U.S. patent application number 10/829820 was filed with the patent office on 2007-07-19 for advanced erosion resistant carbonitride cermets.
Invention is credited to Robert Lee Antram, Narasimha-Rao Venkata Bangaru, ChangMin Chun, Christopher John Fowler, Hyun-Woo Jin, Jayoung Koo, John Roger Peterson.
Application Number | 20070163382 10/829820 |
Document ID | / |
Family ID | 33479309 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070163382 |
Kind Code |
A1 |
Chun; ChangMin ; et
al. |
July 19, 2007 |
ADVANCED EROSION RESISTANT CARBONITRIDE CERMETS
Abstract
The invention includes a cermet composition represented by the
formula (PQ)(RS) comprising: a ceramic phase (PQ) and a binder
phase (RS) wherein, P is a metal selected from the group consisting
of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Mn and mixtures thereof, Q
is carbonitride, R is a metal selected from the group consisting of
Fe, Ni, Co, Mn and mixtures thereof, S comprises at least one
element selected from Cr, Al, Si and Y.
Inventors: |
Chun; ChangMin; (Belle Mead,
NJ) ; Bangaru; Narasimha-Rao Venkata; (Annandale,
VA) ; Jin; Hyun-Woo; (Phillipsburg, NJ) ; Koo;
Jayoung; (Bridgewater, NJ) ; Peterson; John
Roger; (Ashburn, VA) ; Antram; Robert Lee;
(Warrenton, VA) ; Fowler; Christopher John;
(Springfield, VA) |
Correspondence
Address: |
ExxonMobil Research and Engineering Company
P.O. Box 900
Annandale
NJ
08801-0900
US
|
Family ID: |
33479309 |
Appl. No.: |
10/829820 |
Filed: |
April 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60471994 |
May 20, 2003 |
|
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Current U.S.
Class: |
75/238 |
Current CPC
Class: |
C23C 30/00 20130101;
C22C 29/04 20130101 |
Class at
Publication: |
075/238 |
International
Class: |
C22C 29/04 20060101
C22C029/04 |
Claims
1. A cermet composition represented by the formula (PQ)(RS)
comprising: a ceramic phase (PQ) and a binder phase (RS) wherein, P
is a metal selected from the group consisting of Ti, Zr, HC, V, Nb,
Ta, Cr, Mo, W, Fe, Mn and mixtures thereof, Q is carbonitride, R
comprises Fe and a metal selected from the group consisting of Ni,
Co, Mn and mixtures thereof, S comprises Cr, at least one element
selected from Al, Si and Y, and at least one aliovalent element
selected from the group consisting of Y, Ti, Zr, Hf, Ta, V, Nb, Cr,
Mo, W, and wherein the combined weights of said Cr, Al, Si, Y and
mixtures thereof is at least 12 wt %, and the combined weights of
said at least one aliovalent element is from 0.01 to 5 wt % based
on the weight of the binder phase (RS), and wherein the ceramic
phase (PQ) ranges from about 50 to 95 vol % based on the volume of
the cermet.
2. The cermet composition of claim 1 wherein the ceramic phase (PQ)
ranges from of abate 70 to 95 vol % based on the volume of the
cermet.
3. The cermet composition of claim 1 wherein the molar ratio of P:Q
in the ceramic phase (PQ) can vary in the range of 1:3 to 3:1.
4. The cermet composition of claim 1 wherein said ceramic phase
(PQ) is dispersed in the binder phase (RS) as spherical particles
in the size range of 0.5 microns to 3000 microns diameter.
5. The cermet composition of claim 1 wherein the binder phase (RS)
is in the range of 5 to 50 vol % based on the volume of the cermet
and the mass ratio of R to S ranges from 50/50 to 90/10.
6. (canceled)
7. (canceled)
8. The cermet composition of claim 1 further comprising secondary
carbonitrides (P'Q) wherein P' is selected from Ti, Zr, Hf, V, Nb,
Ta, Cr, Mo, W. Fe, Ni, Co, Mn, Al, Si, Y and mixtures thereof.
9. The cermet composition of claim 1 having a fracture toughness of
greater than about 3 MPa m.sup.1/2.
10. The cermet composition of claim 1 having an erosion rate less
than about 1.times.10.sup.-6 cc/gram loss when subject to 1200
g/min of 10 .mu.m to 100 .mu.m SiC particles in air with an impact
velocity of at least about 45.7 m/sec (150 ft/sec) and at an impact
angle or about 45 degrees and a temperature of at least about
732.degree. C. (1350.degree. F.) for at least 7 hours.
