In-situ synthesis of Ti6Al4V-TiC composites with controlled microstructure and mechanical properties by additive manufacturing

This study is concerned with in-situ synthesis of functionally gradient Ti6Al4V embedded with TiC reinforcements. Especially, the influences of melting degree of embedded TiC reinforcements on microstructure and mechanical properties of laser direct deposited Ti6Al4V-TiC composites are described. The melting degree of embedded TiC was controlled by the input laser energy density and the added TiC content. The formation of detrimental primary dendritic TiC grains was successfully avoided by properly adjusting the deposition conditions and the particle size range of TiC reinforcements. The resultant compression test revealed the ultimate strength increasing from 1381 ± 19 MPa to 1636 ± 23 MPa as the TiC content increased from 0 to 15 vol.% while ductility of 0.141 ± 0.002 was still retained for 15 vol.% TiC. The defect-free functionally graded Ti6Al4V-TiC with 0 to 40 vol.% TiC achieved an increased hardness from HRC ~39 to HRC ~65. The presentation will also reveal the formation mechanism and process of resolidified dendritic TiC_x in directed energy deposited Ti-40vol.%TiC composite via a combination of a thermodynamic consistent phase field (PF) model and a thermo-fluid model.