgy in general
includes iron-, copper-, stainless-, titanium-, and tungsten-based
metal and metal used for thermal spraying in general includes zinc,
aluminum, copper and the like. They can be all included in the
material of the powdery metal material in the present
invention.
[0058] The powdery metal material to be used can be manufactured by
various methods, e.g. spraying methods represented by an atomizing
method which is a manufacturing method of the powdery metal
material used in general in the powder metallurgy and thermal
spraying, and various known methods such as mechanical crushing,
electrolytic deposition and the like.
[0059] A shape of the powder may be spherical but this is not
limiting and those with various shapes can be used.
[0060] The crystal grain diameter of the powdery metal material
before treatment is a crystal grain diameter of the aforementioned
coarse grain region as it is, and if the crystal grain diameter of
the coarse grain region is set within a predetermined range, a
powdery metal material with a corresponding crystal grain diameter
is selected. Though not particularly limiting, the average crystal
grain diameter of the coarse grain region is several to several
tens .mu.m as an example.
Medium Substance
[0061] As the aforementioned medium substance which collides
against the powdery metal material, various substances can be used
as long as it has hardness equal to or higher than that of the
powdery metal material, and not only those made of metal but those
made of ceramic can be used.
[0062] If the medium substance made of ceramic not subjected to
work hardening is to be used, it is preferable that ceramic having
hardness equal to or higher than that of the powdery metal material
after the surface treatment of the present invention is used so
that the powdery metal material can maintain the same or improved
hardness after the work hardening.
[0063] By constituting the medium substance itself by the
aforementioned powdery metal material, the aforementioned fine
grain region may be formed in the both of the powdery metal
material as the treatment target and the powdery metal material as
the medium substance by collision between the powdery metal
materials.
[0064] A shape of the medium substance needs to be constituted as
powder when the medium substance is to be used as the ejection
powder, but when the treatment is to be performed by using the
aforementioned powdery metal material as the ejection powder, the
medium substance does not have to be powder but may be constituted
in a form of a plate body or the like.
Blasting Method and Blasting Machine
[0065] The collision between the powdery metal material and the
medium substance described above is made by blasting means of the
blasting machine.
[0066] As this blasting, as described above, it may be so
configured that the powdery metal material is ejected as the
ejection powder to the medium substance and made to collide against
said medium substance, or to the contrary, a powdery medium
substance may be prepared as the ejection powder and ejected to the
powdery metal material so as to cause a collision against said
powdery metal material. Moreover, it may be so configured that the
ejection powder and the object to be collided are both constituted
by the powdery metal material having the same average grain
diameter and made of the same material, and the powdery metal
materials are made to collide against each other.
[0067] As the blasting machine 1 to be used, those with various
known constitution can be used as long as it is a blasting machine
having a cabinet 21 as a processing chamber and a dust collection
function of suctioning an inside of the cabinet 21 for dust
collection, and the blasting machine of either one of a direct
pressure type and a gravity type may be used.
[0068] A constitution example of the gravity type blasting machine
1 and a constitution example of the direct pressure type to be used
for the surface treatment of the present invention are illustrated
in FIG. 1A and FIG. 1B, respectively.
[0069] An example in which the surface treatment of the present
invention is performed with the blasting machine 1 by using the
powdery metal material having the same material and the same
average grain diameter for both the ejection powder and the object
to be collided will be described below. However, the blasting
machine 1 used in the method for surface treatment of the present
invention is not limited to illustrated constitution.
[0070] The blasting machine 1 illustrated in FIGS. 1A and 1B
comprises: the cabinet 21 which becomes a processing chamber for
accommodating an ejection nozzle 22 and a workpiece and performing
blasting; and a dust collecting machine 38 for suctioning an inside
of this cabinet 21. The blasting machine 1 is provided with a
cyclone type collection tank 23 between this dust collecting
machine 38 and the cabinet 21 for collecting into the collection
tank 23 the powdery metal material collected by suctioning of the
inside of the cabinet 21 in a state mixed with powder dusts and can
collect into the dust collecting machine 38 the powder dusts
separated from the powdery metal material in the cyclone type
collection tank 23.
[0071] It is configured that the powdery metal material collected
in the collection tank 23 as described above can be ejected again
by an ejection nozzle 22 in the cabinet 21.
[0072] At a destination to which a tip end of the ejection nozzle
22 is directed inside the aforementioned cabinet 21, a barrel
basket 24 which is a container rotating during ejection of the
ejection powder and opened upward is provided, and the powdery
metal material which is the object to be collided can be input
therein.
