Effects of processing on microstructure and mechanical properties of a titanium alloy (Ti-6Al-4V) fabricated using electron beam melting (EBM), Part 2: Energy input, orientation, and location

Selective electron beam melting (EBM) is a layer-by-layer additive manufacturing technique that shows great promise for fabrication of medical devices and aerospace components. Before its potential can be fully realized, however, a comprehensive understanding of processing-microstructure-properties relationships is necessary. Titanium alloy (Ti-6Al-4V) parts were built in a newly developed, unique geometry to allow accurate investigation of the following intra-build processing parameters: energy input, orientation, and location. Microstructure evaluation (qualitative prior-β grain size, quantitative α lath thickness), tensile testing, and Vickers microhardness were performed for each specimen. For a wide range of energy input (speed factor 30-40), small differences in mechanical properties (2% change in ultimate tensile strength (UTS) and 3% change in yield strength (YS)) were measured. Vertically built parts were found to have no difference in UTS or YS compared to horizontally built parts, but the percent elongation at break (% EL) was 30% lower. The difference in % EL was attributed to a different orientation of the tensile axis for horizontal and vertical parts compared to the elongated prior-β grain and microstructural texture direction in EBM Ti-6Al-4V. Orientation within the x-y plane as well as location were found to have less than 3% effect on mechanical properties, and it is possible a second order effect of thermal mass contributed to these results.