Influence of Er-doping on the microstructure and properties of β-Ti high temperature shape memory alloy

Abstract

The influence of Er-doping on the microstructure evolution and corresponding properties of Ti82-xNb16Al2Erx high temperature shape memory alloys were systematically investigated in the present study. A small number of Er-rich phases were observed except for the α″ martensite phase when Er content was above 0.3 at.%. The Er-rich phase accrued and agglomerated with the increasing of Er doping. The Er-rich phase would affect the nucleation and growth of martensite plates. The martensite morphology was featured with the fine martensite plates at the nearby of Er-rich phase. The martensitic transformation temperatures of Ti82-xNb16Al2Erx alloys decreased firstly and then increased as the Er contents increased, which was mainly ascribed to the variation of the matrix composition, grain refinement and the formation of the non-transformation Er-rich phase. It was noteworthy that the yield strength and fracture strength raised firstly and then dropped sharply. The yield strength and fracture strength up to 780Mpa and 902 MPa could be obtained in the Ti81Nb16Al2Er1 alloy. The shape memory properties could be optimized by doping the proper Er content. The maximum recoverable strain of 3.1% could be gained with 4% pre-strain.