SYNTHESIS OF HIGH HARDNESS INTERMETALLIC COMPOUND BY PULSE ELECTRODISCHARGE CONSOLIDATION OF AMORPHOUS TIAL POWDER

Instrumented pulse electro-discharge consolidation of mechanically alloyed amorphous TiAl powder is proposed as a method for synthesizing a high-strength titanium aluminide compact composed of fully densified nano-scaled structure by controlling the process variables of temperature, stress and pulse electric current. We obtained a fully densified compact consisting of titanium aluminide {gamma (TiAl) + alpha2 (Ti3Al)} with the dispersion of an island-shaped alpha (Ti) phase and Al3Ti particles using a relatively low stress of 29 MPa with an electro-discharge consolidating time less than 600 s. The consolidating temperature necessary to obtain a fully densified TiAl compact decreases from 1312 to 1051 K with increasing applied stress from 29 to 147 MPa. Such a decrease is conducive to the great decreases in size of titanium aluminide grains and Al3Ti second phase particles. Moreover, we found that the fully densified compact of titanium aluminide has an increasing Vickers hardness up to 1050 DPN at 1100 K, following a decrease with decreasing consolidating temperature. The process viscosity (eta) for pulse electro-discharge consolidation of amorphous TiAl is fairly well expressed by an Arrhenius-type equation of eta = eta(o) exp (H(V)/kT) with 87-115 kJ mol-1 for activation energy (H(V)), which is smaller than 339 kj mol-1 for specimen viscosity, and a significantly decreasing eta(o) with increasing applied current. These results indicate that pulse electro-discharging strongly accelerates the rate of the densification via viscous flow in an amorphous TiAl powder compact.