Effects of heat input on layer heterogeneity of selective laser melting Ti-6Al-4V components

Due to the layer-by-layer manufacturing characteristics, metallurgical process of selective laser melting (SLM) is inherently different in the building direction because of varying conditions, thereby resulting inter-layer heterogeneity. To mitigate such anisotropy, it is of great significance to understand the effects of processing parameters on the property evolution and thus metallurgy of fabrication process. This research proposes one-factor-at-a-time experiment to investigate the influences of laser power and scanning speed on the surface quality, microstructures and mechanical properties of selective laser melted Ti-6Al-4V parts. Surface quality is assessed by roughness around the printings while mechanical properties are evaluated through microhardness and tensile strengths. Phases in microstructure are quantified by XRD to correlate with mechanical properties. Fracture morphology is analyzed to understand the effect of defects and microstructure on mechanical performance. The optimized parameter corresponding to best surface quality and mechanical properties has been found respectively in laser power of 190 W and scanning speed of 800 mm/s. After optimization, surface roughness has decreased by 44.47% for upper surface. Yielding strength, tensile strength and elongation rate have improved by 13.17%, 43.34% and 64.51%, respectively, with similar hardness and Young’s modulus. In addition, heterogeneity of mechanical properties has great improvement by a range of 31.63%−92.68%.