U.S. patent application number 11/968888 was filed with the patent office on 2008-07-03 for enhancement of material properties by infiltration of powder metal part: formulation and method of application thereof.
Invention is credited to Arun K. Chattopadhyay, Jessu Joys.
Application Number | 20080156401 11/968888 |
Document ID | / |
Family ID | 39582226 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080156401 |
Kind Code |
A1 |
Chattopadhyay; Arun K. ; et
al. |
July 3, 2008 |
Enhancement of Material Properties by Infiltration of Powder Metal
Part: Formulation and Method of Application Thereof
Abstract
Infiltration compositions comprising chromium and at least about
80% copper. The infiltration compositions may further comprise
iron, zinc, manganese, antimony and/or lubricants. Also, methods
for infiltrating powder metal parts comprising contacting a powder
metal part with the infiltration composition comprising chromium
and at least about 80% copper and heating the powder metal part and
infiltration composition to a temperature sufficient to melt the
infiltration composition and allow the infiltration composition to
infiltrate through pores in the powder metal part.
Inventors: |
Chattopadhyay; Arun K.;
(Bridgewater, NJ) ; Joys; Jessu; (Holland,
PA) |
Correspondence
Address: |
NORRIS MCLAUGHLIN & MARCUS, P.A.
P O BOX 1018
SOMERVILLE
NJ
08876
US
|
Family ID: |
39582226 |
Appl. No.: |
11/968888 |
Filed: |
January 3, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60883192 |
Jan 3, 2007 |
|
|
|
Current U.S.
Class: |
148/514 ;
148/22 |
Current CPC
Class: |
C23C 10/52 20130101;
C23C 10/30 20130101; C22C 9/00 20130101; B22F 3/26 20130101; C23C
26/02 20130101; B22F 1/0059 20130101 |
Class at
Publication: |
148/514 ;
148/22 |
International
Class: |
C23C 10/30 20060101
C23C010/30; B22F 7/00 20060101 B22F007/00; C22C 9/00 20060101
C22C009/00 |
Claims
1. An infiltration composition comprising at least about 80% copper
and chromium.
2. The infiltration composition of claim 1 further comprising at
least about 0.5% iron or at least about 0.5% manganese.
3. The infiltration composition of claim 1 comprising about 0.1% to
about 3.5% chromium.
4. The infiltration composition of claim 3 comprising about 0.1% to
about 3.5% iron, up to about 0.2% zinc, up to about 0.2% manganese
and up to about 0.2% lubricants.
5. The infiltration composition of claim 4 wherein the lubricant is
fatty acid based.
6. The infiltration composition of claim 1 comprising at least
about 90% by weight copper.
7. The infiltration composition of claim 1 further comprising
antimony.
8. The infiltration composition of claim 7 comprising about 0.01%
to about 0.5% antimony.
9. The infiltration composition of claim 1 wherein the chromium is
part of an alloy with a metal selected from the group consisting of
iron, manganese, copper and combinations thereof.
10. The infiltration composition of claim 1 wherein chromium powder
is bound to the infiltration composition by a binder selected from
the group consisting of hydrocarbon binder, acrylic binder,
phenolic binder and combinations thereof.
11. The infiltration composition of claim 1 in the form of a
paste.
12. The infiltration composition of claim 11 wherein the copper is
in the form of a spherical powder, irregular powder or combinations
thereof.
13. The infiltration composition of claim 11 wherein the paste
comprises pre-alloyed copper powders of Cu--Zn, Cu--Sn, Cu--Cr,
Cu--Ni, Cu--Mn, Cu--Sb, Cu--Pb, Cu--Bi, Cu--P, Cu--Al and
combinations thereof.
14. The infiltration composition of claim 11 wherein the paste
further comprises a material selected from the group consisting of
gelled petroleum, ethereal poly-alcohols, fatty alcohols, mineral
oil and combinations thereof.
15. A powder metal part comprising the infiltration composition of
claim 1.
16. A method for infiltrating a powder metal part with an
infiltration composition comprising the steps of providing an
infiltration composition comprising at least about 80% copper and
chromium, providing the powder metal part, contacting powder metal
part with the infiltration composition and heating the powder metal
part while the powder metal part is in contact with the
infiltration composition to a temperature that allows the
infiltration composition to melt and infiltrate through pores in
the powder metal part.
17. The method of claim 16 wherein the infiltration composition
comprises at least about 0.1% by weight chromium.
