Antiwear and Self-repairing Mechanisms of Magnesium Hydroxysilicate Composite Powder as a Lubricating Oil Additive for Steel-Steel Pair

An MM-200 ring-on-block friction and wear tester is performed to evaluate the friction-reducing and antiwear behavior of magnesium hydroxsilicate composite mineral powder as a lubricating oil additive for steel-steel (AISI-1045) pair. The morphology of worn steel ring surfaces and of mineral powder additive in the lubricating oil is analyzed using a scanning electron microscope. The elemental composition of worn steel ring surfaces is analyzed using an energy dispersive spectrometer, while the roughness of worn steel ring surfaces is measured using a surface profiler. The antiwear and self-repairing mechanisms of the composite mineral powder additive is explored based on results of surface analysis.It is found that magnesium hydroxsilicate composite mineral powder as a lubricating oil additive shows good friction-reducing and antiwear behavior for steel-steel pair. Under the lubrication of base stock, wear mechanisms of the steel-steel pair are transformed from mild scuffing to severe scuffing and adhesion wear with increasing load. Whereas, only mild scuffing is seen on worn steel ring. The surface at a low load (300 N) under the lubrication of base stock containing the mineral powder additive has slighter degree of scuffing than that under the lubrication of the base stock alone. Besides, worn steel ring surfaces are quite smooth at a high load (600 or 900 N) under the lubrication of base stock containing mineral powder additive, showing slight signs of adhesion wear. The reasons lie in that, on one hand, the mineral powder additive is able to agglomerate at a low load forming spherical aggregates with various sizes and transform sliding contact of the steel-steel pair to rolling contact by way of "micro-ball bearing effect", thereby leading to significantly reduced friction coefficient and greatly increased antiwear ability. On the other hand, the composite mineral powder additive is easy to form a self-repairing antiwear layer on worn steel surfaces at a high load to prevent direct metal-to-metal contact, thereby considerably reducing friction and wear.