U.S. patent application number 16/717869 was filed with the patent office on 2020-05-07 for wear resistant material and system and method of creating a wear resistant material.
This patent application is currently assigned to ESCO GROUP LLC. The applicant listed for this patent is ESCO GROUP LLC. Invention is credited to Srinivasarao Boddapati.
Application Number | 20200139431 16/717869 |
Document ID | / |
Family ID | 48870491 |
Filed Date | 2020-05-07 |
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United States Patent
Application |
20200139431 |
Kind Code |
A1 |
Boddapati; Srinivasarao |
May 7, 2020 |
WEAR RESISTANT MATERIAL AND SYSTEM AND METHOD OF CREATING A WEAR
RESISTANT MATERIAL
Abstract
A system and method of forming a wear resistant composite
material includes placing a porous wear resistant filler material
in a mold cavity and infiltrating the filler material with a matrix
material by heating to a temperature sufficient to melt the matrix
material, then cooling the assembly to form a wear resistant
composite material. The system and method can be used to form the
wear resistant composite material on the surface of a substrate,
such as a part for excavating equipment or other mechanical part.
One suitable matrix material may be any of a variety of ductile
iron alloys.
Inventors: |
Boddapati; Srinivasarao;
(Bothell, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ESCO GROUP LLC |
Portland |
OR |
US |
|
|
Assignee: |
ESCO GROUP LLC
Portland
OR
|
Family ID: |
48870491 |
Appl. No.: |
16/717869 |
Filed: |
December 17, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13752521 |
Jan 29, 2013 |
10543528 |
|
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16717869 |
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61593091 |
Jan 31, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y10T 428/24545 20150115;
B22D 19/00 20130101; B32B 3/26 20130101; B22D 23/06 20130101; Y10T
428/12479 20150115; C22C 37/10 20130101; Y10T 428/12389 20150115;
B22D 19/08 20130101; Y10T 428/2495 20150115; Y10T 428/24997
20150401; B32B 7/02 20130101; B32B 5/16 20130101; B32B 15/01
20130101; B32B 7/04 20130101; B32B 15/16 20130101; B32B 2264/107
20130101; B32B 2307/554 20130101; Y10T 428/12042 20150115; Y10T
428/12403 20150115; C22C 1/1036 20130101; B32B 3/28 20130101; B32B
2260/025 20130101; C22C 37/06 20130101; C22C 33/0271 20130101; Y10T
428/24537 20150115; C22C 37/08 20130101 |
International
Class: |
B22D 19/00 20060101
B22D019/00; C22C 33/02 20060101 C22C033/02; C22C 37/08 20060101
C22C037/08; C22C 37/10 20060101 C22C037/10; B32B 15/16 20060101
B32B015/16; C22C 1/10 20060101 C22C001/10; C22C 37/06 20060101
C22C037/06; B22D 19/08 20060101 B22D019/08; B22D 23/06 20060101
B22D023/06; B32B 15/01 20060101 B32B015/01; B32B 7/02 20060101
B32B007/02; B32B 7/04 20060101 B32B007/04; B32B 3/28 20060101
B32B003/28; B32B 5/16 20060101 B32B005/16; B32B 3/26 20060101
B32B003/26 |
Claims
1-65. (canceled)
66. A wear part for earth engaging equipment comprising: a metal
substrate including a working portion for engaging earthen
material, the working portion including a surface; an expendable
sheet metal shell connected by welding or brazing to the substrate,
a portion of the sheet metal shell being spaced from the substrate
to define a cavity between the surface of the substrate and the
shell; and a composite material substantially filling the cavity
and forming a coating on at least a portion of the surface of the
substrate, the composite coating comprising a porous wear resistant
material infiltrated by a ductile iron matrix material, wherein the
matrix material is principally ductile iron and bonds the coating
to the working portion and the shell.
67. The wear part of claim 66, wherein the matrix material has a
composition comprising, in weight percent, approximately 3.0-4.0%
carbon, approximately 1.8-2.8% silicon, approximately 0.1-1.0%
manganese, approximately 0.01-0.03% sulfur, and approximately
0.01-0.1% phosphorous, with the balance being iron and incidental
elements and impurities.
68. The wear part of claim 67, wherein the composition of the
matrix material further comprises up to 37 wt. % nickel.
69. The wear part of claim 67, wherein the composition of the
matrix material further comprises up to 5.5 wt. % chromium.
70. The wear part of claim 67, wherein the composition of the
matrix material further comprises up to 5.5 wt. % silicon.
71. The wear part of claim 66, wherein the wear resistant material
is a particulate material, and the matrix material bonds the wear
resistant material together.
72. The wear part of claim 66, wherein the wear resistant material
comprises one or more materials selected from the group consisting
of: carbides, nitrides, borides, silicides, intermetallic compounds
of transition metals, and combinations thereof.
73. The wear part of claim 66, wherein the shell is connected to
the substrate by welding or brazing rearward of the cavity.
74. The wear part of claim 66, where the wear resistant material
within the cavity is primarily particles less than 1 mm in
size.
75. A wear part for earth engaging equipment comprising: a
substrate including a base portion for attachment to the earth
engaging equipment and a working portion for engaging earthen
material, the working portion including a surface; and a composite
material substantially filling the cavity and forming a coating on
at least a portion of the surface of the substrate, the composite
coating comprising a porous wear resistant material infiltrated by
a ductile iron matrix material, wherein the matrix material is
principally ductile iron and bonds the coating to the working
portion and the shell.
76. The wear part of claim 75, further comprising a mold connected
by welding or brazing to the substrate, a portion of the mold being
spaced from the substrate to define a cavity between the surface of
the substrate and the mold.
77. The wear part of claim 75, wherein the matrix material has a
composition comprising, in weight percent, approximately 3.0-4.0%
carbon, approximately 1.8-2.8% silicon, approximately 0.1-1.0%
manganese, approximately 0.01-0.03% sulfur, and approximately
0.01-0.1% phosphorous, with the balance being iron and incidental
elements and impurities.
78. The wear part of claim 77, wherein the composition of the
matrix material further comprises up to 37 wt. % nickel.
79. The wear part of claim 75, wherein the wear resistant material
is a particulate material, and the matrix material bonds the wear
resistant material together.
80. The wear part of claim 75, wherein the wear resistant material
comprises one or more materials selected from the group consisting
of: carbides, nitrides, borides, silicides, intermetallic compounds
of transition metals, and combinations thereof.
81. The wear part of claim 75, where the wear resistant material
within the cavity is primarily particles less than 1 mm in size.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to and the benefit
of U.S. Provisional Application No. 61/593,091, filed Jan. 31,
2012, which application is incorporated by reference herein in its
entirety and made part hereof.
TECHNICAL FIELD
[0002] The present invention generally relates to systems and
methods for creating a wear resistant material, and more
specifically, to systems and methods that utilize infiltration
techniques to form the wear resistant material and connect the
material to a substrate by brazing, as well as a product of the
system and method.
BACKGROUND
[0003] Various types of excavating equipment have points, edges,
surfaces, and other parts that are subjected to repeated impacts
and stresses, which may result in wearing or fracture of such
parts. Accordingly, materials having high hardness and wear
resistance coupled with good toughness are desirable for such
applications. Materials with high hardness and wear resistance may
be useful in other applications as well, including applications
where similar challenges are faced.
[0004] One common technique for producing wear resistant parts is
casting the part by pouring a molten metal (e.g. cast iron) around
a hard, wear resistant material placed in the mold to attach the
wear resistant material to the cast metal part and create a wear
resistant composite. A major drawback of this method is that the
substrate onto which the wear resistant material is attached by
this method is limited to the materials that are suitable for
casting. Additionally, the wear resistant material is generally
limited to volume fraction ranges of 5-50% and limited to particles
greater than 50 .mu.m, and the parts are generally limited to
thicknesses less than 6.25 mm (0.250 inch). Further, this method
requires superheating the molten alloy to about 200.degree. C. to
400.degree. C., which leads to significant dissolution of carbide
particles and thereby degrades the properties of the resultant
composite. Still further, because such casting is done in air,
there is a possibility for oxidation of both hard particles and the
matrix metal, and oxides may become entrapped in the composite and
degrade the wear and mechanical performance.
