High-pressure sintering of the amorphous TiAl powder (特集各種粉末の焼結機構と新しい焼結技術の展開)

概要

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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 (Cm) of the amorphous Ti50Al50 powder follows a simplified Cooper-Eaton equation of Cm =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(cσeff/kT)exp(-Hp/kT) with a decreased value of 50 kJ mol-1 for the apparent activation energy, Hp. 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.