Tribological properties of TiC-Fe coatings obtained by plasma spraying reactive powders

Abstract

Titanium carbide-based coatings have been considered for use in sliding wear resistance applications. Carbides embedded in a metal matrix would improve wear properties, providing a noncontinuous ceramic surface. TiC-Fe coatings obtained by plasma spraying of spray-dried TiC-Fe composite powders containing large and angular TiC particles are not expected to be as resistant as those containing TiC particles formed upon spraying. Coatings containing 60 vol% TiC dispersed in a steel matrix deposited by plasma spraying reactive micropellets, sintered reactive micropellets, and spray-dried TiC-Fe composite powders are compared. The sliding wear resistance of these coatings against steel was measured following the test procedure recommended by the Versailles Advanced Materials and Standards (VAMAS) program, and the inherent surface porosity was evaluated by image analysis. Results show that, after a 1-km sliding distance, TiC-Fe coatings obtained after spraying sintered reactive powders exhibit scar ring three times less deep than sprayed coatings using spray-dried TiC-Fe composite powders. For all coatings considered, porosity is detrimental to wear performance, because it generally lowers the coating strength and provides cavities that favor the adhesion of metal. However, porosity can have a beneficial effect by entrapping debris, thus reducing friction. The good wear behavior of TiC-Fe coatings manufactured by plasma spraying of sintered reactive powders is related to their low coefficient of friction against steel. This is due to the microstructure of these coatings, which consists of 0.3 to 1 μm TiC rounded particles embedded in a steel matrix.