18. The method of claim 17 wherein the infiltration composition
comprises about 0.5% to 3.5% by weight chromium, about 0.1% to 3.5%
by weight iron, up to about 2.0% by weight of zinc, up to about 2%
by weight of manganese and up to about 2% by weight of
lubricants.
19. The method of claim 18 wherein the lubricant is fatty acid
based.
20. The method of claim 16 wherein the infiltration composition
comprises at least about 90% copper.
21. The method of claim 16 wherein the infiltration composition
further comprises antimony.
22. The method of claim 21 wherein the antimony is used in amounts
of about 0.01% to about 0.5%.
23. The method of claim 16 wherein the infiltration composition is
in a form selected from the group consisting of compressed blocks,
extruded bars, extruded cylinders, extruded hollow tubes and solid
pastes.
24. The method of claim 16 wherein the solid pastes are compounded
with a material selected from the group consisting of gelled
petroleum, ethereal poly-alcohols, fatty alcohols, mineral oil and
combinations thereof.
25. The method of claim 16 wherein the temperature is at least
about 800.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/883,192 filed on Jan. 3, 2007, which is
incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention concerns improvement in material properties of
powder metal parts upon infiltrating with copper based formulations
with addition of chromium and chromium based alloys. Metallographic
studies indicate the homogeneity of distribution of
copper-eutectoids throughout the interstices of iron-based powder
metal parts. This method exhibits superior mechanical properties
compared to the conventional infiltrating compounds and alloys
available in any physical forms.
[0004] 2. The Related Art
[0005] Enhancing the properties of powder metal parts produced by
powder compression and sintering requires infiltration using a
metal composition of melting point lower than that of the metal
constitute powder metal parts. The compressed powder metal parts
upon sintering leave a network of interconnecting void channels or
capillaries. The process of infiltration using a metal composition
that melts at a lower temperature than the powder metal parts
allows the infiltrating material to percolate through the
capillaries and fill in the voids resulting in the improvement of
material properties of the powder metal parts. In general for
powder metal parts comprising iron and its alloys, the infiltration
compositions are typically based on copper.
[0006] The infiltration process involves placing the infiltration
composition in contact with the powder metal parts, and then
subjecting them to a temperature close to the melting point of the
infiltrating composition under a reducing atmosphere in order to
avoid the formation of metal oxides. Upon melting, the infiltrating
material diffuses through the capillaries thereby forming
microstructures throughout the interstices and strengthening the
properties of the powder metal parts. The uniformity of
distribution of infiltrated materials and the formation of
microstructures there from brings about the enhancement of material
properties.
[0007] The use of chromium in copper in the alloyed forms is known
for enhancing material strength, corrosion resistance and
electrical conductivity. Copper-chromium alloys are generally high
copper solid solutions of chromium. These alloys undergo changes in
properties due to the precipitation of chromium out of the solid
solution as the temperature of the molten phase of the alloy cools
down. The strength of fully aged chromium copper is nearly twice
that of pure copper and its conductivity remains high at 85% IACS,
or 85% that of pure copper. These high strength alloys retain their
strength at elevated temperatures. The corrosion resistance of
chromium copper alloys is better than that of pure copper because
chromium improves the chemical properties of the protective oxide
film. Chromium copper has excellent cold formability and good hot
workability. It is used in applications such as resistance welding
electrodes, seam welding wheels, switch gears, cable connectors,
circuit breaker parts, molds, spot welding tips, and electrical and
thermal conductors that require strength. Chromium copper alloys
are designated as UNS C18050 through C18600, the cast alloys are
C81400 through C81540.
[0008] All parts and percentages set forth in this specification
are on a weight-by-weight basis, unless otherwise specified.
SUMMARY OF INVENTION
[0009] An aspect of the invention pertains to methods to improve
material properties of iron based powder metal parts that involves
infiltration that allows formation of unique uniform
microstructures in the capillaries providing enhanced material
strength. The infiltration composition comprises copper and copper
alloys, and in an embodiment of the invention the total copper
content in the composition is at least about 80%, by weight. The
infiltration composition further comprises metallic chromium and
its alloys which are used in the invention to achieve refined
microstructures of metals in powder metal parts. In an embodiment
of the invention, the chromium alloy has a chromium content of at
least about 0.1%, by weight, or more. The infiltration composition,
optionally, further comprises iron and/or manganese either in their
individual metallic forms or in their alloyed forms. In an
embodiment of the invention, the infiltration composition comprises
at least about 0.1%, by weight of iron and/or manganese,
respectively, preferably at most about 0.5% iron and/or manganese.