[0005] Another common technique for producing wear resistant parts
is the infiltration of nickel based alloys, copper based alloys,
and/or cast iron into a porous mass of both pure tungsten carbide
and cemented carbide particles. However, nickel and copper based
alloys are expensive, and cast iron does not have toughness that is
satisfactory for all applications. Ductile iron represents a much
more economical material that is castable and has good fracture
toughness. However, the conditions employed for these techniques
are not suitable for ductile iron infiltration. In addition, the
infiltration temperatures involved in these techniques are so high
that significant degradation of hard particles takes place. In the
case of infiltration of cast iron into spherical cast carbides
using these techniques, the original carbide particles may
completely disintegrate. As a result of metallurgical interaction
between the molten binder metals with hard carbide particles, the
particle size for such techniques must typically be kept above 1.14
mm (0.045 inch), so that even after reaction there is still
comparatively significant fraction of hard particle left to provide
wear resistance.
[0006] Accordingly, while certain existing products and methods
provide a number of advantageous features, they nevertheless have
certain limitations. The present invention seeks to overcome
certain of these limitations and other drawbacks of the prior art,
and to provide new features not heretofore available.
BRIEF SUMMARY
[0007] The following presents a general summary of aspects of the
invention in order to provide a basic understanding of the
invention. This summary is not an extensive overview of the
invention. It is not intended to identify key or critical elements
of the invention or to delineate the scope of the invention. The
following summary merely presents some concepts of the invention in
a general form as a prelude to the more detailed description
provided below.
[0008] Aspects of the present invention relate to a method for use
in forming a wear resistant composite coating on a substrate. A
mold is positioned proximate a surface of the substrate, such that
the surface is in communication with a cavity of the mold, and a
porous wear resistant material is placed within the cavity, in
close proximity to the surface. A metallic matrix material is then
placed in communication with the cavity, and the mold and the
matrix material are heated to a temperature above a melting point
of the matrix material. The temperature is held above the melting
point for a time sufficient for the matrix material to infiltrate
the wear resistant material in molten form and contact the surface
of the substrate. Thereafter, the mold and the matrix material are
cooled to solidify the matrix material and form a wear resistant
composite coating that includes the wear resistant material
embedded within the matrix material on the surface of the
substrate. The matrix material may be ductile iron in one
embodiment, and the ductile iron may have a composition that
includes, in weight percent, approximately 3.0-4.0% carbon,
approximately 1.8-2.8% silicon, approximately 0.1-1.0% manganese,
approximately 0.01-0.03% sulfur, and approximately 0.01-0.1%
phosphorous, with the balance being iron and incidental elements
and impurities. It is understood that other elements and additions
may be included in the ductile iron, such as nickel (up to 37 wt.
%), chromium (up to 5.5 wt. %), and/or silicon (up to 5.5 wt.
%).
[0009] According to one aspect, the wear resistant material may
include one or more materials selected from the group consisting
of: carbides, nitrides, borides, silicides, intermetallic compounds
of transition metals, and combinations thereof. Examples of
carbides that may be used include: WC, TiC, SiC, Cr.sub.3C.sub.2,
VC, ZrC, NbC, TaC, (W,Ti)C, B.sub.4C, and Mo.sub.2C, and
combinations thereof. Examples of nitrides that may be used
include: TiN, BN, Si.sub.3N.sub.4, ZrN, VN, TaN, NbN, HfN, CrN,
MoN, and WN, and combinations thereof. Examples of borides that may
be used include: titanium boride, chromium boride, tungsten boride,
nickel boride, zirconium boride, hafnium boride, tantalum boride,
niobium boride, vanadium boride, molybdenum boride, silicon boride,
aluminum boride, and other borides of transition metals, and
combinations thereof. Examples of silicides that may be used
include silicides of transition metals. The wear resistant material
may further have a wetting compatible coating.
[0010] According to another aspect, the composite coating may be
formed on a plurality of surfaces of the substrate, or may be
formed on only a portion of the surface of the substrate.
[0011] According to a further aspect, the porous wear resistant
material may be in the form of a loose particulate material or in
the form of a porous preform formed of a particulate material
bonded together to form the porous preform. The particulate
material in the preform may be bonded together in several different
ways, such as by sintering or by a polymer material. If a polymer
material is used for bonding, the material may be selected so that
the brazing temperature is sufficient to remove the polymer
material from the particulate material during heating.
[0012] According to yet another aspect, the mold may be or include
a sheet metal shell connected to the substrate to define the
cavity. The shell may have an opening to an exterior of the shell,
and the porous wear resistant material may be placed within the
cavity by insertion through the opening. Such a shell may have a
wall thickness significantly lower than the thickness of the
substrate, and may be welded to the outer surface of the
substrate.
[0013] According to a still further aspect, the heating is
performed within a furnace chamber, and the chamber may be
evacuated (e.g. 0.0001 or 0.001 Torr to 0.010 Torr, or even lower
pressure) prior to the temperature reaching the melting point of
the matrix material. An inert gas may be introduced into the
chamber after the matrix material has melted. Alternately, the
melting may be performed in the presence of an inert gas, such as
by introducing argon gas into the chamber before the matrix
material has melted. In this embodiment, the mold has a permeable
portion in contact with the porous wear resistant material to
permit residual gas to escape from the permeable portion during
infiltration.
[0014] According to an additional aspect, the matrix material may
be positioned at least partially laterally or horizontally to the
wear resistant material, and the method may further include placing
a displacement medium (e.g. a flowable medium such as ceramic
beads) adjacent to the matrix material and opposite the wear
resistant material. The displacement medium supports the molten
matrix material and displaces the molten matrix material as the
molten matrix material infiltrates the wear resistant material. A
barrier may further be placed between the displacement medium and
the matrix material, to resist permeation of the molten matrix
material into the displacement medium. One example of lateral
infiltration is when the substrate is a tubular structure, such
that the molten matrix material infiltrates laterally outward to
form the composite coating on the inner surface of the tubular
structure. In this configuration, the displacement medium is placed
at a center of the tubular structure and displaces outwardly as the
molten matrix material infiltrates the wear resistant material.
[0015] Additional aspects of the invention relate to a system for
use in forming a wear resistant composite coating on a surface of a
substrate. The system may include a mold positioned in proximity to
the surface of the substrate, such that the surface is in
communication with the mold cavity, a porous wear resistant
material within the cavity, in close proximity to the surface, and
a metallic matrix material in communication with the cavity. The
system may be usable in connection with a method according to the
aspects described above, such as heating the mold and the matrix
material to a temperature above a melting point of the matrix
material and holding the temperature for a time sufficient for the
matrix material to infiltrate the wear resistant material in molten
form and contact the surface of the substrate, and then cooling the
mold and the matrix material to solidify the matrix material and
form a wear resistant composite coating on the surface of the
substrate. As described above, the matrix material may be ductile
iron.
[0016] According to one aspect, the wear resistant material may
include one or more materials selected from the group consisting
of: carbides, nitrides, borides, silicides, intermetallic compounds
of transition metals, and combinations thereof, including the
materials described above.
[0017] According to another aspect, the porous wear resistant
material may be in the form of a loose particulate material or in
the form of a porous preform formed of a particulate material
bonded together to form the porous preform, as described above.
[0018] Further aspects of the invention relate to an article of
manufacture, which may be manufactured according to a systems
and/or a method according to the aspects described above or by
other systems and/or methods. The article includes a metallic
substrate having a surface with a wear resistant composite coating
bonded to the surface. The wear resistant composite coating
includes a wear resistant particulate material, as well as a
metallic matrix material bonding together the wear resistant
particulate material. The coating may be a continuous coating. The
matrix material is further bonded to the surface of the substrate
to bond the wear resistant composite coating to the substrate. The
metallic matrix material may be ductile iron, which may have a
composition as described above. The method may be used to make
coatings having thicknesses of at least 0.005 inches, and typically
greater than 0.040 inches. The method may achieve infiltration
distances of up to 6 inches or more, or up to 7.5 inches or more in
some embodiments, and may therefore be used to make coatings having
a greater thickness than the substrate itself, such as up to 6
inches or more, up to 7.5 inches or more, or even greater
thicknesses in various embodiments.
[0019] According to one aspect, the wear resistant material may
include one or more materials selected from the group consisting
of: carbides, nitrides, borides, silicides, intermetallic compounds
of transition metals, and combinations thereof, including the
examples described above.
