THE EFFECT OF WEAR ON THE TETRAGONAL-TO-MONOCLINIC TRANSFORMATION ANDTHE RESIDUAL-STRESS DISTRIBUTION IN ZIRCONIA-TOUGHENED ALUMINA CUTTING TOOLS

Zirconia-toughened alumina cutting tools have been examined after mach ining an AISI 1040 steel. The Raman spectrum of zirconia and the fluor escence spectrum from alumina have been used to determine the extent o f the tetragonal-to-monoclinic (t-m) transformation and the residual s tresses in and around the worn-out crater, respectively. Although abou t 15% vol. m-zirconia is present even in a brand new cutting tool, it was shown that the crater region undergoes the t-m transformation up t o 40% vol. In both cases, the transformed zone is concentrated near th e surface. The residual stresses in alumina are slightly compressive i n the new cutting tool and away from the crater region, but they becom e tensile inside the crater, where the t-m transformation of zirconia has occurred to a larger extent. A stochastic model has been used to p redict the stresses and it has been found to reproduce very well the e xperimental data. Some evidence of the formation of a spinel reaction product in the crater region has been found, likely (Mg, Fe)AlO4. (C) 1998 Elsevier Science S.A.