Processing of powders of a refractory metal based alloy for high densification

Abstract

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.

Description

FIELD OF INVENTION[0001]The invention relates to a chromium alloy in general and to an alloy for use as an interconnect in high temperature fuel cell systems, such as solid oxide fuel cell (SOFC) systems and methods of making thereof.BACKGROUND OF THE INVENTION[0002]One of the major constraints to producing cost effective SOFC systems or stacks is the cost of functional interconnects. In planar SOFC stacks, a planar or plate shaped interconnect is located between adjacent SOFCs. The interconnect provides reactant gas separation and containment, mechanical support to the cells, and a low resistance path for electrical current between adjacent SOFCs. Moreover, the reactant gas flow channels on either side of the interconnect are designed to ensure distribution of the fuel and the oxidant with minimal pressure drop in the overall SOFC stack, especially in respect to the air flow channels of the interconnect because of the relatively high air flow rates employed to dispose of heat from ...

AI Technical Summary

Benefits of technology

[0007]One embodiment of the invention provides 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.

[0008]Another embodiment of the invention provides 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.

Problems solved by technology

One of the major constraints to producing cost effective SOFC systems or stacks is the cost of functional interconnects.

While these materials had provided some amount of success, the cost had been prohibitive, and the reliability in the various aspects of their function had been less than adequate.

They are also prone to chemistry changes during their life cycle due to loss of oxygen ions in the reducing atmosphere of fuel, such as hydrogen.

Many of the alternatives considered among the ceramic materials also possess unacceptable values of CTE.

However, many of these fail on account of inadequate strength at the temperatures of operation of the SOFC, typically 700 to 1000° C., or by growth of an oxide layer that constrains electrical conductivity.

However, there are metallurgical limitations to producing such alloys by any process involving casting and subsequent metal working.

All such hot consolidation processes, however, lead to slow production rates and result in excessively high costs.

The oxide layer that forms under high temperature oxidation conditions prevalent in the SOFC can be self limiting, and further the oxide is electrically conducting.

However, the simple, comparatively inexpensive PM processing of cold compaction in a die followed by high temperature sintering has the limitation of leading to a material that is porous in nature and therefore generally unacceptable for use as an interconnect.

Images