High-Pressure Sintering of the Amorphous TiAl Powder

抄録

In order to manufacture a pore free amorphous Ti₅₀Al₅₀ product, a pulse electric current sintering of the mechanically alloyed amorphous powder under high-pressure is proposed, with which one can obtain full densification at low temperatures prior to glass transition to a supercooled liquid. The compressibility (C_m) of the amorphous Ti₅₀Al₅₀ powder follows a simplified Cooper-Eaton equation of C_m =Aexp(-k/P) under the applied stress of up to 600 MPa at room temperature, indicating that the powder compaction proceeds mainly via local plastic deformation at their contacted area with nearly non-strain hardening. When a high applied pressure of 600 MPa is used with a specially designed WC die, the amorphous Ti₅₀Al₅₀ powder can be consolidated at a full-density up to 939 K below a glass temperature, avoiding major crystallization; its densification during electric current heating is fairly well expressed with a commonly used equation of Non-Newtonian flow: ε=ε₀ sin h(cσ_eff/kT)exp(-H_p/kT) with a decreased value of 50 kJ mol^-1 for the apparent activation energy, H_p. Dynamic nanoindentation is used to give the value of 0.65 GPa for the level of yield stress for the fully dense amorphous Ti₅₀Al₅₀ sample.