D. Jianxin et al. International Journal of Machine Tools Manufacture 45(2005)1393-1401 Table 1 the composite have been made through additions of Sic Compositions of Al2O,/TiBy/SiCw ceramic tool materials iskers(SiCw) by the authors [9, 15, 16]. Composition(vol %) Nickel-based alloys are the most widely used superalloy, accounting for about 50 wt%o of materials used in an aerospace engine, mainly in the gas turbine compartment Inconel718 is the most frequently used of nickel-based alloys. Ceramic tools are gaining popularity machining of nickel-based alloys because they can with- stand higher cutting conditions than carbide tools. In this study, Al2O/TiB 2/SiCw ceramic cutting tools with different been refined by controlling and improving manufacturing volume fraction of TiB2 particles and SiC whiskers were processes;(2)toughening mechanisms have been devel- produced by hot pressing. The fundamental properties of oped, such as whisker toughening and transformation these composite tool materials were examined. Machining toughening, thus improving the fracture toughness of tests were carried out on the Inconel718 nickel-based alloys ceramic tools while at the same time reducing susceptibility The tool wear rates and the cutting temperature were to thermal shock; (3)new ceramic compositions have been measured. The failure mechanisms of these ceramic tools developed that are suitable for cutting tool application, were investigated and correlated to their mechanical particularly in high speed machining; and (4)surfaces have properties been conditioned by the removal of cracks, egularities and residual stresses. These developments have now enabled ceramic tools to be used in the machining of various types of steels, cast iron, and non-ferrous metals 2. Materials and experimental procedures such as brass, bronze, and refractory nickel based alloys at high speeds and feeds 2.1.Materials and processing Advances in ceramic processing technology have resulted in a new generation of high performance ceramic A monolithic Al]O3(average particle size 0.8 um)was used as the baseline material. Additions of TiB2 particle improvements has been achieved in tool properties such as average particle size 1 um)and Sic whiskers(diameter 1 flexural strength, fracture toughness, thermal shock resist- 3 um, length 20-80 um)were added to Al2O3 matrix ance, hardness, and wear resistance by incorporating one or according to the combinations listed in Table 1. The more other components into the base material to form material was fabricated using colloidal and ultrasonic ceramic-matrix composite tool materials. The reinforcing processing techniques. Filter pressing was used to con- component is often in the shape of particles or whiskers. solidate the multicomponent slurries into green bodies Ceramic tool materials with oxide matrices particularly approximately 60 mm in diameter and 15 mm thick Al2O3 are of increasing interest. Addition of hard particles Following drying, the powdered material was formed and or whiskers to the Al2O3 matrix may enhance its mechanical compacted in a metal dye with a pressure of 60 MPa properties considerably. Some of these tool materials, such Following the forming stage, the compacted powder was as Al2O3/TiC, Al2O,/TiB2, Al2O3/ZrO2, Al2O3/Ti(Cl then filled in a graphite die, and the final densification was Al2O/(WTi)C, and Al2O/SiCw, have been used in various accomplished by hot pressing with a pressure of 35 MPa machining applications and offer advantages with respect to nitrogen atmosphere for 40-60 min to produce a disk. The friction and wear behaviors[6-12]. The strengthening or the required sintering temperature was in the range of 1750- toughening mechanisms of these ceramic tool materials are 1800"C Details of these procedures and specific processing phase transformation toughening, whisker toughening and parameters employed are described elsewhere [9, 16 precipitate or dispersion strengthening [13, 14]. In earlier studies it has already been shown that the additions of TiB 2.2. Material characterization secondary phases to Al2O3 matrix in amounts higher than 20 vol % o improved fracture toughness, hardness, strength Densities of the hot-pressed materials were measured by over the monolithic Al2O3 and offered advantages with the Archimedes's method. Test pieces of 3 mmX4 mmX respect to wear and fracture behavior when used as cutting 36 mm were prepared from the hot-pressed disks by cutting tool materials [7, 11]. Further improvements of and grinding a diamond wheel and were used for Table 2 Composition of Inconel718 work piece material by weight percentage 242980040.121015.15049 0.003 0.01been refined by controlling and improving manufacturing processes; (2) toughening mechanisms have been devel￾oped, such as whisker toughening