Find in Library

The accurate prediction of alloying effects on the martensitic transition temperature (<i>M</i>_s) is still a big challenge. To investigate the composition-dependent lattice deformation strain and the <i>M</i>_s upon the <i>β</i> to <i>α</i>″ 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 <i>M</i>_s by comparing it with the available measurements. The largest elongation and the largest compression due to the lattice strain occur along ±[011]<i>_β</i> and ±[100]<i>_β</i>, respectively. As compared to the overestimation of the <i>M</i>_s from existing empirical relationships, an improved <i>M</i>_s estimation can be realized using our proposed empirical relation by associating the measured <i>M</i>_s with the energy difference between the <i>β</i> and <i>α</i>″ phases. There is a satisfactory agreement between the predicted and measured <i>M</i>_s, implying that the proposed empirical relation could accurately describe the coupling alloying effect on <i>M</i>_s. Both Al and Ta strongly decrease the <i>M</i>_s, which is in line with the available observations. A correlation between the <i>M</i>_s and elastic modulus, <i>C</i>₄₄, is found, implying that elastic moduli may be regarded as a prefactor of composition-dependent <i>M</i>_s. This work sheds deep light on precisely and directly predicting the <i>M</i>_s of Ti-containing alloys from the first-principles method.