FIELD OF THE INVENTION
The present invention is directed to materials, articles, and methods for forming
articles. More particularly, the present invention is directed to materials, articles,
and methods for forming articles having tungsten semicarbide.
BACKGROUND OF THE INVENTION
Tungsten carbide is used industrially due to its high hardness and toughness,
which may be beneficial properties for any number of uses. Bulk tungsten carbide,
typically includes at least two chemical species of tungsten and carbon, actual
tungsten carbide (WC) and tungsten semicarbide (W2C). Bulk tungsten carbide
typically includes about 5 vol% to about 10 vol% tungsten semicarbide and about
90 vol% to about 95 vol% actual tungsten carbide. Due to the typically low
presence of tungsten semicarbide, the presence of this species is often ignored,
particularly as a matter of nomenclature. As such, herein, tungsten carbide is used
exclusively to refer to WC, tungsten semicarbide is used exclusively to refer to
W2C, and mixtures of the two are referenced as bulk tungsten carbide. Also,
tungsten carbide is known for its high hardness, tungsten semicarbide is actually
the harder of the two species. However, tungsten semicarbide is also more brittle
than tungsten carbide, which has limited the industrial uses of tungsten
semicarbide.
Coal crusher rolls are used to crush coal which is fed to a boiler for producing
steam, reducing the size of the coal units from about 20 mm to about 200 mesh
size. During the crushing process, the grinding surfaces of the coal crusher rolls
become worn due to the inherent abrasive nature of the coal which is being
crushed. Coals which have elevated ash content are typically more abrasive than
coals with lower ash content, and may cause faster erosion of the grinding
surfaces of the coal crusher roles, both by attrition and wear from the crushing
loads applied on the coal crusher rolls. Further degradation of the coal crusher
rolls may be caused by contaminants in the coal supply such as iron and stone,
which may cause sudden impacts when introduced into the coal crusher.
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Additionally, during production or operation of coal crusher rolls, cracks may
form, either in coatings applied to a substrate of the coal crusher rolls or in the
substrates of the coal crusher rolls. The presence of such cracks, either in the
substrates or in the coatings applied to the substrates, may increase the rates of
attrition and wear during coal crushing operations. Coal crusher rolls may be
encased in sinter-cast materials to extend the useful life, but such solutions are
expensive and are limited in the increase in useful life they provide.
BRIEF DESCRIPTION OF THE INVENTION
In an exemplary embodiment, a material includes a matrix and a plurality of
particles dispersed in the matrix. The plurality of particles includes a plurality of
tungsten semicarbide particles constituting at least about 30 vol% of the plurality
of particles.
In another exemplary embodiment, an article includes a material including a
matrix and a plurality of particles dispersed in the matrix. The plurality of
particles includes a plurality of tungsten semicarbide particles constituting at least
about 30 vol% of the plurality of particles.
In another exemplary embodiment, a method for forming an article includes
applying a material. Applying the material includes forming a matrix and
dispersing a plurality of particles in the matrix. The plurality of particles includes
a plurality of tungsten carbide particles. The plurality of tungsten carbide particles
is at least partially decarburized, transforming at least a portion of the plurality of
tungsten carbide particles into a plurality of tungsten semicarbide particles such
that the plurality of tungsten semicarbide particles constitutes at least about 30
vol% of the plurality of particles.
Other features and advantages of the present invention will be apparent from the
following more detailed description of the preferred embodiment, taken in
conjunction with the accompanying drawings, which illustrate, by way of
example, the principles of the invention.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an article, according to an embodiment of the
present disclosure.
FIG. 2 is a sectional view along lines 2–2 of the article of FIG. 1 wherein the
article consists of a material, according to an embodiment of the present
disclosure.
FIG. 3 is a sectional view along lines 3–3 of the article of FIG. 1 wherein the
article includes a material disposed on a substrate, according to an embodiment of
the present disclosure.