11. The cermet composition of claim 1 having corrosion rate less
than about 1.times.10.sup.-10 g.sup.2/cm.sup.4s or an average oxide
scale of less than 150 .mu.m thickness when subject to 100 cc/min
air at 800.degree. C. for at least 65 hours.
12. The cermet composition of claim 1 having an erosion rate less
than about 1.times.10.sup.-6 cc/gram when subject to 1200 g/min of
10 .mu.m to 100 .mu.m SiC particles in air with an impact velocity
of at least about 45.7 m/sec (150 ft/sec) and at an impact angle of
about 45 degrees and a temperature of at least about 732.degree. C.
(1350.degree. F.) for at least 7 hours and a corrosion rate less
than about 1.times.10.sup.-10 g.sup.2/cm.sup.4s or an average oxide
scale of less than 150 .mu.m thickness when subject to 100 cc/min
air at 800.degree. C. for at least 65 hours.
13. The cermet composition of claim 1 having embrittling phases
less than about 5 vol % based on the volume of the cermet.
14. (canceled)
15. (canceled)
16. (canceled)
17. A bulk cermet material represented by the formula (PQ)(RS)
comprising: a ceramic phase (PQ) and a binder phase (RS) wherein, P
is a metal selected from the group consisting of Ti, Zr, Hf; V, Nb,
Ta, Cr, Mo, W, Fe, Mn and mixtures thereof; Q is carbonitride, R
comprises Fe and a metal selected from the group consisting of Ni,
Co, Mn and mixtures thereof, S comprises Cr, at least one element
selected from Al, Si and Y, and at least one aliovalent element
selected from the group consisting of Y, Ti, Zr, if, Ta, V, Nb, Cr,
Mo, W, wherein the combined weights of said Cr, Al, Si, Y and
mixtures thereof is at least 12 wt %, and the combined weights of
said at least one aliovalent element is from 0.01 to 5 wt % based
on the weight of the binder phase (RS), wherein the ceramic phase
(PQ) ranges from about 50 to 95 vol % based on the volume of the
cermet, and wherein the overall thickness of the bulk cermet
material is greater than 5 millimeters.
18. The bulk cermet material of claim 17 wherein the ceramic phase
(PQ) ranges from of about 70 to 95 vol % based on the volume of the
cermet.
19. The bulk cermet material of claim 17 wherein the molar ratio of
P:Q in the ceramic phase (PQ) can vary in the range of 1:3 to
3:1.
20. The bulk cermet material of claim 17 wherein said ceramic phase
(PQ) is dispersed in the binder phase (RS) as spherical particles
in the size range of 0.5 microns to 3000 microns diameter.
21. The bulk cermet material of claim 17 wherein the binder phase
(RS) is in the range of 5 to 50 vol % based on the volume of the
cermet and the mass ratio of R to S ranges from 50150 to 90/10.
22. The bulk cermet material of claim 17 further comprising
secondary carbonitrides (P'Q) wherein P' is selected from Ti, Zr,
Hf; V, Nb, Ta, Cr, Mo, W, Fe, Ni, Co, Mn, Al, Si, Y and mixtures
thereof.
23. The bulk cermet material of claim 17 having a fracture
toughness of greater than about 3 MPa m.sup.1/2.
24. The bulk cermet material of claim 17 having an erosion rate
less than about 1.times.10.sup.-6 cc/grim loss when subject to 1200
g/min of 10 .mu.m to 1100 .mu.m SiC particles in air with an impact
velocity of at least about 45.7 n/sec (150 ft/sec) and at an impact
angle of about 45 degrees and a temperature of at least about
732.degree. C. (1350.degree. F.) for at least 7 hours.
25. The bulk cermet material of claim 17 having corrosion rate less
than about 1.times.10.sup.-10 g.sup.2/cm.sup.4s or an average oxide
scale of less than 150 .mu.m thickness when subject to 100 cc/min
air at 800.degree. C. for at least 65 hours.