[0020] According to another aspect, the substrate has a plurality
of protrusions connected to the surface and extending outwardly
from the surface. The protrusions are embedded within the wear
resistant composite coating. As one example, the protrusions may be
a plurality of rib or plate members symmetrically distributed on
the outer surface of the substrate.
[0021] According to a further aspect, the article may be a wear
member for excavating, mining, or other earthmoving equipment, and
the substrate may be formed by a working portion of the wear
member, such that the composite coating overlays the working
portion.
[0022] Other features and advantages of the invention will be
apparent from the following description taken in conjunction with
the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] To allow for a more full understanding of the present
invention, it will now be described by way of example, with
reference to the accompanying drawings in which:
[0024] FIG. 1 is a schematic illustration showing an example of
vertical infiltration from above to form a wear resistant composite
material, according to one embodiment of the present invention;
[0025] FIG. 2 is a schematic illustration showing an example of
vertical infiltration from below to form a wear resistant composite
material, according to one embodiment of the present invention;
[0026] FIG. 3 is a schematic illustration showing an example of
horizontal infiltration to form a wear resistant composite
material, according to one embodiment of the present invention;
[0027] FIG. 4 is a schematic illustration showing one embodiment of
a system and method of forming a wear resistant composite material
on a substrate using vertical infiltration, prior to infiltration,
according to aspects of the present invention;
[0028] FIG. 5 is a schematic illustration showing the substrate
having the wear resistant composite material formed thereon using
the method as shown in FIG. 4, after infiltration, according to
aspects of the present invention;
[0029] FIG. 6 is a schematic illustration showing another
embodiment of a system and method of forming a wear resistant
composite material on a substrate using outward infiltration, prior
to infiltration, according to aspects of the present invention;
[0030] FIG. 7 is a schematic illustration showing a cross-section
of the system as shown in FIG. 6;
[0031] FIG. 8 is a schematic illustration showing another
embodiment of a system and method of forming a wear resistant
composite material on a substrate using vertical and horizontal
infiltration, prior to infiltration, according to aspects of the
present invention;
[0032] FIG. 9 is a schematic illustration showing another
embodiment of a system and method of forming a wear resistant
composite material on a substrate using vertical and horizontal
infiltration, prior to infiltration, according to aspects of the
present invention;
[0033] FIG. 10 is a photomicrograph illustrating an example of
spherical cast tungsten carbide particles in a ductile iron matrix,
produced using a method according to the present invention;
[0034] FIG. 11 is a photomicrograph illustrating an interface
between a spherical cast tungsten carbide/ductile iron composite
and excess ductile iron remaining after the infiltration process
using a method according to the present invention;
[0035] FIG. 12 is a schematic illustration showing another
embodiment of a substrate having the wear resistant composite
material formed thereon using an infiltration method, according to
aspects of the present invention;
[0036] FIG. 13 is a schematic illustration showing an example of a
system and method for infiltration of a porous wear resistant
material with a braze material in a furnace under vacuum
conditions, according to another embodiment of the present
invention;
[0037] FIG. 14 is a schematic illustration showing an example of a
system and method for infiltration of a porous wear resistant
material with a braze material in a furnace under vacuum conditions
prior to melting of the braze material, according to one embodiment
of the present invention;
[0038] FIG. 15 is a schematic illustration of the system and method
of FIG. 14, with partial Ar pressure introduced into the furnace
after melting of the braze material;
[0039] FIG. 16 is a schematic illustration showing an example of a
system and method for infiltration of a porous wear resistant
material with a braze material in a furnace under partial Ar
pressure, according to another embodiment of the present
invention;
[0040] FIG. 17 is a perspective view of another embodiment of a
substrate configured for use according to aspects of the present
invention, in the form of a point for excavating or mining
equipment;
[0041] FIG. 18 is a cross-sectional view of the substrate of FIG.
17, having a wear resistant composite material formed on an outer
surface thereof;
[0042] FIG. 19 is a perspective view of one embodiment of a shell
configured for use as a mold for forming a wear resistant composite
material according to aspects of the present invention; and
[0043] FIG. 20 is a cross-sectional view of the shell of FIG. 19
connected to one embodiment of a substrate in the form of a point
for excavating or mining equipment, configured for use in forming a
wear resistant composite material according to aspects of the
present invention.
DETAILED DESCRIPTION
[0044] While this invention is susceptible of embodiment in many
different forms, there are shown in the drawings, and will herein
be described in detail, preferred embodiments of the invention with
the understanding that the present disclosure is to be considered
as an exemplification of the principles of the invention and is not
intended to limit the broad aspects of the invention to the
embodiments illustrated and described.
[0045] In general, aspects of the invention relate to systems and
methods of forming a wear resistant composite material that include
placing a porous wear resistant filler material in a mold cavity
and infiltrating the filler material with a matrix material by
heating to a temperature sufficient to melt the matrix material,
then cooling the assembly to form a wear resistant composite
material. The resultant composite material includes the matrix
material intermixed with the filler material and bonded to the
filler material, where the matrix material bonds the composite to
the substrate and also may bond together the filler material. The
system and method can be used to form the wear resistant composite
material on the surface of a substrate, such as a part for mining,
excavating, or other earthmoving equipment or other mechanical
part. It is understood that the "surface" of a substrate as
described herein may include a plurality of different surfaces, and
does not imply any specific contour to such surface(s) unless
explicitly noted. The substrate can be any material with a melting
point that is suitable for the infiltration process, for example
having a melting point that is higher than the matrix material.
Examples of such substrates include cast, wrought, and powder
metallurgy-produced metallic materials, as well as ceramics and
ceramic-based materials such as metallized ceramics. In one
embodiment, the substrate may be carbon steel, alloy steel,
stainless steel, or tool steel. The system and method can
alternately be used to form the wear resistant composite material
as a unitary piece.
[0046] In one embodiment, the method utilizes ductile iron as the
matrix material and produces a dense, hard, and tough composite
with excellent wear resistance and toughness. Additionally, ductile
iron has a melting point that is sufficiently low to enable melting
without excess heating. All types/grades of ductile iron may be
usable in accordance with the invention, including any ductile iron
that is within the scope defined by ASTM standard A536-84
(Reapproved, 2004), which is incorporated by reference herein. In
one embodiment, a ductile iron matrix material may have a
composition, in weight percent, of approximately 3.0-4.0% carbon;
approximately 1.8-2.8% silicon; approximately 0.1-1.0% manganese,
approximately 0.01-0.03% sulfur, and approximately 0.01-0.1%
phosphorous, with the balance being iron and incidental elements
and impurities. As used herein, the term "approximately" designates
a variance of +/-10% of the nominal values listed (e.g. the
endpoints of the composition ranges). In another embodiment, the
composition may not include this variance. In a further embodiment,
the above composition may include further alloying additions, such
as additions of Ni, Cr, and/or Si, to improve corrosion resistance,
wear resistance, and/or high temperature properties of the matrix
material. For example, Ni may be added in amounts of up to 37 wt.
%, Cr may be added in amounts of up to 5.5 wt. %, and/or Si may be
added in amounts up to about 5.5 wt. % in various embodiments. A
ductile iron alloy may include still further alloying additions in
other embodiments, including alloying additions that may increase
performance. Ductile iron alloys with such alloying additions are
known as high-alloy ductile irons and generally fall within the
scopes of ASTM A439 and A571, which are also incorporated herein by
reference. Such alloys may also be utilized in accordance with
embodiments of the system and method described herein. In other
embodiments, any alloying additions can be utilized to achieve
different properties and/or microstructures, provided that they do
not adversely affect the properties or microstructure in an
excessive manner, such as increasing the infiltration temperature
significantly and/or degrading the properties of the matrix or the
resultant wear resistant material. The method may be utilized to
create a composite with a metallic matrix material other than
ductile iron, in an alternate embodiment.
[0047] The matrix material may be provided in a variety of forms.
For example, in one embodiment, the matrix material may be provided
in monolithic form, such as one or more blocks, billets, etc. In
another embodiment, the matrix material may be provided in
particulate form, such as powder, fibers, whiskers, etc. In a
further embodiment, the matrix material may be provided in a porous
form. The matrix material may be provided in a combination of such
forms in additional embodiments.
