Processing of powders of a refractory metal based alloy for high densification
A powder metallurgy method of making a chromium base alloy includes blending a first powder comprising a chromium powder and a second powder comprising at least one of titanium, titanium hydride, zirconium or zirconium hydride, annealing the first powder and the second powder in a reducing atmosphere after the step of mixing, compacting a blend of the first and the second powders, and sintering the compacted blend to form a chromium base alloy. The chromium alloy may be used as an interconnect for a solid oxide fuel cell, and includes least one of iron or nickel greater than zero and equal to or less than 7 weight percent, yttria greater than zero and equal to or less than 2 weight percent, at least one of titanium or zirconium greater than zero and equal to or less than 1 weight percent and at least 90 weight percent chromium.
1 . A powder metallurgy method of making a chromium base alloy, comprising:
blending a first powder comprising a chromium powder and a second powder comprising at least one of titanium, titanium hydride, zirconium or zirconium hydride;
annealing the first powder and the second powder in a reducing atmosphere after the step of mixing;
compacting a blend of the first and the second powders; and
sintering the compacted blend to form a chromium base alloy.
2 . The method of claim 1 , wherein the step of annealing is conducted before the step of compacting.
3 . The method of claim 1 , wherein the step of annealing is conducted after the step of compacting.
4 . The method of claim 1 , wherein the step of annealing is conducted before and after the step of compacting.
5 . The method of claim 1 , wherein the step of annealing is conducted in a temperature range of about 800 to about 1200° C. in a hydrogen atmosphere.
6 . The method of claim 1 , wherein the first powder comprises chromium powder having a bimodal distribution comprising a blend of coarse and fine chromium powders.
7 . The method of claim 1 , wherein the blend contains 1 weight percent or less of the second powder.
8 . The method of claim 1 , further comprising blending the first powder and the second powder with at least one of iron powder, nickel powder and yttria powder to form the blend.
9 . The method of claim 8 , wherein the annealing is conducted after the step of blending the first powder and the second powder and before the step of blending the first powder and the second powder with at least one of iron powder, nickel powder and yttria powder.
10 . The method of claim 8 , wherein the yttria powder has an average particle diameter of less than one micron.
11 . The method of claim 8 , wherein the blend comprises at least one of iron and nickel powder greater than zero and equal to or less than 7 weight percent, yttria powder greater than zero and equal to or less than 2 weight percent, at least one of titanium, titanium hydride, zirconium or zirconium hydride powder greater than zero and equal to or less than 1 weight percent and at least 90 weight percent chromium powder.
12 . The method of claim 1 , wherein:
the step of compacting comprises cold compacting at least the first powder and the second powder; and
the step of sintering is conducted in an atmosphere containing hydrogen at a temperature of about 1300 to about 1500° C.
13 . The method of claim 1 , wherein the sintered alloy comprises an interconnect for a solid oxide fuel cell, such that the interconnect has a coefficient of thermal expansion from 30° C. to 1000° C. of between about 11×10 −6 /° C. and about 13×10 −6 /° C.
14 . The method of claim 13 , further comprising providing the interconnect into a solid oxide fuel cell stack.
15 . A powder metallurgy method of making a chromium base alloy, comprising:
blending a first powder comprising a chromium powder and a second powder comprising yttria powder having an average particle size of less than 1 micron;
compacting a blend of the first and the second powders; and
sintering the compacted blend to form a chromium base alloy.
16 . The method of claim 15 , further comprising:
blending the first powder and a third powder comprising at least one of titanium, titanium hydride, zirconium or zirconium hydride before, after or during the step of blending the first powder and the second powder; and
annealing at least the first powder and the third powder in a reducing atmosphere after the step of blending the first powder and the third powder.
17 . A chromium alloy interconnect for a solid oxide fuel cell comprising least one of iron or nickel greater than zero and equal to or less than 7 weight percent, yttria greater than zero and equal to or less than 2 weight percent, at least one of titanium or zirconium greater than zero and equal to or less than 1 weight percent and at least 90 weight percent chromium.
18 . The alloy interconnect of claim 17 , wherein the alloy comprises 2 to 5 weight percent iron and 0.25 to 2 weight percent nickel.
19 . The alloy interconnect of claim 17 , wherein the alloy comprises 3 to 7 weight percent of either iron or nickel.
20 . The alloy interconnect of claim 17 , wherein the interconnect is located in a solid oxide fuel cell stack and the interconnect comprises gas flow channels.