Relaxation of indentation residual stress in alumina: Experimental observation by X-ray diffraction

The residual stress field generated by Vickers indentation in an alumina ceramic material was studied by an X-ray diffraction technique. A specifically designed stress/texture diffractometer was used to measure the residual strain at different locations around the indentation site, and the experimental values were compared with the theoretical stress field calculated on the basis of previous work. A compressive stress state was shown to prevail around the indentation site, the magnitude being a decreasing function of the distance from the contact point. The indented alumina specimens were then subjected to annealing treatments at temperatures up to 1000 °C. The measurement of the stress field by the X-ray technique allowed the observation that the indentation residual stress can be completely removed by heat treatment at temperature around 900 °C.