26. The bulk cermet material of claim 17 having an erosion rate
less than about 1.times.10.sup.-6 cc/gram when subject to 1200
g/min of 10 .mu.m to 100 .mu.m SiC particles in air with an impact
velocity of at least about 45.7 m/sec (150 ft/sec) and at an impact
angle of about 45 degrees and a temperature of at least about
732.degree. C. (1350.degree. F.) for at least 7 hours and a
corrosion rate less than about 1.times.10.sup.-10 g.sup.2/m.sup.4s
or an average oxide scale of less than 150 .mu.m thickness when
subject to 100 cc/min air at 800.degree. C. for at least 65
hours.
27. The bulk cermet material of claim 17 having embrittling phases
less than about 5 vol % based on the volume of the cermet.
Description
[0001] This application claims the benefit of U.S. Provisional
application 60/471,994 filed May 20, 2003.
FIELD OF INVENTION
[0002] The present invention is broadly concerned with cermets,
particularly cermet compositions comprising a metal carbonitride.
These cermets are suitable for high temperature applications
wherein materials with superior erosion and corrosion resistance
are required.
BACKGROUND OF INVENTION
[0003] Erosion resistant materials find use in many applications
wherein surfaces are subject to eroding forces. For example,
refinery process vessel walls and internals exposed to aggressive
fluids containing hard, solid particles such as catalyst particles
in various chemical and petroleum environments are subject to both
erosion and corrosion. The protection of these vessels and
internals against erosion and corrosion induced material
degradation especially at high temperatures is a technological
challenge. Refractory liners are used currently for components
requiring protection against the most severe erosion and corrosion
such as the inside walls of internal cyclones used to separate
solid particles from fluid streams, for instance, the internal
cyclones in fluid catalytic cracking units (FCCU) for separating
catalyst particles from the process fluid. The state-of-the-art in
erosion resistant materials is chemically bonded castable alumina
refractories. These castable alumina refractories are applied to
the surfaces in need of protection and upon heat curing hardens and
adheres to the surface via metal-anchors or metal-reinforcements.
It also readily bonds to other refractory surfaces. The typical
chemical composition of one commercially available refractory is
80.0% Al.sub.2O.sub.3, 7.2% SiO.sub.2, 1.0% Fe.sub.2O.sub.3, 4.8%
MgO/CaO, 4.5% P.sub.2O.sub.5 in wt %. The life span of the
state-of-the-art refractory liners is significantly limited by
excessive mechanical attrition of the liner from the high velocity
solid particle impingement, mechanical cracking and spallation.
Therefore there is a need for materials with superior erosion and
corrosion resistance properties for high temperature applications.
The cermet compositions of the instant invention satisfy this
need.
[0004] Ceramic-metal composites are called cermets. Cermets of
adequate chemical stability suitably designed for high hardness and
fracture toughness can provide an order of magnitude higher erosion
resistance over refractory materials known in the art. Cermets
generally comprise a ceramic phase and a binder phase and are
commonly produced using powder metallurgy techniques where metal
and ceramic powders are mixed, pressed and sintered at high
temperatures to form dense compacts.
[0005] The present invention includes new and improved cermet
compositions.
[0006] The present invention also includes cermet compositions
suitable for use at high temperatures.
[0007] Furthermore, the present invention includes an improved
method for protecting metal surfaces against erosion and corrosion
under high temperature conditions.
[0008] These and other objects will become apparent from the
detailed description which follows.
SUMMARY OF INVENTION
[0009] The invention includes a cermet composition represented by
the formula (PQ)(RS) comprising: a ceramic phase (PQ) and a binder
phase (RS) wherein,
P is a metal selected from the group consisting of Ti, Zr, Hf, V,
Nb, Ta, Cr, Mo, W, Fe, Mn and mixtures thereof,
Q is carbonitride,
R is a metal selected from the group consisting of Fe, Ni, Co, Mn
and mixtures thereof,
S comprises at least one element selected from Cr, Al, Si and
Y.
BRIEF DESCRIPTION OF THE FIGURES
[0010] FIG. 1 is a scanning electron microscope (SEM) image of
TiC.sub.0.7N.sub.0.3 cermet made using 30 vol % 304 stainless steel
(304SS) binder illustrating the Ti(C,N) ceramic phase particles
dispersed in binder and the reprecipitation of new phase
M.sub.2(C,N) where M is mainly Cr, Fe, and Ti and M(C,N)
carbonitride where M is mainly Ti and Ta. Also shown in the
micrograph is the formation of M(C,N) rim around the Ti(C,N)
ceramic.
[0011] FIG. 2 is a transmission electron microscope (TEM) image of
the same cermet shown in FIG. 1.