In further embodiments, the infiltration composition comprises
antimony. Depending upon the preferred forms of application, the
infiltration composition further, optionally, comprises lubricants
and in an embodiment, the amount of lubricant in the infiltration
composition does not exceed more than 2%, by weight. The lubricant
may be a fatty acid based lubricant.
[0010] Another aspect of the invention involves application of the
infiltration composition in various physical forms, such as,
compressed blocks (wafers, cylinders, bars etc.) prepared from the
powder form of infiltration composition. The infiltration
composition can also be applied in the form of pastes, such as
those prepared from liquid or gelled petroleum oils and also from
glycol ethers, long chain fatty alcohols and their combinations.
The infiltration composition can also be applied in the form of
extruded objects drawn from the powdered form of the infiltration
composition. Thus, the invention concerns methods for enhancement
of material properties of powder metal parts by infiltrating a
composition which methods comprise the steps of providing the
infiltration composition described herein, providing a powder metal
part, contacting the infiltration composition to the powder metal
part and heating the combined powder metal part and infiltration
composition.
DETAILED DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1A is a chart of the Rockwell Hardness (H Scale) versus
the weight percent of chromium after infiltration of powder metal
parts forms with infiltration compositions in accordance with
embodiments of the invention.
[0012] FIG. 1B is a chart of the Rockwell Hardness (H Scale) versus
the weight percent of antimony after infiltration of powder metal
parts forms with infiltration compositions in accordance with
embodiments of the invention.
[0013] FIG. 1C is a chart of the Transverse Rupture Strength (KSI)
versus the weight percent of chromium after infiltration of powder
metal parts forms with infiltration compositions in accordance with
embodiments of the invention.
[0014] FIG. 2 is a set of scanning electron microscope ("SEM") and
energy dispersion X-ray technique ("EDX") pictures of polished
metallographic sections infiltrated (10% by weight of the powder
metal part) by the comparative infiltration composition which does
not comprise chromium.
[0015] FIG. 3A is a set of SEM and EDX pictures of polished
metallographic sections infiltrated (10% by weight of the powder
metal part) by an infiltration composition in accordance with
embodiments of the invention (Example 2) comprising 0.3%
chromium.
[0016] FIG. 3B is a set of SEM and EDX pictures of polished
metallographic sections infiltrated (10% by weight of the powder
metal part) by an infiltration composition in accordance with an
embodiment of the invention (Example 2) comprising 0.6%
chromium.
[0017] FIG. 4 is a chart of the Rockwell Hardness (H Scale) versus
the weight percent of chromium of a wafer compacted with bonded
powder in accordance with embodiments of the invention.
[0018] FIG. 4A is a set of SEM pictures showing chromium powder,
copper powder, bonded copper and chromium powders showing adhered
chromium particles on copper particles and blended copper and
chromium powders showing random mixtures of both copper and
chromium in accordance with embodiments of the invention.
[0019] FIG. 5 is a chart of the Rockwell Hardness (H Scale) versus
the weight percent of chromium of a wafer compacted from a
pre-alloyed blend in accordance with embodiments of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The invention concerns copper based infiltration
compositions comprising (a) at least about 80% by weight copper,
(b) about 0.1 to 3.5% by weight chromium, preferably about 0.5% to
3.5% by weight chromium, either in single metal or alloyed forms,
(c) optionally about 0.1 to 3.5% by weight iron as single metal, or
alloy, or metal complex forms, (d) optionally about 0 to 2.0% by
weight of zinc either as single metal or alloyed forms, (e)
optionally about 0 to 2% by weight of manganese either as single
metal or alloyed forms and (f) optionally about 0 to 2% by weight
of lubricants, such as those derived from organic fatty acids as
their esters, amides, amine neutralized salts and their metal
salts. Examples of lubricants include stearamides; alkali or
alkaline metal salts; such as salts of lithium, sodium, potassium,
ribidium, cesium, and francium; alkali or alkaline earth metal
salts such as salts of beryllium; magnesium, calcium, strontium,
barium and radium; transition metal salts and combinations thereof.