[0048] Various hard and wear resistant materials may be used as the
filler material in connection with different embodiments, including
various carbides, nitrides, borides, and silicides, as well as
other hard and wear resistant materials and mixtures of such
materials, including other types of ceramic materials. Such
materials may be provided in virgin form and/or with suitable
coatings that provide wetting compatibility. For example, where the
wear resistant material particles are not wetting-compatible with
the matrix material, the wear resistant material particles may be
coated with wetting-compatible coatings before they are used for
forming the composite material by infiltration brazing. Carbides
that may be used as the filler material include tungsten carbide
(WC), TiC, SiC, Cr.sub.3C.sub.2, VC, ZrC, NbC, TaC, (W,Ti)C,
B.sub.4C, and Mo.sub.2C, and other carbides. In one embodiment,
spherical cast WC, crushed cast WC, and/or cemented WC is used as
the filler material. Nitrides that may be used as the filler
material include TiN, BN, Si.sub.3N.sub.4, ZrN, VN, TaN, NbN, HfN,
CrN, MoN, WN, and other nitrides. Borides that may be used as the
filler material include borides of transition metals such as
titanium boride, chromium boride, tungsten boride, nickel boride,
zirconium boride, hafnium boride, tantalum boride, niobium boride,
vanadium boride, molybdenum boride, silicon boride, and aluminum
boride, as well as other borides. Silicides that may be used as the
filler material include silicides of transition metals. Other
materials that may be used as filler materials include
intermetallic compounds of transition metals. In one embodiment,
the filler material may be selected based on the material having
limited solubility in the molten braze material, in order to limit
or prevent dissolution of the filler material in the braze
material. As used herein, the terms "matrix material" and "filler
material" should not be considered to imply that the matrix
material or the filler material forms any specific proportion of
the composite material. For example, the matrix material need not
form a majority or a plurality of the composite material, and the
filler material may form a majority or a plurality of the composite
material in some embodiments.
[0049] The porous filler material may be provided in one or more
different forms. In one embodiment, the porous filler material may
be in the form of a loose particulate material, such as powder,
fibers, whiskers, etc. The method may utilize a wide range of
particle sizes in various embodiments, including particle sizes
less than 50 .mu.m or particle sizes less than 1 mm. In one
embodiment, the particulate filler material may have a particle
size that is greater than 0.1 .mu.m. In another embodiment, the
particulate filler material may have a particle size that is
greater than 0.1 .mu.m and up to 5 mm. In a further embodiment, the
particulate filler material may have an average particle size of
approximately 500 .mu.m. In one embodiment, the filler material may
be provided in multiple particle sizes, such as a combination of
coarse and fine particles, which combination can be used to achieve
greater density and/or volume fraction of the filler material. At
any given volume fraction of filler material, such use of fine
particles generally leads to finer pore sizes and can increase the
yield strength of the matrix material that fills these pores,
thereby increasing the overall wear resistance of the material.
When the particulate material is placed in a mold cavity, the
spaces between the particles form a porous structure that may be
infiltrated by the matrix material. In another embodiment, the
porous filler material may be in the form of a porous preform. The
porosity of the porous preform can range from 5% to 95% in one
embodiment. For example, the porous preform may include a
particulate material that is bonded together by a binder material,
such as a polymer binder. A preform may be attached to the
substrate material, such as by an adhesive that will volatilize
during the infiltration process. Upon infiltration, the molten
matrix material has sufficient temperature to remove the binder
material (such as by melting, volatilization, etc.) so that the
matrix material can fill the pores left by the removal of the
binder in addition to the pores between the particles. As another
example, the porous preform may include a particulate material that
is bonded together by sintering so that pores exist between the
particles. In one embodiment, a pre-sintered preform may have a
pore size that is on the order of the particle size, since the part
may be sintered slightly to achieve neck growth between particles
and provide some mechanical handling strength. Other porous
materials may be used as well, such as woven fiber mats or fabrics.
In a further embodiment, the porous filler material may be provided
in a combination of different forms. For example, in one
embodiment, the filler material may include one or more preforms
forming a portion of the filler material, with other portions being
formed by a particulate material (e.g. loose powder, fibers,
whiskers, etc.) and/or woven fiber mats or fabrics.
[0050] The brazing operation by infiltration of the filler material
by the matrix material may generally be accomplished by heating the
matrix material to above its melting point while it is in contact
or otherwise in communication with the filler material, to allow
the molten matrix material to contact the filler material and
infiltrate the porous filler material. The filler material is
generally placed in contact or otherwise in communication with the
substrate during infiltration, in order for the matrix material to
contact the substrate material during infiltration to connect the
resultant composite material to the substrate. Various molds may be
utilized in connection with infiltration, as described below. FIGS.
1-3 illustrate various infiltration configurations according to
various embodiments, each schematically illustrating a molten
matrix material 16 infiltrating a filler material 15 in a cavity 11
of a mold 12. FIG. 1 illustrates downward vertical infiltration, in
which gravity assists the infiltration. However, because the
infiltration is mainly driven by capillary action, horizontal
infiltration, upward vertical infiltration, outward/radial
infiltration, and other infiltration configurations which may not
utilize gravity or may work against gravity. FIG. 2 illustrates an
example of upward vertical infiltration, and FIG. 3 illustrates an
example of horizontal infiltration. FIGS. 6-7, discussed in greater
detail below, illustrate an example of outward or radial
infiltration, which may be considered another example of horizontal
infiltration. In any non-downward infiltration embodiments, a
technique may be utilized to displace molten matrix material 16
that has infiltrated the filler material 15, in order to keep the
molten matrix material 16 in contact with the filler material 15
until infiltration is complete. For example, the mold 12 may be
moved during infiltration to keep the matrix material 16, the
filler material 15, and the substrate in proper
contact/communication. As another example, a ram or other pressure
mechanism may be used to ensure that the matrix material 15 is
always in contact with the filler material during infiltration. In
a further example, a movable material such as ceramic beads, may be
used to displace the infiltrated matrix material, as described
below and shown in FIGS. 6-9.
[0051] In one embodiment, the matrix or braze material is
superheated 25.degree. C. to 75.degree. C. greater than the melting
point, which is significantly lower than the superheating typically
required for casting. In one example embodiment, where a ductile
iron material is used as the matrix material, the infiltration can
be conducted at a temperature range of 2150.degree. F. to
2275.degree. F., or a temperature of 2175.degree. F. in another
embodiment. The holding time period for the infiltration may be
from 1 to 60 minutes in one embodiment, with greater infiltration
lengths generally utilizing longer infiltration times. The
infiltration may be conducted in an inert atmosphere in one
embodiment, such as an argon (Ar) atmosphere, which can avoid
volatilization-induced molten metal splatter at temperatures above
the melting point. In one embodiment, the argon pressure during
infiltration may be approximately 6.5.times.10.sup.-5 atm to
4.times.10.sup.-4 atm. Various atmospheres that may be used for
infiltration are discussed in greater detail below and illustrated
in FIGS. 13-16. After infiltration, the part may be cooled, for
example, cooling to 1700.degree. F. over about 20-30 minutes and
then cooling more slowly to room temperature in one embodiment.
Depending on the nature of the materials involved, particularly the
substrate material, post processing such as machining and/or heat
treatment may be performed. For example, depending on the identity
of the substrate, heat treatments such as normalizing, hardening
followed by tempering, or martempering followed by tempering may be
performed according to known techniques. It is understood that some
substrates would not benefit from some (or any) heat treatments.
Machining may or may not be desired, based on the intended
application of the resultant part.
[0052] The infiltration of the filler material as described above
is mainly driven by capillary action, i.e. capillary pressure
acting on the infiltration front. The pressure differential at the
infiltration front depends on many factors, including surface
tension of the molten matrix material, contact angle of the molten
matrix material with respect to the filler material, geometric
characteristics of the filler material (e.g. porosity, tortuosity,
variation in pore size and shape, and its effect on the apparent
contact angle of the molten material), and the pressure of any
residual gas within the filler material. The freedom to control
many of these factors may be limited within a specific
matrix/filler system. Residual gas pressure can be at least
partially controlled, and minimization of residual gas pressure
within the filler material can maximize the pressure differential
and the driving force for capillary action. This, in turn, can
maximize the potential distance that the matrix material can
infiltrate the filler material. In at least some configurations,
the use of filler material in the form of a preform or preforms may
maximize the infiltration distance as compared to other forms of
filler material.
