Towards the understanding the effect of surface integrity on the fatigue performance of silicon carbide particle reinforced aluminium matrix composites

The fatigue performance of metal matrix composites (MMCs) is highly related to their surface integrity due to the intensive tool-particle interactions and metallographic alterations of matrix, especially under extreme cutting parameters, which could largely result in surface morphologic defects and subsurface damage on the components. Although the fatigue performance of bulk MMCs has been extensively studied, the influence of machining-induced surface anomalies on the fatigue failure mechanism still needs to be understood. This paper investigates the effect of two distinct surface integrities induced by two cutting regimes (ductile, and semi-brittle regime) on the fatigue performance of MMCs. The ductile and semi-brittle regime were represented by different surface integrities regarding the particle behaviours and their effect on the mechanical and metallographic alterations of matrix materials. In-depth analysis in terms of surface topography, subsurface damage, and residual stresses of the machined workpieces has been carried out before the three-point bending fatigue test. The results showed that the samples machined by finish milling (very low feed – semi-brittle regime) unexpectedly presented lower fatigue lives compared to the rough-milled counterparts (high feed – ductile regime), despite the former displayed compressive residual stress and lower surface roughness. It was found that the particles have pronounced influence on the fatigue performance in two different ways: under low cycle fatigue, the particles were prone to be fractured by the high stress applied (which accelerated the formation of crack initiations and therefore shortened the fatigue life), while under high cycle fatigue, the reinforcement particles were not fractured and instead they could inhibit the crack growth up to some extent. Therefore, fatigue lives of the rough-milled samples (high feed – ductile regime) were enhanced due to the retardation of reinforcement particles.