Development Of High-temperature Alloys Research Articles

Interdiffusion in systems with components with differing melting points

In the development of high-temperature alloys the use of refractory metals with a high melting point — Ta and W — for alloying is becoming conventional. These metals, and also the alloys based on them, may come into contact with metals and alloys whose melting points are much lower (for example, in composite-type materials). Upon heating there develop in the areas of contact of the metals differing in their melting point the processes of mutual diffusion, knowledge of which makes it possible to determine the chemical composition of the transition zone and the thermal stability of the composite material. Since production of the refractory metals involves great difficulties, intermediate products are prepared from them by the powder metallurgy method. The powder materials contain more defects, particularly pores, in comparison with the cast materials, which must be considered in studying the diffusion. In the present article we examine on the basis of experimental data and thermodynamic analysis the characteristics of the kinetics of the process of mutual diffusion of vanadium and the refractory metals in cast and powder variants at various temperatures.

Other applications of superalloys

Abstract It is the intention in this paper to put into context the development of high-temperature alloys to their present position in non-gas-turbine applications, and to identify new alloy systems capable of improving performance in hostile industrial environments. The rise of superalloys from ferritic steels to the current γ′-hardened nickel-base materials, the best of which experience strength limitations above l000°C, is traced. Desired increases in temperature capability are possible with oxide dispersion strengthened powder alloys, which were originally developed for gas turbine usage and are now being produced on a large tonnage basis by the mechanical alloying (MA) process. The MA technique and commercial alloys are described and examples given of the replacement of more conventional materials by fabricated MA components in a diversity of industries. MA alloys exhibit combinations of strength and corrosion resistance capable of meeting many industrial demands for economic improvements to processi...

Some limiting factors in the use of alloys at high temperatures

Over recent years, research has established some of the more basic principles associated with the complex reactions of gases with alloys at high temperatures. The most suitable alloys are based on Fe, Ni, or Co, protected with SiO2, Cr2O3, or A12O3 scales and the upper limit of temperature at which metals can be used in most engineering operations appears tobe about 1200° C (2200° F). A system of superimposing oxidation data on alloy phase diagrams is outlined that indicates suitable basic compositions for the development of high temperature alloys. The system is called “oxide mapping.” The principle used is described and its application to the two systems Ni-Cr-Al at 1000° C and Co-Cr-Al at 1100° C is used to illustrate how suitable ternary compositions are selected as the basis of new alloys.

NASA programs for development of high- temperature alloys for advanced engines.

NASA programs for development of high temperature alloys for advanced air breathing engines emphasizing cast Ni-base alloy