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Y. Li et al. /Materials Research Bulletin 37(2002)1401-1409 ■- Fracture Strentgh 口- Fracture Toughness BN Content(vol‰%) Fig. 4. Effects of h-BN content on fracture strength and fracture toughness of Al2O3/BN composites. Two macrographs of a series of typical drill holes in the Al,O3/30 vol. %0 BN anocomposite ceramics are shown in Fig. 5. The holes are cleanly drilled with no evidence of cracking or chipping. The machinability was also tested with the sample bonded onto a piece of graphite liner, and the holes drilled without lubrication. Load force on the drill bit ranged from 1 to 12N and a fixed drill revolutions 700 rpm. Drilling depths were approximately 2 mm. Each test was done three times under the same conditions. A new drill bit was used at the beginning of each set to avoid systematic effects due to wearing of the drill. Drilling rates show a nonlinear relation with the load in the experimental range, as shown in Fig. 6. When the load on the drill bit gets to 10 N, we obtain the satisfying drill rate. The surface roughness(R,) of Fig. 5.(a) Top surface and(b) section views of the holes drilled in Al2O,/BN composite ceramics sing hard metal alloy drill bits with different diameter 4.1 and 3.0 mm, respectively6 % % , & ) (/0 L/ ?/ 6 , & & (& % 5 / 6 , & & & % & & & / & % & & % * * & H3 & & ( ;)) / 7 & 3 , / 2 & & &/ & & % (& , %% & % &/ 7 & 3 L/ E/ Q & & *) %, & / 6 % #!.' % L/ </ 2%% % - % & % % / L/ ?/ #' 6 % & #' ( % & & & , & &%% & </* & /) ( ,/ )* * + ! , - ./ /0 1 *<);