[0012] FIG. 3 is a SEM image of a TiC.sub.0.3N.sub.0.7 cermet made
using 25 vol % Haynes.RTM. 556 alloy binder illustrating Ti(C,N)
ceramic phase particles dispersed in binder and the reprecipitation
of new phase M.sub.2(C,N) where M is mainly Cr, Fe, and T.sub.1 and
M.sub.2(C,N) where M is mainly Mo, Nb, Cr, and Ti.
[0013] FIG. 4 is a transmission electron microscope (TEM) image of
the same cermet shown in FIG. 3.
[0014] FIG. 5 is a graph showing the thickness (am) of oxide layer
as a measure of oxidation resistance of titanium carbonitride
cermets of the instant invention made using 30 vol % binder exposed
to air at 800.degree. C. for 65 hours. The oxidation resistance of
titanium carbide and nitride cermets are also shown for
comparison.
DETAILED DESCRIPTION OF THE INVENTION
[0015] One component of the cermet composition represented by the
formula (PQ)(RS) is the ceramic phase denoted as (PQ). In the
ceramic phase (PQ), P is a metal selected from the group consisting
of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Mn and mixtures thereof. Q
is carbonitride. Thus the ceramic phase (PQ) in the carbonitride
cermet composition is a metal carbonitride. The molar ratio of P to
Q in (PQ) can vary in the range of 1:3 to 3:1. Preferably in the
range of 1:2 to 2:1. As non-limiting illustrative examples, when
P=Ti, (PQ) can be Ti(C,N) wherein P:Q is 1:1. When P=Cr then (PQ)
can be Cr.sub.2(C,N) wherein P:Q is 2:1. The ceramic phase imparts
hardness to the carbonitride cermet and erosion resistance at
temperatures up to about 1000.degree. C.
[0016] The ceramic phase (PQ) of the cermet is preferably dispersed
in the binder phase (RS). It is preferred that the size of the
dispersed ceramic particles is in the range 0.5 to 3000 microns in
diameter. More preferably in the range 0.5 to 100 microns in
diameter. The dispersed ceramic particles can be any shape. Some
non-limiting examples include spherical, ellipsoidal, polyhedral,
distorted spherical, distorted ellipsoidal and distorted polyhedral
shaped. By particle size diameter is meant the measure of longest
axis of the 3-D shaped particle. Microscopy methods such as optical
microscopy (OM), scanning electron microscopy (SEM) and
transmission electron microscopy (TEM) can be used to determine the
particle sizes. In another embodiment of this invention, the
ceramic phase (PQ) is dispersed as platelets with a given aspect
ratio, i.e., the ratio of length to thickness of the platelet. The
ratio of length:thickness can vary in the range of 5:1 to 20:1.
Platelet microstructure imparts superior mechanical properties
through efficient transfer of load from the binder phase (RS) to
the ceramic phase (PQ) during erosion processes.
[0017] Another component of the carbonitride cermet composition
represented by the formula (PQ)(RS) is the binder phase denoted as
(RS). In the binder phase (RS), R is the base metal selected from
the group consisting of Fe, Ni, Co, Mn and mixtures thereof. S is
an alloying metal comprising at least one element selected from Cr,
Al, Si and Y. S can further comprise an aliovalent element selected
form the group consisting of Y, Ti, Zr, Hf, Ta, V, Nb, Cr, Mo, W
and mixtures thereof. The combination weight of Cr, Al, Si, Y and
mixtures thereof are of at least about 12 wt % based on the weight
of the binder (RS). The aliovalent element is about 0.01 wt % to
about 5 wt %, preferably about 0.01 wt % to about 2 wt % of based
on the weight of the binder. The elements Ti, Zr, Hf, Ta, V, Nb,
Cr, Mo, W are aliovalent elements characterized by multivalent
states when in an oxidized state. These elements decrease defect
transport in the oxide scale thereby providing enhanced corrosion
resistance.
[0018] In the carbonitride cermet composition the binder phase (RS)
is in the range of 5 to 50 vol %, and preferably 5 to 30 vol %,
based on the volume of the cermet. The mass ratio of R to S can
vary in the range from 50/50 to 90/10. In one preferred embodiment
the chromium content in the binder phase (RS) is at least 12 wt %
based on the weight of the binder (RS). In another preferred
embodiment the combined zirconium and hafnium content in the binder
phase (RS) is about 0.01 wt % to about 2.0 wt % based on the total
weight of the binder phase (RS).
