Structure and wear resistance of coatings produced by the short-pulse laser alloying of titanium carbohydride-based mechanocomposites

Abstract

The study covers the phase composition, morphology and properties of coatings deposited on steel by means of short pulse selective laser alloying of titanium carbohydride-based mechanocomposites. Mechanocomposites were fabricated by milling of Ti and Ti–Cu powders in a liquid hydrocarbon environment. The synthesized mechanocomposites and fabricated coatings are investigated by X-ray diffraction, scanning electron microscopy and optical microscopy. The phase composition of mechanocomposites is represented by titanium carbohydride phase with a size of powder particles ranging from 2 to 30 μm for powders without copper, and from 1 to 10 μm for copper-containing powders. Coatings fabricated from powder mechanocomposites have a gradient structure. The Ti(C,H) powder coating contains 48 vol.% of the titanium carbide phase in a shell of Fe–Ti intermetallic compounds. The Ti(C,H)–Cu powder coating contains 85 vol.% of titanium carbide inclusions surrounded by Ti(Fe,Cu) and CuTi2 phases. Round-shaped carbide inclusions formed have a size of 50 to 200 nm, and dendritic ones are up to 5 μm. Coatings have a microhardness of 10 GPa and 8 GPa for compositions without and with copper, respectively. Coatings were tested for wear resistance under the conditions of dry friction in pairs with the balls made of steel and VK6 tungsten carbide alloy. Coefficients of friction for both coating types are 0.16–0.3 with the ball made of VK6 tungsten carbide alloy and 0.2–0.4 with the ball made of hardened steel. Coatings almost do not wear out under the counterbody load of 10 N and testing time of 20 min.