TiAl/RGO (reduced graphene oxide) bulk composites with refined microstructure and enhanced nanohardness fabricated by selective laser melting (SLM)

This work for the first time investigated the effect of laser scan line spacing on the microstructure, phase evolution and nanohardness of Ti-48Al-2Cr-2Nb/RGO (reduced graphene oxide) metal matrix composites (MMCs) fabricated by selective laser melting (SLM). The results show that with increasing the laser scan line spacing from 80 to 140 mu m, the average grain size generally decreases from 10.13 to 8.12 mu m. The SLM-processed Ti-48Al-2Cr-2Nb/RGO parts are dominated by high-angle ( > 15 degrees) grain boundaries (HAGBs) and alpha(2) (Ti3Al) phase. With the increase in laser scan line spacing, the contents of HAGBs and alpha(2) phase both decrease. Due to instantaneous high temperature during the SLM process, some RGO sheets transform to amorphous carbon. The nanohardness of SLM-processed Ti-48Al-2Cr-2Nb/RGO parts increase from 8.13 +/- 0.39 GPa to 9.85 +/- 0.46 GPa when increasing the laser scan line spacing from 80 to 140 mu m, which is much higher than that of the traditional casting TiAl counterparts (4.98 +/- 0.10 GPa).