Tailoring the in-situ formation of intermetallic phases in the self-lubricating Al-WS2 composite for enhanced tribological performance with wear track evolution analysis

Abstract

Self-lubricating aluminium matrix composites with enhanced tribological properties are sought for weight critical applications. In previous studies, the Al composites incorporating the solid lubricant WS2 have been shown to reduce both the coefficient of friction and wear rate, positioning them as promising candidates in various tribological applications (e.g. automotive industry). However, the impact of interfacial reactions between Al and WS2 during composite production on tribological performance has still not yet been explored. This study highlights the hardening effect of the reaction products. Despite some literature assuming a negative impact of these reactions as they consume WS2 in the composites, this study presents evidence that this cannot be generalised for the overall outcome. Interestingly, a controlled amount is shown to be beneficial for tribological properties. In this work, the tribological influence of the Al-W intermetallic structure forming during spark plasma sintering of the Al-WS2 composites was investigated. The microstructure was tailored by adjusting the manufacturing temperature between 500 and 600 °C. The Al-WS2 fabricated at 580 °C exhibited the lowest coefficient of friction and specific wear rate (reduced by 20% and 97%, respectively, compared to the one fabricated at 500 °C. Furthermore, the worn surface morphology in different stages during friction was evaluated by a novel wear track evolution analysis. This study confirmed that offering a balance between the fraction of solid lubricants and in-situ formed hard intermetallic structure is crucial to the effective formation a protective layer on the worn surface.