An Investigation on the Fatigue Fracture of P/M Al-SiC Nanocomposites

Abstract

A tensile-compression fatigue response of Al matrix composites containing different amount of SiC nanoparticles (50 nm diameter) up to 6 vol. pct was studied. The nanocomposite powders were prepared by a powder metallurgy (P/M) route consisting of mechanical alloying, hot extrusion, and hot closed-die forging. The microstructure of the materials was evaluated by optical microscopy, scanning and transmission electron microscopies, and electron backscattered diffraction. A fine distribution of the nanoparticles in submicron and ultrafine grains was obtained. The low cycle fatigue behavior was examined in stress control mode under fully reversed tension-compression cycle at 1 Hz up to 1000 cycles. High cycle fatigue was conducted using a push-pull test up to 107 cycles with the minimum to maximum stress ratio of 0.1 at a frequency of 40 Hz. Cyclic hardening was observed at a low cycle fatigue regime with an enhanced hardening rate in the presence of SiC nanocomposite. The fatigue endurance limit at 107 cycles was also improved by nanoparticles. Fractographic studies revealed a mixture of ductile-brittle fracture modes with an increase in the ductile fracture mode at higher SiC fractions. The fatigue fracture mechanism was found to be local ductile deformation, microscopic void formation, and coalescence.