Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1988-09-27
1990-08-21
Lechert, Jr., Stephen J.
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
75244, 75245, 419 12, 419 13, 419 19, 419 23, 419 28, 419 29, 419 33, 419 32, 419 66, C22C 2912
Patent
active
049503278
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a sintered alloy consisting of one or several of the high-melting metals Mo, W, Nb, Ta, v, and Cr with a tiered structural arrangement, such alloy having excellent thermal resistance combined with outstanding resistance to creep at high temperatures, as well as to a process for the manufacture of such alloy.
High-melting metals, because of their high melting point and high resistance to heat, are frequently used for molded parts that are expected to withstand high temperatures.
However, in many cases, high-melting metals in the pure form are not usuable for applications where good thermal resistance and high resistance to creep are important, i.e., where good mechanical strength is required at high temperatures over long periods of time.
In the past, two important different types of alloying of high-melting metals have been developed in order to increase the resistance to heat and creep of the high-melting metals at high temperatures.
With the one type of alloying of high-melting metals, certain elements are added to the basic material consisting of high-melting metal, said elements being present in the structure of the finished alloy in the form of finely dispersed particles. In this way, the thermal resistance and the resistance to creep at high temperatures are increased as compared to the high-melting metal in its pure form. It is of importance with such alloys that the enhanced properties are obtained without special mechanical reformation in the course of the manufacturing process.
The best-known representative of this type of alloy is the so-called TZM, which is a molybdenum alloy which typically contains about 0.5% by weight titanium, 0.08% by weight zirconium, and 0.05% by weight carbon.
A high-melting alloy of this type is described in US-PS 3,982,970. According to the latter, the basic material is solidified or strengthened by dispersion with the help of a thermal treatment in a special atmosphere. According to this patent, a suitable atmosphere is one containing particles of thorium oxide or aluminum oxide with a grain size of <1 .mu.m.
Another alloy of this type consisting of high-melting metal based on molybdenum is described in German published patent disclosure DE-OS 34 41 851. This alloy contains 0.2 to 1% by weight oxides of the trivalent or quadrivalent metals as dispersed particles.
With all known alloys of high-melting metals that are produced without special mechanical reforming and in which dispersed particles effect increased heat and creep resistance at high temperatures as compared to the pure highmelting metal, the temperature up to which such resistances are sufficiently maintained is still inadequate for many application cases.
A second type of alloying of high-melting metals has been developed in order to significantly raise the application temperature of high-melting metals with sufficient heat and creep resistance properties. With this type of alloying of high-melting metals, which can be accomplished only in the powder-metallurgical way, the basic material of high-melting metal is doped with certain elements and, in the course of the manufacturing process, subjected to high mechanical reforming with a reforming degree of at least 85 percent. In this way, a highly defined structural arrangement of the alloy of highmelting metal is obtained, i.e., the so-called tiered structure that is characterized by grains shaped in the structure in an oblong form, with a ratio of length to width of the grains of at least 2 : 1.
Known alloys of high-melting metals of this type include, for example, tungsten and molybdenum alloys, which normally are doped with small amounts of aluminum and/or silicon and potassium. It is of importance with these alloys of high-melting metals that at least potassium has to be contained in the alloy so as to obtain the formation of a tiered wire structure. The additional doping elements such as aluminum and/or silicon effect that the potassium, in the course of the sintering step, does not completely diffuse from the material, wher
REFERENCES:
patent: 3954421 (1976-05-01), Heuschkel
patent: 3982970 (1976-09-01), Webster et al.
patent: 4588552 (1986-05-01), Schoder et al.
patent: 4599214 (1986-06-01), Luton
Powder Metallurgy, Sintered and Composite Materials--1st Edition, VEB Deutscher Verlag Fuer Grundstoffindustrie, Leipzig, East Germany, pp. 400-425, by W. Schatt.
Eck Ralf
Leichtfried Gerhard
Bhat N.
Lechert Jr. Stephen J.
Schwarzkopf Development Corporation
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