[0073] In the example illustrated in FIG. 1A, this barrel basket 24
is depicted as a mesh with a large number of small pores formed,
but the illustrated example is not limiting, and the barrel basket
may be constituted without such small pores.
[0074] Prior to the treatment by means of the blasting machine 1
constituted as above, the powdery metal material is contained in
the collection tank 23 and the powdery metal material is also
contained in the barrel basket 24 provided in the processing
chamber, and while the barrel basket 24 is rotated in this state,
ejection of the powdery metal material from the ejection nozzle 22
is started at the ejection speed of 100 to 300 m/sec and then, the
powdery metal material ejected from the ejection nozzle 22 collides
against the powdery metal material in the rotating barrel basket
24.
[0075] An ejection pressure may be 100 m/sec or more in the
treatment of a non-iron based powdery metal material, but 150 m/sec
or more is preferable for the treatment of an iron-based powdery
metal material.
[0076] By performing ejection of the powdery metal material as
described above, the powdery metal material in the barrel basket 24
and the powdery metal material ejected from the ejection nozzle 22
mutually receive energy at the collision so that surface oxides
such as oxidized scale formed on the surface of the powdery metal
materials are exfoliated. Also, the temperature of the surface in
the collision portion is rapidly raised and also cooled so that the
crystal grains on the surface of the collision portion are refined,
and a fine grain region is formed in which a crystal grain with a
diameter smaller than that of the crystal grain on a center portion
of the powdery metal material is formed in the vicinity of the
surface of the powdery metal material.
[0077] It is empirically confirmed that the fine grain region of
the powdery metal material is formed on the surface of the powdery
metal material to a depth of approximately 20% at the maximum with
respect to the grain diameter if the powdery metal material as the
treatment target is less than 100 .mu.m and formed to a depth of
approximately 10% at the maximum with respect to the grain diameter
if the powdery metal material as the treatment target is 100 .mu.m
or more, and thus, in the method for surface treatment of the
present invention with the powdery metal material having an average
grain diameter of 10 to 200 .mu.m as the treatment target, the
aforementioned fine grain region is formed within a range of 2 to
20 .mu.m from the surface at the maximum depending on the grain
diameter of the powdery metal material as the treatment target.
[0078] A description "in the vicinity of the surface" used herein
refers to the surface including the above described range of
depth.
[0079] The powdery metal material ejected from the ejection nozzle
22 collides against the powdery metal material in the barrel basket
24 and then, accumulates in the barrel basket 24 except those
forced out to outside the barrel basket 24 and is stirred with
rotation of the barrel basket 24 with the powdery metal material
having been originally present in the barrel basket 24.
[0080] Thus, if the ejection of the powdery metal material from the
ejection nozzle 22 is continued, the powdery metal material in the
barrel basket 24 increases and overflows from the barrel basket 24
and drops to a bottom part of the cabinet 21.
[0081] The bottom part of the cabinet 21 is formed as a hopper
having an inverted trapezoidal shape, and a lower end of the hopper
communicates with the dust collecting machine 38 through an exhaust
air passage 33 and the collection tank 23 and thus, when the inside
of the cabinet 21 is suctioned by a ventilator 39 provided in the
dust collecting machine 38, the dropped powdery metal material and
powder dusts are suctioned with the air in the cabinet 21 and
supplied into the cyclone type collection tank 23, the powder dusts
and the powdery metal material are classified in this collection
tank 23 and the powdery metal material is collected downward in the
collection tank 23.
[0082] The surface oxides such as oxidized scale generated on the
surface of the powdery metal material are harder and more fragile
as compared with the powdery metal material. Therefore, the surface
oxides are finely crushed when they are exfoliated by an impact
caused by a collision between the powdery metal materials. Thus,
the surface oxides are not collected in the collection tank 23 but
sent to the dust collecting machine 38 as powder dusts through a
pipe 32 connected to an upper part of the collection tank 23 and
collected downward in the dust collecting machine 38, and clean air
is discharged to the outside air by the ventilator 39.
[0083] As described above, the inside of the processing chamber
formed in the cabinet 21 is suctioned at all times, and the powder
dusts and the powdery metal material floating in the air are
removed and kept to the explosion lower limit density or less.
Thus, there is no concern of the powder dust explosion in the
cabinet even by heat generation by ejection, collision and friction
of the ejection powder which is the powdery metal material or
generation of static electricity in this embodiment.
