RESISTANCE OF SI3N4 CERAMIC TOOLS TO THERMAL AND MECHANICAL LOADING IN CUTTING OF IRON-ALLOYS

The mechanisms of wear in two extreme cases relating to the performance of Si3N4-based cutting tools in machining iron alloys were investigated, with the corresponding wear rates correlated with cutting speed, tool and alloy composition and seizure. The sources of discrepancy between the cutting tests and conventional pin-on-disk tests are discussed on the basis of loads, surface speed, wear debris accumulation, reaction with atmospheric oxygen and solid lubrication. The distinct interactions with the ceramic tool of a hard, high temperature deformable alloy and a brittle, composite-like alloy with, in addition, self lubrication at high temperature, yield great differences in the amount of heat generated during the process. The selective corrosion of the ceramic grain boundary phase and the abrasion through grain pullout and ploughing are changed according to the effects of temperature on the metal-ceramic contact surface.