IN VIEW OF their high hardness, chemical inertness and excellent mechanical behavior at high temperatures, ceramic oxides (in particular, alumina) offer excellent advantages over high speed steels and carbides for cutting tool applications. 1-6 A disadvan• tage of ceramic oxide cutting tools at this stage of development is their relatively low strength and impact resistance. King and Wheildon2 showed that the microhardness.of a ceramic cutting tool represents an excellent measure of the total performance in a machining operation. This observation suggested that the wear ' process in ceramic cutting tools is controlled by dislocation mechanisms. Indeed, more recent work has shown that plastic flow ! ~-71 is a contributing factor to the wear during abrasion of sapphire and f-' polycrystalline alumina. 7-9 Kim et al. 10 by the use of transmission electron microscopy of ion-beam-thinned foils showed that high dislocation densities were generated in the crater area of ceramic cutting tools during the wear process. In addition, a good correlation was found berweerr tool rnicrohardness and crater wear resistance, as measured by the total crater area formed during machining. For ceramic cutting tools, high crater wear resistance is particularly important since excessive cratering in effect causes a decrease in the negative rake angle generally required for the successful operation of ceramic cutting tools. A decrease in rake angle leads to increased tensile and shear loading of the tool edge, which in tum can cause premature catastrophic failure. The observations cited above suggest that increasing the microhardness. i.e., increasing the critical stress for lastic should lead to increased tool performance in tennsof red wear. Such results, if positive, should also serve as funbel'
that the wear even of such brittle materials as ceramic controlled by plastic flow mechanisms. erifi hypotheses formed the primary objective of this snld A study was conducted of the effect of solid-solution alloying on the perfor• mance of alumina ceramic cutting tools in the machining of an alloy steel. Vacuum-pressure-sintered cutting tools alloyed with 1 . 5, 10, 20 and 30 mole% chromia exhibited significantly greater crater wear resistance than the nonal• loyed alumina tools. Unexplained wear characteristics were exhibited by the .aturnlna alloyed with five mole % chromia. Metallographic observations showed that crater wear of cecaeniccut• ting tools involves plastic flow, grain pullout due to abrasive wear. creep. crack formation and chemical interac• tion between the cutting tool and steel workpiece.

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