Alloying Effect on Transformation Strain and Martensitic Transformation Temperature of Ti-Based Alloys from Ab Initio Calculations

The accurate prediction of alloying effects on the martensitic transition temperature (M-s) is still a big challenge. To investigate the composition-dependent lattice deformation strain and the M-s upon the beta to alpha '' phase transition, we calculate the total energies and transformation strains for two selected Ti Nb Al and Ti Nb Ta ternaries employing a first-principles method. The adopted approach accurately estimates the alloying effect on lattice strain and the M-s by comparing it with the available measurements. The largest elongation and the largest compression due to the lattice strain occur along +/-[011](beta) and +/-[100](beta), respectively. As compared to the overestimation of the M-s from existing empirical relationships, an improved M-s estimation can be realized using our proposed empirical relation by associating the measured M-s with the energy difference between the beta and alpha '' phases. There is a satisfactory agreement between the predicted and measured M-s, implying that the proposed empirical relation could accurately describe the coupling alloying effect on M-s. Both Al and Ta strongly decrease the M-s,M- which is in line with the available observations. A correlation between the M-s and elastic modulus, C-44, is found, implying that elastic moduli may be regarded as a prefactor of composition-dependent M-s. This work sheds deep light on precisely and directly predicting the M-s of Ti-containing alloys from the first-principles method.