[0053] FIGS. 13-16 illustrate systems or assemblies for forming a
wear resistant composite material, where different atmospheres are
used during the brazing operation to control and/or minimize the
residual gas pressure in the filler material 15. In these
embodiments, the infiltration is performed in a furnace 30 with a
chamber 31 holding the mold 12, the matrix material 16, and the
filler material 15, where the atmosphere inside the chamber 31 can
be controlled. It is understood that the assembly may further
include a substrate (not shown) that is in communication with the
mold 12 as described below. The atmosphere in the brazing operation
can be controlled to assist in achieving a capillary pressure
gradient that is sufficient to drive infiltration of the matrix
material over larger/longer distances through the filler material,
such as distances of about 5-7 inches or greater. In each of the
embodiments described below and shown in FIGS. 13-16, the chamber
31 is substantially evacuated prior to melting of the matrix
material 16. Evacuation at least in the beginning of the
infiltration process is preferred in one embodiment, in order to
avoid oxidation of filler material. Different procedures may be
used in other embodiments, however, such as not evacuating or
evacuating to a lesser degree than discussed above.
[0054] FIG. 13 illustrates one embodiment of a system 500 for
infiltration, where the infiltration is performed under vacuum
conditions. In this embodiment, the entire chamber 31 is evacuated
prior to melting of the matrix material 16 and is maintained under
vacuum conditions throughout the infiltration process. In one
embodiment, the gas pressure after evacuation may be from 0.001 to
0.010 Torr, or may be as low as 0.0001 Torr in another embodiment
(e.g. 0.0001 to 0.010 Torr), or may be below 0.0001 Torr in a
further embodiment. Infiltration may be performed at approximately
2180-2225.degree. F. for about 30-60 minutes in one embodiment. The
evacuation of the chamber prior to melting of the matrix material
16 reduces or eliminates residual gas pressure in the filler
material 15, which assists in driving infiltration through
capillary action. It is noted that splattering due to
volatilization of chemicals within the matrix material may be
encountered as a result of maintaining the system under vacuum
after the matrix material has been melted when certain alloys are
used, particularly alloys with significant manganese content. Such
splattering can not only damage equipment in the furnace 30, but
can also reduce the amount of matrix material 16 available for
brazing. This splattering can be mitigated by keeping the Mn
content of the alloy sufficiently low, although doing so can be
expensive. This splattering can also be avoided by the presence of
Ar or another non-reactive gas in the chamber 31 after the matrix
material 16 has been melted.
[0055] FIGS. 14-15 illustrate another embodiment of a system 600
for infiltration, where Ar gas is introduced into the chamber 31
after the matrix material 16 is melted. As shown in FIG. 14, the
chamber 31 is evacuated as described above prior to the brazing
process, as similarly described above with respect to FIG. 13. As
described above, infiltration may be performed at approximately
2180-2225.degree. F. for about 30-60 minutes in one embodiment.
After the matrix material 16 has melted, argon gas 32 (or another
non-reactive gas) is introduced into the chamber 31. In one
embodiment, the Ar gas 32 is fed into the chamber 31 until the Ar
partial pressure reaches about 0.050-0.100 Torr. The evacuation of
the chamber prior to melting of the matrix material 16 reduces or
eliminates residual gas pressure in the filler material 15, which
assists in driving infiltration as described above, and the later
introduction of the Ar gas 32 assists in reducing splattering
caused by volatile substances. In one example using a system as
shown in FIGS. 14-15, the matrix material 16 was found to
infiltrate at least 7.5 inches of filler material 15 during
infiltration at 2180.degree. F., when the Ar atmosphere was
introduced after melting of the matrix material 16. However when
the Ar atmosphere was introduced prior to melting, the matrix
material 16 was found to infiltrate only 6.5 inches at most,
regardless of how long the system was held at the infiltration
temperature. This indicates that residual gas within the filler
material 15 may limit the length of infiltration that can be
achieved through capillary action.
[0056] FIG. 16 illustrates another embodiment of a system 700 for
infiltration, where Ar gas 32 is introduced into the chamber 31
prior to melting of the matrix material 16. As similarly described
above with respect to FIG. 14, the chamber 31 in this embodiment is
evacuated as described above during the heating process until the
system nearly reaches the melting temperature of the matrix
material 16 (e.g. until the temperature reaches about 2150.degree.
F. for ductile iron). At that point, Ar gas 32 or other
non-reactive gas is introduced into the chamber 31 prior to melting
of the matrix material 16. As similarly described above, the gas 32
may be introduced until a partial Ar pressure of 0.050-0.100 Torr
is reached, in one embodiment. As described above, infiltration may
be performed at approximately 2180-2225.degree. F. for about 30-60
minutes in one embodiment. In order to avoid residual gas pressure
in the filler material 15 limiting infiltration, the mold 12 is
provided with a permeable portion 33 in contact with the filler
material 15. The permeable portion 33 may be porous or otherwise
gas-permeable, to permit residual gas to escape from the filler
material 15 during infiltration, so as not to limit infiltration of
the matrix material 16. The permeable portion 33 may be provided
generally opposite the matrix material 16 to avoid the matrix
material 16 covering or sealing the permeable portion 33 to prevent
escape of residual gas prior to completion of infiltration. As
described above, the presence of the Ar gas suppresses splattering
of the molten matrix material 16. In one example using a system as
shown in FIG. 16, with the mold 12 including the permeable portion
33, the matrix material 16 was found to infiltrate at least 7.5
inches of filler material 15 during infiltration at 2225.degree.
F., when the Ar atmosphere was introduced before melting of the
matrix material 16. However when the mold 12 was sealed and the
infiltration front was not in communication with the atmosphere in
the chamber 31 after melting of the matrix material 16,
infiltration was found to extend only 6.5 inches at most. This
indicates that keeping the infiltration front in communication with
the atmosphere in the chamber 31 can reduce the limiting effect
that residual gas within the filler material 15 may have on the
capillary action driving force.
[0057] FIGS. 4-5 illustrate one example embodiment of a system or
assembly 100 for forming a wear resistant composite material, and a
method utilizing the system or assembly 100. In this embodiment,
the substrate 10 (e.g. a point of an excavating tool) is positioned
with a cavity 11 of a mold 12, such that the mold 12 entraps a
volume in the cavity 11 between the inner surface 13 of the mold 12
and the outer surface 14 of the substrate 10, as shown in FIG. 4.
The substrate 10 may be prepared beforehand, such as by cleaning
and drying to remove oil or greasy substances and/or grit blasting
using garnet grit to remove oxide scales and make the surface
grainy so the matrix material bonds well to the substrate 10. The
mold 12 may be made from any suitable material, such as a
high-melting point metallic material, a ceramic material, or
graphite. If possible, the mold 12 may be welded, brazed, or
otherwise connected to the outer surface 14 of the substrate 10,
such as by welding at points P. In one embodiment, the mold 12 is a
steel shell that is welded to the substrate to create the cavity
11, and may be grit blasted prior to welding in order to avoid
contamination of the mold cavity 11. Such an embodiment is
described in greater detail below and shown in FIGS. 19-20. The
filler material 15 is inserted into the mold cavity 11 in contact
or otherwise in communication with the outer surface 14 of the
substrate 10, such as in the form of a particulate material or a
preform, as shown in FIG. 4. The matrix material 16 is placed in
communication with the filler material 15 and the outer surface 14
of the substrate. The matrix material 16 may be positioned within
the mold cavity 11, such as by simply placing the matrix material
16 on top of the filler material 15 in solid form, as shown in FIG.
4. In one embodiment, the matrix material 16 may be in block or
billet form. In another embodiment, the matrix material 16 may be
positioned in a feeder or injection structure. The system 100 may
then be prepared for infiltration, as described above, such as by
placing the system 100 in a furnace for heating, which may include
an inert atmosphere (e.g. argon). A tray or similar vessel may be
used to support the system 100 in the furnace, such as a stainless
steel tray. During infiltration, the matrix material 16 melts and
infiltrates downward through all of the filler material 15,
eventually contacting the outer surface 14 of the substrate 10.
