Plasma surface enrichment versus volumetric alloying of Fe + 0.6% C + 3% SiC self-lubricating sintered composites: Microstructural and tribological evaluation

Abstract

In the present study, the addition of molybdenum as an alloying element to the Fe + 0.6% C + 3% SiC self-lubricating composite was carried out by two different processing routes: In a novel and original processing route, the addition of Mo is carried out through plasma treatment, creating an average content of 1.6 wt % Mo in the first 10 μm. In the long-established route, Mo powder was added to the powder mix to reach 1.6 wt % Mo average volumetric composition. The two groups of samples were produced by powder injection mould, plasma-assisted debinded and sintered and subjected to a soaking stage to promote bainite formation. Tribological characterisation (scuffing resistance, steady-state friction coefficient, specimen and counter-bodies wear rates) was performed using dry, constant and variable load reciprocating sliding tests. The results, discussed in terms of microstructural modifications and wear mechanisms, indicated that Mo enrichment presented the best results, with a significant increase (4500%) in scuffing resistance and an order of magnitude reduction in the average steady-state friction coefficient. In addition, the wear rate of the volumetric specimens was notably higher (1000%) and even more pronounced in the counter-bodies (four orders of magnitude), proving that surface enrichment of self-lubricating composites is viable, cost-effective, and reliable alternative for improving their tribological properties.