The influence of substrate on partially rapidly solidified Alumina-3 wt % titania nanocrystalline coatings deposited by plasma spray technique

Abstract

In this paper an attempt was made to impose different degrees of rapid solidification by spraying on diverse substrates of varying thermal properties. Substrates such as Copper, Aluminum, Stainless steel, Low alloy steel substrates were used to alter the imposed cooling rate and thereby the amount of residual a phase. A start powder of 3 wt% Alumina-titania powder was Used for spraying to a thickness of 250 mu m on the different substrates specified. In all cases the rapidly solidified phases show nanocrystalline sizes with the most rapidly solidified metastable gamma phase showing finer grain size of less than 25 nm. The surface roughness of the substrate and the coating were characterized by Atomic force microscopy. In contrary to the Alumina-13 wt% titania, coupons of Alumina-3 wt% titania had shown poor indentation fracture toughness with increased amount of residual cc phase. Coupons of stainless steel and low alloy steel had shown the lowest fracture toughness when tested by Vickers type indentation at loads of 3 N and 5 N. In contrast to these results the interfacial toughness when measured by Rockwell indentation technique at loads of 150 N was found to be dependent on the elastic modulus of the substrate more than the coating hardness. The interfacial toughness was found to be lower for softer material such as aluminum and copper than stainless steel and low alloy steel.