Further, the invention concerns methods of enhancement of material
properties of powder metal parts, i.e. improved powder metal parts
and improvements to processes for making powder metal parts by
infiltrating a composition of any conventional physical form, such
as compressed blocks, or solid pastes, or extruded bars or
cylinders. The invention also concerns methods for infiltrating a
powder metal part and making powder metal parts comprising the
steps of (i) providing copper based composition(s) with selective
incorporation of chromium and chromium based alloy(s), comprising
(a) at least about 80% by weight copper, (b) about 0.1 to 3.5%,
preferably about 0.5% to 3.5%, by weight chromium either in single
metal or alloyed forms, (c) optionally about 0.1 to 3.5% by weight
iron as single metal, or alloy, or metal complex forms, (d)
optionally about 0 to 2%, preferably about 0.1% to 2%, by weight of
zinc, either as single metal or alloyed forms, (e) optionally about
0 to 2%, preferably about 0.1% to 2%, by weight of manganese either
as single metal or alloyed forms and (f) optionally about 0 to 2%,
preferably about 0.1% to 2%, by weight of lubricants, such as those
derived from organic fatty acids as their esters, amides, amine
neutralized salts and their metal salts, (ii) providing a powder
metal part(s), (iii) contacting the infiltration composition to the
powder metal part(s), and (iv) heating the combined powder metal
part(s) and infiltration composition to a temperature enabling the
infiltration composition to melt and infiltrate through the pores
of powder metal part(s). The infiltration composition may be
provided in one or more suitable forms, such as (a) compressed
blocks of desired shapes and dimensions (conventionally known as
`Slug`), (b) in the form of extruded bars, or cylinders, or hollow
tubes of desired dimensions, (c) in the form of solid pastes
compounded with gelled petroleum or other liquid organic binders
derived from ethereal poly-alcohols, fatty alcohols, mineral oil,
and combinations thereof, such as hydrocarbon resin (coumer)
solutions in ketonic, alcoholic and hydrocarbon solvents, phenyl
laurapel 81 and combinations thereof. In an embodiment of the
invention the method comprises the temperature to operate
infiltration of least about 800.degree. C., such as from about
800.degree. C. to about 1150.degree. C.
[0021] In embodiments of the invention the infiltration composition
may comprise at least about 90% by weight of copper. In further
embodiments the infiltration composition comprises at least about
0.3%, by weight chromium, preferably at least about 0.6% chromium.
In embodiments the infiltration composition comprises from about
0.1% to 2% chromium, such as about 0.1% to 0.6% chromium.
[0022] The chromium may be in powder form and also may be in
alloyed form in combination with iron, manganese and copper and
combinations thereof. In embodiments of the invention, the powdered
form of chromium is bound with the infiltration composition by
means of a binder, such as materials selected from the group
consisting of hydrocarbon, acrylic, phenolic and combinations
thereof. Examples of binders include polyglycol ether; alcohols
typically octanol, hexadecanol, pentanol and/or dodecanol;
hydrocarbon resin (coumer) solutions in ketonic, alcoholic and
hydrocarbon solvents; and combinations thereof.
[0023] The infiltration composition may be in one of several
physical forms. For example, the infiltration composition may be in
the form of compressed powder (or slug). The infiltration
composition may be in the form of paste, wherein the copper powder
can be of either spherical or irregular or the combination of both,
or the paste can be comprised of pre-alloyed copper powders of
Cu--Zn, Cu--Sn, Cu--Cr, Cu--Ni, Cu--Mn, Cu--Sb, Cu--Pb, Cu--Bi,
Cu--P, Cu--Al, and any combination of metals alone or their
mixtures from the periodic table. The infiltration composition may
be extruded as solid bar, cylinder, or hollow tube.
[0024] In the method, a powdered metal part based on iron may be
sintered. In a further embodiment of the invention, the powder
metal part is an iron based alloy and the infiltrated part has
generally uniform distribution of copper eutectoids. In these
embodiments of the invention, the powder metal part generally has a
higher tensile strength compared to the compositions without
chromium and may further have higher transverse rupture strength
and higher yield strength.
[0025] Inclusion antimony may be used in an embodiment of the
invention in conjunction with copper and chromium of the
infiltration composition and applied in the methods of the present
invention. The presence of antimony provides synergy to the effect
of copper and chromium. The presence of antimony may also provide
lubricity and ease of machining the metal parts. In embodiments of
the invention, the amount of antimony may be about 0.01% to about
0.5%, preferably about 0.1% to about 0.5%.
[0026] The performances of the infiltration compositions of the
invention are compared with conventional infiltration compositions.
The formation of unique uniform micro structures is confirmed by
metallographic studies by SEM and EDX, as shall be discussed
below.
