Abstract
An investigation has been carried out into the development and maintenance of wear-protective oxide on iron-12 per cent chromium-base alloys during sliding in air at 20–600°C, with particular reference to the effects of temperature, of intermittent changes in temperature, and of sliding speed. It has been established that the wear-protective surface develops on and from compacted oxide and oxide-coated metal debris and involves deformation of the oxide. The wear process in the early stages of sliding generates metallic wear debris particles. These are fractured and re-fractured until they have a high surface to volume ratio. These surfaces are oxidized at the ambient temperature, to produce considerable amounts of oxide debris. Additional amounts are generated by transient oxidation of the specimen surfaces and removal of this oxide during each transversal of the sliding action. The rate of production of such oxide debris is determined by the ease of fracture of the metal debris and the rate of oxidation. Under these sliding conditions, this results in a minimum in the time required to generate a wear-protective oxide surface at 400°C. Development of such a surface takes a longer period at higher and lower temperatures, and indeed it does not develop at all at room temperature. Once established, the wear-protective oxide remains adherent and stable during isothermal sliding at 300°C and higher temperatures. Thermal stresses imparted by cooling to room temperature and reheating to 300° C do not cause loss of effectiveness of the oxide on subsequent further sliding at 300°C. However, subsequent sliding at room temperature results in rapid breakdown of the oxide and metal-metal contact, presumably due to a decrease in plasticity of the fine oxide debris with decreasing temperature or to a decrease in the adhesion between the oxide and the metal substrate or in oxide cohesion.
Get full access to this article
View all access options for this article.