U.S. patent application number 10/843300 was filed with the patent office on 2004-10-21 for metal powder including diffusion alloyed molybdenum.
This patent application is currently assigned to HOGANAS AB. Invention is credited to Hallen, Hans, Holmqvist, Ulf.
Application Number | 20040206204 10/843300 |
Document ID | / |
Family ID | 29218057 |
Filed Date | 2004-10-21 |
United States Patent
Application |
20040206204 |
Kind Code |
A1 |
Holmqvist, Ulf ; et
al. |
October 21, 2004 |
Metal powder including diffusion alloyed molybdenum
Abstract
Metal powders for surface coating are disclosed. The metal
powders comprise molybdenum diffusion alloyed to the base powder
particles. Metal powders comprising a prealloyed powder and a
molybdenum source are also disclosed.
Inventors: |
Holmqvist, Ulf; (Jonstorp,
SE) ; Hallen, Hans; (Waterloo, BE) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
HOGANAS AB
Hoganas
SE
|
Family ID: |
29218057 |
Appl. No.: |
10/843300 |
Filed: |
May 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10843300 |
May 12, 2004 |
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10270728 |
Oct 16, 2002 |
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6756083 |
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10270728 |
Oct 16, 2002 |
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09900982 |
Jul 10, 2001 |
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10270728 |
Oct 16, 2002 |
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PCT/SE02/00943 |
May 17, 2002 |
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Current U.S.
Class: |
75/255 |
Current CPC
Class: |
C22C 38/44 20130101;
C22C 38/22 20130101; B32B 15/012 20130101; Y10T 428/12757 20150115;
B22F 1/148 20220101; Y10T 428/12063 20150115 |
Class at
Publication: |
075/255 |
International
Class: |
C22C 001/05 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2001 |
SE |
0101776-3 |
Claims
What is claimed is:
1. A metal powder for surface coating, the metal powder consisting
essentially of particles of a prealloyed powder and from about 4%
to about 15% by weight of Mo diffusion alloyed to the particles of
the prealloyed powder, the prealloyed powder comprising Fe and
optionally at least one element selected from the group consisting
of C, Si, Mn, Cr, V, Mo and W, the balance being inevitable
impurities.
2. The metal powder of claim 1, wherein the amount of molybdenum
diffusion alloyed to the particles of the prealloyed powder is from
about 6% to about 10% by weight of the metal powder.
3. The metal powder of claim 1, wherein the amount of molybdenum
diffusion alloyed to the particles of the prealloyed powder is from
about 4% to about 10% by weight of the metal powder.
4. The metal powder of claim 1, wherein the prealloyed powder is an
atomized powder.
5. A surface coating formed by applying the metal powder according
to claim 1 on a substrate by a thermal spraying process.
6. A surface coating formed by applying the metal powder according
to claim 1 on a substrate by a weld cladding process.
7. A metal powder for surface coating, the metal powder comprising
particles of a prealloyed powder and from about 4% to about 15% by
weight of Mo as the only element diffusion alloyed to the particles
of the prealloyed powder, the prealloyed powder comprising Fe and
optionally at least one element selected from the group consisting
of C, Si, Mn, Cr, V, Mo and W, the balance being inevitable
impurities.
8. The metal powder of claim 7, wherein the amount of molybdenum
diffusion alloyed to the particles of the prealloyed powder is from
about 6% to about 10% by weight of the metal powder.
9. The metal powder of claim 7, wherein the amount of molybdenum
diffusion alloyed to the particles of the prealloyed powder is from
about 4% to about 10% by weight of the metal powder.
10. The metal powder of claim 7, wherein the prealloyed powder is
an atomized powder.
11. A surface coating formed by applying the metal powder according
to claim 7 on a substrate by a thermal spraying process.
12. A surface coating formed by applying the metal powder according
to claim 7 on a substrate by a weld cladding process.
13. A metal powder for surface coating, the metal powder being
produced by heating a mixture consisting essentially of a
prealloyed powder and a molybdenum-containing powder, the metal
powder comprising from 4% to 15% by weight of Mo as the only
element diffusion alloyed to the particles of the prealloyed
powder, the prealloyed powder comprising Fe and optionally at least
one element selected from the group consisting of C, Si, Mn, Cr, V,
Mo and W, the balance being inevitable impurities.
14. The metal powder of claim 13, wherein the mixture is heated at
a temperature that is (i) sufficiently high to ensure diffusion of
molybdenum into the prealloyed powder and (ii) lower than a
temperature required for complete pre-alloying.
15. The metal powder of claim 13, wherein the molybdenum-containing
powder is MoO.sub.3 or metallic molybdenum powder, and the mixture
is heated in a reducing atmosphere at a temperature between
750.degree. C. and 900.degree. C.
16. The metal powder of claim 13, wherein the amount of molybdenum
diffusion alloyed to the base powder particles is from about 6% to
about 10% by weight of the metal powder.
