Enhanced bonding property of ion-plated TiN coating on stainless steel by mechanically pre-forming a gradient nanostructure

Abstract

An enhanced coating/substrate bonding property is crucial for the application of hard coatings (e.g., TiN) on soft substrates (e.g., stainless steel). In the present work, a gradient nanostructure, in which the grain size is ~50 nm in the top surface layer and increases gradually with depth, was pre-formed in 304 stainless steel by means of plate surface mechanical rolling treatment (PSMRT). Subsequently, a TiN coating was deposited on it by using a commercial arc ion plating approach. Scratch tests demonstrated that the critical load of coating detachment was significantly enhanced in the coated PSMRT sample, ~47 % higher than that in the coated coarse-grained counterpart sample. Analyses of the underlying bonding mechanisms revealed that a higher interfacial strength was achieved in the coated PSMRT sample, mostly due to the depressed formation of compounds and the accelerated diffusion of Ti in the interfacial region. In addition, such factors as a higher substrate hardness, a lower friction coefficient between the scratch tip and the coating, and a lower internal stress in the coating might also contribute to the enhanced bonding property in the coated PSMRT sample. This work provided insights on applying a simple mechanical approach to enhance the bonding properties of hard coatings on soft substrates.