Nickel - dependent spectral emissivity calibration maps and real-time microstructural monitoring of NiTi powders: An ex-situ pyrometry analysis for laser powder bed fusion
Year: 2025
Type: article
Abstract: The temperature dynamics during laser-powder bed fusion (L-PBF) plays a pivotal in governing the microstructure features and mechanical properties of printed NiTi parts. In this study, the influence of nickel concentration on the infrared emission characteristics of four NiTi powder compositions: Ni 50.1 at.% (pre-alloyed), Ni 50.6 at.% (pre-alloyed), Ni 52.1 at.% (pre-alloyed), and Ni 52 at.% (elementally blended) were investigated. A high-speed infrared (IR) pyrometer integrated into an optical microscope was employed for ex-situ acquisitions of voltage signals during controlled heating up to 1450 °C under inert atmosphere. Calibration curves were constructed for each NiTi chemical composition, enabling the estimation of spectral emissivity in the short-wave infrared range (SWIR) of 1580 nm to 1800 nm. Experimental results revealed moderate variations in the calibration curves between the pre-alloyed NiTi powders. In contrast, the curves for the blended Ni 52 at.% revealed significant shift towards right, highlight different thermal behavior. Spectral emissivity results showed a steep rise to ∼1200 °C, followed by a steady-state regime for pre-alloyed powders. Overall, a higher emissivity of around 0.52 was observed in the temperature range of 1100 °C to 1450 °C for the Ni 52.1 at.%, whereas the Ni 50.6 at.% and Ni 50.1 at.% powders exhibited a slightly lower range (0.45–0.48) values. The real-time microstructure visual imaging revealed powder oxidation started approximately after 700 °C for all the pre-alloyed powders, followed by powder coalescence beyond 1100 °C, which are in consistent with the spectral emissivity variations. X-ray photoelectron spectroscopy (XPS) analysis revealed temperature-dependent surface oxidation behavior in NiTi powder, characterized by the progressive emergence of Ti 4+ /Ti 3+ states, dynamic evolution of lattice and adsorbed oxygen species, and the absence of distinct Ni 2p features across annealed conditions (i.e., 650 °C to 1450 °C). These findings provide valuable insights into the thermal-dependent spectral emissivity of NiTi powders and supports the development of optimized process parameters for high-quality LPBF of NiTi components.
Source: Measurement
Authors: Rakesh Bhaskaran Nair, Eanna McCarthy, Robert O’ Connor, David Kinahan, Dermot Brabazon
Language: English
Subfield: Mechanical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,760
Award: G7275882595
OpenAlex ID: W7101423440