17. The metal powder of claim 13, wherein the amount of molybdenum
diffusion alloyed to the base powder particles is from about 4% to
about 10% by weight of the metal powder.
18. The metal powder of claim 13, wherein the prealloyed powder is
an atomized powder.
19. A surface coating formed by applying the metal powder according
to claim 13 on a substrate by a thermal spraying process.
20. A surface coating formed by applying the metal powder according
to claim 13 on a substrate by a weld cladding process.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of application
Ser. No. 10/270,728, filed Oct. 16, 2003, which is a
Continuation-in-Part of application Ser. No. 09/900,982, filed on
Jul. 10, 2001; is a divisional application of International
Application No. PCT/SE02/00943, which designates the United States
of America and was filed on May 17, 2002; and claims priority to
Swedish Application No. 0101776-3, filed on May 18, 2001, the
entire disclosure of each of which is hereby incorporated by
reference.
FIELD OF THE INVENTION
[0002] The present invention concerns thermal spray powders, their
production and use. Specifically, the invention concerns coating of
aluminum substrates with thermally sprayed metal powders.
BACKGROUND
[0003] Different methods for producing coatings on aluminum
substrates are previously known. These methods are used in, e.g.,
aluminum engine blocks having cylinder liners which are formed by
thermal spraying.
[0004] U.S. Pat. No. 2,588,422 discloses an aluminum engine block
having cylinder liners which are formed by thermal spraying. These
liners are built up in two layers on the untreated surface of the
engine block, the top layer being a hard slide layer such as steel
about 1 mm in thickness and the lower layer being a molybdous
interlayer about 50 .mu.m in thickness. The interlayer, containing
at least 60% molybdenum, does not constitute a slide layer, but is
necessary in order to bind the hard slide layer to the aluminum
block. Preferably, the interlayer is made up of pure molybdenum.
The slide layer is a layer of hard metal, as for example carbon
steel, bronze or stainless steel, in which the steel may be an
alloy containing nickel, chromium, vanadium or molybdenum, for
example. In principle, this two-layer structure provides a good
slide layer, but the cost of the double coating is substantial.
[0005] In recent thermal spraying methods, the thermal spray
powders are made up by a mixture of powdered steel with powdered
molybdenum, such as described in the U.S. Pat. No. 6,095,107. The
risk of segregation due to differences in properties between the
base steel powder and the powder of crushed molybdenum is however a
problem which may result in non-uniform coatings. Another
disadvantage is that comparatively large amounts of molybdenum are
required due to the segregation effect.
[0006] A main object of the present invention is to provide an
inexpensive metal powder for thermal coating of substrates,
especially for aluminum.
[0007] Another object is to provide a powder, which does not
segregate and wherein the amount of expensive molybdenum alloying
metal can be reduced in comparison with currently used methods.
[0008] A further object is to provide a thermal powder, which has
high deposition efficiency and gives excellent coating quality.
[0009] Another object is to provide a thermal powder giving
coatings of suitable porosity and oxide content and wherein the
pores are predominantly closed, isolated and have an advantageous
range of pore diameters.
SUMMARY
[0010] These objects are obtained by a metal powder comprising a
pre-alloyed iron base powder having particles of molybdenum, such
as reduced molybdenum trioxide, diffusion alloyed to the particles
of the base powder.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] In the attached drawings:
[0012] FIG. 1 is a micrograph of a metal powder in which molybdenum
is diffusion alloyed to the surface of base powder particles.
[0013] FIG. 2 is a map showing the distribution of molybdenum in
the metal powder shown in FIG. 1.
[0014] FIG. 3 is a map showing the distribution of iron in the
metal powder shown in FIG. 1.
[0015] FIG. 4 is a micrograph of a coating formed by applying the
metal powder shown in FIG. 1 on an aluminum substrate by plasma
spraying.
DETAILED DESCRIPTION
[0016] The type and particle size of the iron base powder is
selected in view of the desired properties of the final coating and
the substrate. The base powders are preferably pre-alloyed with
elements desired in the coating. Also, a minor part of the
molybdenum content may be included in the pre-alloyed powder. Other
elements, which may be included in the pre-alloyed base powder are
C, Si, Mn, Cr, V and W. In the following, all % are in weight
unless otherwise indicated. The pre-alloyed powder may be prepared
by atomization with water or gas. The particle sizes of the base
powder are below 500 .mu.m, preferably between 25 and 210 .mu.m for
PTA and less than 90 .mu.m, preferably less than 65 .mu.m, for
high-velocity oxygen fuel (HVOF) or plasma spraying.