FIG. 4 is a perspective view of an assembly including an article having a material,
according to an embodiment of the present disclosure.
Wherever possible, the same reference numbers will be used throughout the
drawings to represent the same parts.
DETAILED DESCRIPTION OF THE INVENTION
Provided are exemplary materials, articles, and methods for forming the articles.
Embodiments of the present disclosure, in comparison to articles and methods not
utilizing one or more features disclosed herein, decrease costs, increase process
efficiency, increase durability, increase reliability, increase service lifetime,
decrease erosion, decrease wear, or a combination thereof.
Referring to FIGS. 1 and 2, in one embodiment, an article 100 includes a material 200. The material 200 includes a matrix 202 and a plurality of particles 204
dispersed in the matrix 202. The plurality of particles 204 includes a plurality of
tungsten semicarbide particles 206, and the plurality of tungsten semicarbide
particles 206 constitutes at least about 30 vol% of the plurality of particles 204.
The plurality of particles 204 may be randomly dispersed in the matrix 202, multimodally
dispersed in the matrix 202, essentially uniformly dispersed in the matrix
202, uniformly dispersed in the matrix 202, dispersed in the matrix 202 per a
predetermined pattern, or combinations thereof. As used herein, “multi-modally
dispersed” indicates a region having a greater concentration and a region having a
lesser concentration, and “essentially uniformly dispersed” indicates a variance in
concentration of less than about 20%, alternatively, less than about 15%,
alternatively less than about 10%, alternatively less than about 5%, alternatively
less than about 1%. “Multi-modally dispersed” further may refer to the
distribution of different sizes within the plurality of particles 204.
In one embodiment, the plurality of particles 204 is dispersed in the matrix 202 at
a density (average, by weight) of at least about 50%, alternatively at least about
55%, alternatively at least about 60%, alternatively at least about 65%,
alternatively at least about 75%, alternatively at least about 80%, alternatively at
least about 85%, alternatively at least about 90%, alternatively between about
50% to about 99%, alternatively between about 60% to about 95%, alternatively between about 75% to about 94%, alternatively between about 85% to about 93%,
alternatively between about 90% to about 95%, alternatively about 93%.
In addition to the plurality of tungsten semicarbide particles 206, the plurality of
particles 204 may include a plurality of tungsten carbide particles 208. Tungsten
carbide may include both α-W2C and β-W2C in any suitable proportions. In one
embodiment, the plurality of particles 204 consists essentially of the plurality of
tungsten semicarbide particles 206 and the plurality of tungsten carbide particles
208, excluding up to about 5 wt% impurities and decarburization products,
alternatively up to about 2 wt%, alternatively up to about 1 wt%, alternatively up
to about 0.5 wt%, alternatively up to about 0.1 wt%. In a further embodiment, the
plurality of particles 204 consists of the plurality of tungsten semicarbide particles
206 and the plurality of tungsten carbide particles 208. The plurality of tungsten
semicarbide particles 206 and the plurality of tungsten carbide particles 208 may,
independently, include particles having mixtures of tungsten carbide and tungsten
semicarbide, or may include particles having subparticles of tungsten carbide and
subparticles of tungsten semicarbide, wherein the subparticles are fused or
adhered together, provided that such multiphase arrangements are considered as
separate particles for purposes of determining volume percent of tungsten carbide
and tungsten semicarbide. In one embodiment, such multiphase arrangements
constitute less than about 10 vol% of the plurality of particles 204, alternatively
less than about 5 vol%, alternatively less than about 2 vol%, alternatively less than
about 1 vol%, alternatively less than about 0.5 vol%, alternatively less than about
0.1 vol%.
