Improvement in mechanical strength of low-cost β-type Ti-Mn alloys fabricated by metal injection molding through cold rolling

In order to develop new low-cost and high-strength β-type titanium alloys, a Ti-13Mn was fabricated by metal injection molding. For improving its tensile strength, Ti-13Mn was subjected to cold-rolling at reduction ratios of 60% and 90%, respectively. The solutionized Ti-13Mn has pores and titanium carbide (Ti carbide) precipitates and consists of a β phase and an athermal ω phase. The porosity of the alloy decreases from 6.1% to 0.01% after cold-rolling at a reduction ratio of 90%. Moreover, during cold-rolling, the Ti carbides are fragmented and a deformation-induced ω phase is formed. The ultimate tensile strength, 0.2% proof stress, Vickers hardness, and Young's modulus of Ti-13Mn increase from 888 MPa to 1852 MPa, from 827 MPa to 1823 MPa, from 279 Hv to 461 Hv, and from 96 GPa to 108 GPa, respectively, after cold-rolling at a reduction ratio of 90%. On the other hand, the elongations of both the solutionized and cold rolled Ti-13Mn are less than 2%. Although the elongation of Ti-13Mn is less than 2%, the tensile strength of the cold rolled Ti-13Mn is extremely high compared with that of existing titanium alloys. This large-improvement in the tensile strength of the cold rolled Ti-13Mn is attributed to the increase in the dislocation density, decrease in grain size, decrease in porosity, and formation of a deformation-induced ω phase.