Microstructure and properties of diamond/Ti6Al4V composites manufactured by laser melting deposition synchronously assisted by ultrasonic field

Laser melting deposition (LMD) of metal matrix composites often poses challenges such as inhomogeneous reinforcement distribution and coarse microstructures, which adversely impact the mechanical performance of these composites. In this study, an ultrasonic field was employed synchronously to assist the LMD process to fabricate diamond/Ti6Al4V composites. The effects of ultrasonic field on the microstructure and properties of the composites containing 2 vol% and 5 vol% diamond were systematically investigated. The findings indicate that partial diamond dissolution creates a dual reinforcement system of undissolved diamonds and in-situ TiC. In the as-deposited composites, the agglomeration of undissolved diamond particles is notably pronounced. The 2 vol% composite features primarily chain-like eutectic TiC with some granular particles, whereas the 5 vol% composite contains coarser chain-like eutectic TiC and minor dendritic primary TiC. Ultrasonic field application reduces undissolved diamond aggregation and refines chain-like and dendritic TiC into granular particles. The titanium matrix microstructure is significantly refined, with the α-Ti phase transforming from coarse elongated structures to fine laths and the β-Ti network fragmenting. These microstructural modifications increase the hardness of the 2 vol% and 5 vol% diamond reinforced composites, from 416.97 HV_0.5 and 489.39 HV_0.5 to 424.56 HV_0.5 and 504.51 HV_0.5, respectively. Concurrently, the wear rates decrease significantly from 116.958 × 10⁻⁵ mm³ N⁻¹ m⁻¹ and 104.715 × 10⁻⁵ mm³ N⁻¹ m⁻¹ to 81.290 × 10⁻⁵ mm³ N⁻¹ m⁻¹ and 69.002 × 10⁻⁵ mm³ N⁻¹ m⁻¹. The tensile strength increases by 14.4 % and 8.1 %, and the fracture strain by 24.4 % and 18.3 %, for the 2 vol% and 5 vol% composites respectively, enhancing overall composite performance.