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

• Porous Ti-Ni-Mo bulks with 75% porosity were synthesized using the alloy fibers.
• Strain of stress-plateau associated with the stress-induced B2 → B19′ transformation was 5%.
• Elastic modulus of the porous Ti-Ni-Mo alloy was as small as about 1 GPa.
• Small elastic modulus is ascribed to the high porosity of Ti-Ni-Mo shape memory alloys.

Ti50Ni49.7Mo0.3, Ti50Ni49.6Mo0.4 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 (Af) of R → B2 decreased from 43 to −42 °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 Ti50Ni49.6Mo0.4 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.

Figure optionsDownload as PowerPoint slide