Abstract
Refining microstructure is an important issue for laser additive manufacturing (LAM) of titanium alloy. In the present work, the microstructures of LAM-fabricated Ti6Al4V alloy were refined using a low energy density with the combination of a small spot diameter, a low laser power, and a high scanning speed. The microstructure, hardness, wear performance, and molten pool thermal behavior of LAM-fabricated Ti6Al4V coatings were studied. The results show that the grain sizes of both prior β and α phases are strongly dependent on the cooling rate of the molten pool. The fine prior β grains and submicron-scale acicular α phases were obtained under a low energy density of 75 J mm−2 due to the high cooling rate of the molten pool. In addition, the as-fabricated Ti6Al4V sample with submicron-scale acicular α phase showed a very high hardness of 7.43 GPa, a high elastic modulus of 133.6 GPa, and a low coefficient of friction of 0.48. This work provides a good method for improving the microstructure and mechanical performance of LAM-fabricated Ti6Al4V alloy.
Highlights
Titanium and titanium alloys have been widely used in many industries, especially aerospace, energy, and biomedical industries, due to their high specific strength, excellent corrosion resistance, and good biocompatibility [1,2,3]
The solidification microstructure is related to the thermal behavior of the molten pool
Ti6Al4V coatings were fabricated by laser additive manufacturing (LAM) with different processing parameters
Summary
Titanium and titanium alloys have been widely used in many industries, especially aerospace, energy, and biomedical industries, due to their high specific strength, excellent corrosion resistance, and good biocompatibility [1,2,3]. LAM with coaxial powder feeding generally uses a high-energy laser to simultaneously melt and deposit metal powders onto a substrate and fabricates parts layer by layer. During the LAM process, the rapid cooling of the molten pool creates a high cooling rate, a steep temperature gradient, and a non-equilibrium solidification. These processing features generally lead to special microstructures and mechanical properties of LAM-fabricated parts, compared to conventional manufacturing techniques. LAM-fabricated titanium alloys often exhibit high strength due to refined microstructure and low ductility due to the high level of residual stress [7,15,16,17,18]
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