Production of a Highly Porous Ti-Ni Shape Memory Alloy by Solid State Sintering of Rapidly Solidified Fibers

Abstract

Fibers of Ti50Ni50, Ti-49.Ni-75(50.25), Ti49.5Ni50.5 and Ti49.25Ni50.75 alloys were prepared by a melt overflow process. The martensitic transformation start temperature (M-s) of B2 -> B19' in Ti50Ni50 fibers is 52.4 degrees C. Upon increasing the Ni-content from 50 to 50.75 at%, the M-s of the B2-B19' transformation keeps decreasing. Cylindrical billets of Ni-rich Ti-Ni alloy with 75% porosity were produced by vacuum sintering using as-cast alloy fibers. Cyclic compression mechanical testing carried out on the porous specimens revealed shape memory deformation recovery of up to 0.91%, while the superelastic behavior resulted in reversible deformation of up to 4.31%. The permanent plastic strain resulting from the subsequent three cycles was only 0.78%. Because of the high porosity of the sintered specimen, an elastic modulus of about 3.2 GPa could be obtained.