High-strength intermetallic TiAl synthesized via high-temperature crystallization of the amorphous alloy

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Abstract
In order to manufacture a high-strength titanium aluminide, an electrical discharge consolidation method combined with the high-rate heating of amorphous Ti50Al50 powders is proposed, with which one can control full densification in heating and hence crystallization at high temperatures up to near the melting point. The dc used is found to be a dominant process variable; at 1500 A it leads to an increase in temperature of up to 1480 K necessary for full densification of the amorphous material and a concomitant decrease to 25 s in processing time. With a heating rate above 14 Ks−1, the amorphous Ti50Al50 powder can be consolidated to full density and its densification is fairly well expressed by an Arrhenius-type equation of viscous flow: ηp equals; ηp0 exp(H/kT), where ηp is the process viscosity, with a decreasing activation energy H with increasing current. The amorphous (AM) Ti50Al50 then undergoes high-temperature crystalization according to AM→γ(TiA1) + α(Ti) having an increasing volume fraction of the α-phase with increasing temperature from approximately 1500 K. The fully densified intermetallic Ti50Al50 bulk, consolidated after the discharging of a rectangular pulse, shows well defined yielding and good ductility at ambient temperature in compression. The highest fracture strength is 3.03 GPa at the minimum γ grain size of 17 nm observed near the lowest temperature of high-temperature crystallization.

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