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Materials Research Bulletin Materials Research Bulletin 37(2002)1401-1409 Machinable Al2O3/bn composite ceramics with strong mechanical properties Yongli Li, Guanjun Qiao, Zhihao Jin State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University Xi'an 710049. PR China ( Refereed) Received 22 August 2001: accepted I May 2002 Abstract Al2O /BN composite ceramics with nano-sized BN dispersions ranging from 0 to 30 vol. were successfully fabricated by hot-pressing a-Al2O3 powders with turbostratic BN(t-BN coating, which was prepared through chemical processes using boric acid and urea. SEM observations revealed that the nano-sized hexagonal bn(h-BN) particulates were homoge- neously dispersed within Al2O3 grains as well as at grain boundaries. Vickers hardness of materials decreased with an increase in BN content. The fracture toughness was improved but the fracture strength had a small decrease, in comparison to Al2O3 monolithic ceramics. The nanocomposite ceramics with bn content more than 20 vol. exhibited excellent machin- ability, which could be drilled using conventional hard metal alloy drills. Drilling rates and normal forces demonstrate the ease of machining of these materials. The preliminary informa- tion on the relationship between microstructures and properties are provided. The mechanism of naterial removal is also discussed. C 2002 Elsevier Science Ltd. All rights reserved Keywords: A Ceramics; B Chemical synthesis; C Electron microscopy; D Mechanical properties; D Machinability 1. Introduction eramic materials like alumina have been widely used as engineering materials in automotive parts and cutting tools because of their high strength, high hardness high wear resistance, and abundant reserves in the earths crust. However, most Corresponding author E-mailaddress:waterle@hotmail.com(Y.Li) 0025-5408/02/S- see front matter C 2002 Elsevier Science Ltd. All rights reserved PI:S0025-5408(02)00786-9 ! " ! " #$ % &' $ ( & ))*+ & * , )) -. & & % ) ) (/0 % , % & , - - & #-' & & & / 12 ( ( & -. & 3 #-' - , & & & / 45 & % & & / 6 % ( & % & & / 6 ) (/0 3 & 3 - , & & & ( & , &/ 7 & % & % % / 6 , %- & (& &/ 6 % ( & &/ )) 2 ( 1 &/ ( &/ # $% / 8 + / 8 , + 8/ 2 ,+ 7/ + 7/ , 8 5 ( & , & ( & % & & & ( 9 / : ( $ ; # )) ' *<)*=*<)> )) ?-?<)@) A = % )) 2 ( 1 &/ ( &/ BCCD 1 )) ?-?<)@#) '));@E-> 8 & / &'( $$ % F/ #/ '/