U.S. patent application number 10/829823 was filed with the patent office on 2008-11-13 for erosion-corrosion resistant carbide cermets for long term high temperature service.
Invention is credited to Robert Lee Antram, Narasimha-Rao Venkata Bangaru, ChangMin Chun, Christopher John Fowler, Hyun-Woo Jin, Jayoung Koo, Shiun Ling, John Roger Peterson, Neeraj Srinivas Thirumalai.
Application Number | 20080276757 10/829823 |
Document ID | / |
Family ID | 38716263 |
Filed Date | 2008-11-13 |
United States Patent
Application |
20080276757 |
Kind Code |
A1 |
Bangaru; Narasimha-Rao Venkata ;
et al. |
November 13, 2008 |
EROSION-CORROSION RESISTANT CARBIDE CERMETS FOR LONG TERM HIGH
TEMPERATURE SERVICE
Abstract
Cermets are provided in which the ceramic phase is selected from
the group consisting of Cr.sub.23C.sub.6, Cr.sub.7C.sub.3,
Cr.sub.3C.sub.2 and mixtures thereof. The binder phase is selected
from certain specified Ni/Cr alloys and certain Fe/Ni/Cr alloys.
These cermets are particularly useful in protecting surfaces from
erosion at high temperatures.
Inventors: |
Bangaru; Narasimha-Rao Venkata;
(Annandale, NJ) ; Chun; ChangMin; (Belle Mead,
NJ) ; Thirumalai; Neeraj Srinivas; (Phillipsburg,
NJ) ; Ling; Shiun; (Washington, NJ) ; 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: |
38716263 |
Appl. No.: |
10/829823 |
Filed: |
April 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60471789 |
May 20, 2003 |
|
|
|
Current U.S.
Class: |
75/240 |
Current CPC
Class: |
C22C 29/067
20130101 |
Class at
Publication: |
75/240 |
International
Class: |
C22C 29/08 20060101
C22C029/08 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. A bulk cermet material comprising: (a) about 50 vol % to about
95 vol %, based on the total volume of the cermet composition, of a
ceramic phase, wherein the ceramic phase being a chromium carbide
selected from the group consisting of Cr.sub.23C.sub.6,
Cr.sub.7C.sub.3, Cr.sub.3C.sub.2 and mixtures thereof; and (b) a
binder phase comprising alloys containing about 4 wt % to about 52
wt % Fe; about 36 wt % to about 78 wt % Ni, and about 12 wt % to
about 18 wt % Cr; and wherein the overall thickness of the bulk
cermet material is greater than 5 millimeters.
15. (canceled)
16. The bulk cermet material of claim 14 wherein the chromium
carbide is Cr.sub.23C.sub.6.
17. The bulk cermet material of claim 14 wherein the chromium
carbide is Cr.sub.7C.sub.3.
18. The bulk cermet material of claim 17 wherein the ceramic phase
further comprises Cr.sub.3C.sub.2.
19. The bulk cermet material of claim 14 wherein the chromium
carbide is Cr.sub.3C.sub.2.
20. (canceled)
21. (canceled)
22. (canceled)
23. (canceled)
24. (canceled)
25. The bulk cermet material as in any one of claim 14 or 16-19
having a long term microstructural stability lasting at least 25
years when exposed at temperatures up to 1000.degree. C.
Description
[0001] This application claims the benefit of U.S. Provisional
application 60/471,789 filed May 20, 2003.
FIELD OF INVENTION
[0002] The present invention relates to cermet compositions. More
particularly the invention relates to chromium carbide containing
cermet compositions and their use in high temperature erosion and
corrosion applications.
BACKGROUND OF INVENTION
[0003] Abrasive and chemically resistant materials find use in many
applications where metal surfaces are subjected to substances which
would otherwise promote erosion or corrosion of the metal
surfaces.
[0004] Reactor vessels and transfer lines used in various chemical
and petroleum processes are examples of equipment having metal
surfaces that often are provided with materials to protect the
surfaces against material degradation. Because these vessels and
transfer lines are typically used at high temperatures protecting
them against degradation is a technological challenge. Currently
refractory liners are used to protect metal surfaces exposed at
high temperature to erosive or corrosive environments. The lifespan
of these refractory liners, however, is significantly limited by
mechanical attrition of the liner, especially when exposed to high
velocity particulates, often encountered in petroleum and
petrochemical processing. Refractory liners also commonly exhibit
cracking and spallation. Thus, there is a need for liner material
that is more resistant to erosion and corrosion at high
temperatures.