[0084] On the other hand, the powder dusts classified in the
cyclone type collection tank 23 and collected in the dust
collecting machine 38 are accommodated in the dust collecting
machine 38 with an inflammable powder such as powder of calcium
carbonate, for example, so that a density of flammable powder dusts
in the air in the dust collecting machine 38 becomes the explosion
lower limit density or less, whereby a risk of powder dust
explosion in the dust collecting machine 38 is also avoided.
[0085] The powdery metal material collected in the collection tank
23 is ejected again by the ejection nozzle 22 toward the powdery
metal material in the barrel basket 24, and the aforementioned
process is repeated so that the surface oxides such as oxidized
scale are removed from the surfaces of any powdery metal materials,
and the fine grain region is formed so as to cover the entirety in
the vicinity of the surface.
[0086] When the powdery metal material on which the fine grain
region is formed in the vicinity of the surface as described above
is used as a material for powder metallurgy such as sintering or is
used for formation of a metal film of thermal spraying or the like,
in the obtained sintered metal or metal coating, harmonic structure
metal in which the coarse grain region is harmonically arranged in
the network of the fine grain structures formed by mutually
connecting parts of the fine grain regions is obtained. In such
harmonic structure metal, excellent characteristics of realization
of both the high ductility and high strength are obtained.
[0087] Particularly in the powdery metal material treated by the
method of the present invention, the surface oxides such as
oxidized scale causing lowered strength in sintering or deposition
can be favorably removed and thus, strength of the obtained
sintered metal or metal coating can be further improved.
[0088] In the aforementioned description, the constitution is
described in which the ejection powder and the object to be
collided are both the powdery metal materials and the ejection
powder and the object to be collided are made to collide against
each other in the barrel basket 24 provided in the cabinet 21, but
a plate body formed of a material having hardness equal to or
higher than that of the ejection powder is accommodated as the
medium substance in the cabinet 21 instead of the aforementioned
barrel basket 24, and the surface treatment of the present
invention may be configured to be performed by ejecting the powdery
metal material as the ejection powder to this plate body and making
to collide against the same.
[0089] Moreover, it may be so constituted that the aforementioned
blasting machine 1 provided with the barrel basket 24 is used, a
powdery medium substance is used as the ejection powder, and the
medium substance as the ejection powder is ejected to the powdery
metal material contained in the barrel basket 24, and in this case,
the powdery metal material and the medium substance are classified
after the treatment and collected, respectively.
EXAMPLES
[0090] Examples in which the method for surface treatment of the
present invention is applied to the powdery metal materials of
various materials will be described below.
Example 1
[0091] The method for surface treatment of the present invention
was performed to stainless powder (SUS304 equivalent: #80) as the
powdery metal material. Treatment conditions are shown in Table 1
below:
TABLE-US-00001 TABLE 1 Treatment conditions for Example 1 (SUS304)
Blasting Type Direct pressure type ("FD-4LD" by Fuji machine
Manufacturing Co., Ltd.) Barrel made of SUS304, no pores, 4
rotations per basket minute Nozzle Nozzle diameter: (.phi.5 mm
Oscillation: 100 mm in width, 60 times per minute Powdery Material
Stainless powder (SUS-304 equivalent) metal (0.2 to 0.3%C
<1.8%Si <1.0%Mn 18 to material 20%Cr 8 to 10.5%Ni) Grain #80
(105 to 250 .mu.m/177 .mu.m on average) diameter Medium Same as
powdery metal material substance Blasting Ejection 0.6 MPa
conditions pressure Ejection 150 m/sec or more speed Ejection 300
mm distance Ejection 6 kg /min rate Ejection 3 hours time
Throughput 30 kg
[0092] The stainless powder in 10 kg was contained in the barrel
basket provided in the processing chamber of the blasting machine
and 20 kg into the collection tank, and the treatment of ejecting
the stainless powder in the collection tank by the ejection nozzle
into the barrel basket was performed continuously for 3 hours under
the condition shown in the aforementioned Table 1.
[0093] As the result of the aforementioned treatment, in the
stainless powder after the treatment, the oxidized scale was
removed and the surface was cleaned, and moreover, hardness of the
stainless powder which was 250 to 350 HV before the treatment rose
to 450 to 550 HV after the treatment, and it is expected from the
result that the crystal grains in the vicinity of the surface were
refined.
[0094] Refining of the crystal grain diameter can be evaluated from
an increase of a line width of an X-ray analysis peak using the
Scherrer (Sherrer, 1918) formula. In the X-ray analysis result
(FIG. 3) after the treatment by the present invention, the line
width of the peak drastically increased with respect to the X-ray
analysis result (see FIG. 2) of the untreated stainless powder.