EXAMPLES
Example 1
Comparative
Preparation of Conventional Infiltration Composition
[0027] The conventional non-residue type infiltration composition
was prepared by blending 97 weight (wt) % of Copper, 2 wt % of
Iron, and 1 wt % of Zinc. The powder blend was further mixed with
0.5 wt % of Lithium (Li) stearate, or optionally a blend of
Li-stearate and Stearamide waxes (commercially available as
Acrawax). This blend was further converted in the following
physical forms. Infiltration was carried out by placing one of the
following infiltrant forms on the powder metal parts of dimension
1.25''.times.0.5''.times.0.25'' made by compressing iron based
alloyed powders or premix of MPIF (Metal Powders Industrial
Federation) standard (F-0008), which is incorporated by reference
herein in its entirety. The powder metal part is compressed to a
density 6.7 g/cc. The infiltrant forms used are 10 wt % of the
powder metal parts.
[0028] (i) Compressed infiltrant wafer: The infiltration
composition mixes of example 1, 10 wt % of the powder metal parts,
was compressed in the form of rectangular wafer of density 7.5
g/cc. The compressed wafer was placed on the powder metal part and
sintered together to allow infiltration to occur in a furnace of
reducing atmosphere at 2050.degree. F. (or 1121.degree. C.). Then
the infiltrated parts were cooled down to room temperature and the
mechanical properties were tested.
[0029] (ii) Extruded infiltrant bar: By adopting Conform Extrusion
technique of powders (U.S. Pat. No. 5,503,796, which is
incorporated by reference herein in its entirety), the infiltration
composition of Example 1 was extruded in the form of cylindrical
rods of dimension 0.1'' in diameter. A length of the rod weighing
10 wt % of the powder metal part was placed and followed
sintering-infiltration as in subpart (i) of this Example.
[0030] (iii) Infiltrant paste: The infiltration composition of
Example 1 was pasted in petroleum jelly (and also alternately in
alkylated glycolethers, mineral oils, higher fatty alcohols, for
example dodecanol, hexadecanol etc.). Then a proportionate amount
of the paste equivalent to 10 wt % of the powder metal part was
spread on the object and subjected to sintering and infiltration as
mentioned above. The comparative results are given in Table 1A.
Example 2
Preparation of the Infiltration Composition of the Invention
[0031] The infiltration composition of the invention was prepared
by blending 92-97 weight (wt) % of Copper, and 0-4 wt % of
Chromium, 2 wt % of Iron, and 1 wt % of Zinc. The composition with
no chromium is a comparative example and the infiltrant
compositions of the invention in the example contained from 0.3 to
3.5% chromium. The powder blends of different weight percent of
chromium were further mixed with 0.5 wt % of Lithium (Li) stearate,
or optionally a blend of Li-stearate and Stearamide waxes
(commercially available as Acrawax). These blends were further
converted in the following physical forms. Infiltrations were
carried out by placing one of the following infiltrant forms on the
powder metal parts of dimension 1.25''.times.0.5''.times.0.25''
made by compressing iron based alloyed powders as described in
Example 1. The powder metal part is compressed to a density 6.7
g/cc. The infiltrant forms used are 10 wt % of the powder metal
parts. These compositions were also studied with a small addition
of antimony (0.1-0.5 wt %) for synergistic effects on the material
strength. The results on the synergistic effects for the
powder-metal parts infiltrated with a composition comprising
antimony and chromium are given in Table 1B. The transverse rupture
strengths of the infiltrated powder metal parts of the present
invention are given in FIG. 1C.
[0032] (i) Compressed infiltrant wafer: The infiltration
compositions mixes of Example 2, each consisting of 10 wt % of the
powder metal parts, were compressed in the form of rectangular
wafers of density 7.5 g/cc. The compressed wafer was placed on the
powder metal part and sintered together to allow infiltration to
occur in a furnace of reducing atmosphere at 2050.degree. F. (or
1121.degree. C.). Then the infiltrated parts were cooled down to
room temperature and the mechanical properties were tested. The
comparative results are given in Table 1A.
[0033] (ii) Extruded infiltrant bar: By adopting Conform Extrusion
technique of powders (U.S. Pat. No. 5,503,796), the infiltration
compositions of Example 2 were extruded in the form of cylindrical
rods of dimension 0.1'' in diameter. For each of the compositions
of Example 2, a length of the rod weighing 10 wt % of the powder
metal part was placed and followed sintering-infiltration as in
Subpart (i) of this Example. The comparative results are given in
Table 1A.
