The influences of melting degree of TiC reinforcements on microstructure and mechanical properties of laser direct deposited Ti6Al4V-TiC composites

Highlights: • The melting degree of reinforced TiC was controlled by the laser energy density and the TiC content. • The high melting degree of reinforced TiC caused the formation of dendritic carbides, inducing premature failure. • The detrimental dendritic carbides were eliminated by adjusting the laser deposition conditions and reinforced TiC size. • The improved mechanical properties and strengthening mechanisms for different melting degrees of TiC were investigated. This study is concerned with the influences of melting degree of embedded TiC reinforcements on microstructure and mechanical properties of laser direct deposited Ti6Al4V-TiC composites and a functionally graded material. 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 premixed TiC content increased from 0 to 15 vol% while a true strain of 0.141 ± 0.002 was still retained for 15 vol% TiC. The primary strengthening mechanism for composites with the most melting control of TiC is the solid solution strengthening induced by carbon, while that for the least melting control is dominated by the unmelted TiC particulates and the refined microstructure resulting from the resolidified carbides. The defect-free functionally graded Ti6Al4V-TiC with 0 to 40 vol% TiC achieved an increased hardness from HRC ~ 39 to HRC ~ 65.