The plurality of tungsten semicarbide particles 206 may include any suitable
particle size. In one embodiment, the plurality of tungsten semicarbide particles
206 includes a maximum particle size of less than about 50 µm, alternatively less
than about 250 µm, alternatively less than about 10 µm, alternatively less than
about 5 µm, alternatively less than about 1 µm, alternatively less than about 0.5
µm, alternatively less than about 0.1 µm. In another embodiment, the plurality of
tungsten semicarbide particles 206 includes a particle size distribution (normal
distribution) of between about 1 nm to about 25 µm, alternatively between about 5
nm to about 10 µm, alternatively between about 10 nm to about 5 µm,
alternatively between about 20 nm to about 1 µm.
In one embodiment, the material 200 may include a plurality of additional
particles (not shown). The plurality of additional particles may be intermixed with
the plurality of particles 204 and dispersed in the matrix 202, and may include a
plurality of ceramic particles. Suitable ceramic particles may include, but are not
limited to, metal carbides, metal borides, metal oxides, boron nitrides, boron
carbides, boron carbon nitrides, zirconia toughened aluminas, silicon carbides,
silicon nitrides, silicon oxy-nitrides, silicon aluminum oxy-nitrides, or
combinations thereof. The plurality of additional particles may include any
suitable particle size distribution, including, but not limited to, a particle size
distribution of up to about 10 nm, alternatively up to about 20 nm, alternatively up
to about 25 nm, alternatively up to about 10 mm, alternatively up to about 20 mm,
alternatively up to about 25 mm, alternatively from about 1 nm to about 25 mm,
alternatively from about 1 nm to about 25 nm, alternatively from about 1 mm to
about 25 mm. In one embodiment, the plurality of additional particles includes
fine particles having a fine particle size distribution up to about 25 nm, and coarse particles having a coarse particle size distribution from about 1 mm to about 25
mm, the fine particles and the coarse particles being intermixed. The intermixed
fine particles coarse particles may be distributed to optimize protection against
erodent abrasive particles having different sizes. The fine particles may also fill in
gaps in the plurality of particles 204, thereby enhancing the resistance of the
plurality of additional particles to erosion and abrasion.
The plurality of tungsten semicarbide particles 206 may include any suitable
conformation including, but not limited to conformations having a reduced
occurrence of orthogonal facets relative to a cuboid conformation. In one
embodiment, the plurality of tungsten semicarbide particles 206 includes an
essentially spheroidal conformation 210. As used herein, “essentially spheroidal”
indicates that substantial deviations from a perfect sphere or spheroid are
contemplated provided that the overall conformation approximates a sphere or
spheroid. Without being bound by theory, it is believed that an essentially
spheroidal conformation, having reduced orthogonal and acute facets in
comparison to a cuboidal conformation, reduces the susceptibility of the plurality
of tungsten semicarbide particles 206 to fracture, thereby decreasing brittleness
and increasing toughness of the plurality of tungsten semicarbide particles 206.
The plurality of tungsten semicarbide particles 206 may constitute any suitable
proportion of the plurality of particles 204. In one embodiment, the tungsten
semicarbide particles 206 constitute at least 30 vol% of the plurality of particles
204, alternatively at least about 40 vol%, alternatively at least about 50 vol%,
alternatively at least about 60 vol%, alternatively at least about 70 vol%,
alternatively at least about 75 vol%, alternatively at least about 80 vol%,
alternatively at least about 85 vol%, alternatively about 90 vol%, alternatively up
to about 90 vol%, alternatively between about 40 vol% to about 95 vol%,
alternatively between about 45 vol% to about 92 vol%, alternatively between
about 50 vol% to about 90 vol%.
The matrix 202 may include any suitable matrix material, including, but not
limited to cobalt, cobalt-chromium alloys, nickel-chromium alloys, nickel-
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chromium-boron-silicon alloys, cobalt-chromium-boron-silicon alloys, ironchromium-boron-silicon
alloys, Hadfield steel alloys, or combinations thereof.
