Rapid Consolidation of Ti-6Al-4V Powders by Thermal Transformation-Mismatch Plasticity

The densification kinetics of Ti-6Al-4V powders with spherical or angular shapes are compared in uniaxial die pressing experiments between isothermal conditions (at 1020 °C, in the beta-field, where deformation occurs by creep) and during thermal cycling (860-1020 °C, within the range of the alpha-beta phase transformation of the alloy, where transformation-mismatch superplasticity is activated). Densification kinetics are markedly faster under thermal cycling than under isothermal conditions, as expected from the higher deformation rate achieved under transformation-mismatch plasticity conditions as compared to creep conditions. The densification curves are successfully modeled for both creep and superplastic deformation mechanisms using (i) simple closed-form solutions and (ii) the finite-element method. Densification kinetics, under isothermal and thermal cycling conditions, of Ti-6Al-4V powders containing 5-20 vol.% ceramic particles are also presented.