Micromechanical behaviour and wear resistance of hybrid plasma-sprayed TiC reinforced Tribaloy-400

Cobalt-based alloys such as Tribaloy-400 are known for their sliding wear resistance at room as well as elevated temperature. However, further enhancement in terms of hardness and wear resistance could be achieved by creating metal matrix composites reinforced by ceramic particles. For this purpose, Tribaloy-400 based coatings were deposited with the addition of different amounts of TiC reinforcement (≈25 vol%, ≈40 vol%, ≈60 vol%) through a “hybrid” plasma spray process, using a dry Tribaloy-400 powder with 10–45 μm particle size and a water-based TiC suspension (d50 = 2.2 μm). Pure Tribaloy and pure TiC coatings were employed for comparison. During spraying, TiC was partly oxidized but could nonetheless be embedded between the bigger Tribaloy-400 lamellae. Specifically, the coating containing ≈ 25 vol% TiC shows a homogeneous microstructure, whilst greater amounts of hard phase lead to some agglomeration. Accordingly, the coating with 25 vol% TiC exhibits a good combination of hardness and toughness (the latter being assessed by scratch testing) and low sliding wear rates of ≈10−5–10−6 mm3/(N·m) from room temperature up to 700 °C in ball-on-disc tests against an Al2O3 counterbody. At room temperature, the tribological behaviour of the coatings is controlled by abrasive grooving and spallation due to surface fatigue. With increasing temperature, tribochemical phenomena take on an ever-increasing role and, at 700 °C, a uniform, oxide-based tribofilm is developed, so that the wear rates are often lower than are recorded at 400 °C.