Thus, it was confirmed that hardness of the aforementioned powdery
metal material rose, and refining of the crystal grain diameter on
the surface was also confirmed from the X-ray diffraction
result.
Example 2
[0095] The method for surface treatment of the present invention
was performed to a powder high-speed tool steel (SKH equivalent:
#150) as the powdery metal material. The treatment conditions are
shown in Table 2 below:
TABLE-US-00002 TABLE 2 Treatment conditions for Example 2 (Powder
high-speed tool steel: SKH equivalent) Blasting Type Gravity type
("SGK-4LD" by Fuji machine Manufacturing Co., Ltd.) Barrel made of
SUS304, no pores, 4 rotations basket per minute Nozzle Nozzle
diameter: .phi.9 mm Oscillation: 100 mm in width, 60 times per
minute Powdery Material Powder high-speed tool steel ("SPM30" by
metal Sanyo Special Steel Co., Ltd.) material (1.3%C 4.0%Cr 5%Mo
6%W 3%V 8%Co) Grain #150 (44 to 125 .mu.m/85 .mu.m on average)
diameter Medium Same as powdery metal material substance Blasting
Ejection 0.6 MPa conditions pressure Ejection 150 m/sec or more
speed Ejection 200 mm distance Ejection 5 kg /min rate Ejection 5
hours time Throughput 20 kg
[0096] The powdery high-speed tool steel in 10 kg was contained in
the barrel basket provided in the processing chamber of the
blasting machine and 10 kg into the collection tank, and the
treatment of ejecting the powdery high-speed tool steel in the
collection tank by the ejection nozzle into the barrel basket was
performed continuously for 5 hours under the conditions shown in
the aforementioned Table 2.
[0097] As a result, hardness of the powdery high-speed tool steel
at 650 to 750 HV before the treatment rose to 900 to 1000 HV after
the treatment.
[0098] Moreover, in the powdery high-speed tool steel after the
treatment, the oxidized scale was removed and the surface was
cleaned, and from the X-ray diffraction result, the line width of
the X-ray analysis peak increased (see FIG. 5) as compared with the
untreated one (see FIG. 4), and the refining of the surface
structure by the treatment according to the method of the present
invention was confirmed (see FIGS. 4 and 5).
Example 3
[0099] The method for surface treatment of the present invention
was performed to powder of an alloy steel for mechanical structure
(SCM equivalent: #150) as the powdery metal material. The treatment
conditions are shown in Table 3 below:
TABLE-US-00003 TABLE 3 Example 3: Treatment conditions for powder
of alloy steel for mechanical structure (SCM equivalent) Blasting
Type Gravity type ("SGK-4LD" by Fuji machine Manufacturing Co.,
Ltd.) Barrel made of SUS304, no pores, 4 rotations basket per
minute Nozzle Nozzle diameter: .phi.9 mm Oscillation: 100 mm in
width, 60 times per minute Powdery Material Alloy steel for
mechanical structure metal (SCM equivalent) material (0.23%C 0.2%Mo
1.5%Cr) Grain #150(44 to 125 .mu.m/85 .mu.m on average) diameter
Medium Same as powdery metal material substance Blasting Ejection
0.6 MPa conditions pressure Ejection 150 m/sec or more speed
Ejection 200 mm distance Ejection 5 kg /min rate Ejection 5 hours
time Throughput 20 kg
[0100] The power of alloy steel for mechanical structure in 10 kg
was contained in the barrel basket provided in the processing
chamber of the blasting machine and 10 kg into the collection tank,
and the treatment of ejecting the powder of the alloy steel for
mechanical structure in the collection tank by the ejection nozzle
into the barrel basket was performed continuously for 5 hours under
the conditions shown in the aforementioned Table 3.
[0101] As a result, hardness of the powder of alloy steel for
mechanical structure at 150 to 200 HV before the treatment rose to
300 to 350 HV after the treatment.
[0102] Moreover, in the powder of the alloy steel for mechanical
structure after the treatment, the oxidized scale was removed and
the surface was cleaned, and it is considered from the
aforementioned rise of hardness that the refined structure is
formed on the surface.
