Effects of porosity on delamination wear behaviour of sintered plain iron

The role of porosity on the wear behaviour of sintered iron was investigated. Sintered iron was used in preference to steel because the various alloy additions and matrix heterogeneity in the latter might affect the microwear behaviour and the role of porosity. The wear tests were performed in a pin on disc test bed under 10-40 N loads at 0·56 m s-1 sliding speed in air. For the given tribological conditions, it was found that the wear mechanism is delamination or mechanical wear, which is basically similar to that of wrought materials according to subsurface crack generation and crack propagation processes. However, the open pores on the surface act as a site for generation and collection of wear debris. Furthermore, the pores affect the stress distribution and the metal deformation of subsurface layers during dry sliding. Accumulation of the plastic shearing on the subsurface results in nucleation of cracks that further grow by shearing: the fracture process. The propagation of subsurface cracks at a critical depth parallel to and eventually up to the sliding surface results in the formation of flakelike debris. This paper presents the role of porosity, which is the peculiar property of PM materials, on the dry sliding behaviour of sintered iron as a model material. The implication of Archard's law for describing the results obtained is presented. The shortcomings in evaluation of the wear behaviour of sintered materials are addressed and compared with non-porous materials.