Sliding wear performance of Al–Co alloys fabricated by vacuum arc melting and correlation with their microstructure

Al–Co alloys of various compositions (2–20 wt% Co) have been fabricated by vacuum arc melting and evaluated with respect to their microstructure and dry sliding wear performance. A variety of microstructures have been attained, ranging from that of a dual fibrous and lamellar Al/Al9Co2 eutectic (Al-2 wt. % Co), to that of coarse primary Al9Co2 plates within an Al-matrix (Al-20 wt% Co). Despite their hypereutectic compositions, the alloys behave as in-situ Al9Co2/Al composites: with increasing the Co content and, consequently, the Al9Co2 volume fraction, the hardness of the alloys increases and their wear rate decreases. The alloys exhibit lower wear rates compared to widely used Al-alloys, as-fabricated and heat-treated. The friction behavior has been analyzed and correlated with the good interfacial Al9Co2/Al bonding and the promotion of abrasive wear by the reinforcement. Raman spectroscopy of wear debris manifested its contribution to a mild wear mode through the absolute predominance of oxide-based phases with lubricating properties. A wear mechanism has been formulated based on the wear track morphology, debris nature and friction coefficient trends. Adhesive wear and abrasive wear assisted by oxidative wear have been identified as the main wear modes. The predominance of adhesion decreases and that of abrasion increases as the Co content increases.