Structure-property correlation and high-temperature erosion performance of Inconel625-Al2O3 plasma-sprayed bimodal composite coatings

Abstract

In the present experimental work, Inconel-625 (IN625) was reinforced with Al2O3 (30 wt%) to develop composite coatings with plasma spraying technique on ASTM SA210 GrA1 boiler steel. Three composite coatings were developed by varying Al2O3 particle sizes in micrometric, nano, and bimodal forms. The Inconel625 + 30 wt% micrometricAl2O3, Inconel625 + 30 wt% nano-Al2O3 and Inconel625 + 15 wt% micrometric Al2O3 + 15%nano-Al2O3 combinations were considered. The developed composite coatings were analyzed for the detailed microstructure studies, microhardness, fracture toughness, and elevated temperature erosion test. The elevated temperature erosion tests for bare substrate and coatings were conducted at 900 °C by using an erosion test rig (air jet) at two impingement angles 30° and 90°. By studying the eroded surfaces through scanning electron microscopy (SEM) micrographs, the mechanism of material removal was predicted. The existence of grooves and lips at a 30° and 90° impact angle on surfaces indicate the erosion mechanism consists of ploughing and micro-cutting action in the substrate. At 30° and 90° impact angles, all composite coatings exhibited a brittle erosion mode as erosion characteristics. The micrographs of eroded surfaces indicated splat removal, cracks, and fracture as the main erosion mechanism. The outcomes of the tests revealed that the bimodal composite coatings successfully protect the underlying substrate owing to their hardness and fracture toughness which is higher than the other two coatings. The better outcome of bimodal coatings was related to refined microstructures and good interaction among nano and micrometric Al2O3 reinforcement.