Formation of dual quasi-continuous networked structure and its strengthening effect in Ti-6Al-4V alloy reinforced with graphene via powder bed fusion

A dual-networked distribution of the reinforcements holds promise for achieving a balance between high-strength and moderate plasticity in titanium matrix composites (TMCs). Unfortunately, achieving this improvement in TMCs via additive manufacturing (AM) methods, presents significant challenges. Those challenges arise from the inherent differences in chemical and physical properties, which often led to agglomeration of the reinforcement and cracks caused by the high thermal residual stresses. To overcome those issues, this study focuses on the development of Ti-6Al-4V (Ti64) alloys incorporated with 0.5 wt% graphene nanosheets (GNSs) constructing a dual quasi-continued TiC network structure via powder bed fusion. The results exhibited a super-high tensile yield strength (1307 MPa), accompanied by a moderated elongation of 2.6% with reduced residual stress. The microstructure, phase contents, and mechanical performance were thoroughly investigated. A thermo-metallurgical-mechanical coupling model was developed, considering factors such as laser absorption effects and laser scanning strategy. Finally, a reasonable dual-network model was built to elucidate the contribution of various strengthening factors. Overall, this study illustrates that the strength of GNS/Ti64 composites is affected by the factors of GNS distribution, quasi-continue network in-situ TiC particles, temperature and residual stress field, offering a reference for fabricating high-strength nanocarbon/Ti64 composites by AM methods.