The Influence of Strain on Texture Changes and Phase Transformations in the Quenched Ti_92.5Nb₅Mo_2.5 Alloy

The strain-induced martensitic transformation in a medical alloy from the ternary Ti-Nb-Mo system was studied. The low-doped Ti92.5Nb5Mo2.5 alloy was produced by arc remelting, followed by annealing, rolling at room temperature, reannealing, and water quenching. X-ray diffraction analysis showed that thermomechanical processing resulted in the alloy primarily consisting of orthorhombic martensite (& alpha;") with a small amount of the & beta;-titanium phase. Hysteresis loops were recorded in loading-unloading cycles with 1% strain increments up to a total strain of 4% under compression testing, employing a precision strain gauge. Young's modulus under loading varied from 51.2 GPa at the initial section to 39.7 GPa after a 2% residual strain. Young's modulus remains unchanged, within 74.3 GPa, during unloading. Elastic, pseudoelastic, and plastic strains were found to significantly depend on the previous strain within the first three loading-unloading cycles. To examine the impact of higher strains (up to 23.4%) on structural rearrangements and phase transformations, the samples were compressed without a precision strain gauge. X-ray diffraction analysis revealed that only the crystalline texture of the alloy changed after compression. Strains exceeding 23.4% were achieved by rolling at room temperature. After rolling to a strain of 64%, the diffraction patterns indicated an increased amount of the & beta;-phase, as evidenced by the (200) diffraction peak, not observed previously. The increased amount of the & beta;-phase suggests that strain prompted the reverse martensitic transformation (& alpha;" & RARR; & beta;).