Tailoring deformation and superelastic behaviors of beta-type Ti-Nb-Mn-Sn alloys.

A group of Ti-25Nb-xMn-ySn (in wt%; x = 2, 4 and y = 1, 5) alloys were designed using the "BF-d-electron superelasticity" empirical relationship and subsequently were cast in order to investigate their microstructure, deformation and superelastic behaviors. Monolithic β phase is found in all investigated alloys except in Ti-25Nb-2Mn-1Sn alloy which exhibits α"+β dual-phase microstructure. During compression testing, the Ti-25Nb-2Mn-1Sn alloy fails and demonstrates sufficient plasticity of ~ 41% and ultimate compressive strength of ~ 1800 MPa, where other alloys do not fail within the load capacity of 100 kN. Among all the investigated alloys, Ti-25Nb-4Mn-1Sn alloy exhibits the highest yield strength (~ 710 MPa) while Ti-25Nb-2Mn-1Sn alloy possesses the highest hardness (~ 244 HV). In this work, yield strength is influenced by solid solution and grain boundary strengthening while hardness is affected by the amount of constituent phases in each alloy. Additionally, Ti-25Nb-4Mn-1Sn shows highest recoverable strain (2.35%) and superelastic recovery ratio (90%) during cyclic loading-unloading up to 3% strain level, with highest total energy absorption among the investigated alloys. Moreover, all the Ti-25Nb-xMn-ySn alloys display shear bands except that Ti-25Nb-2Mn-1Sn alloy displays shear bands together with some cracks on the outer surface of compressively deformed morphologies.