Lattice misfit variation of Al 3(Ti,V,Zr) in Al  Ti  V  Zr alloys

Abstract

It seems likely that high-strength Al-base alloys useful up to 698K can be developed in view of the behavior of nickel base superalloys which resist degradation of mechanical properties to 75 pct of their absolute melting temperature. For high temperature Al alloys, the dispersed hardening phase must not undergo phase transformation to an undesirable phase during long time exposure at the temperature of interest. An additional factor to be considered is the stability of the hardening phase with respect to Ostwald ripening. This coarsening resistance is necessary so that the required strength level can be maintained after the long-time service at high temperatures. A good lattice matching between the intermetallic compound and the aluminum matrix is necessary to promote a low interfacial energy and thus, a low driving force for particle coarsening. In this paper, several Al-base systems containing transition metal elements for potential elevated temperature use were suggested based on low values of diffusivities and solubilities. The equilibrium crystal structures of Al{sub 3}Ti, Al{sub 3}V and Al{sub 3}Zr are tetragonal DO{sub 22}, DO{sub 22} and DO{sub 23}, respectively. At the temperatures of interest, around 698K, vanadium and titanium are mutually substitutable in the form of Al{sub 3}(Ti, V). Muchmore » of titanium and vanadium can be substituted for zirconium in the DO{sub 23}-type Al{sub 3}Zr compound, creating Al{sub 3}(Ti, Zr) and Al{sub 3}(V, Zr), respectively.« less