[0058] After infiltration has been conducted and the system 100
cooled as described above, a part 17 having a composite coating 18
on the outer surface 14 is formed, as shown in FIG. 5. The part 17
may be removed from the mold 12, which may require cutting or
breaking the mold 12 away if welded to the substrate 10 and/or
bonded to the coating 18. The composite coating 18 contains the
filler material 15 bound together and connected to the substrate 10
by the matrix material 16. In one embodiment, the filler material
16 may have a volume fraction of 5-95% in the composite material
18. In another embodiment, the filler material 16 may have a volume
fraction of 30-85%. In some embodiments, the part 17 may have
excess matrix material 19 on at least a portion of the outside of
the composite coating 18. The excess material 19 may be
intentionally created and left on the part 17, such as to serve as
a base for welding or attaching another piece. The excess material
19, if present, may instead be removed, such as by machining. The
composite coating 18 may be formed with wide range of thicknesses,
depending on the desired application. In one embodiment, a part 17
may be formed with a composite coating 18 that is about 0.5''
thick, which may be usable in a wide variety of applications. The
part 17 may be a point, edge, or other portion of a piece of
equipment that sustains repeated impacts and stress, and the
excellent wear resistance and toughness of the composite coating 18
enhances performance in such applications. Excavating/mining
equipment represents one example of an application for a part 17
produced according to the systems and methods described herein.
FIG. 12 illustrates an additional embodiment of a part 17' produced
according to one embodiment of the system and method described
herein, in the form of a wear member for earthmoving equipment
(e.g., a steel mining point) with a working portion forming the
substrate 10' overlaid on its outer surface 14' with a wear
resistant composite material layer 18' as described above. In one
embodiment, the composite material layer 18' consists of spherical
cast tungsten carbide particles or other wear resistant material in
a ductile iron matrix material.
[0059] FIGS. 17-18 illustrate another embodiment of a substrate 10
(e.g. a point of an excavating or mining tool) that may be used in
connection with the system or assembly 100 as shown in FIGS. 4-5,
or a similar system/assembly, for producing a wear resistant
composite coating 18. Depending on the identity and nature of the
material of the substrate 10, the filler material 15, and/or the
matrix material 16, the coefficients of thermal expansion (CTE) of
the substrate 10 and the coating 18 may be mismatched. For example,
when a steel substrate 10 is used, the steel typically has a higher
CTE than the coating 18. One example of such a CTE difference may
be about 2.times.10.sup.-6/.degree. C., depending on materials
used. This, in turn, can cause debonding between the substrate 10
and the coating 18, particularly when the coating 18 is formed on
the outside surface of the substrate 10 (e.g. as shown in FIGS.
4-5). In the embodiment of FIGS. 17-18, the substrate 10 is
provided with protrusions 28 in the form of ribs on the outer
surface 14. The protrusions 28 can assist in mitigating the
problems caused by differences in CTE between the substrate 10 and
the coating 18 by plastically deforming in response to the
pressures exerted as the substrate 10 and the coating 18 cool after
brazing. In one embodiment, the protrusions 28 may be formed of a
material with a relatively low yield strength and good ductility in
order to ease plastic deformation. Other considerations in
selecting the material for the protrusions 28 are its compatibility
for connection to the substrate 10 (e.g. by welding or other
technique) and for bonding to the coating 18. One example of
material suitable for use as protrusions bonded to a steel
substrate 10 is mild steel, such as AISI 1008. Other examples of
suitable materials may include 304 stainless steel, AISI 1018, and
AISI 1010, among others. The protrusions 28 also provide additional
surfaces for bonding of the coating 18, and may therefore further
enhance bonding between the coating 18 and the substrate 10. As
seen in FIG. 18, the coating 18 forms around the protrusions 28
such that the protrusions 28 are embedded within the coating 18 and
bonded to the coating 18 in the finished part 17. However in other
embodiments, the protrusions 28 may extend at least to the outer
surface of the coating 18 and may be substantially flush with the
outer surface of the coating 18.
[0060] The protrusions 28 in the embodiment of FIGS. 17-18 extend
outwardly from the outer surface 14 of the substrate 10 and are in
the form of ribs or plates having a length and height significantly
greater than their thickness. In one example, the protrusions 28
may have a length of about 1-2 inches (parallel to the surface of
the substrate 10), a height of about 0.25 inches (parallel to the
thickness direction of the coating 18), and a thickness of about
0.125 inches. Additionally, the protrusions 28 in this embodiment
are oriented in a generally axial manner and distributed fairly
evenly and symmetrically on all facets of the outer surface 14 of
the substrate 10. In one embodiment, the protrusions 28 may have a
thickness, length, and width selected in such a way that some or
all of the strain resulting from thermal expansion mismatch is
accommodated by deformation of the protrusions 28. Additionally, in
one embodiment, the length of each protrusion may be greater than
the height, which may in turn be greater than the thickness (i.e.,
length>width>thickness). Protrusions 28 using this
dimensional relationship increase potential bonding area for the
coating 18, as the potential bonding area added by the protrusion
28 is greater than the potential bonding area of the substrate 10
covered by the protrusion 28. The dimensions of the protrusions 28
may be modified depending on the thickness of the coating and
dimensions of the substrate. The distance between the protrusions
28 may also depend on the location and geometry of the substrate
10, and can vary from 1'' to 3'' in one embodiment. In other
embodiments, the protrusions 28 may have a different form, such as
rods, cones, pegs, etc., and may be distributed and/or oriented in
a different manner. The protrusions 28 as shown in FIG. 17 are
welded to the outer surface 14 of the substrate 10. The substrate
10 may be grit blasted after welding. Other techniques for
connecting the protrusions 28 to the substrate 10 may be used in
other embodiments. It is understood that, the protrusions 28 may be
formed of the same material as the substrate 10, and may be
integrally formed with the substrate 10 in one embodiment. It is
also understood that the substrate 10 having the protrusions 28 may
require a heat treatment or modified versions of traditional heat
treatments after welding and/or after brazing, depending on the
materials and structures used. Further, the finished part 17 as
shown in FIGS. 17-18 is a wear member, such as a point for
earthmoving equipment, and the substrate 10 is formed by a working
portion of the wear member, such that the protrusions 28 are
connected to the working portion. It is understood that other types
of protrusions 28 may be utilized with such a wear member, and also
that protrusions 28 as shown in FIGS. 17-18 may be utilized with
other types of articles of manufacture.
[0061] FIGS. 6-9 illustrate other systems and methods for creating
a wear resistant composite according to aspects of the invention.
FIGS. 6-7 illustrate a system 200 for forming a composite material
on an inner surface 20 of a substrate 10 through outward or radial
infiltration. In this embodiment, the substrate 10 is tubular in
form, and the substrate 10 is used along with a mold 12 and a plate
21 to create a mold cavity 11 on the inside of the substrate 10.
The plate 21 may be formed of any suitable material, including any
material mentioned above for mold construction (e.g. graphite,
metal, or ceramic). If the plate 21, the mold 12, and/or the
substrate 10 are made of weldable materials, any of these
components may be connected by welding, however welding is not
necessary. The porous filler material 15 is positioned on the inner
surface 20 of the substrate 10 in position to form the composite,
and the matrix material 16 is placed in contact or otherwise in
communication with the filler material 15. Ceramic beads 22 or
another displacement material are also placed in the mold cavity
11, in position to displace the matrix material 16 during
infiltration. It is understood that the displacement of the matrix
material 16 is done in order to support the matrix material 16 in
constant contact with the filler material 15 during infiltration,
and that the infiltration of the matrix material 16 is primarily
driven by other forces (e.g. capillary action), rather than force
exerted by the ceramic beads 22. Alternately, another displacement
technique may be used. In the embodiment in FIGS. 6-7, the matrix
material 16 may be placed in the mold cavity 11 in tubular form
(see FIG. 7), in contact with the filler material 15, and
infiltrates outwardly into the filler material 15. The matrix
material 16 may instead be provided as a plurality of billets
arranged in a circular formation around the filler material 15 in
another embodiment. In this configuration, the ceramic beads 22 are
placed inside the inner diameter of the tubular matrix material 16,
and the beads 22 move outwardly to displace the infiltrated matrix
material 16. Alternately, another displacement technique may be
used. The system 200 can be placed in a furnace and processed as
described above to complete infiltration. The resulting part has a
ceramic material on the inner surface 21 of the substrate, and may
include excess matrix material, as described above.