[0005] Ceramic metal composites or cermets are known to possess the
attributes of the hardness of ceramics and the fracture toughness
of metal but only when used at relatively moderate temperatures,
for example, from 25.degree. C. to no more than about 300.degree.
C. Tungsten carbide (WC) based cermets, for example, have both
hardness and fracture toughness making them useful in high wear
applications such as in cutting tools and drill bits cooled with
fluids. WC based cermets, however, degrade at sustained high
temperatures, greater than about 600.degree. F. (315.degree.
C.).
[0006] Chromium carbide has been a potentially suitable ceramic
phase for use in cermets because its three crystallographic forms:
the cubic (Cr.sub.23C.sub.6) the hexagonal (Cr.sub.7C.sub.3) and
the orthorhombic (Cr.sub.3C.sub.2) have excellent oxidation
resistance at elevated temperatures; yet cermets formed from these
carbides typically undergo transformations at elevated temperatures
which result in the formation of microstructural phases which have
a deleterious effect on the properties of such cermets.
[0007] The object of the present invention is to provide new and
improved cermet compositions.
[0008] Another object of the invention is to provide chromium
carbide containing cermet compositions suitable for use at high
temperatures.
[0009] Another object of the invention is to provide chromium
carbide containing cermet compositions with long term
microstructural stability suitable for long term service at high
temperatures.
[0010] Yet another object of the invention is to provide an
improved method for protecting metal surfaces against erosion and
corrosion under high temperature conditions.
[0011] These and other objects will become apparent from the
detailed description which follows.
SUMMARY OF INVENTION
[0012] Broadly stated, the present invention is a cermet
composition comprising a chromium carbide ceramic phase dispersed
in a binder phase. The ceramic phase which constitutes about 50 vol
% to about 95 vol % of the total volume of the cermet composition
is a chromium carbide selected from the group consisting of
Cr.sub.23C.sub.6, Cr.sub.7C.sub.3, Cr.sub.3C.sub.2 and mixtures
thereof.
[0013] The binder phase is selected from the group consisting of
(i) alloys containing about 60 wt % to about 98 wt % Ni; about 2 wt
% to about 35 wt % Cr; and up to 5 wt % of an element selected from
the group consisting of Al, Si, Mn, Ti and mixtures thereof; and
(ii) alloys containing about 0.01 wt % to about 35 wt % Fe; about
25 wt % to about 97.99 wt % Ni, about 2 wt % to about 35 wt % Cr;
and up to about 5 wt % of an element selected from the group
consisting of Al, Si, Mn, Ti and mixtures thereof, the wt % in each
instance based on the total weight of the alloy.
[0014] This and other embodiments of the invention, including where
applicable those preferred, will be elucidated in the detailed
description which follows.
BRIEF DESCRIPTION OF THE FIGURES
[0015] FIG. 1 is a scanning electron microscopy (SEM) image of the
surface of a cermet made with an initial Cr.sub.3C.sub.2 in 30 vol
% Ni-20 Cr binder. Ni-20 Cr indicates 80 wt % Ni and 20 wt %
Cr.
[0016] FIG. 2 is a SEM image of the surface of a cermet made with
an initial Cr.sub.7C.sub.3 in 30 vol % Ni-20 Cr binder.
[0017] FIG. 3 is a SEM image of the surface of a cermet made with
an initial Cr.sub.23C.sub.6 in a 30 vol % Ni-20 Cr binder.
[0018] FIG. 4 is a SEM image of the surface of a cermet made with
an initial Cr.sub.3C.sub.2 in a 30 vol % 304 stainless steel
(304SS) binder after exposure to 800.degree. C. for 1000 hours.
DETAILED DESCRIPTION OF THE INVENTION
[0019] In one embodiment the invention is a cermet composition
comprising a chromium carbide ceramic phase dispersed in a
continuous binder phase.
[0020] The ceramic phase constitutes about 50 vol % to about 95 vol
% of the total volume of the cermet composition, the ceramic phase
being a chromium carbide selected from the group consisting of
Cr.sub.23C.sub.6, Cr.sub.7C.sub.3, Cr.sub.3C.sub.2, where this
group is intended to include sub and super stoichiometric variances
thereof.
[0021] The particle size diameter of the ceramic phase typically is
below about 3 mm, preferably below about 100 .mu.m and more
preferably below about 50 .mu.m. 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.
[0022] The binder phase is selected from the group consisting of
(i) alloys containing about 60 wt % to about 98 wt % Ni; about 2 wt
% to about 35 wt % Cr; and up to about 5 wt % of an element
selected from the group consisting of Al, Si, Mn, Ti and mixtures
thereof; and (ii) alloys containing about 0.01 wt % to about 35 wt
% Fe; about 25 wt % to about 97.99 wt % Ni, about 2 wt % to about
35 wt % Cr; and up to about 5 wt % of an element selected from the
group consisting of Al, Si, Mn, Ti and mixtures thereof, the wt %
in each instance based on the total weight of the alloy.