[0017] According to the present invention the base powder and the
alloying powder, i.e., the source of the alloying element, which is
preferably molybdenum trioxide, are mixed according to the
prescribed formulation and the mixture is heated to a temperature
below the melting point of the obtained mixture. The temperature
should be sufficiently high to ensure adequate diffusion of the
alloying element into the iron base powder in order to form a
partially or diffusion alloyed powder. On the other hand, the
temperature should be lower than the temperature required for
complete pre-alloying. Usually the temperature is between
700.degree. and 1000.degree. C., preferably between 750.degree. and
900.degree. C., and the reduction is performed in a reducing
atmosphere, e.g., hydrogen, for a period of 30 minutes to 2 hours
for reduction of the molybdenum trioxide, which is a preferred
molybdenum source. As an alternative molybdenum source, metallic
molybdenum may be used.
[0018] Metal powders having molybdenum diffusion alloyed to base
powder particles are known. See, e.g., Japanese Patent Publication
Nos. 8-209202, 63-137102 and 3-264642. These known powders are,
however, used within the powder metallurgical industry for
producing sintered products of various shapes and sizes.
Furthermore, and in contrast to the powders according to the
present invention, these known powders often have not only
molybdenum, but also copper and/or nickel diffusion alloyed to the
base powder particles. In these known powders the content of the
diffusion alloyed molybdenum is usually low, whereas in the
inventive powder for thermal coating, the diffusion alloyed
molybdenum is preferably high in order to obtain efficient sliding.
The most interesting results that have been obtained are with
powders having a content of diffusion alloyed molybdenum above
about 4% by weight. Furthermore, only molybdenum is diffusion
alloyed to the base powder particles in the powder used for thermal
spraying according to the present invention. The upper limit of
this diffusion alloyed molybdenum is decided by how much molybdenum
the base particles can carry, which appears to be about 15% by
weight, as described below.
[0019] The particle size of the final thermal sprayed powder is
essentially the same as that of the pre-alloyed base powder, as the
molybdenum particles, which are obtained when the molybdenum
trioxide is reduced, are very small in comparison with the
particles of the base powder. The amount of the molybdenum that is
diffusion alloyed to the base powder should be at least 2% by
weight of the total powder composition. Preferably, the amount of
molybdenum should be between 2 and 15, and most preferably between
3 and 10% by weight.
[0020] The different methods for applying the diffusion alloyed
powders on the metal base substrate are spray or weld cladding
processes, such as flame spray, HVOF and plasma spray or PTA.
[0021] The invention is further illustrated by, but should not be
limited to, the following preparation and example.
EXAMPLE
[0022] For the experiment on the new material for thermal coating
based on water atomized Fe-based (Fe-3Cr-0.5Mo)+5% Mo.
[0023] Used base materials and chemical analysis:
[0024] Water atomized iron powder (Fe-3Cr-0.5Mo)-71 .mu.m
Molybdenum trioxide MoO.sub.3 (average particle size 3-7 .mu.m)
1 Chemical Analysis (Fe--3Cr-0.5 Mo) % O-tot 1.22 C 0.48 Fe Base Ni
0.05 Mo 0.52 Mn 0.10 S 0.01 P 0.01 Cr 2.95 Si <0.01 Sieve
Analysis (Fe--3Cr-0.5 Mo) .mu.m % 71-106 0.1 63-71 0.8 53-63 4.7
45-53 23.4 36-45 23.1 20-36 33.3 -20 14.6
[0025] Procedure
[0026] 92.46% of the water atomized (Fe-3Cr-0.5Mo powder) and 7.54%
of MoO.sub.3 were mixed together in a Lodige mixer and the
annealing was carried out as follows:
[0027] Temperature: 820.degree. C.
[0028] Time: 60 min
[0029] Atmosphere: Reducing atmosphere (type H.sub.2, N.sub.2,
CO.sub.2 and mixtures of these gases)
[0030] After annealing the powder cake was crushed and sieved to a
particle size below 75 .mu.m.
[0031] Sieve analysis and chemical composition (powder mix after
annealing):
2 Chemical Analysis (Fe--3Cr-0.5 Mo) % O-tot 1.5 C 0.60 Fe Base Ni
0.05 Mo 5.57 Mn 0.10 S 0.01 P 0.01 Cr 2.75 Si <0.1 Sieve
Analysis (Fe--3Cr-0.5 Mo) .mu.m % 71-106 0.1 63-71 1.4 53-63 6.5
45-53 34.1 36-45 20.4 20-36 30.8 -20 6.7
[0032] The obtained powder was used in a plasma spraying process
for coating an aluminum base substrate. An unexpectedly homogenous
and excellent coating was obtained with a minimum amount of
molybdenum. FIG. 1 is a micrograph of the powder showing molybdenum
diffusion alloyed to the surface of the base powder particles. FIG.
2 is a map showing the distribution of molybdenum (in light spots)
in the metal powder shown in FIG. 1. FIG. 3 is a map showing the
distribution of iron in the metal powder shown in FIG. 1. FIG. 4
shows the plasma sprayed coating applied on the Al base
substrate.
[0033] While the invention has been described in detail with
reference to preferred embodiments thereof, it will be apparent to
those skilled in the art that various changes and modifications can
be made, and equivalents employed, without departing from the scope
of the appended claims.
* * * * *