Effect of laser energy density on tensile properties and strengthening mechanisms of laser powder bed fusion formed graphene-modified Titanium-matrix nanocomposites

To prepare titanium-matrix nanocomposites (TMNCs) with synergistic high strength and high toughness, the microstructure, tensile behaviour, and strengthening toughening mechanisms of 0.05 wt.% graphene modified TMNCs fabricated by laser powder bed fusion (LPBF) were investigated. The volumetric laser energy density (ϵ) was used as a variable parameter to analyze these characteristics. It revealed that at ϵ of 63.2 J/mm3, the laser printed TMNCs exhibited ultimate tensile strengths (UTS) of 1069 MPa at room temperature and UTS of 908 MPa at a test temperature of 300 °C. Upon increasing ϵ to 105.3 J/mm3, the UTS reached 1306 MPa at room temperature and UTS of 1038 MPa at 300 °C. Compared with pure Ti6Al4 V alloy, the graphene-modified TMNCs demonstrated significantly improved mechanical properties at various test temperatures. This enhancement was primarily attributed to (i) the uniformly distributed TiC nanoparticles with a nanorod structure, which were generated by the in-situ reaction between graphene and the Ti matrix; and (ii) these TiC nanoparticles refining the β columnar grains and improving the distribution of the acicular α′ martensite. This work confirms that the incorporation of graphene nanoscale reinforcement provides the significant strengthening-toughening effects for titanium alloys, offering insights into a design strategy for highperformance TMNCs.