The effect of residual stresses in functionally graded alumina–ZTA composites on their wear and friction behaviour

In this work we have evaluated the effect of compressive stress levels in functionally graded alumina–ZTA composites on their wear and friction behaviour during sliding in water. Neutron diffraction, X-ray diffraction and scanning electron microscopy were employed to analyze the samples and assess the acting tribological mechanisms. The results, which are compared to results from homogeneous alumina, show that with increasing residual compressive stresses in the samples of functionally graded material (FGM) both the wear and the friction are reduced. As a consequence of reduced crack formation and debris detachment from the surface (due to increased residual compressive stress) the tribochemical layer became thinner, with fewer topographical irregularities at the surface. This increases the role of the tribochemical actions compared to the mechanical wear, which beneficially affects the tribological performance in water.