摘要：

ofA sintered alumina-based ceramic has a relative density of equal to or higher than 95%, an average grain size in a range of 10 - 25 mu m and a fracture toughness Kc equal to or lower than 3.0 MPam Furthermore. In a machinability evaluation test using a surface grinder, the ceramic exhibits equal to or less than 310 W of increase in the load on a motor rotating a grinding wheel of the surface grinder. The machinability evaluation test is performed under the following condition. (1) The dimension of a test piece of the sintered alumina-based ceramic is larger than 15 mm in width, larger than 30 mm in length and larger than 10 mm in height. (2) The test piece is fixed on a table of said surface grinder and ground by the grinding wheel along a direction of its length. (3) The grinding wheel has a dimension of 10 mm in width and 200 mm in outer diameter, and consists of synthetic (or artificial) diamond abrasive grains more than 80 wt% of which are in a grain size range of 74 - 88 mu m, and which are resin-bonded at 3.3 cts/cm of weight content per unit volume. (4) The circumferrential speed of said grinding wheel is 2400 m/min, the table traversing speed is 60 mm/min, and the infeed per traverse is 3 mm.

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