Deposition of Oxidation-Resistant Hard Aluminide Layers on Hastelloy C-276: A Study on Microstructural and Kinetic Analysis

Abstract By aluminizing at varying temperature (600–700 °C) and time (2–6 h) cycles, defect-free, continuous and homogeneous thick Ni–Al deposition layers are obtained on Hastelloy C276 surface. Metallurgical analysis performed on surface/sub-surface indicates that NiAl 3 and Ni 2 Al 3 phases are the dominant phases within aluminide coatings (11–41 μm). Since the experimental aluminizing process is a diffusion-controlled process, the processing output with variable temperature and time parameters made it possible to study the process kinetics, and the process-specific activation energy is calculated as 51 kJ/mol. An equation is also derived from the regression model to estimate the coating thickness, and there is a good agreement between the coating thicknesses determined by the experimental and calculated values. The effect of temperature/time on the layer thickness is investigated with variance analysis. Although no significant change in the surface hardness value (~ 800 HV) is measured regardless of the layer thickness, an increase in the layer thickness over time on material surface processed at the lowest temperature causes a significant decrease in the oxidation rate due to the presence of a stable Al-rich oxide. All these findings reveal the lowest cost coating conditions that can reduce the chemical degradation of Hastelloy C276 caused by oxidation at high temperatures.