Effect of hot isostatic pressing (HIP) on microstructure and mechanical properties of Ti6Al4V alloy fabricated by cold spray additive manufacturing

Cold spray (CS) technique has attracted increasing attention as an effective additive manufacturing method. It allows the fabrication of high-quality bulk materials through the solid-state deposition at a temperature lower than melting point. However, the interior defects such as pore and crack cannot be completely eliminated in the cold-sprayed samples. Such defects may act as stress raiser and crack initiations under loading. In this work, aiming at the N2 and He-processed Ti6Al4V samples, the hot isostatic pressing (HIP) with high temperature and pressure was adopted to reduce the interior defects, adjust the microstructure and improve the mechanical properties. To characterize the pore morphologies and porosity, cold sprayed Ti6Al4V sample is characterized by optical microscope and X-ray computed tomography. The effect of HIP treatment on microstructure evolution was studied by scanning electron microscopy (SEM) and EBSD. The microhardness and tensile properties were also investigated. The results showed that the residual pores caused by insufficient particle deformation can be removed by the HIP treatment. The tensile test showed that ductility of CS Ti6Al4V can be largely improved by the enhanced diffusion and metallurgical bonding. Thus, HIP treatment is a promising method to densify the CS coating and improve the mechanical properties.