Effect of the spraying process on the microstructure and tribological properties of bronze-alumina composite coatings

In the present paper, aluminum bronze-alumina composite coatings have been applied on mild steel substrate using conventional plasma spray and a new route based on cold spray techniques. The microstructure, phase distribution, microhardness, adhesion strength and tribological behavior of the composite coatings, consisting of alumina reinforcing phase distributed in a bronze matrix, were studied. Ball-on-disk dry sliding wear tests, Rubber Wheel tests and Erosion tests were conducted to examine the tribological behavior of the composite coatings. The tribological properties of the bronze coatings were improved by the addition of alumina. Friction coefficient of coatings depends strongly on the reinforcing particles content and spraying process. Wear mechanisms of the composite coatings, such as ploughing and particle delamination, were considered. In the case of abrasive wear test, the wear rate was greatly reduced due to the reinforcing ceramic particles. Relationships between size and volume fraction of the ceramic reinforcement Al2O3 and the wear rate are discussed. On the other hand, erosion wear behavior of coatings with higher bronze content showed the best results.