Microstructure and mechanical properties of Ti-2Al alloyed with Mo formed in laser additive manufacture

A series of Ti-2Al-yMo (y = 2,5,7,9,12) alloy samples were produced from blended elemental Ti, Al and Mo powders using the laser solid forming technology. The influence of the beta stabilizer Mo on the morphology of the grains, the size and the distribution of the a laths, the Vickers hardness and the tensile properties of Ti-2Al-yMo alloys were explored under designated laser processing parameters. It was found that the microstructure in Ti-2Al-5Mo, Ti-2Al-7Mo, Ti-2Al-9Mo, and Ti-2Al-12Mo deposited layers were composed of irregular columnar grains that grow epitaxially, with some small equiaxed grains in the upper region, while that of the Ti-2Al-2Mo alloy was composed of large columnar grains. The grain size decreased, while the thickness of equiaxed grains layer increased with increasing Mo content. This indicates a tendency towards columnar-to-equiaxed transition with increasing Mo. The dominant b grains form a basketweave microstructure composed of primary a laths, secondary a laths and retained b phase. It was also observed that with increasing Mo content, both the size of primary a laths and secondary a laths decreased significantly, while the number of secondary a laths increased sharply, and the Ti-2Al-12Mo is also constituted of a phase and b phase. The Young's modulus of Ti-2Al-7Mo, Ti-2Al-9Mo, and Ti-2Al-12Mo were basically the same within experimental error. Tensile testing of the specimens showed that Ti-2Al-7Mo exhibits a good combination of strength and elongation to failure. As a result, this material can be considered suitable as a viable feedstock for laser additive manufacturing. (C) 2017 Published by Elsevier B.V.