Densification behaviour of laser powder bed fusion processed Ti6Al4V: Effects of customized heat treatment and build direction

Abstract

The present work exploits the customized heat treatment, and laser powder bed fusion process to build direction effects on the densification behaviour and microstructural development in Ti6Al4V alloy. Optical microscopy evaluates the porosity and microstructure in different conditions. Further, the porosities are classified as inter-micropores (size < 10 µm) and super-micropores (size > 10 µm). Classification and quantifications of the porosities of laser powder bed fusion processed Ti6Al4V alloy under both directions due to customized heat treatment. The effect of customized heat treatment, the corresponding pore self-healing mechanism, and microstructure refinement on laser powder bed fusion-processed Ti6Al4V alloy were discussed. Moreover, the X-ray diffraction technique was used to analyse the different phases during laser powder bed fusion and customized heat treatment. The elevated customized heat treatment helps to reduce the overall porosity by two times that of as-printed samples due to the sintering self-healing phenomenon. Interestingly, the super micropores observed in as-printed samples are reduced via customized heat treatment ∼ 44% in a horizontal direction and ∼ 46% in a vertical direction, respectively, which is favourable for enhancing mechanical properties. This is because reducing these micropores leads to improved ductility. The ductility of the customized heat treatment executed sample was ∼ 68% in a horizontal orientation and ∼180% in a vertical orientation. The isotropic index for ductility in as-printed Ti6Al4V in the horizontal and vertical directions is 0.61. In contrast, it is 0.97 for customized heat treatment in both orientations showing high isotropy for customized heat treatment samples compared to as-printed samples. This study reveals that the customized heat treatment technique can be beneficial in introducing isotropic microstructure and densifying the distinctive laser powder bed fusion components.