[0034] (iii) Infiltrant paste: The infiltration compositions of
Example 2 were pasted in petroleum jelly (and also alternately in
alkylated glycol ethers, mineral oils, higher fatty alcohols, for
example dodecanol, hexadecanol etc.). Then a proportionate amount
of each of the pastes of the compositions of Example 2, equivalent
to 10 wt % of the powder metal part, was spread on the object and
subjected to sintering and infiltration as mentioned above. The
comparative results are given in Table 1A.
[0035] The plot of Rockwell hardness versus percentage of chromium
in the infiltration composition for the various forms of powder
metal parts comprising the infiltration composition forms of
Example 2 is shown in FIG. 1A. The plots on the synergistic effect
caused by the addition of antimony to the infiltration compositions
of Example 2 are shown in FIG. 1B. The plot of transverse rupture
strengths of the infiltrated powder metal parts of Example 2 at
various percentages of chromium is shown in FIG. 1C.
Example 3
Metallographic Studies on the Infiltration Compositions
[0036] The microstructures of the infiltrated powder metal parts of
Examples 1 and 2 were further studied and compared by
metallography. The specimens of the excised sections of the
infiltrated powder metal parts were polished and etched using 2%
Nital solution (ethanolic solution of nitric acid). All of the
polished and etched specimens of the infiltrated parts were
examined by SEM (scanning electron microscope) at various
magnifications followed by EDX (energy dispersion x-ray technique).
The polished and etched transverse rupture sections were placed
within the chamber of a scanning electron microscope under vacuum.
Each sample was subjected to X-rays to provide an image of the
surface of the sample and to get the profiles of microstructures of
elemental or eutectoid forms of metal compositions. This was
accomplished using an auxiliary energy dispersive cell to obtain
the surface topography and maps of the constituents within the
microstructures of the infiltrated specimens. The EDX pictures of
the infiltrated locations of the powder metal interstices enriched
by the microstructures of copper-chromium eutectoids are shown in
FIGS. 2, 3A and 3B.
[0037] FIG. 2 includes a SEM picture 1 of a specimen that comprises
an infiltration composition that does not contain chromium. In EDX
photograph 2, the infiltration composition does not contain copper
and this EDX photograph shows profiles of an iron-rich location,
i.e., an iron map. EDX photograph 3 shows a copper map for a
composition that does not comprise chromium showing copper-rich
locations 4 (brighter sections) within the powder metal part.
[0038] FIG. 3A includes a SEM picture 5 of a specimen that
comprises an infiltration composition having 0.3% chromium. EDX
photograph 6 is an iron map which shows the iron-rich locations of
the specimen comprising an infiltration composition having 0.3%
chromium. EDX photograph 7 shows a copper map for the specimen
comprising 0.3% chromium showing copper-rich locations 8 (brighter
sections) within the powder metal part.
[0039] FIG. 3B includes a SEM picture 9 of a specimen that
comprises an infiltration composition having 0.6% chromium. EDX
photograph 10 is an iron map which shows the iron-rich locations of
a specimen comprising an infiltration composition having 0.6%
chromium. EDX photograph 11 shows a copper map for a specimen
comprising 0.6% chromium showing copper-rich locations 12 (brighter
sections) within the powder metal part.
[0040] The respective microstructures and the location of their
constituents in samples with and without chromium revealed the
differences. For example, FIG. 3B shows the evidence of copper
microstructures resulting from the formation of eutectoids in the
presence of chromium, whereas the FIG. 2 (which did not contain
chromium) showed poor reaction of copper within the interstices of
iron particles.
Example 4
Preparation of the Infiltration Composition of the Invention Using
Bonded Copper-Chromium Granules
[0041] In this example, the copper and chromium powders were
pre-bonded using low molecular weight poly methyl methacrylate,
condensation polymers of oleic acid and acrylic acid, and
hydrocarbon resin (coumer) solutions in ketonic, alcoholic and
hydrocarbon solvents. The polymeric binders used as 5-10% solutions
in either of those solvents. Copper and chromium powders having the
amounts of copper and chromium of Example 2 were blended with 5%
(wt) of the polymer solutions described above in a rotary tumbler.
