Martensitic microstructures and mechanical properties of as-quenched metastable β-type Ti–Mo alloys

Microstructures and tensile properties were investigated in metastable β-type Ti–10Mo, Ti–15Mo, and Ti–20Mo alloys after solution treatment. In addition to β phase, different martensitic structures with various sizes and morphologies were found in these alloys. In the Ti–10Mo alloy, acicular α″ plates were uniformly distributed in the β matrix. Transmission electron microscopy (TEM) revealed {111} α″-type twins had formed in α″ plates, and the orientation relationship between the β and α″ is close to (110) β//(001) α″, ( $$ 1\bar{1}2 $$ ) β//(110) α″, and [ $$ \bar{1}11 $$ ] β//[ $$ \bar{1}10 $$ ] α″. In the Ti–15Mo alloy, nanoparticles of athermal ω phase containing {112} β-type twins were observed in the β matrix. Smaller ω particles were found in the Ti–20Mo alloy than in the Ti–15Mo alloy. When tensile tested, the Ti–10Mo and Ti–15Mo alloys exhibited large plastic strains of 24 and 29 %, respectively, with ultimate tensile stresses of 756 and 739 MPa. The Ti–20Mo alloy displayed a higher ultimate tensile stress of 792 MPa but much smaller plastic strain (2 %). Although β phase dominates in all the metastable β-type Ti–Mo alloys, the nanostructured martensites also play an important role in the mechanical properties of the alloys.