CERAMIC CUTTING TOOL INSERTS

This invention is concerned with a hard, tough, thermally conductive ceramic cutting tool insert consisting essentially of a zirconia alloy in a hard refractory ceramic insert and the product thereof. The ceramic cutting tool insert exhibits performance conducive to use in turning operations and/or milling operations. In particular the invention provides a ceramic cutting tool insert exhibiting a hardness greater than 15 GPa, a toughness greater than 6 MPa 2ROOT m, and a thermal conductivity greater than 14 Wm K consisting essentially, expressed in terms of percent by weight, of 20-45% zirconia alloy and 55-80% hard refractory ceramic matrix, said alloy consisting essentially, expressed in terms of mole percent on the oxide basis, of 1-4% of a toughening agent selected from the group consisting of YNbO4, YTaO4, MNbO4, MTaO4, and mixtures thereof, wherein M consists of a cation which replaces a Y cation on a mole basis selected from the group consisting of Mg , Ca , Sc , and a rare earth metal ion selected from the group consisting of La , Ce , Ce , Pr , Nd , Sm , Eu , Gd , Tb , Dy , Ho , Er , Tm , Yb , Lu , and mixtures thereof, and the remainder zirconia.