Nanoindentation-based mapping of phase-dependent mechanical response in additively manufactured NiTi alloys
Аннотация
Nickel-Titanium (NiTi) shape memory alloy specimens were fabricated using Laser Powder Bed Fusion (L-PBF) to investigate the influence of processing parameters on localized mechanical response. Rather than relying solely on bulk-averaged properties, this study implements high-density nanoindentation mapping (up to 2500 indents per sample) to resolve spatial variations in Young’s modulus, hardness, and energy dissipation at the microscale. The mechanical maps were correlated with microstructural features identified by SEM and room-temperature XRD, enabling assessment of phase-dependent heterogeneity associated with B19′ martensite, retained B2 austenite, and defect-rich regions. While volumetric energy density (VED) was used as a comparative parameter, the results demonstrate that identical VED values can yield distinct local mechanical behavior due to differences in scan speed and hatch spacing. Intermediate energy input conditions promoted improved densification and reduced porosity, whereas insufficient or excessive energy input introduced mechanical variability linked to melt pool instability. Phase fractions were estimated using XRD peak integration and interpreted in conjunction with mechanical mapping. The findings establish a structure–property framework for understanding microscale mechanical heterogeneity in L-PBF NiTi alloys relevant to functional applications.