Cutting edge controlled wear of alumina inserts

Abstract

Zirconia-toughened alumina tool inserts were chosen for turning medium carbon steel at high cutting speeds of up to 1000 m/min. Careful study of the tool after the machining revealed that the wear mechanisms along the cutting edge and at the flank wear land are distinctively different. The cutting edge wears by plastic rounding, microspallation and sporadic edge chipping, while edge breakage may occur for tools of imperfect microstructure. On the other hand, the wear features observed at the flank wear land are superficial plastic deformation and necking fracture, plastic smearing of spalled grains from the cutting edge, micro/macro-spallation of the smeared layer with the underlying tool material (a form of adhesive wear), and thermal crack induced spallation. The flank wear rate is low when plastic rounding and/or microspallation are the main wear mechanisms taking place at the cutting edge, moderate when sporadic edge chipping prevails, and high when edge breakage occurs. Material parameters controlling the cutting edge wear of alumina tools are examined. Controlled microspallation at the cutting edge, via properly engineered hardness and toughness of the tool material, and a fine grain size are the key attributes for high flank wear resistance of alumina tool inserts.