Enhanced densification of metal powders by transformation-mismatch plasticity

The densification of titanium powders is investigated in uniaxial die pressing experiments carried out isothermally at 980 degrees C (in the B-field of titanium) and during thermal cycling between 860 and 980 degrees C (about the alpha/beta phase transformation of titanium). Thermal cycling is found to enhance densification kinetics through the emergence of transformation-mismatch plasticity (the mechanism responsible for transformation superplasticity) as a densification mechanism. The isothermal hot-pressing data compare favorably with existing models of powder densification, and these models are successfully adapted to the case of transformation-mismatch plasticity during thermal cycling. Similar conclusions are reached for the densification of titanium powders containing 1, 5, or 10 vol.% ZrO2 particles. However, the addition of ZrO2 hinders densification by dissolving in the titanium matrix during the hot-pressing procedure. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.