Dual-phase Cr-Ta alloys for structural applications

Details Dual-phase Cr-Ta alloys for structural applications Dual-phase Cr-Ta alloys for structural applications

1999-03-26

2001-06-12

King, Roy (Department: 1742)

Metal treatment

Stock

Chromium, molybdenum, or tungsten base

C420S428000

Reexamination Certificate

active

06245164

ABSTRACT:

FIELD OF THE INVENTION
This invention is directed towards alloys for high temperature structural applications having a Cr-rich solid solution and containing a Ta-rich Laves phase primarily in eutectic or hypoeutectic alloy compositions. The alloys can be used in both cast and fabricated conditions.
BACKGROUND OF THE INVENTION
High temperature energy conversion systems require materials having both high strength and high stability at temperatures which soften or oxidize currently available metals. We previously reported development of a two-phase Cr—Nb alloys which were two-phase systems having mechanical properties superior to Ni-based “superalloys” currently used in very high temperature conditions. We described and disclosed in U.S. Pat. No. 5,282,907 systems having five to eighteen percent Nb, one to ten percent Re and 0.5 to 10% Al and up to about 1 percent of any elements selected from V, Ta, Hf, Zr, and Y. These alloys display excellent strength and creep resistance at temperatures up to 1250° C. under compression tests and acceptable oxidation resistance up to 1,000° C. Unfortunately, the fracture strength is less than 50 ksi in tension at 1,000° C. and surface spalling is observed during cyclic oxidation to 1,000° C. These characteristics impose limitations which may not be acceptable in terms of weight, shock resistance and regular exposure to very high temperatures as would occur, for example, in high performance turbine engines which are routinely stopped and started.
SUMMARY OF THE INVENTION
It is an object of this invention to produce Cr-based alloys having very high strength at temperatures above 1,000° C.
It is another object of this invention to produce alloys which are Cr-based which possess excellent oxidation resistance when cycled repeatedly to temperatures of 1,000° C.
It is an object of this invention to disclose how to make Cr-based alloys having properties of superior strength and oxidation resistance.
It is a further object of this invention to disclose methods for fabricating articles according to the previous objects of this invention.
These and other objects of the invention are achieved by a dual-phase alloy having up to 11 percent Ta, up to 7% Mo and minor amounts of Ti, Si, Ge Ce, La, Y and other rare-earth elements. The objects of this invention are achieved by melting and casting the pure metals into alloy ingots and by subsequent hot fabrication, such as hot extrusion at high temperatures. (The alloys can be used as both cast and fabricated material.)


REFERENCES:
patent: 3015559 (1962-01-01), McGurthy et al.
patent: 3138456 (1964-06-01), Edwards
patent: 5282907 (1994-02-01), Liu et al.
patent: 5338379 (1994-08-01), Kelly
Max Hansen, 1958, Constitution of Binary Alloys, p. 563.

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