INFLUENCE OF DEFORMATION ON TEXTURE CHANGES AND PHASE TRANSFORMATIONS IN THE quenched Ті_92.5Nb₅Мо_2.5 ALLOY

Abstract

The deformation-induced martensitic transformation in a medical alloy from the ternary Ti–Nb–Mo system was studied. The low-doped Ті_92.5Nb₅Мо_2.5 alloy was produced by arc remelting followed by annealing, rolling at room temperature, reannealing, and water quenching. X-ray diffraction studies showed that thermomechanical processing resulted in the alloy primarily consisting of orthorhombic martensite (α^") with a small amount of the β-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 displacement 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 deformations were found to significantly depend on the previous deformation within the first three loading–unloading cycles. To examine the impact of higher strains (up to 23.4%) structural rearrangements and phase transformations, compression was performed without a precision strain gauge. X-ray diffraction analysis determined 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%, diffraction patterns indicated an increased amount of the β-phase, as evidenced by the (200) diffraction maximum, which was not observed previously. The increased amount of the β-phase suggests that deformation prompted the reverse martensitic transformation (α^" → β).