Upon blending, the organic solvent was removed from the blend by
drying. These dried bonded powder(s) of copper and chromium were
then mixed with the remaining portion of other components like
iron, zinc, and lubricant in the amounts and as described in
Example 2. The purpose of pre-bonding copper and chromium powders
was to prevent the possibility of segregation and to provide more
intimacy to perform while transiting through the eutectic phase of
the melt during infiltration process. The results of mechanical
properties of the powder metal parts of this example after
infiltration are given in Table 2 and a chart (FIG. 4) showing the
Rockwell Hardness as a function of the amount of chromium in the
infiltration composition. FIG. 4A is a series of SEM pictures of
blended copper-chromium powders versus bonded copper-chromium
powders of the invention which reveal the intimately adhered
particle boundaries of copper-chromium. In FIG. 4A, photograph 13
shows chromium powder, photograph 14 shows copper powder,
photograph 15 shows bonded copper and chromium powders with adhered
chromium particles on the copper particles and photograph 16 shows
blended copper and chromium powders with random mixtures of both
copper and chromium.
Example 5
Preparation of the Infiltration Composition of the Invention Using
Copper and Copper-Chromium Alloy Powder
[0042] The preparation of infiltration composition of the invention
was followed according to the Example 4, wherein the chromium was
incorporated to the formulation by means of using high-copper and
chromium alloy UNS C18200. The formulation comprising copper powder
and powdered form of UNS C18200 were present as 37-40 wt % of
copper powder, 55-60 wt % of the powdered form of copper-chromium
alloy of grade UNS C18200, 2 wt % of Iron, and 1 wt % of Zinc. The
powder blends were further mixed with 0.5 wt % of Lithium (Li)
stearate, or optionally a blend of Li-stearate and Stearamide waxes
(commercially available as Acrawax). Infiltration experiments were
carried out as per the method described in Example 2. The results
of mechanical properties of the metal powder parts upon
infiltration, i.e. Rockwell Hardness v. weight percent of chromium,
are shown in Table 3 and FIG. 5.
TABLE-US-00001 TABLE 1A Wafer from compacted Wt. % of powder
Extruded by Infiltrant paste Chromium as Rockwell conform process
Rockwell in Examples Hardness Rockwell Hardness Hardness 1 and 2 (H
scale) (H scale) (H scale) 0 88 88 88 0.3 98 98.5 97 0.6 100 100.5
98 1 100 100 98 2 98 98 97 3.5 95 94.5 93
TABLE-US-00002 TABLE 1B Wafer from Extruded by compacted conform
Wt. % of Wt. % of powder process Chromium Antimony Rockwell
Rockwell Infiltrant Paste as in as in Hardness Hardness Rockwell
Hardness Example 2 Example 2 (H scale) (H scale) (H scale) 0.3 0 98
98.5 97 0.3 0.1 99 99 98 0.3 0.2 101 101.5 99 0.3 0.3 103 102 97.5
0.3 0.5 98.5 98 96
TABLE-US-00003 TABLE 2 Wafer from compacted powder of Example 4 Wt.
% of Chromium Rockwell Hardness in Example 2 (H scale) 0 88 0.3 96
0.6 103 1 102 2 98 3.5 96
TABLE-US-00004 TABLE 3 Wafer from compacted powder of example 5 Wt.
% of Chromium Rockwell Hardness in Example 1 (H scale) 0 88 0.3 98
0.6 99 1 101 2 95 3.5 94
Example 6
[0043] Copper infiltration of iron parts was carried out with
F-0008 and FY-4500 iron powders based on the standards in powder
metallurgy as described in the Material Standard for PM Structural
Parts, MPIF Standard 35 which is incorporated herein by reference
in its entirety (see, for example pages 36 and 56, 2000 Edition,
Published by Metal Powders Industries Federation). The general
properties and characteristics of the F-0008 and FY-4500 iron
powders studied in this example are set forth in Table 4. The iron
parts were compressed at various densities ranging between 6.7
g/cm.sup.3 to 7.2 g/cm.sup.3. Infiltration of the iron parts were
verified using the infiltration composition of Example 2 and a
conventional infiltrant system, as described in Example 1. The
results (Table 5 and 6) showed improved performance of mechanical
properties for the infiltration composition of the invention. The
consistency in dimensional changes with the infiltration
composition of the invention is evident at various densities of the
iron parts studied.
TABLE-US-00005 TABLE 4 Properties F-0008 FY-4500 AD, g/cm.sup.3
3.16 3.11 Hall Flow, s/50 g 39 28.7 Green Strength, psi 1500 1930
Compressibility at 6.8 6.8 30tsi, g/cm.sup.3 Lube, % 1 0.75
Transverse Rupture 101 107 Strength, 10.sup.3 psi
TABLE-US-00006 TABLE 5 Comparison of mechanical properties of the
sintered parts using iron powder F-0008 by conventional method of
infiltration (A) as well as the method of the invention (B).
