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Microstructure and Mechanical Property of High Strength and High Toughness Titanium Alloy by Laser Deposition Manufacturing

In this study, the high strength and high toughness Ti-6Al-3Mo-2Sn-2Zr-2Cr alloy was fabricated by the laser deposition manufacturing (LDM) technology. The effect of process parameters on the forming quality of LDMed alloy was studied. The microstructure and mechanical properties of LDMed Ti-6Al-3Mo-2Sn-2Zr-2Cr alloy was deeply analysed by the optical microscope, scanning electron microscope, tensile tester and impact tester. The results show that the optimized process parameters are as follows: laser power is 2.4 kW, scanning speed is 10 mm/s and scanning interval is 2.4 mm. Due to the temperature gradient, the LDMed titanium alloy shows obvious microstructure anisotropy exhibiting fine β equiaxed grain in scanning direction (XY direction), but shows coarse β columnar grain in deposition direction (Z direction). The micro-morphology exhibits classic dual-phase microstructure with basket appearance composing of equally distributed α phase and metastable β-transformed phase. Due to the grain boundary strengthening effect, obvious mechanical anisotropy can also be observed in LDMed titanium alloy showing a higher tensile strength, lower plasticity and impact toughness in XY direction, but reverses in Z direction.