High temperature back-stress strengthening by heterogeneous nano TiBw in TC4 alloy

Back-stress strengthening has been proven to be an effective strategy in breaking the room temperature strength–ductility dilemma in hetero-structural metals matrix composite materials, which is difficult to achieve at high-temperature because of grain boundaries softening, dislocation annihilation and grain rotation. Hence, we induced back-stress strengthening to improve the high-temperature tensile properties of Ti alloy by the heterogeneous distribution of nano TiB whisker (TiBw). In this work, electron beam powder bed fusion (EB-PBF) with rapid solidification technology was employed to in-situ generate heterogeneous nano TiBw at both grain boundaries (GBs) and grain interiors. Grains can be significantly strengthening by high temperature back-stress due to the effective blockage of dislocation movement, grain boundary migration and grain boundary slip by nano-TiBw on GBs. Remarkably, intragranular nano TiBw (IG nano-TiBw) dramatically enhances the dislocation storage density. The heterogeneous distribution of nano TiBw achieves a 50°C increase in the service temperature of TC4 alloy.