The article 100 may be any suitable article, including, but not limited to, a
grinding article, a grinding roll 102, a coal grinding roll, a gas turbine component,
a gas turbine transition piece, a gas turbine liner, a gas turbine liner stop, a gas
turbine bully horn, a gas turbine blade (bucket), a gas turbine blade (bucket) tip, a
gas turbine shroud, a gas turbine inner shroud, a coal feed pump rotor, a coal feed
pump outlet pipe, a cutting tool, a mining drill bit, a rub-resistant abradable article
tip, a pump dry seal, or combinations thereof. In one embodiment, wherein the
article 100 is a grinding article, the article 100 includes a grinding surface 212
formed by the material 200.
Referring to FIG. 2, in one embodiment, the article 100 consists essentially of the
material 200, excluding any coatings disposed on the article 100. In a further
embodiment, the article 100 consists of the material 200.
Referring to FIG. 3, in another embodiment, the article 100 includes a substrate
300, and the material 200 forms a layer 302 disposed on the substrate 300. The
substrate 300 may include any suitable substrate material 304, including, but not
limited to chrome-iron alloy including, by weight, at least about 30% chrome, cast
iron, spheroidal graphite iron, white cast iron, cast iron including niobium, cast
iron including chromium, cast iron including titanium, iron alloy, steel, Hadfield
steel, cast steel, locomotive wheel steel, or combinations thereof. The layer 302
may be disposed directly on a substrate surface 310 of the substrate 300 (shown),
or there may be an intermediate layer (not shown) disposed between the layer 302
and the substrate 300. The intermediate layer may include any suitable coatingtype,
including, but not limited to, a bond coat, an abrasive coating, a grinding
coating, a thermal barrier coating, an environmental barrier coating, a diffusion
aluminide coating, or combinations thereof. Suitable bond coats include, but are
not limited to, molybdenum, Ni-5Al, Ni-20Al, Ni-20Cr, MCrAlY (where M is
nickel, cobalt, or iron), or combinations thereof.
The substrate 300 may include any suitable dimensions. In one embodiment, wherein the substrate 300 is a rotatable grinding article, such as, but not limited to,
a grinding roll 102, the substrate may include any suitable substrate average
diameter 306, including, but not limited to, a substrate average diameter 306 of
between about 10 mm and about 3 m, alternatively between about 25 mm and
about 2.5 m, alternatively between about 50 mm and about 2 m. The layer 302
may include any suitable layer thickness 308, including, but not limited to, a layer
thickness 308 of between about 0.05 mm and about 50 mm, alternatively between
about 0.1 mm and about 10 mm, alternatively between about 0.25 mm and about 5
mm, alternatively between about 0.5 mm and about 3 mm.
Referring to FIGS. 1 and 4, the article 100 may be an independent component or
the article 100 may be a component, such as a grinding roll 102, of a grinding
apparatus 400, such as, but not limited to, a bowl mill, a ball and race mill, a drum
and ball mill, a coal crusher, or combinations thereof.
Referring to FIGS. 1–3, in one embodiment, a method for forming an article 100
includes applying a material 200. Applying the material 200 includes forming the
matrix 202 and dispersing the plurality of particles 204 in the matrix 202, wherein
the plurality of particles 204 include a plurality of tungsten carbide particles 208.
The plurality of tungsten carbide particles 208 are at least partially decarburized,
transforming at least a portion of the plurality of the tungsten carbide particles 208
into the plurality of tungsten semicarbide particles 206, such that the plurality of
tungsten semicarbide particles 206 constitutes at least about 30 vol% of the
plurality of particles 204.
Transforming at least the portion of the plurality of tungsten carbide particles 208
into the plurality of tungsten semicarbide particles 206 may include forming the
plurality of tungsten semicarbide particles 206 having the essentially spheroidal
conformation 210, or the plurality of tungsten carbide particles 208 may include
the essentially spheroidal conformation 210 prior to the transforming of at least
the portion of the plurality of tungsten carbide particles 208 into the plurality of
tungsten semicarbide particles 206. In one embodiment, the plurality of tungsten
semicarbide particles 206 are formed having the essentially spheroidal conformation 210 by controlling kinetics and surface activation energies during a
thermal spray process, which, along with the thermal spray process itself, may
bend, oxidize and dissolve sharp edges. Without being bound by theory, it is
believed that oxidizing and dissolving sharp edges transforms the particles to
become essentially spheroidal.
