RESIDUAL-STRESS RELAXATION BEHAVIOR IN AL2O3-SIC NANOCOMPOSITE

A novel indentation technique was used to investigate and compare the residual stress relaxation behavior in single-phase Al2O3 with that of a ''nanocomposite'' material consisting of Al2O3-5 vol.% 0.15 mu m SiC. Specifically, the degree of asymmetry in the radial crack pattern generated at small secondary ''satellite'' indents was used to probe the residual stress field introduced by a large primary indentation. In the ''as-dented'' case, where the secondary indentations were made immediately following the primary indentation, the crack pattern of the small indents was highly asymmetrical because of the influence of the residual stress field around the large indentation. In the ''annealed'' case, where the primary indentation was made prior to annealing, but the secondary indents were made after annealing at 1300 degrees C, the appearance of the radial cracking around the satellite indents was different for the two materials. In Al2O3, the crack configuration at the small indents was now symmetrical, whereas, in the nanocomposite, the crack morphology still exhibited significant asymmetry. These observations indicate that annealing completely relaxed the residual stresses in Al2O3, but only partially relieved the stresses in the nanocomposite.