Shape memory characteristics of porous Ti-Ni-Mo alloys prepared by solid state sintering

Abstract

Ti50Ni49.7Mo0.3, TisoNi(49.6)Mo(0.4) and Ti50Ni49.5Mo0.5 alloy fibers were prepared by a melt overflow process. Two-step B2-R-B19' transformation was observed in the rapidly solidified Ti-Ni-Mo fibers. Upon increasing the Mo-content from 0.3 to 0.5 at.%, the austenite transformation finish temperature (A(f)) of R -> B2 decreased from 43 to -42 degrees C. Porous shape memory alloy pellets with 75% porosity were fabricated by a vacuum sintering technology, using the alloy fibers. Mechanical properties and shape memory effect of the highly porous TisoNi(49.6)Mo(0.4) alloy, of which Af is lower than room temperature, were investigated using a compressive test. The plateau of a stress-strain curve was observed at about 2 MPa and resulted in 5% elongation associated with stress-induced martensitic transformation. It was also found that a recovered strain was 1.8% on heating after the compressive deformation. Because of the high porosity of this specimen, an elastic modulus of 0.91 GPa could be obtained. (C) 2016 Elsevier Ltd. All rights reserved.