Martensitic transformation behaviors of rapidly solidified Ti-Ni-Mo powders

For the fabrication of bulk near-net-shape shape memory alloys and porous metallic biomaterials, consolidation of Ti-Ni-Mo alloy powders is more useful than that of elemental powders of Ti, Ni and Mo. Ti50Ni49.9Mo0.1 shape memory alloy powders were prepared by gas atomization, and transformation temperatures and microstructures of those powders were investigated as a function of powder size. XRD analysis showed that the B2-R-B19 martensitic transformation occurred in powders smaller than 150 mu m. According to DSC analysis of the as-atomized powders, the B2-R transformation temperature (T-R) of the 25-50 mu m powders was 18.4 degrees C. The T-R decreased with increasing powder size, however, the difference in T-R between 25-50 mu m powders and 100-150 mu m powders is only 1 degrees C. Evaluation of powder microstructures was based on SEM examination of the surface and the polished and etched powder cross sections and the typical images of the rapidly solidified powders showed cellular morphology. Porous cylindrical foams of 10 mm diameter and 1.5 mm length were fabricated by spark plasma sintering (SPS) at 800 degrees C and 5 MPa. Finally these porous TiNi alloy samples are heat-treated for 1 h at 850 degrees C, and then quenched in ice water. The bulk samples have 23% porosity and 4.6 g/cm(3) density and their T-R is 17.8 degrees C. (C) 2012 Elsevier Ltd. All rights reserved.