[0023] Illustration of cermet compositions suitable for use at
elevated temperatures include:
[0024] (1) about 50 vol % Cr.sub.7C.sub.3 in a binder comprising 78
wt % Ni, about 4 wt % Fe and 18 wt % Cr;
[0025] (2) about 70 vol % Cr.sub.7C.sub.3 in a binder comprising 78
wt % Ni, about 4 wt % Fe and 18 wt % Cr;
[0026] (3) about 94 vol % Cr.sub.7C.sub.3 in a binder comprising 75
wt % Ni, about 7 wt % Fe, and about 18 wt % Cr;
[0027] (4) about 50 vol % Cr.sub.23C.sub.6 in a binder comprising
72 wt % Ni, about 10 wt % Fe, and 18 wt % Cr;
[0028] (5) about 50 vol % Cr.sub.23C.sub.6 in a binder comprising
67 wt % Ni, 15 wt % Fe and 18 wt % Cr; and
[0029] (6) about 90 vol % Cr.sub.23C.sub.6 in a binder comprising
77 wt % Ni, 5 wt % Fe and 18 wt % Cr.
[0030] Preferred cermet compositions are the follows:
[0031] (1) 50 vol % to 90 vol % Cr.sub.23C.sub.6 in binder (i);
[0032] (2) 50 vol % to 90 vol % Cr.sub.7C.sub.3 in binder (i);
[0033] (3) 65 vol % to 95 vol % of a mixture of Cr.sub.3C.sub.2 and
Cr.sub.7C.sub.3 where the latter is about 1 vol % to about 18 vol %
of the mixture and binder (i).
[0034] (4) 50 vol % to 95 vol % of Cr.sub.3C.sub.2 in binder
(i).
[0035] The cermet compositions are made by general powder
metallurgical techniques such as mixing, milling, pressing,
sintering and cooling, employing as starting materials a chromium
carbide ceramic powder and a binder powder in the volume ratio of
50:50 to 95:5 respectively. Preferably the chromium carbide powder
is one of Cr.sub.23C.sub.6, Cr.sub.7C.sub.3 and Cr.sub.3C.sub.2
although mixtures of these may be used. Preferably the binder is
one of the alloy compositions set forth in Table 1.
TABLE-US-00001 TABLE 1 Alloy Type Composition (wt %) NiCr Bal Ni:20
Cr NiCrSi Bal Ni:20.1 Cr:2.0 Si:0.4 Mn:0.09 Fe FeNiCr Bal Fe: >
12 Cr > 36 Ni Bal = Balance
[0036] These powders are milled in a ball mill in the presence of a
sufficient amount 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 green body is then sintered at
temperatures above about 1200.degree. C. up to about 1600.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 instance, 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 production according to
the process described herein allows fabrication of bulk cermet
bodies exceeding 5 mm in thickness.
[0037] These processing conditions result in the dispersion of the
carbide or carbides in the binder. Additionally, the processing
results in some compositional changes in the ceramic and binder.
For example when the carbide ceramic employed is Cr.sub.3C.sub.2
and the binder is a Ni-20Cr alloy, the resultant cermet contained
both Cr.sub.3C.sub.2 and Cr.sub.7C.sub.3 phases with some depletion
of Cr in the binder phase. On the other hand, when the ceramic
employed is Cr.sub.23C.sub.6 in the same binder there is
substantially no change in the composition of the ceramic.
[0038] 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 chromium carbide ceramic
phase.
[0039] One feature of the cermets of the invention is their long
term 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 1000.degree. C. This stability permits
their use for prolonged time periods, for example greater than 2
years. In contrast many known cermets undergo transformations at
elevated temperatures which result in the formation of phases which
have a deleterious effect on the properties of the cermet.
[0040] The long term microstructural stability of the cermets of
the instant invention was confirmed by computational thermodynamics
using calculation of phase diagram (CALPHAD) methods known to one
of ordinary skill in the art of computational thermodynamic
calculation methods. These calculations confirmed that the various
carbide phases, their amounts, the binder amount and the respective
chemistries lead to cermet compositions with long term
microstructural stability. Further, lab experiments were conducted
in which the cermet compositions of the instant invention were
exposed at 800.degree. C. for 1000 hours in air. Analysis of the
bulk microstructure of the resultant cermet after this 1000 h high
temperature exposure showed that the starting microstructure was
substantially preserved as determined by SEM.