[0062] FIG. 8 illustrates a system 300 for forming a composite
material on an outer surface 14 of a substrate 10 through both
horizontal and downward vertical infiltration. In this embodiment,
a portion of the substrate 10 is placed inside the mold cavity 11,
and a plate 21 is used with the mold 12 to enclose the mold cavity
11. The plate 21 may be formed of any suitable material, including
any material mentioned above for mold construction (e.g. graphite,
metal, or ceramic). If the plate 21, the mold 12, and/or the
substrate 10 are made of weldable materials, any of these
components may be connected by welding, however welding is not
necessary. An additional member 23 may be used for sealing purposes
and/or for terminating infiltration, and may be positioned adjacent
the plate 21. Graphite foil or ceramic wool may be used as the
additional member 23 to accomplish these functions, as the matrix
material 15 does not wet or penetrate these materials. The porous
filler material 15 is positioned on the outer surface 14 of the
substrate 10 in position to form the composite, and the matrix
material 16 is placed in contact or otherwise in communication with
the filler material 15. As shown in FIG. 8, the matrix material 16
is placed above the filler material 15 for downward infiltration
and alongside the filler material 15 for horizontal infiltration.
Ceramic beads 22 or another displacement material are also placed
in the mold cavity 11, in position to displace the matrix material
16 during infiltration. Alternately, another displacement technique
may be used. In the embodiment in FIG. 8, the matrix material 16 is
placed in the mold cavity 11 around the filler material 15, and
infiltrates horizontally and vertically into the filler material
15. In this configuration, the ceramic beads 22 are placed
horizontally around the matrix material 16, and the beads 22 move
inwardly to displace the horizontally infiltrated matrix material
16. A barrier 24, such as a flexible ceramic fiber mat or a woven
fabric, may be placed between the beads 22 and the matrix material
16. The barrier 24 may generally be impermeable to the molten
matrix material 16, and may also be flexible and may transmit
pressure from the ceramic beads 22 onto the matrix material 15. No
displacement of the vertically infiltrated matrix material 16 is
necessary. The system 300 can be placed in a furnace and processed
as described above to complete infiltration. The resulting part has
a ceramic material on the outer surface 14 of the substrate, and
may include excess matrix material, as described above.
[0063] FIG. 9 illustrates a system 400 for forming a composite
material on an outer surface 14 of a substrate 10 through both
horizontal and downward vertical infiltration. In this embodiment,
a portion of the substrate 10 is placed inside the mold cavity 11,
and a plate 21 is used with the mold 12 to enclose the mold cavity
11. The plate 21 may be formed of any suitable material, including
any material mentioned above for mold construction (e.g. graphite,
metal, or ceramic). If the plate 21, the mold 12, and/or the
substrate 10 are made of weldable materials, any of these
components may be connected by welding, however welding is not
necessary. An additional member 23 may be used for sealing purposes
and/or for terminating infiltration, and may be positioned adjacent
the plate 21. Graphite foil or ceramic wool may be used as the
additional member 23 to accomplish these functions, as the matrix
material 15 does not wet or penetrate these materials. The porous
filler material 15 is positioned on the outer surface 14 of the
substrate 10 in position to form the composite, and the matrix
material 16 is placed in contact or otherwise in communication with
the filler material 15. As shown in FIG. 9, the matrix material 16
is placed above the filler material 15 for downward infiltration
and alongside the filler material 15 for horizontal infiltration.
Ceramic beads 22 or another displacement medium are also placed in
the mold cavity 11, in position to displace the matrix material 16
during infiltration. Alternately, another displacement technique
may be used. In the embodiment in FIG. 9, the matrix material 16 is
placed in the mold cavity 11 around the filler material 15, and
infiltrates horizontally and vertically into the filler material
15. In this configuration, the ceramic beads 22 are placed
horizontally and vertically around the matrix material 16, and the
beads 22 move inwardly and downwardly to displace the infiltrating
matrix material 16. The system 400 can be placed in a furnace and
processed as described above to complete infiltration. The
resulting part has a ceramic material on the outer surface 14 of
the substrate, and may include excess matrix material, as described
above.
[0064] FIGS. 19-20 illustrate another example of a system 800 for
forming a composite material on an outer surface 14 of a substrate
10 mainly through downward vertical infiltration. The system 800 of
FIGS. 19-20 utilizes a mold in the form of a shell 314 made from a
sheet material, which is shown being used in conjunction with a
substrate 312 in the form of an excavating/mining point that may be
similar to the substrates 10, 10' as shown in FIGS. 4-5 and 12. The
shell 314 shown in FIGS. 19-20, along with other such shells, are
described in greater detail in U.S. Provisional Application No.
61/472,470, filed Apr. 6, 2011, and U.S. patent application Ser.
No. 13/440,273, filed Apr. 5, 2012, and published as U.S. Patent
Application Publication No. 2012/0258273 on Oct. 11, 2012, which
applications are incorporated by reference herein in their
entireties and made parts hereof. The shell 314 may be utilized to
form a composite coating 18 as similarly described above and shown
in FIGS. 4-5. In one embodiment, the filler material 15 may be
poured through the opening 317 in the shell 314, and the matrix
material 16 may thereafter be placed on top of the filler material
15, as similarly shown in FIG. 4. The opening 317 may have a
funnel-like configuration to aid insertion of the filler material
15 and/or the matrix material 16. In other embodiments, the opening
317 may be located elsewhere on the shell 314, such as if the shell
314 is positioned in a different orientation during brazing.
[0065] The sheet metal of the shell 314 may be made of any material
capable of being formed or fabricated to a particular desired shape
and capable of withstanding dissolution, melting, or undue
weakening by the infiltrating material, or generally by the
temperatures required for infiltration brazing, during the
infiltrating process. In one example, the shell 314 may be formed
of low-carbon "mild" steel. For example, shell 314 may have an
average shell thickness of approximately 0.105 in. In one
embodiment, the shell 314 may be made of sheet metal in the range
of 16 Ga (0.060 in. thick) to 10 Ga (0.135 in. thick), which may be
useful for a wide range of applications. In contrast, the substrate
312 in FIG. 20 may have a thickness ranging from 1.000 to 3.450
inches in the region covered by the shell. In other embodiments,
the shell 314 may have any other suitable thickness. For example,
in further embodiments, the shell 314 may be made of a steel or
other metallic plate having a thickness of approximately 0.25
inches, or may be cast, machined from bar stock, or formed in a
different manner. It is understood that different portions of the
shell 314 may have different thicknesses.
[0066] The relative thinness of the shell 314 when compared to the
substrate 312 means that the shell 314 may be formed easily,
relatively inexpensively. For simple shapes of a shell, a
relatively low-cost shell 314 may be made by cutting pieces of
sheet metal, and welding or brazing those pieces together. Slightly
more complicated shapes may be made by bending pieces of sheet
metal in particular configurations, and then welding the bent sheet
metal pieces together. Complex shapes can be made by sheet metal
forming processes such as deep drawing, forming by the Guerin
process (rubber pad forming), hydroforming, and/or explosive
forming. Precision (`lost wax") casting could be used as well,
although the cost of the lost wax process would often be
uneconomical. For particularly complicated shapes, pieces of the
shell could be formed by one or more of these processes, and then
joined by welding or brazing.
[0067] As shown in FIGS. 19-20, the shell 314 is formed of two
parts, having a two-part conformal band 320. A two-part shell body
316 of shell 314 may be initially formed from a front half piece
326 and a back half piece 328, having a front flange 330 or a rear
flange 332, respectively. Front flange 330 extends transversely
from the back edge of the front half 326 and rear flange 332
extends transversely from the front edge of the back half 328.
Front flange 330 may be joined to rear flange 332 by welding or
brazing with a brazing material having a higher melting temperature
than the material intended for infiltration. The shell 314 may have
a conformal band 320 configured to be placed in surface-to-surface
contact with a portion of the surface of the substrate 312 around
an entire periphery of the shell 314, such that the shell 314 is
connected to the substrate 312 by welding or brazing at least at
the conformal band 320, as described below. In other embodiments,
the shell 314 may be formed of a single piece (in which flanges
330, 332 may not be present) or a larger number of pieces. The
two-part shell 314 may be more easily formed than a corresponding
one-part shell, in certain configurations. The two-part shell 314
may also be more easily joined to a corresponding substrate, in
certain configurations, when compared to such joining with a
corresponding one-part shell.
