Effect of temperature on the microstructure and tensile properties of micro-crack free hastelloy X produced by selective laser melting

The high-temperature behaviour of micro-crack free Hastelloy X produced by SLM has been studied. The microstructure and mechanical behaviour of as-built parts and heat-treated (at 1177 and 800 °C) parts were investigated. Quasi-static tensile tests were performed at room temperature and elevated temperatures (650, 750 and 850 °C) for the three heat treatment conditions. In order to better understand the tensile test performance, the microstructure evolution of as-built samples as function of temperature was studied using confocal scanning laser microscopy (CSLM). CSLM allows in situ observation of the microstructure evolution while the sample temperature is increased. During tensile testing, a significant decrease in tensile strain was observed at a testing temperature of 750 °C that was attributed to the precipitation of carbides and Mo-rich intermetallic phases, as observed during and after CSLM. The samples heated at 1177 °C showed less carbide formation due to their more homogeneous starting microstructure, which resulted in a tensile ductility increase as compared to the as-built and 800 °C heat-treated samples.