A functionally graded coating from ZrN to Ti: Experimental characterization, erosion behavior and design concept

In functionally graded coatings (FGCs), the elemental composition, or structure, within a coating changes progressively as a function of depth, allowing for the property gradual transition from coating to matrix. One method for preparing FGCs with continuous component distribution is double glow plasma alloying (DGPA) technique. In this work, a sandwich-like ZrN/Ti FGC was fabricated, consisting of a single ZrN ceramic layer on the topmost layer, a ceramic/metal intermediate transition layer, and a metallic Ti layer in the inner layer. The transition layer derived from atom diffusion made the metallurgical bonding for entire coating, which endowed the coating with high adhesion. The erosion tests exhibited that the coating improved the erosion resistance of substrate effectively, which was attributed to the high hardness and elastic work consumption. Besides, the transition layer with coexistence of metal and ceramic phases deflected the radial crack propagation, and thus increased the plastic work consumption. The thermodynamic calculation using two sub-lattice and Miedema models showed that controlling the Zr diffusion thickness over N diffusion thickness can increase the ZrN phase content and reduce the unfavorable TiN and Ti2N phase. The experiment results and design concept described herein for characterizing FGCs can be used to promote the understanding and design of other FGCs.