Influence of evolution in reinforcement scale characteristic parameters on the microstructure and properties of Ti6Al4V-TiBw composites fabricated by electron beam powder bed fusion

The size, aspect ratio, and distribution of reinforcement, referred to as the scale characteristic parameters (SCP), are critical factors that influence the mechanical properties of discontinuous reinforced titanium matrix composites (DRTMCs). To investigate the impact of SCP evolution on the microstructure and mechanical properties of TiBw, this study employed spherical Ti6Al4V-TiBw composite powder prepared by electrode induction melting gas atomization (EIGA) as feedstock for fabricating Ti6Al4V-TiBw composites through electron beam powder bed fusion (EB-PBF) process. By implementing a two-step rapid cooling approach in EIGA and EB-PBF processes to “freeze” the TiBw at nanoscale within Ti6Al4V-TiBw composites, a significantly wider regulation window for microstructure and mechanical properties was achieved. Subsequently, heat treatment was conducted at temperatures ranging from 850 to 1200 °C to systematically elucidate the mutual influence regulation among SCPs, microstructure, and mechanical properties of TiBw. Based on our findings, it can be concluded that when subjected to heat treatment temperatures higher than 950 °C, an orientation relationship between TiBw and α-Ti is observed: {0001} _α-Ti//{001} _TiBw, {11 $\bar{2}$ 0} _α-Ti//{010} _TiBw, {10 $\bar{1}$ 0} _α-Ti//{100} _TiBw. Additionally, the cross-section of columnar-shaped TiBw exhibits semi-coherent interfaces with coherent interfaces bonded to Ti along its (100) crystal plane while displaying incoherent interfaces with Ti matrix along its (101) and (10 $\bar{1}$) crystal planes. The strength of Ti6Al4V-TiBw composites exhibited a trend of initial increase followed by decrease with the evolution of TiBw scale characteristic parameters, while the elongation demonstrated an overall decreasing pattern. This research aims to establish a foundation for microstructure and properties control of DRTMCs and provide experimental references and theoretical basis for high-performance DRTMCs research.