The influence of alumina crystal structures on the morphology and surface erosion of PMMA composite materials exposed to cavitation testing

Composites are materials that reach many users and therefore, it is necessary to correlate the properties of every component on the behaviour of the material. Alumina is used as reinforcement with the aim of improving hardness. It was proven that the hardness depends on the crystal structure of the reinforcement. As the hardness is related to cavitation resistance, the influence of different reinforcements on the composite cavitation resistance was studied. Alumina and iron(III) oxide doped alumina particles were prepared by the sol-gel technique, starting from soluble salts of both elements. The gels were calcined at three different temperatures: 700, 800 and 900 degrees C. Poly(methyl methacrylate), PMMA, was used as the polymer matrix reinforced with alumina particles. The reinforcement content of all the samples was 3 wt %. Cavitation erosion of the samples was measured using a standard ultrasonic vibratory setup with a stationary sample. The cavitation resistance of the samples was studied using the classical mass loss method and the surface defects resulting from cavitation were analyzed. The morphologies of the defects after 1 h of cavitation erosion were examined by field emission scanning electron microscopy (FE-SEM). The images were characterized using the image analysis procedure. The results showed that the alumina crystal structure resulting at different calcination temperatures influences the defect morphology, cavitation resistance and the hardness of the composites.