[0041] The cermet compositions of the instant invention can exhibit
long term microstructural stability lasting at least 25 years when
exposed to temperatures up to 1000.degree. C.
[0042] Another feature of the cermets of this invention is that
they have fracture toughness of greater than about 3 MPam.sup.1/2,
preferably greater than about 5 MPam.sup.1/2, and most 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. The binder phase of the cermet of the instant invention as
described in the earlier paragraphs is primarily responsible for
imparting this attribute.
[0043] 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, side 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 1000.degree. C. are protected by providing
the surface with a layer of the ceramic 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
[0044] 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:
[0045] The weight percent of elements in the cermet phases was
determined by standard EDXS analyses.
[0046] The following non-limiting examples are included to further
illustrate the invention.
Example 1
[0047] 70 vol % of 14.0 .mu.m average diameter of Cr.sub.3C.sub.2
powder (99.5% purity, from Alfa Aesar) and 30 vol % of Ni-20Cr
alloy binder powder (Alfa Aesar, screened below 325 mesh) were
dispersed with ethanol in high density polyethylene milling jar.
The powders in ethanol were mixed for 24 hours with yttria
toughened zirconia 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 for 30 min for residual
solvent removal. The disc was then heated to 1450.degree. C. at
15.degree. C./min in argon and held at 1450.degree. C. for 1 hour.
The temperature was then reduced to below 100.degree. C. at
-15.degree. C./min. The resulting cermet comprises:
i) 63 vol % Cr.sub.3C.sub.2 with average grain size of 20 .mu.m ii)
12 vol % Cr.sub.7C.sub.3 with average grain size of 20 .mu.m iii)
25 vol % Cr-depleted alloy binder (87Ni: 13Cr in wt %).
[0048] FIG. 1 is a SEM image of the cermet processed according to
this example, wherein the bar represents 20 .mu.m. In this image
the chromium carbide phase appears light and the binder phase
appears dark.
Example 2
[0049] The mixing and pressing procedures of Example 1 was followed
using 70 vol % of 14.0 .mu.m average diameter of Cr.sub.7C.sub.3
powder (99.5% purity, from Alfa Aesar) and 30 vol % of Ni-20Cr
alloy binder powder (Alfa Aesar, screened below 325 mesh). The disc
was then heated to 1400.degree. C. for 1 hour at 15.degree. C./min
in hydrogen. The temperature was then reduced to below 100.degree.
C. at -15.degree. C./min.
[0050] The resulting cermet comprised:
i) 67 vol % Cr.sub.7C.sub.3 with average grain size of 20 .mu.m ii)
33 vol % Cr-enriched alloy binder (76Ni:24Cr in wt %).
[0051] FIG. 2 is a SEM image of the cermet processed according to
this example, wherein the bar represents 20 .mu.m. In this image
the chromium carbide phase appears light and the binder phase
appears dark.
Example 3
[0052] The procedure of Example 2 was followed using 70 vol % of
14.0 .mu.m average diameter of Cr.sub.23C.sub.6 powder (99.5%
purity, from Alfa Aesar) and 30 vol % of Ni-20Cr alloy binder
powder (Alfa Aesar, screened below 325 mesh). The result cermet
comprised of:
i) 67 vol % Cr.sub.23C.sub.6 with average grain size of 20 .mu.m
ii) 33 vol % Cr-enriched alloy binder (69Ni:31Cr in wt %).
[0053] FIG. 3 is a SEM image of the cermet processed according to
this example, wherein the bar represents 20 .mu.m. In this image
the chromium carbide phase appears light and the binder phase
appears dark.
Example 4
[0054] The procedure of Example 2 was followed using 85 vol % of
14.0 .mu.m average diameter of Cr.sub.3C.sub.2 powder (99.5%
purity, from Alfa Aesar) and 15 vol % of Ni-20Cr alloy binder
powder (Alfa Aesar, screened below 325 mesh).
[0055] During heating, some Cr.sub.3C.sub.2 phase is replaced by
Cr.sub.7C.sub.3 phase. As result, carbide volume fraction increases
and Cr content is depleted in the binder. The result cermet
comprised of:
i) 80 vol % Cr.sub.3C.sub.2 with average grain size of 20 .mu.m ii)
7 vol % Cr.sub.7C.sub.3 with average grain size of 20 .mu.m iii) 13
vol % Cr-depleted alloy binder (85Ni: 15Cr in wt %).
Example 5
[0056] The cermet compositions of examples 1, 2 and 3 were exposed
in air at 800.degree. C. for 1000 hours in a Lindberg box furnace.