In one embodiment, forming the matrix 202 and dispersing the plurality of
particles 204 in the matrix 202 includes thermally spraying the matrix and the
plurality of particles. Any suitable thermal spray technique may be utilized,
including, but not limited to, cored wire arc spraying, wire arc spraying, high
velocity air fuel spraying, high velocity oxy-fuel spraying, air plasma spraying,
twin wire arc spraying, cold spraying, or combinations thereof. In one
embodiment, parameters used for forming tungsten semicarbide in a high velocity
air fuel spraying process or a high velocity oxy-fuel spraying process include gas
flows and ratios which promote higher temperature as well as elevated ratios of
oxygen which may induce decarburization of tungsten carbide to tungsten
semicarbide. The stoichiometry gas flow may follow the equation 2H2 + O2 =
2H2O, and the amount of oxygen may be controlled to control the amount of
tungsten semicarbide formed. Higher amounts of oxygen and higher temperature
may, independently, increase decarburization. In another embodiment, parameters
for forming tungsten semicarbide in an air plasma spraying process may include
increasing power and temperature to increase decarburization. In another
embodiment, decarburization may be controlled by adjusting the particle
feedstock size used for spraying. Without being bound by theory, it is believed
that finer particle sizes decarburize more easily relative to coarser particle sizes,
and so the amount of decarburization may be controlled by adjusting a mix of fine
and coarse feedstock particles. In one embodiment, fine particles include a size of
typically 1 µm or less, and coarse particles include a size of typically about 1 µm
to about 5 µm
The method may further include heat treating following thermally spraying the
plurality of tungsten carbide particles 208, wherein heat treating at least partially
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decarburizes the plurality of tungsten carbide particles 208, formingthe plurality
of tungsten semicarbide particles 206. In one embodiment, heat treating may
include a predetermined partial pressure of oxygen to control the phase of
tungsten semicarbide formed during decarburization.
Referring to FIGS. 3 and 5, in one embodiment, the method for forming the article
100 includes applying the material 200 to a substrate 300. Referring to FIG. 5, in
an embodiment wherein the substrate 300 includes at least one crack 500, the
layer 302 may be at least partially disposed within the crack 500, sealing the crack
500. The layer 300 may form a treated surface 502 which is substantially flush
with a substrate surface (FIG. 5), or the layer 300 may form a layer 302 which
extends over at least a portion of the substrate surface 310 (FIG. 3). As used
herein, “substantially flush” indicates that the treated surface 502 is neither
elevated nor depressed relative to the substrate surface 310 where they meet by
more than about 1 mm.
While the invention has been described with reference to a preferred embodiment,
it will be understood by those skilled in the art that various changes may be made
and equivalents may be substituted for elements thereof without departing from
the scope of the invention. In addition, many modifications may be made to adapt
a particular situation or material to the teachings of the invention without
departing from the essential scope thereof. Therefore, it is intended that the
invention not be limited to the particular embodiment disclosed as the best mode
contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

WE CLAIM:
1. A material, comprising:
a matrix; and
a plurality of particles dispersed in the matrix, the plurality of particles
including a plurality of tungsten semicarbide particles,
wherein the plurality of tungsten semicarbide particles constitutes at
least about 30 vol% of the plurality of particles.
2. The material as claimed in claim 1, wherein the plurality of
particles consists essentially of the plurality of tungsten semicarbide particles and
a plurality of tungsten carbide particles.
3. The material as claimed in claim 1, wherein the plurality of
tungsten semicarbide particles includes an essentially spheroidal conformation.
4. The material as claimed in claim 1, wherein the plurality of tungsten semicarbide particles constitutes at least about 75 vol% of the plurality of
particles.
