Surface observations of a powder layer during the damage process under particulate lubrication

Loose powder is used to lubricate the tribopair with the replenishing mechanism. This work analyzes the contact and the damage behavior of the powder layer during powder lubrication. The typical life cycle of a powder layer includes the full powder layer, partial detachment, serious detachment, and complete destruction, which can be concluded from the powder layer images. The carbon and copper content remaining on the surface are analyzed using scanning electron microscopy and energy dispersive X-ray spectroscopy. Layer blistering, partial detachment, delamination, and scuffing, which represent the different forms of damage and deterioration grades, are observed using an optical microscope. Layer blistering, partial detachment, and delamination are the damage forms that occur at earlier stages. Meanwhile, most of the speed difference is accommodated via shearing and sliding of the powder layer. Scuffing, which indicates direct contact and rubbing between the steel surface of the top sample and the copper surface of the bottom sample, is a serious form of damage and is often observed before the full destruction of the powder layer.