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During gear shifting, the contact between teeth composes a tribological system of considerable importance regarding energy dissipation in road vehicles. Improvement of tribological system efficiency leads to costs and pollutant emission reductions. Powder metallurgy (PM) is a near-net-shape technique that allows the production of parts with complex geometry - such as gears, lower costs and larger range of material utilization compared to other manufacturing processes. Furthermore, the presence of pores in sintered material could be a beneficial factor for friction reduction and wear resistance, due to oil reservoir and debris trapping effects, and film thickness variation that could enhance lubricant load support capacity. This work aims to evaluate the lubricant effect on support capacity due to surface pores in sintered steel with different levels of porosity. Results were compared with standard gear material based on friction coefficient results.

The differences between tribological performance of nitrided and non-nitrided samples of SAE XEV-F valve steel were investigated in dry sliding conditions. Experimental tests were conducted using an SRV-4 tribometer in a ball-on-disc configuration (i.e. non-conformal contact) with reciprocating type of movement. Two kinds of samples (discs) were tested: valve steel and nitrided valve steel. The ball (i.e. the counter-body) was made of AISI 52100 bearing steel. Room temperature and fixed conditions of time, load, frequency and stroke were used. Wear was evaluated by means of mass loss, from both disc and ball, and post examination of the worn surfaces. Post examination was conducted using scanning electron microscopy (SEM), coherence correlation interferometry (CCI), and X-Ray diffraction (XRD). Wear debris resulting from tribological interaction were also investigated using SEM and XRD.