Analysis of real-time thermal signatures and Scheil simulation for track geometry, microstructure, and phase formation in LMD of NiCoCrAlY for gas-turbine components

Abstract

This study presents an integrated approach combining real-time process temperature monitoring and Scheil-based CALPHAD simulations to investigate the process–structure–property relationship in laser metal deposition (LMD) of NiCoCrAlY tracks on an Inconel 718 substrate, aimed at gas turbine applications. Real-time thermal signatures captured by an IR pyrometer were analyzed to correlate those with track geometry, microstructure, phase formation, and mechanical properties. Concurrently, Scheil-based CALPHAD simulations, validated through XRD and Rietveld refinement, were used to predict phase evolution based on compositional changes induced by varying process parameters. The β-NiAl (BCC) and γ-Ni (FCC) phases were identified as dominant constituents, with their relative proportions highly sensitive to dilution, governed primarily by scan speed rather than power. Increased scan speed led to greater dilution and higher γ-Ni fraction, reducing β-NiAl content from 58 % to 14 %, which directly correlated with a drop in microhardness from 510 to 346 HVN₀.₂. Thermal analysis revealed that melt pool life and peak temperature, rather than cooling rate, exhibited a strong correlation with resulting mechanical properties. A longer melt pool life (180–230 ms) and a peak temperature around 1940–2000 °C are attributed to β-dominated microstructures with enhanced hardness. The optimized track, produced at 800 W and 600 mm/min, demonstrated a scratch hardness of 2.85 ± 0.22 GPa, more than twice that of the substrate, indicating superior wear resistance. This study highlights that combining thermal signature analysis with Scheil simulation provides a reliable predictive framework for controlling phases and mechanical properties in LMD of NiCoCrAlY coatings.