and transformation toughening, thus improving the fracture toughness of ceramic tools while at the same time reducing susceptibility to thermal shock; (3) new ceramic compositions have been developed that are suitable for cutting tool application, particularly in high speed machining; and (4) surfaces have been conditioned by the removal of cracks, irregularities, and residual stresses. These developments have now enabled ceramic tools to be used in the machining of various types of steels, cast iron, and non-ferrous metals such as brass, bronze, and refractory nickel based alloys at high speeds and feeds. Advances in ceramic processing technology have resulted in a new generation of high performance ceramic cutting tools exhibiting improved properties. Considerable improvements has been achieved in tool properties such as flexural strength, fracture toughness, thermal shock resist￾ance, hardness, and wear resistance by incorporating one or more other components into the base material to form ceramic–matrix composite tool materials. The reinforcing component is often in the shape of particles or whiskers. Ceramic tool materials with oxide matrices particularly Al2O3 are of increasing interest. Addition of hard particles or whiskers to the Al2O3 matrix may enhance its mechanical properties considerably. Some of these tool materials, such as Al2O3/TiC, Al2O3/TiB2, Al2O3/ZrO2, Al2O3/Ti(CN), Al2O3/(WTi)C, and Al2O3/SiCw, have been used in various machining applications and offer advantages with respect to friction and wear behaviors [6–12]. The strengthening or the toughening mechanisms of these ceramic tool materials are phase transformation toughening, whisker toughening and precipitate or dispersion strengthening [13,14]. In earlier studies it has already been shown that the additions of TiB2 secondary phases to Al2O3 matrix in amounts higher than 20 vol.% improved fracture toughness, hardness, strength over the monolithic Al2O3 and offered advantages with respect to wear and fracture behavior when used as cutting tool materials [7,11]. Further improvements of the composite have been made through additions of SiC whiskers (SiCw) by the authors [9,15,16]. Nickel-based alloys are the most widely used superalloy, accounting for about 50 wt% of materials used in an aerospace engine, mainly in the gas turbine compartment. Inconel718 is the most frequently used of nickel-based alloys. Ceramic tools are gaining popularity in the machining of nickel-based alloys because they can with￾stand higher cutting conditions than carbide tools. In this study, Al2O3/TiB2/SiCw ceramic cutting tools with different volume fraction of TiB2 particles and SiC whiskers were produced by hot pressing. The fundamental properties of these composite tool materials were examined. Machining tests were carried out on the Inconel718 nickel-based alloys. The tool wear rates and the cutting temperature were measured. The failure mechanisms of these ceramic tools were investigated and correlated to their mechanical properties. 2. Materials and experimental procedures 2.1. Materials and processing A monolithic Al2O3 (average particle size 0.8 mm) was used as the baseline material. Additions of TiB2 particles (average particle size 1 mm) and SiC whiskers (diameter 1– 3 mm, length 20–80 mm) were added to Al2O3 matrix according to the combinations listed in Table 1. The material was fabricated using colloidal and ultrasonic processing techniques. Filter pressing was used to con￾solidate the multicomponent slurries into green bodies approximately 60 mm in diameter and 15 mm thick. Following drying, the powdered material was formed and compacted in a metal dye with a pressure of 60 MPa. Following the forming stage, the compacted powder was then filled in a graphite die, and the final densification was accomplished by hot pressing with a pressure of 35 MPa in nitrogen atmosphere for 40–60 min to produce a disk. The required sintering temperature was in the range of 1750– 1800 8C. Details of these procedures and specific processing parameters employed are described elsewhere [9,16]. 2.2. Material characterization Densities of the hot-pressed materials were measured by the Archimedes’s method. Test pieces of 3 mm!4 mm! 36 mm were prepared from the hot-pressed disks by cutting and grinding using a diamond wheel and were used for Table 1 Compositions of Al2O3/TiB2/SiCw ceramic tool materials Specimen Composition (vol.%) Al2O3 TiB2 SiCw ABW05 76 19 5 ABW10 72 18 10 ABW20 64 16 20 ABW30 56 14 30 Table 2 Composition of Inconel718 work piece material by weight percentage Ni Mo Si Co Ti Nb Al Cr P Mn Ca Cu Me Fe 32.4 2.98 0.04 0.12 1.01 5.15 0.49 18.7 0.003 0.02 0.01 0.02 0.01 Balance 1394 D. Jianxin et al. / International Journal of Machine Tools & Manufacture 45 (2005) 1393–1401