Example 4
[0103] The method for surface treatment of the present invention
was performed to powder of the copper alloy (#150) as the powdery
metal material. The treatment conditions are shown in Table 4
below:
TABLE-US-00004 TABLE 4 Treatment conditions for Example 4 (copper
alloy) Blasting Type Gravity type ("SGK-4LD" by Fuji machine
Manufacturing Co., Ltd.), No barrel basket Nozzle Nozzle diameter =
.phi.9 mm Oscillation: 100 mm in width, 60 times per minute Powdery
Material Copper alloy metal (21%Zn 17%Ni 0.34%Mn, the material
remnant Cu) Grain #150 (44 to 125 .mu.m/85 .mu.m on average)
diameter Medium SKD11 plate having diameter of 400 mm substance and
thickness of 20 mm Blasting Ejection 0.4 MPa conditions pressure
Ejection 100 m/sec or more speed Ejection 200 mm distance Ejection
4 kg /min rate Ejection 7 hours time Throughput 20 kg
[0104] The copper alloy powder in 20 kg was contained in the
collection tank, and the treatment of ejecting the copper alloy
powder in the collection tank by the ejection nozzle toward a
position where a core was shifted by 100 mm from a center of a
plate (.phi.400 mm, thickness 20 mm) made of SKD11 arranged in the
processing chamber was performed for 7 hours continuously.
[0105] As a result, hardness of the copper alloy powder at 160 to
200 HV before the treatment rose to 220 to 260 HV after the
treatment.
[0106] Moreover, in the copper alloy powder after the treatment,
the oxidized scale was removed and the surface was cleaned, and it
is considered from the aforementioned rise of hardness that the
refined structure is formed on the surface.
Example 5
[0107] The method for surface treatment of the present invention
was performed to powder of aluminum alloy (AC8A: #80) as the
powdery metal material. The treatment conditions are shown in Table
5 below:
TABLE-US-00005 TABLE 5 Treatment conditions for Example 5: Aluminum
alloy (AC8A) Blasting Type Gravity type ("SGK-4LD" by Fuji machine
Manufacturing Co., Ltd.) Barrel made of SUS304, with (.phi.1 mm
pores, 4 basket rotations per minute Nozzle Nozzle diameter: .phi.9
mm Oscillation: 100 mm in width, 60 times per minute Powdery
Material Aluminum alloy metal (AC8A: 12%Si 0.8%Fe 1.1%Cu 0.15%Mn
material 1%Mg 1.1%Ni, the remnant Al) Grain #80 (105 to 250
.mu.m/177.mu.m on average) diameter Medium Shot made of a high
speed steel (#400, substance 45 .mu.m on average) Blasting Ejection
0.4 MPa conditions pressure Ejection 100 m/sec or more speed
Ejection 200 mm distance Ejection 4 kg /min rate Ejection 7 hours
time Throughput 10 kg
[0108] A barrel basket in which a large number of holes, each
having a diameter of 1 mm, are formed was provided in the
processing chamber, and the powder of the aluminum alloy (AC8A) was
input in 10 kg into this barrel basket, and a treatment of ejecting
a shot made of a high speed steel collected in the collection tank
into the barrel basket was performed for 7 hours continuously.
[0109] As a result of the aforementioned treatment, hardness of the
aluminum alloy powder at 120 to 140 HV before the treatment rose to
200 to 250 HV after the treatment.
[0110] Moreover, in the aluminum alloy powder after the treatment,
the oxidized scale was removed and the surface was cleaned, and
from the aforementioned rise of hardness, it is considered that a
component of the high speed steel which is the medium substance is
diffused and penetrated into the surface of the powder of the
aluminum alloy and the refined structure was formed on the
surface.
Sintering Test Result
[0111] Then, discharge plasma sintering was performed by using the
powdery metal material treated by the method for surface treatment
of the present invention described as above as Examples 1 to 5.
[0112] As a result, also in the sintered metal obtained by
sintering the powdery metal material of any one of examples 1 to 5,
the "harmonic structure" in which the coarse grain structures are
arranged harmonically in the network formed by connecting the fine
grain regions to each other is provided, and it was confirmed that
the method for surface treatment of the present invention is a
method for surface treatment which can treat the powdery metal
material used for manufacture of the harmonic structure metal
simply, in a large quantity and moreover, safely.
DESCRIPTIONS OF REFERENCE NUMERALS
[0113] 1. Blasting machine [0114] 21. Cabinet [0115] 22. Ejection
nozzle [0116] 23. Collection tank (cyclone type) [0117] 24. Barrel
basket [0118] 32. Pipe [0119] 33. Exhaust air passage [0120] 38.
Dust collecting machine [0121] 39. Ventilator
* * * * *