[0019] The cermet composition can further comprise secondary
carbonitrides (P'Q) wherein P' is selected from Ti, Zr, Hf, V, Nb,
Ta, Cr, Mo, W, Fe, Ni, Co, Mn, Al, Si, Y and mixtures thereof.
Stated differently, the secondary carbonitrides are derived from
the metal elements from P, R, S and combinations thereof of the
cermet composition (PQ)(RS). The ratio of P' to Q in (P'Q) can vary
in the range of 3:1 to 1:3. The total ceramic phase volume in the
cermet of the instant invention includes both (PQ) and the
secondary carbonitrides (P'Q). In the carbonitride cermet
composition (PQ)+(P'Q) ranges from of about 50 to 95 vol % based on
the volume of the cermet. Preferably from 70 to 95 vol % based on
the volume of the cermet.
[0020] The volume percent of cermet phase (and cermet components)
excludes pore volume due to porosity. The cermet can be
characterized by a porosity in the range of 0.1 to 15 vol %.
Preferably, the volume of porosity is 0.1 to less than 10% of the
volume of the cermet. The pores comprising the porosity is
preferably not connected but distributed in the cermet body as
discrete pores. The mean pore size is preferably the same or less
than the mean particle size of the ceramic phase (PQ).
[0021] One aspect of the invention is the micro-morphology of the
cermet. The ceramic phase can be dispersed as spherical,
ellipsoidal, polyhedral, distorted spherical, distorted ellipsoidal
and distorted polyhedral shaped particles or platelets. The cermet
may also include layered structure having a core carbonitride
surrounded by a layer of secondary carbonitride. Preferably, at
least 50% of the dispersed particles is such that the
particle-particle spacing between the individual carbonitride
ceramic particles is at least 1 nm. The particle-particle spacing
may be determined for example by microscopy methods such as SEM and
TEM.
[0022] In crystalline solids such as metals and ceramics, the
individual atoms or ions are arranged in such as way that they
display three dimensional periodicity in arrays described as
crystal lattice. Ceramic phases such as metal carbides and metal
nitrides are crystalline solids with inter-penetrating metal atom
and non-metal atom sublattices, respectively. For instance, in the
case of TiC ceramic phase, there are two sublattices, one of Ti
metal and the other of C non-metal wherein the interchange of
lattice positions of Ti and C is not allowed. However, in many
carbides and nitrides, carbon or nitrogen can substitute readily
for each other on the non-metal sublattice for the whole range of
possible chemistries, that is, pure carbide to pure nitride. Thus,
in these cases there is complete mutual solubility wherein carbide
and nitride of the same metal dissolve in each other through the
entire range from pure carbide to pure nitride. For instance, TiC
and TiN can dissolve in each other producing mixed carbidenitride,
commonly referred to as a carbonitride phase, and denoted by
Ti(C,N). In this case, carbon and nitrogen freely substitute for
each other in either carbon atom or nitrogen atom sublattice.
However, the ratio of total metal atom to total non-metal atoms can
still be maintained as 1:1 in these carbonitrides. Similarly
substitutions of Ti with other metal atoms can also happen. For
instance, Nb can partially or fully substitute for Ti forming
(Ti,Nb)(C,N). Again the total metal to total non-metal atom ratio
is maintained in these mixed carbonitrides as 1:1. This is a
characteristic of the prominent mono-carbides and mono-nitrides,
that is, total metal to total non-metal atom ration is 1:1, of
Group IV (Ti, Zr, Hf) and Group V (V, Nb, Ta) elements. One
exception is VC and VN, which are only partially soluble in each
other. Carbon content in carbonitride (C,N) can be varied from
about 0.01 to about 0.99, preferably from about 0.1 to about 0.9,
and more preferably from about 0.3 to about 0.7 and abbreviated as
(C,N).
[0023] The cermet compositions of the instant invention possess
enhanced erosion and corrosion properties. The erosion rates were
determined by the Hot Erosion and Attrition Test (HEAT) as
described in the examples section of the disclosure. The erosion
rate of the carbonitride cermets of the instant invention is less
than 1.0.times.10.sup.-6 cc/gram of SiC erodant. The corrosion
rates were determined by thermogravimetric (TGA) analyses as
described in the examples section of the disclosure. The corrosion
rate of the carbonitride cermets of the instant invention is less
than 1.times.10.sup.-10 g.sup.2/cm.sup.4s.
