Fatigue behaviour of Ti sputtered Al composites

Remarkable enhancement of fatigue life and endurance limit of Al matrix composites has been achieved by thin coatings of Ti sputtered at room temperature. Three materials have been investigated. They differ for matrix (6061, A359, 2618), reinforcement particles (SiC and Al2O3) and preparation process (casting and powder metallurgy). Fatigue tests employing a rotating bending machine showed that the method works on all of them, higher effectiveness has been observed in the composite (6061/ 20%SiCp) which has more homogeneous reinforcement distribution. An improvement of fatigue behaviour has been observed also in tests performed on the composite A359/20%SiCp at 200°C, typical working temperature for some industrial applications of Al matrix composites. Coatings seal the defects present on the external surface of the composites, retard crack growth thus lead to an improvement of fatigue behaviour. The effect of coating on fatigue behaviour is discussed with reference to the surface state, which has been investigated by scanning electron microscopy (SEM), scanning tunnelling microscopy (STM), X-ray diffraction (XRD) and microhardness tests.