[0068] The shell 314 is shown joined to a portion of a
corresponding substrate 312 in the form of a point, in FIG. 20. An
outer geometry for substrate 312 may include a primary body 334
that defines a bonding surface 335 for welding or brazing to the
conformal band 320. The substrate 312 may provide at least some
recess or other relief for the bonding of the hard material, such
as a plateau 336 and the surrounding surfaces. A distal end of the
substrate 312 may be shaped to define an angular edge 344, and/or a
rounded face 346. In another embodiment, the substrate 312 may not
provide any recess or other relief for the hard material. As seen
in FIG. 20, the shell 314 extends smoothly away from the conformal
band 320, defining a cavity 350 between substrate 312 and shell
314. The cavity 350 defines a resulting thickness of the coating
(not shown) bonded to substrate 312, and the inner geometry of the
shell 314 defines an ultimate outer geometry of a finished
part.
[0069] The light sheet metal shell 314 as shown in FIGS. 19-20 may
be readily moved for precise alignment on a substrate, and then
welded to the substrate, regardless of most orientations of the
substrate. The thin metal shell is easy to attach reliably to the
underlying substrate by welding or high temperature brazing,
without the need for clamping or fixtures, and the joint created is
fluid-tight even at the high temperatures required for infiltration
brazing. In any type of infiltration hardfacing involving molds,
the molten metal brazing material should remain inside the mold.
With the thin metal shells of the present disclosure, reliable
attachment to a substrate is achieved without extra clamping or
fixtures. The resulting assembly is therefore more easily placed in
a furnace for infiltration brazing, allowing substantially greater
ease of infiltration hardfacing heavy items.
[0070] It is understood that various features of the systems 100,
200, 300, 400, 500, 600, 700, 800 described above and shown in the
figures, as well as variations thereof, may be combined and
interchanged within the scope of the present invention. Likewise,
any of the techniques of the methods described above, or variations
thereof, may be utilized in connection with any of the systems 100,
200, 300, 400, 500, 600, 700, 800 described above.
[0071] FIGS. 10-11 illustrate photomicrographs of a composite
material 18 formed using a system similar to the system 100 of FIG.
4 and using a method as described above. FIGS. 10-11 illustrate the
spherical cast WC filler material 15 surrounded by a ductile iron
matrix material 16. The matrix material 16 includes graphite
nodules 25, which is characteristic of ductile iron. As seen in
FIGS. 10-11 the spherical shapes of most of the WC particles 15
have been preserved, indicating minimal reaction or dissolution of
the filler material 15 with the molten matrix material 16. FIG. 11
illustrates the interface 26 between the composite material 18 and
the excess matrix material 19.
[0072] Composite coatings produced according to the systems and
methods described herein exhibit excellent wear resistance and
toughness. In one example, samples were prepared using a system
similar to the system 100 of FIG. 4 and using a method as described
above, using spherical cast WC, crushed cast WC, and cemented WC
with a ductile iron matrix. Samples of cast and cemented WC
reinforced with nickel based alloys and copper by vacuum
infiltration at 2050.degree. F. were prepared for comparison. D2
steel was also used for comparison. Dry sand rubber wheel (DSRW)
abrasion tests (ASTM G65) were conducted on these samples, pursuant
to Procedure A of ASTM G65. The test conditions were as
follows:
[0073] Total revolutions: 6000
[0074] Load on the sample: 30 lbs
[0075] Sand flow rate: 300-400 g/min.
[0076] Two consecutive DSRW tests were done on the same wear scar
region and the mass loss during the second test was taken as
representative of abrasive wear loss of material. As it can be seen
from Table 1 below, spherical cast tungsten carbide/ductile iron
followed by crushed cast tungsten carbide/ductile iron showed
excellent abrasion resistance compared to other materials. The
samples were prepared as coatings, and the substrate was removed by
machining and grinding in order to expose the surface close to the
substrate for testing.
TABLE-US-00001 TABLE 1 Dry sand rubber wheel (DSRW) test data on
different materials Rock- Calcu- Vol- well Mass lated ume Hard- SI.
Carbide loss, density, loss, ness, No material g g/cc mm.sup.3 HRC
1 Spherical cast WC/DI 0.03 12.18 2.46 50 2 Crushed cast WC/DI 0.06
12.18 4.93 45 3 Cemented carbide/DI 0.19 10.95 17.35 57 4 Spherical
cast 0.19 12.58 15.10 55 WC/Ni--7Cr--3Fe--4.5Si--3.1B 5 Cemented
carbide/ 0.10 11.37 8.79 51 Ni--7Cr--3Fe--4.5Si--3.1B 6 Crushed
cast WC/ 0.14 12.58 11.13 50 Ni--7Cr--3Fe--4.5Si--3.1B 7 Crushed
cast WC/Cu 0.08 13.02 6.14 5 8 Cemented carbide/Cu 0.37 11.83 31.28
9 9 D2 tool steel 0.25 7.8 32.05 60
[0077] As seen from the results in Table 1 above, the use of
ductile iron in combination with spherical cast WC and crushed cast
WC resulted in lower mass and volume loss as compared to other
combinations. Additionally, the combinations of WC and ductile iron
had hardnesses that were comparable to other combinations. Further,
ductile iron is considerably less expensive than the other matrix
alloys tested, particularly Ni and Cu alloys. Accordingly, this
testing illustrates the advantageous use of a composite made from a
ductile iron matrix material and WC filler material using systems
and methods according to embodiments of the present invention.
[0078] The various embodiments of the system, method, and product
described herein provide benefits and advantages over existing
technology. For example, the resultant composite product exhibits
excellent wear resistance and toughness, and can be produced
economically. As another example, the system and method can be used
to apply a wear resistant material to a large variety of different
substrates, including wrought, cast, and powder metallurgy metallic
substrates, as well as non-metallic substrates such as ceramics or
ceramic-based composites, as long as the melting point of the
material is suitable for the infiltration process. As another
example, the use of brazing techniques allows for the material
formation and bonding to the substrate to be accomplished in a
single step. Additionally, the brazing techniques typically utilize
a longer time for infiltration as compared to casting and other
techniques, which in turn allows for longer infiltration lengths
(up to 8-10'' or greater in some embodiments). Accordingly, thicker
coatings can also be produced as compared to existing techniques,
including casting, as well as other hardfacing processes such as
plasma transferred arc weld overlay, thermal spray, etc. As another
example, the system and method may utilize lower superheating than
other processes (e.g. casting), which results in less reaction
between the filler material and the matrix material and sound
microstructures that exhibit high wear resistance and toughness. In
addition, the lower degree of reaction permits smaller particle
sizes, or multiple particle sizes, to be used for the filler
material, by which greater density of the hard filler material can
be achieved. As described above, greater yield strength of the
matrix material and greater overall wear resistance of the
composite material can also be achieved. As another example, the
use of an inert atmosphere in the system and method minimizes or
prevents oxidation of the components and can control the
evaporation of volatile elements from the matrix material, reducing
splashing. Still other benefits and advantages are recognized by
those skilled in the art.
[0079] Several alternative embodiments and examples have been
described and illustrated herein. A person of ordinary skill in the
art would appreciate the features of the individual embodiments,
and the possible combinations and variations of the components. A
person of ordinary skill in the art would further appreciate that
any of the embodiments could be provided in any combination with
the other embodiments disclosed herein. It is understood that the
invention may be embodied in other specific forms without departing
from the spirit or central characteristics thereof. The present
examples and embodiments, therefore, are to be considered in all
respects as illustrative and not restrictive, and the invention is
not to be limited to the details given herein. Relative terms such
as "top," "bottom," etc., as used herein, are intended for
illustrative purposes only and do not limit the embodiments in any
way. Nothing in this specification should be construed as requiring
a specific three dimensional orientation of structures in order to
fall within the scope of this invention, unless specifically
recited in the claims. Also, the reader is advised that the
attached drawings are not necessarily drawn to scale. Additionally,
the term "plurality," as used herein, indicates any number greater
than one, either disjunctively or conjunctively, as necessary, up
to an infinite number. Further, "Providing" an article or
apparatus, as used herein, refers broadly to making the article
available or accessible for future actions to be performed on the
article, and does not connote that the party providing the article
has manufactured, produced, or supplied the article or that the
party providing the article has ownership or control of the
article. Accordingly, while specific embodiments have been
illustrated and described, numerous modifications come to mind
without significantly departing from the spirit of the invention
and the scope of protection is only limited by the scope of the
accompanying Claims.
* * * * *