[0024] The cermets of the instant invention possess fracture
toughness of greater than about 3 MPam.sup.1/2, preferably greater
than about 5 MPam.sup.1/2, and more preferably greater than about
10 MPam.sup.1/2. Fracture toughness is the ability to resist crack
propagation in a material under monotonic loading conditions.
Fracture toughness is defined as the critical stress intensity
factor at which a crack propagates in an unstable manner in the
material. Loading in three-point bend geometry with the pre-crack
in the tension side of the bend sample is preferably used to
measure the fracture toughness with fracture mechanics theory. (RS)
phase of the cermet of the instant invention as described in the
earlier paragraphs is primarily responsible for imparting this
attribute.
[0025] Another aspect of the invention is the avoidance of
embrittling intermetallic precipitates such as sigma phase known to
one of ordinary skill in the art of metallurgy. The carbonitride
cermet of the instant invention has preferably less than about 5
vol % of such embrittling phases. The cermet of the instant
invention with (PQ) and (RS) phases as described in the earlier
paragraphs is responsible for imparting this attribute.
[0026] The cermet compositions are made by general powder
metallurgical technique such as mixing, milling, pressing,
sintering and cooling, employing as starting materials a suitable
ceramic powder and a binder powder in the required volume ratio.
These powders are milled in a ball mill in the presence of an
organic liquid such as ethanol for a time sufficient to
substantially disperse the powders in each other. The liquid is
removed and the milled powder is dried, placed in a die and pressed
into a green body. The resulting green body is then sintered at
temperatures above about 1200.degree. C. up to about 1750.degree.
C. for times ranging from about 10 minutes to about 4 hours. The
sintering operation is preferably performed in an inert atmosphere
or a reducing atmosphere or under vacuum. For example, the inert
atmosphere can be argon and the reducing atmosphere can be
hydrogen. Thereafter the sintered body is allowed to cool,
typically to ambient conditions. The cermet prepared according to
the process of the invention allows fabrication of bulk cermet
materials exceeding 5 mm in thickness.
[0027] One feature of the cermets of the invention is their
microstructural stability, even at elevated temperatures, making
them particularly suitable for use in protecting metal surfaces
against erosion at temperatures in the range of about 300.degree.
C. to about 850.degree. C. It is believed this stability permits
their use for time periods greater than 2 years, for example for
about 2 years to about 10 years. In contrast many known cermets
undergo transformations at elevated temperatures which results in
the formation of phases which have a deleterious effect on the
properties of the cermet.
[0028] The high temperature stability of the cermets of the
invention makes them suitable for applications where refractories
are currently employed. A non-limiting list of suitable uses
include liners for process vessels, transfer lines, cyclones, for
example, fluid-solids separation cyclones as in the cyclone of
Fluid Catalytic Cracking Unit used in refining industry, grid
inserts, thermo wells, valve bodies, slide valve gates and guides
catalyst regenerators, and the like. Thus, metal surfaces exposed
to erosive or corrosive environments, especially at about
300.degree. C. to about 850.degree. C. are protected by providing
the surface with a layer of the cermet compositions of the
invention. The cermets of the instant invention can be affixed to
metal surfaces by mechanical means or by welding.
EXAMPLES
Determination of Volume Percent:
[0029] The volume percent of each phase, component and the pore
volume (or porosity) were determined from the 2-dimensional area
fractions by the Scanning Electron Microscopy method. Scanning
Electron Microscopy (SEM) was conducted on the sintered cermet
samples to obtain a secondary electron image preferably at
1000.times. magnification. For the area scanned by SEM, X-ray dot
image was obtained using Energy Dispersive X-ray Spectroscopy
(EDXS). The SEM and EDXS analyses were conducted on five adjacent
areas of the sample. The 2-dimensional area fractions of each phase
was then determined using the image analysis software: EDX
Imaging/Mapping Version 3.2 (EDAX Inc, Mahwah, N.J. 07430, USA) for
each area. The arithmetic average of the area fraction was
determined from the five measurements. The volume percent (vol %)
is then determined by multiplying the average area fraction by 100.
The vol % expressed in the examples have an accuracy of +/-50% for
phase amounts measured to be less than 2 vol % and have an accuracy
of +/-20% for phase amounts measured to be 2 vol % or greater.
Determination of Weight Percent:
[0030] The weight percent of elements in the cermet phases was
determined by standard EDXS analyses.
