Effect of processing conditions on the microstructure, porosity, and mechanical properties of Ti-6Al-4V repair fabricated by directed energy deposition

In this study, the effect of processing parameters in directed energy deposition (DED) additive manufacturing (AM) on the microstructure and mechanical properties of Ti-6Al-4V was evaluated. A commercial DED system was used to deposit square patches of Ti-6Al-4V onto a substrate with the same nominal composition, with varying conditions to represent those that may be found in actual repair applications. A design of experiments was used to study the effect of substrate thickness, interlayer dwell time (time between deposition of subsequent layers), initial substrate temperature, hatch pattern, and number of deposited layers on the microstructure, porosity, and hardness of the deposition. Varying these processing parameters elucidates how each independently, or all collectively, impact the resulting microstructure and properties of Ti-6Al-4V deposits. As internal pores, or defects, significantly affect the properties of additively manufactured components, this study aimed to identify and quantify those defects in DED. The results from the current study show that with decreasing substrate thickness, the depth of the heat affected zone increased by an average of 400 μm. The density of the part was affected by the number of deposited layers and the initial substrate temperature, increasing with increasing the number of deposited layers, but decreasing with higher initial substrate temperatures. Lastly, the hardness increased with increasing substrate thickness, but was not impacted significantly by the other parameters studied.