Investigation of the mechanisms by which hot isostatic pressing improves the fatigue performance of powder bed fused Ti-6Al-4V

•Analysis of literature data provides insight into the mechanisms by which HIP improves fatigue life.•HIP improves fatigue life of PBF Ti-6Al-4V by decreasing the fraction of the defect population that can initiate fatigue cracks and by changing the microstructure surrounding defects.•The idea that microstructure near defects evolves differently than the microstructure away from defects during HIP treatment is supported by EBSD orientation maps.•The gained understanding provides initial guidance on HIP soak parameters (Temperature-Pressure-Time) to improve high cycle fatigue performance in PBF Ti-6Al-4V. Hot isostatic pressing (HIP) is often needed to obtain powder bed fused (PBF) Ti-6Al-4V parts with good fatigue performance. This manuscript attempts to clarify the mechanisms through which HIP treatment acts to improve high cycle fatigue performance. Several mechanisms are considered and examined against experimental data sets available in the literature. The results suggest that HIP may act most significantly by decreasing the fraction of the defect population that can initiate fatigue cracks, both by decreasing defect sizes below a threshold and by changing the microstructure that surrounds defects. Given the novelty of the latter conclusion, an electron backscatter diffraction microscopy study was performed for validation. The gained understanding provides initial guidance on the choice of optimum HIP soak parameters (Temperature-Pressure-Time) for the high cycle fatigue performance of PBF Ti-6Al-4V.