After exposure the samples were analyzed using SEM. No significant
precipitation of new phases, change in the proportion of the
original phase composition or change in the respective chemistry
was observed in any of the 3 aforestated samples. Thus the cermet
composition of example 1, 2 and 3 were determined to possess long
term microstructural stability.
Example 6
Comparative Example
[0057] A comparative example of a system that does not form a
preferred thermodynamically stable cermet is prepared using the
procedure of Example 1 and 70 vol % of 14.0 .mu.m average diameter
of Cr.sub.3C.sub.2 powder (99.5% purity, from Alfa Aesar) and 30
vol % of 6.7 .mu.m average diameter 304SS alloy binder powder
(Osprey Metals, Fe(balance): 18.5Cr:9.6Ni: 1.4Mn:0.63Si, 95.9%
screened below -16 .mu.m). The disc was then heated to 1400.degree.
C. at 15.degree. C./min in argon and held at 1400.degree. C. for 1
hour. During heating, a significant vol % of Cr.sub.3C.sub.2 phase
is replaced by Cr.sub.7C.sub.3 phase. As net result, carbide volume
fraction increases and Cr content is depleted in the binder.
[0058] The result cermet comprised of the non-equilibrium
microstructure:
i) 8 vol % Cr.sub.3C.sub.2 with average grain size of 20 .mu.m ii)
72 vol % Cr.sub.7C.sub.3 with average grain size of 20 .mu.m iii)
20 vol % Cr-depleted alloy binder
[0059] Next, the sintered disc was heated in air at 800.degree. C.
for 1000 hours. After exposure to 800.degree. C. in air for 1000
hours this cermet comprises:
i) >9.5 vol % Cr.sub.3C.sub.2
ii) >85.5 vol % Cr.sub.7C.sub.3
[0060] iii) <5 vol % Cr-depleted alloy binder
(13.2Si:9.4Cr:8.9Fe:68.5Ni in wt %).
[0061] FIG. 4 is a SEM image of the cermet after heating in air
according to this example, wherein the bar represents 10 .mu.m. In
this image the chromium carbide phase appears light and the binder
phase appears dark. This figure shows <5 vol % 304SS and >95
vol % chrome carbides after this relative shortterm exposure to
high temperature. The metal composition has become depleted in
chromium content thereby decreasing the fracture toughness of the
cermet.
Example 7
[0062] Each of the cermets of Examples 1 to 4 was subjected to a
hot erosion and attrition test (HEAT) and was found to have an
erosion rate of less than 1.0.times.10.sup.-6 cc/gram SiC erodant.
The procedure employed was as follows:
[0063] 1) A specimen cermet disk of about 35 mm diameter and about
5 mm thick was weighed.
[0064] 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 m/sec.
[0065] 3) Step (2) was conducted for 7 hrs at 732.degree. C.
[0066] 4) After 7 hrs the specimen was allowed to cool to ambient
temperature and weighed to determine the weight loss.
[0067] 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 in Table 2 to the
Reference Standard. In Table 2 any value greater than 1 represents
an improvement over the Reference Standard.
TABLE-US-00002 TABLE 2 Starting Finish Weight Bulk Improvement
Cermet Weight Weight Loss Density Erodant Erosion [(Normalized
{Example} (g) (g) (g) (g/cc) (g) (cc/g) erosion).sup.-1] Cr3C2 L 30
18.6737 15.0660 3.6077 7.350 5.04E+5 7.3766E-7 1.4 NiCr {1} Cr7C3 L
30 23.6681 21.0301 2.6380 7.360 5.34E+5 6.7121E-7 1.6 NiCr {2}
Cr23C6 L 30 23.5976 21.6016 1.9960 7.350 5.04E+5 5.3882E-7 1.9 NiCr
{3} Cr3C2 L 15 19.6071 17.6609 1.9462 7.090 5.04E+5 5.4464E-7 1.9
NiCr {4}
Example 8
[0068] Each of the cermets of Examples 1 to 4 was subjected to a
corrosion test and found to have a corrosion rate less than about
1.0.times.10.sup.-11 g.sup.2/cm.sup.4s. The procedure employed was
as follows:
[0069] 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.
[0070] 2) The specimen was then exposed to 100 cc/min air at
800.degree. C. in thermogravimetric analyzer (TGA).
[0071] 3) Step (2) was conducted for 65 hours at 800.degree. C.
[0072] 4) After 65 hours the specimen was allowed to cool to
ambient temperature.
[0073] 5) Thickness of oxide scale was determined by cross
sectional microscopy examination of the corrosion surface.
[0074] 6) All the thickness of oxide scale formed on specimen
surface was less than 1 .mu.m, representing superior corrosion
resistance.
* * * * *