Microstructure and mechanical properties of laser powder bed fusion Ti-6Al-4V after HIP treatments with varied temperatures and cooling rates

Abstract

This work investigated non-standard HIP cycles for PBF-L Ti-6Al-4V and characterized microstructure and tensile properties to compare between material that originated from the same build. For 920 °C, faster cooling rates (100 °C/min, 2000 °C/min) were found to promote bi-lamellar α microstructure, while the 2000 °C/min cooling rate improved the strength. For HIP with lower temperature (800 °C, 200 MPa), coarsening was minimized resulting in strength improvement. The slow cooling rate (12 °C/min) showed the highest strength as faster rates increased the amount of orthorhombic martensite (${\alpha }^{″}$). For HIP with higher temperature (1050 °C), the as-built crystallographic texture was reduced and equiaxed prior-β grain morphology resulted, leading to more isotropic tensile properties. However, the cooling rate (2000 °C/min) was not enough to prevent formation of grain boundary α, which reduced strength and elongation. Machine learning was carried out on the dataset via Principal Component Analysis (PCA) to reduce the dimensionality of the parameters and microstructural features.