MACHINABILITY OF HIGH-STRENGTH POROUS SILICON-NITRIDE CERAMICS

A machinability of porous Si3N4 ceramics composed of columnar beta-Si3 N4 grains was evaluated by turning and milling with cemented carbide c utting tools to investigate a possibility of application of the porous Si3N4 to machinable ceramic use. The porosity and the flexural streng th of specimens were about 43% and 270 MPa, respectively. The machinin gs were carried out with a cemented carbide throw-away tip of K-10 gra de. The condition of turning was cutting speeds of 50 to 150 m/min, fe ed rates of 0.05 to 0.40 mm/rev, and a cutting depth of 0.5 mm, and th at of milling was cutting speeds of 20 to 200 m/min, feed rates of 0.0 5 to 0.20 mm/rev and a cutting depth of 0.5 mm. Machinability was judg ed from the maximum surface roughness, R-max, after machining; it was defined that a material was machinable when R-max, was below 10 mu m. In the case of turning, the R-max, increased with increasing cutting s peed and feed rate. R-max, below 10 mu m was obtained under conditions that satisfied both a cutting speed of 50 m/min and feed rates below 0.1 mm/rev. In the case of milling, although the R-max increased with increasing feed rate, serious cutting speed dependence of R-max could not be seen. R-max values below 10 mu m were obtained at feed rates be low 0.1 mm/rev, independent of cutting speed.