[0031] The following non-limiting examples are included to further
illustrate the invention.
Example 1
[0032] 70 vol % of 1.3 .mu.m average diameter of
TiC.sub.0.7N.sub.0.3 powder (from Japan New Metals Company) and 30
vol % of 6.7 .mu.m average diameter 304 stainless steel (SS) powder
(Osprey Metals, Fe(balance):18.5Cr:9.6Ni:1.4Mn:0.63Si, 95.9%
screened below -16 .mu.m) were dispersed with ethanol in HDPE
milling jar. The powders in ethanol were mixed for 24 hours with
Yttria Toughened Zirconia (YTZ) balls (10 mm diameter, from Tosoh
Ceramics) in a ball mill at 100 rpm. The ethanol was removed from
the mixed powders by heating at 130.degree. C. for 24 hours in a
vacuum oven. The dried powder was compacted in a 40 mm diameter die
in a hydraulic uniaxial press (SPEX 3630 Automated X-press) at
5,000 psi. The resulting green disc pellet was ramped up to
400.degree. C. at 25.degree. C./min in argon and held at
400.degree. C. for 30 min for residual solvent removal. The disc
was then heated to 1500.degree. C. at 15.degree. C./min in argon
and held at 1500.degree. C. for 2 hours. The temperature was then
reduced to below 100.degree. C. at -15.degree. C./min.
[0033] The resultant cermet comprised: [0034] i) 69 vol %
TiC.sub.0.7N.sub.0.3 with average grain size of about 1.5 .mu.m
[0035] ii) 2 vol % secondary carbonitride M.sub.2(C,N) with average
grain size of about 0.5 .mu.m, where M=63Cr:24Fe:13Ti in wt %
[0036] iii) 29 vol % Cr-depleted alloy binder.
[0037] FIG. 1 is a SEM image of TiC.sub.07N.sub.0.3 cermet
processed according to this example, wherein the bar represents 2
.mu.m. In this image the TiC.sub.0.7N.sub.0.3 phase appears dark
and the binder phase appears light. The Cr-rich secondary
M.sub.2(C,N) phase is also shown in the binder phase. By M-rich,
for instance Cr-rich, is meant the metal M is of a higher
proportion than the other constituent metals comprising M. M(C,N)
carbonitride where M is mainly Ti and Ta is formed as a rim around
TiC.sub.0.7N.sub.0.3 core. Ta is believed to be an impurity from
TiC.sub.0.7N.sub.0.3 powder. FIG. 2 is a TEM image of
TiC.sub.0.7N.sub.0.3 cermet processed according to this example,
wherein the bar represents 0.5 .mu.m. In this image the
TiC.sub.0.7N.sub.0.3 phase appears light and the binder phase
appears dark. The Cr-rich secondary M.sub.2(C,N) phase is also
shown in the binder phase. M(C,N) rim is formed around
TiC.sub.0.7N.sub.0.3 core. The chemistry of binder phase is
Cr-depleted due to the precipitation of Cr-rich secondary
M.sub.2(C,N) phase and Ti-enriched due to the dissolution of
TiC.sub.0.7N.sub.0.3.
Example 2
[0038] 75 vol % of 1.3 .mu.m average diameter of
TiC.sub.0.3N.sub.0.7 powder (from Japan New Metals Company) and 25
vol % of 6.7 .mu.m average diameter Haynes.RTM. 566 alloy powder
(Osprey Metals, Fe(balance):20.5Cr:20.3Ni: 17.3Co:2.9Mo:2.5W:
0.92Mn:0.45Si:0.47Ta, 96.2% screened below -16 .mu.m) were used to
process the cermet disc as described in Example 1. The cermet disc
was then heated to 1500.degree. C. at 15.degree. C./min in argon
and held at 1500.degree. C. for 2 hours. The temperature was then
reduced to below 100.degree. C. at -15.degree. C./min.
[0039] The resultant cermet comprised: [0040] i) 74 vol %
TiC.sub.0.3N.sub.0.7 with average grain size of about 2 .mu.m
[0041] ii) 2 vol % secondary carbonitride M.sub.2(C,N) with average
grain size of about 0.5 .mu.m, where M=65Cr:9Mo:12Ti:10Fe:3Co:1Ni
in wt % [0042] iii) 1 vol % secondary carbonitride M.sub.2(C,N)
with average grain size of about 0.5 .mu.m, where
M=49Cr:30Mo:7Ti:10Fe:3Co:1Ni in wt % [0043] iv) 23 vol %
Cr-depleted alloy binder (36Fe:18Cr:22Ni:21Co:3Ti in wt %).
