Shape memory behavior of Ti–20Zr–10Nb–5Al alloy subjected to annealing treatment

Abstract

The effects of annealing temperature on microstructures, phase transformation, mechanical properties, and shape memory effect of Ti–20Zr–10Nb–5Al alloy were investigated. X-ray diffraction (XRD) patterns show that the alloy is composed of single hexagonal α′-martensite phase for both as-rolled sample and sample annealed at 773 K for 30 min, while single orthorhombic α″ phase exists in the samples annealed at 873 and 973 K for 30 min. The optical observations indicate that the alloy is recrystallized when annealed at 873 K, and the grain size of the sample annealed at 973 K is about five times larger than that annealed at 873 K. Both of the samples annealed at 873 and 973 K show almost the same reverse martensite transformation start temperature of 483 K as demonstrated by thermal dilatation tests. The critical stress values for martensite reorientation (σ _M) are 392 and 438 MPa for the alloys annealed at 873 and 973 K, respectively. The maximum shape memory strain is 2.8 %, which is obtained in the alloy annealed at 873 K due to the lower σ _M. Moreover, the sample annealed at 873 K exhibits larger tensile stress and tensile strain due to the smaller grain size.