Microstructures and Mechanical Properties of Carbon-Added Ti Composites Fabricated by Laser Powder Bed Fusion or Spark Plasma Sintering

The densification process plays a critical role in determining the microstructure and performance of Ti matrix composites (TMCs). Herein, a comparative study was performed on a graphene oxide (GO)/Ti-6Al-4V composite fabricated by laser powder bed fusion (L-PBF) and spark plasma sintering (SPS). The flexible GO sheets were homogeneously decorated onto the Ti-6Al-4V powders via an electrostatic self-assembly without significantly changing the particle size or sphericity. Under high-energy laser irradiation, the GO sheets were completely dissolved into the matrix. The L-PBF-produced composite was composed of fine alpha' martensite structures due to the rapid solidification and the solute carbon atoms. In contrast, the GO was reacted with Ti matrix and completely transformed into submicron TiC particles during SPS; the composite consisted of alpha + beta phases with randomly dispersed TiC. Moreover, the L-PBF-produced composite exhibited a higher hardness of 481HV as compared with the SPS-produced one of 367HV, attributing to the fine alpha' microstructures and high residual stresses. The present work offers deep understanding on the structural evolution of GO during high-temperature densifications, and shows new insights for fabrication of high-performance TMCs with tailored microstructures.