STUDY ON SURFACE CRACKING OF ALUMINA SCRATCHED BY SINGLE-POINT DIAMONDS

Scratching experiments have been carried out on hot-pressed alumina by using single-point diamonds of conical shape (conical angle 85, 108, 128 and 65 degree and nose radius 1. 6, 1. 1, 1. 9 and 45. 0 mu m, respectively). With an increase of the scratching depth, the material exhibits the following behavior: macroscopic plastic deformation yields scale-like cracking yields cracking or chipping. Cracking or chipping is absent only if the groove depths are less than certain values which vary with the diamond shape. The crack penetration depth is approximately in proportion to the depth of cut. For a depth of cut less than 2 mu m, the penetration depth of a crack induced by a diamond of nose radius 45. 0 4mum is almost 8 times that produced by the other diamonds. For a depth of cut more than 2 mu m, the former is more than twice the latter. The coefficients of pile-up increase as the depths of cut decrease. 7 Refs.