[0044] FIG. 3 is a SEM image of TiC.sub.0.3N.sub.0.7 cermet
processed according to this example, wherein the bar represents 2
.mu.m. In this image the TiC.sub.0.7N.sub.0.3 phase appears dark
and the binder phase appears light. The Cr-rich secondary
M.sub.2(C,N) phase and Mo-rich secondary M.sub.2(C,N) phase are
also shown in the binder phase. FIG. 4 is a TEM image of
TiC.sub.0.3N.sub.0.7 cermet processed according to this example,
wherein the bar represents 0.5 .mu.m. In this image the
TiC.sub.0.3N.sub.0.7 phase appears light and the binder phase
appears dark. The Cr-rich secondary M.sub.2(C,N) phase is also
shown in the binder phase. Both Cr-rich secondary M.sub.2(C,N) and
Mo-rich secondary M.sub.2(C,N) phases are also shown in the binder
phase. The chemistry of binder phase is Cr-depleted and
Ti-enriched.
Example 3
[0045] Each of the cermets of Examples 1 and 2 was subjected to an
oxidation test. The procedure employed was as follows:
[0046] 1) A specimen cermet of about 10 mm square and about 1 mm
thick was polished to 600 grit diamond finish and cleaned in
acetone.
[0047] 2) The specimen was then exposed to 100 cc/min air at
800.degree. C. in thermogravimetric analyzer (TGA).
[0048] 3) Step (2) was conducted for 65 hours at 800.degree. C.
[0049] 4) After 65 hours the specimen was allowed to cool to
ambient temperature.
[0050] 5) Thickness of oxide scale was determined by cross
sectional microscopy examination of the corrosion.
[0051] 6) In FIG. 5 any value less than 150 .mu.m represents
acceptable corrosion resistance.
[0052] The FIG. 5 showed that thickness of oxide scale formed on
TiC, Ti(C,N) and TiN cermet surface. It is obvious that Ti(C,N)
cermet has superior oxidation resistance than TiC or TiN cermet.
For Ti(C,N) cermets, the thickness of oxide scale formed on cermet
made using Haynes.RTM. 556 alloy binder is slightly lower than that
made using 304 SS regardless of lower binder content. This
improvement is caused by aliovalent elements present in Haynes.RTM.
556 alloy binder. The oxidation mechanism of TiC cermet is the
growth of TiO.sub.2, which is controlled by outward diffusion of
interstitial Ti.sup.+4 ions in TiO.sub.2 crystal lattice. When
oxidation starts, aliovalent elements, which are present in carbide
or metal phases, dissolves substitutionally in TiO.sub.2 crystal
lattice since the cation size of aliovalent element (e.g.,
Nb.sup.+5=0.070 nm) is comparable with that of Ti.sup.+4 (0.068
nm). Since the substantially dissolved Nb.sup.+5 ions increase the
electron concentration of the TiO.sub.2 crystal lattice, the
concentration of interstitial Ti.sup.+4 ions in TiO.sub.2
decreases, thereby oxidation is suppressed. This example
illustrates beneficial effect of aliovalent elements providing
superior oxidation resistance.
Example 4
[0053] Each of the cermets of Examples 1 and 2 was subjected to a
hot erosion and attrition test (HEAT). The procedure employed was
as follows:
[0054] 1) A specimen cermet disk of about 35 mm diameter and about
5 mm thick was weighed.
[0055] 2) The center of one side of the disk was then subjected to
1200 g/min of SiC particles (220 grit, #1 Grade Black Silicon
Carbide, UK abrasives, Northbrook, Ill.) entrained in heated air
exiting from a tube with a 0.5 inch diameter ending at 1 inch from
the target at an angle of 45.degree.. The velocity of the SiC was
45.7 n/sec.
[0056] 3) Step (2) was conducted for 7 hours at 732.degree. C.
[0057] 4) After 7 hours the specimen was allowed to cool to ambient
temperature and weighed to determine the weight loss.
[0058] 5) The erosion of a specimen of a commercially available
castable refractory was determined and used as a Reference
Standard. The Reference Standard erosion was given a value of 1 and
the results for the cermet specimens are compared to the Reference
Standard.
* * * * *