正在加载图片...
Y. Li et al. /Materials Research Bulletin 37(2002)1401-1409 EEEE品∝a 02▲ Drilling Load(N) ig. 6. Measurements of drilling rates as a function of normal force for Al,O3/BN ite ceramics drilled section was 3+0.2 um, measured by a light-section microscope under the conditions that satisfied a fixed load of 10 N on the drill bit. Significant cracks were not observed on the surface The convenience of machining is presumably attributed to the cleavage of the ano-sized h-bn particles homogeneously dispersed in the matrix, which may confine the machining damage to a very small region under the tip of the tools through microcracking to absorb and disperse the damage force during the machining operations. Linking of the microcracks results in the ease of machining. Separate phases could not be distinguished on the machined surface by scanning electron microscopy, and the ratio of Al2O3 and bn was consistent with Al2O3/30 vol %o BI by EDs analysis. However, further confirmation of the microstructure within this surface layer needs a higher resolution of transmission electron microscopy(TEM) 4. Conclusions (1) The Al2O3/BN nanocomposite ceramics, including the nano-sized Bn up to 30 vol %, were fabricated by hot-pressing the al-Al2O3 powders covered with t-BN. The SEM observations revealed the h-BN particles were homogenously dispersed within the a-Al2O3 grains and at the grain boundaries 2) There was no significant decrease in the fracture strength of these nano- omposite ceramics with the increase of h-BN content. The enhancement of the fracture toughness was chiefly attributed to the soft layer-structure and& & ) & , - & & H & H3 & & % *) & / 1H 5 ( & % / 6 ( % , & ( % -. & - , & & 3 , H & ( , & % 5 & & & % & / 5 % 5 % / 1 & & & & % , , & % & ) (/0 , 271 ,/ : ( % H % % , & % , #62'/ #*' 6 & -. & ) (/0 % & , - - & ( & -/ 6 12 ( ( & - , & & - & & / # ' 6 H & % % - % - / 6 % % M, & % , - & L/ E/ % & % % % % / *<)@ )* * + ! , - ./ /0 1