Metallurgical reactions and tribological properties of self-lubricating Al-WS2 composites: Laser powder bed fusion Vs. spark plasma sintering

Abstract

Self-lubricating aluminium-based composites reinforced with solid lubricants promise to meet the demand for lightweight materials in green tribological applications. The design advantages granted by additive manufacturing (AM) processes coupled with their capacity for in-situ production of composite materials are yet to be exploited in the realm of Al-transition metal dichalcogenides composites. In this work, laser powder bed fusion (LPBF) was deployed for the in-situ fabrication of Al-WS2 composites for the first time, elucidating the process-structure–property relationships in comparison to reference spark plasma sintering (SPS) samples. The WS2 response to the respective fabrication technique was also firstly investigated through a holistic characterisation. The formation of new phases (W for LPBF, Al5W and Al12W for SPS) provided the potential for microstructural tailoring for optimal tribological performance. For tribological properties, LPBF Al-WS2 exhibited a coefficient of friction (COF) 0.55 ± 0.01 and specific wear rate 3.4 ± 0.3 × 10−3 mm3/N∙m, slightly better than the SPS counterpart (COF 0.57 ± 0.02, specific wear rate 3.6 ± 0.3 × 10−3 mm3/N∙m). Furthermore, a novel methodology for studying the evolution of worn surfaces is proposed and validated, by which a tribo-layer formed at lower friction cycles was observed for the LPBF samples, meaning that AM will also be advantageous for the performance aspect of self-lubricating materials.