Erosion performance of direct-aged Al2O3-reinforced plasma-sprayed composite coatings at high-temperature conditions

Abstract

The present investigation evaluates the influence of furnace heat-treatment (HT) on the microstructure, microhardness, fracture toughness and erosion resistance of three plasma sprayed composite coatings: a Inconel625–30 wt% micron-sized Al2O3 (In625-MHT) coating, a Inconel625–30 wt% nano-sized Al2O3 (In625-NHT) coating and a Inconel625–15 wt% micron-sized Al2O3 + 15 wt% nano-sized Al2O3 (In625-BHT/bimodal) coating. High temperature solid particle erosion tests were conducted at 900 °C temperature and with at two different impingement angles (90 and 30) in simulated environment using standard erosion-test rig. Coatings were subjected to detailed mechanical and microstructural analysis in order to better understand their erosion mechanism and structure–property correlation. By healing pores and cracks, the furnace HT increases the coatings’ erosion resistance in the order of In625-BHT, In625-NHT, and In625-MHTcoating. In addition, the mechanical properties of In625-BHT coating like porosity (1.0 ± 0.09%), micro-hardness (1299 ± 25Hv) and fracture toughness (5.9 MPa√m) are significantly improved after HT. The presence of grooves and lips on the surfaces of uncoated substrates provides clear evidence that the erosion mechanism involves the combined processes of micro-ploughing and micro-cutting indicating ductile erosion mode. However unimodal and bimodal composite coatings demonstrated a brittle erosion mode.