Theoretical analysis and design of Ti-based shape memory alloys correlating composition and electronic properties to transformation temperatures for high temperature applications

The influence of electronic parameters, such as the atomic number of the alloy (Z), valence electron concentration (c(v)), number of valence electrons per atom (e(v)/a ratio), and pseudopotential radius (P), on the phase transformation temperatures (M-s, A(s)) of binary, ternary and quaternary shape memory alloys (SMAs) based on Ti is investigated. These temperatures (M-s, A(s)) are correlated with the composition and ev/a of the alloys using multiple linear regression. The dependence of thermal hysteresis on the atomic radius of the alloys is also studied. The alloys investigated comprise of both low (e(v)/a < 5) and medium (5 < e(v)/a < 7.5) valence electrons groups. The phase transition temperatures are raised with an increase in ev/a ratio, Z and P for medium ev/a group alloys, while for low ev/a group alloys, the trend is quite the opposite. As c(v) increases, the transformation temperatures (TTs) decrease for the medium ev/a group, while they increase with c(v) for the low e(v)/a group. The two different trends observed for low and medium ev/a groups are explained in the light of elastic modulus of the alloys. The effect of Z, c(v), electron orbital occupancy and alloying elements on the elastic modulus, and in turn on the temperatures of transition of the alloys, is also discussed.