Transverse Rockwell Dimensional Sintered Green Strength Hardness
Change Density Density (.times. 1000 PSI) (B Scale) (%) (g/cc)
(g/cc) A B A B A B A B 6.7 160.10 167.10 82.10 84.00 0.70 0.69 7.15
7.18 7 185.20 198.64 85.10 89.60 0.83 0.70 7.47 7.57 7.2 204.20
229.50 88.40 94.20 0.90 0.69 7.61 7.71 A: Conventional Infiltrating
system as described in Example-1 [section (i)] B: Method of present
invention as described in Example-2 [Section (ii)]
TABLE-US-00007 TABLE 6 Comparison of mechanical properties of the
sintered parts using iron powder FY-4500 by conventional method of
infiltration (A) as well as the method of the invention (B).
Transverse Rockwell Dimensional Sintered Green Strength Hardness
Change Density Density (.times. 1000 PSI) (B Scale) (%) (g/cc)
(g/cc) A B A B A B A B 6.7 162 171 82.7 85.8 0.80 0.78 7.21 7.27 7
196 201 88.3 91.2 0.87 0.80 7.42 7.53 7.2 207 214 91.7 94.0 0.98
0.90 7.64 7.67 A: Conventional infiltrating system as described in
Example-1 [section (i)] B: Method of present invention as described
in Example-2 [Section (ii)]
Example 7
Helical Gear
[0044] A standard iron gear part, a helical gear, was selected to
test and compare the performance of an infiltration system in
accordance with the invention versus a conventional system. The
iron helical gears, compacted to a green density of 6.7 g/cc were
infiltrated with an infiltration composition in accordance with the
invention [Example 2; Section (ii)], a conventional infiltrant
system [Example 1; Section (i)] and without infiltrant. The gear
was compressed from the iron powder grade F-0008 (Table 4). The
surface hardness of the infiltrated parts was measured using the
Rockwell Hardness Tester. The results are given in Table 7 showing
improvement in surface hardness. The amount of infiltration
composition is about twelve weight percent of the base iron
part.
[0045] Further, the infiltrant system of the invention [Example 2,
Section (ii)] resulted in helical gear having a clean and smooth
surface finishing compared to the helical gear prepared with
conventional infiltration compositions and systems. The powder
metal part prepared with the convention infiltration composition
and system had a rough surface after the process. Without being
bound to any theory, the inventors believe that the rough surface
on the part prepared with conventional infiltration compositions
resulted from traces of infiltrant residue on the surface of the
powder metal part because the infiltration composition did not
completely infiltrate the surface of the part thus causing
imperfect infiltration.
Cylindrical Bushing
[0046] An iron cylindrical bushing was also selected to measure the
performance of the infiltration system of the invention. The
cylindrical shape limits the contact area between the base part,
i.e. the cylindrical bushing, and the infiltrant system. Because of
this, conventional infiltration compositions and systems tend to
show poor surface finishing, traces of sooty residues and
dimensional instability. The cylindrical bushings prepared for this
example were compacted to a green density of 6.7 g/cc and
infiltrated with the infiltration composition and system of the
invention [Example 2; Section (ii)], with a conventional infiltrant
system [Example 1; Section (i)] and without incorporating any
infiltrant. The bushings were made from the iron powder grade of
FY-4500. The surface hardness of the infiltrated parts was measured
using the Rockwell Hardness Tester. The results are given in Table
7 showing improvement in surface hardness for the metal part
prepared in accordance with the invention. Also, the cylindrical
bushing prepared in this example with the infiltration composition
and system of the invention had a clean and smooth surface
finishing whereas the part prepared with the conventional system
had a surface with an undesired sooty appearance. The amount of
infiltrant used in all experiments was approximately twelve weight
percent of the base iron part.
TABLE-US-00008 TABLE 7 Surface hardness comparison of the
infiltration system of the invention versus conventional iron
powdered metal parts. Rockwell Hardness (B Scale) A B C Helical 85
93 60 Gear Cylindrical 85 92 51 Bushing A: Conventional
infiltrating system as described in Example-1 [section (i)] B:
Infiltration composition and method of invention as described in
Example-2 [Section (ii)] C: As sintered iron powder metal part
(without any infiltration)
* * * * *