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

The interior porous defects formed during the layer-by-layer fabrication process have attracted increasing attention for different additive manufacturing (AM) techniques and are regarded as a crucial factor affecting the overall performance. In this work, aiming at the cold spray Ti6Al4V bulk materials, the hot isostatic pressing (HIP) treatment is adopted to reduce the interior defects, adjust the microstructure, and improve the mechanical properties. To characterize the pore morphologies and porosity evolution, the CS Ti6Al4V sample is characterized by optical microscopy and X-ray computed tomography (XCT). The 3D reconstructions by XCT show that the fully dense Ti6Al4V alloy can be obtained through the high temperature diffusion and high pressure compacting of the HIP sample. After the HIP treatment, the severely deformed grains experience an obvious growth with the uniformly distributed beta precipitates around equiaxed alpha grains. The tensile test shows that the strength of CS Ti6Al4V alloys can be largely improved by the enhanced diffusion and resultant metallurgical bonding. With the HIP treatment, the CS samples exhibit highly densified morphology and adjusted micro-structure that can benefit the improvement of mechanical properties.