AbstractA range of sialon compositions have been used to machine the nickel-base alloy Incoloy 901. Wear measurements, taken throughout the machining tests, have shown that tool life and flank wear resistance increase withα-sialon content. An examination of the wear mechanisms involved suggests that this can be ascribed to the increased resistance to dissolution into the work piece, afforded by the higher aluminium and oxygen levels inα-sialon compared with those inβ–sialon. At higher cutting speeds one of the main mechanisms of tool wear was rake face flaking, and resistance to this mechanism was found to increase with tool material grain size. A model has been proposed for the initiation and propagation of the cracks which produce this type of failure. At lower cutting speeds depth-of-cut notch wear was of major importance, and resistance to this mechanism was found to decrease with increasing grain size.MST/249