Effect of Deposition Time and Heat Treatment on Structural and Mechanical Properties of Ni<sub>3</sub>Al Coating Deposited by Air Plasma Spraying on Tool Steel

Abstract

This study focuses on the effect of deposition time and heat treatment on Ni3Al coatings with respect to mechanical and microstructural properties of the material. Air plasma spraying technique was employed to deposit Ni3Al on hot work tool steel samples for different deposition times i.e. 15-45 seconds. The coated samples were then heat treated at 900 °C for 20 to 100 hours at an interval of 20 hours each. The characterization tools such as X-Ray diffraction (XRD), optical and scanning electron microscopy (SEM) were used to study the homogeneity, phases formed and structure of coatings. All the coatings showed lamellar structure with distinctive boundaries along with the presence of some porosity and oxide particles. The XRD analysis of as prepared samples showed characteristic peaks of Ni3Al whereas of heat treated samples revealed NiO formation that increased with increasing heat treatment time. Micro-hardness and wear resistance measurements of the coated layer showed that they were increasing with the deposition time due to formation of more thick and dense layers. Formation of NiO, due to heat treatment imparted greater hardness and wear resistance to the coating. Moreover, the SEM study of heat-treated samples showed presences of alumina and spinel phases which were confirmed by energy dispersive spectroscopic analysis.