Phase transformation and microstructure and mechanical properties of as cast NiTiRe shape memory alloys

AbstractThe microstructure, martensitic transformation and mechanical properties of as cast Ni52Ti48−xRex shape memory alloys (SMAs) were investigated. The microstructure of these alloys consists of B19′ martensite phase as a matrix and B2 austenite in small percentages in addition to some precipitations of NiTi intermetallic compounds. There are two types of NiTi precipitates: the first one is Ti2Ni, which can be seen in the all microstructures of the three alloys, and the other is Ni2Ti, which is found only in the microstructure of Ni52Ti47·7Re0·3 alloy. According to differential scanning calorimetry measurements, one stage of transformation reaction B2 to B19′ accompanied with forward and backward martensitic transformation was observed. The martensitic peak and the austenitic peak were increased with the addition of rhenium. Both are increased as the number of valence electron per atom increase and the valence electron concentration decrease. Hardness measurements of Ni52Ti48−xRex SMAs are improved by...