Correlating Microstructure and Residual Stress Improvement in HIP Processed LPBF Ti6Al4V Using Nanoindentation Property Mapping

Integrating microscale mechanical mapping with microstructural and residual-stress analysis provides a robust approach to establishing process–structure–property relationships at a fine scale in additively manufactured (AM) metals. This study examines the microscale mechanical response of Ti-6Al-4V fabricated by laser powder bed fusion (PBF-LB), followed by hot isostatic pressing (HIP) as a post-process, alongside a conventionally processed (CP) sample as a baseline reference for wrought material. Microstructural and nanoindentation mapping, combined with porosity analysis, showed that as-printed (AP) samples exhibited higher hardness (5.74 GPa) due to a fine α′ martensitic network, with 1.927% porosity. HIP reduced porosity to 0.014% and transformed the microstructure to a coarsened α + β phase, yielding slightly lower hardness (5.61 GPa). The CP condition displayed negligible porosity, a fine equiaxed α + β microstructure, and the lowest hardness (4.79 GPa). A coefficient of variation (CV%) analysis further revealed greater hardness variability in HIP than in AP, attributable to their differing β-phase fractions. Residual stress measurements indicated high tensile stress in AP (0.275 GPa), a uniform, near-stress-free state with minimal tensile stress in HIP (~ 0.02 GPa), and moderate tensile stress in CP (0.129 GPa). The experimental results fell within the simulated range, confirming consistency between the two approaches. Validation of experimental and simulated residual-stress results demonstrates the effectiveness of integrating nanoindentation–electron backscatter diffraction (EBSD) mapping to precisely characterize localized mechanical behavior, thereby supporting structural reliability and performance-driven design in AM metals.