5. The material as claimed in claim 1, wherein the matrix includes a
matrix material selected from the group consisting of cobalt, cobalt-chromium
alloys, nickel-chromium alloys, nickel-chromium-boron-silicon alloys, cobaltchromium-boron-silicon
alloys, iron-chromium-boron-silicon alloys, Hadfield
steel alloys, and combinations thereof.
6. An article, comprising:
a material, the material including:
a matrix; and
a plurality of particles dispersed in the matrix, the plurality of
particles including a plurality of tungsten semicarbide particles,
wherein the plurality of tungsten semicarbide particles constitutes
at least about 30 vol% of the plurality of particles.
7. The article as claimed in claim 6, wherein the plurality of particles
consists essentially of the plurality of tungsten semicarbide particles and a
plurality of tungsten carbide particles.
8. The article as claimed in claim 6, wherein the plurality of tungsten
semicarbide particles includes an essentially spheroidal conformation.
9. The article as claimed in claim 6, wherein the plurality of tungsten
semicarbide particles constitutes at least about 75 vol% of the plurality of
particles.
10. The article as claimed in claim 6, wherein the matrix includes a
matrix material selected from the group consisting of cobalt, cobalt-chromium
alloys, nickel-chromium alloys, nickel-chromium-boron-silicon alloys, cobaltchromium-boron-silicon
alloys, iron-chromium-boron-silicon alloys, Hadfield
steel alloys, and combinations thereof.
11. The article as claimed in claim 6, wherein the article is a grinding
article, and the article includes a grinding surface formed by the material.
12. The article as claimed in claim 11, wherein the grinding article is
selected from the group consisting of a coal grinding roll, a gas turbine
component, a gas turbine transition piece, a gas turbine liner, a gas turbine liner
stop, a gas turbine bully horn, a gas turbine blade (bucket), a gas turbine blade
(bucket) tip, a gas turbine shroud, a gas turbine inner shroud, a coal feed pump
rotor, a coal feed pump outlet pipe, a cutting tool, a mining drill bit, a rub-resistant
abradable article tip, a pump dry seal, and combinations thereof.
13. The article as claimed in claim 6, wherein the article includes a
substrate, and the material forms a layer disposed on the substrate.
14. The article as claimed in claim 12, wherein the substrate includes a
substrate material selected from the group consisting of chrome-iron alloy
including, by weight, at least about 30% chrome, cast iron, spheroidal graphite
iron, white cast iron, cast iron including niobium, cast iron including chromium,
cast iron including titanium, iron alloy, steel, Hadfield steel, cast steel, locomotive
wheel steel, or combinations thereof.
15. The article as claimed in claim 6, wherein the plurality of tungsten
semicarbide particles includes a maximum particle size of less than about 10 µm.
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16. The article as claimed in claim 6, wherein the plurality of tungsten
semicarbide particles includes a particle size distribution of between about 10 nm
to about 5 µm.
17. A method for forming an article, comprising:
applying a material, including:
forming a matrix; and
dispersing a plurality of particles in the matrix, the plurality of
particles including a plurality of tungsten carbide particles;
at least partially decarburizing the plurality of tungsten carbide
particles, transforming at least a portion of the plurality of tungsten carbide
particles into a plurality of tungsten semicarbide particles such that the
plurality of tungsten semicarbide particles constitutes at least about 30 vol%
of the plurality of particles.
18. The method as claimed in claim 17, wherein transforming at least
the portion of the tungsten carbide particles into the plurality of tungsten
semicarbide particles includes forming the plurality of tungsten semicarbide
particles having an essentially spheroidal conformation.
19. The method as claimed in claim 17, wherein forming the matrix
and dispersing the plurality of particles in the matrix includes thermally spraying
the matrix and the plurality of particles.
20. The method as claimed in claim 17, further including heat treating
following applying the material, wherein heat treating at least partially
decarburizes the plurality of tungsten carbide particles.