8 AO AOS1 AOS2 AOS3 AOS4 C1 AO AOS1 AO Tool materals Tool Materals various cutting tools during machining heat-treated Fig. 6. Tool life of various cutting tools during machining gray cast iron AlsI 4140 at a cutting speed of 160 m/min with a feed rate of 0. 2 mm/rev at a cutting speed of 330 m/min with a feed rate of 0.2 mm/rev and a and a depth of cut of 0.25 mm(asterisk(*)denotes tools broken during depth of cut of 0. 5mm machining) The variation of the flank wear of the homemade and mercially tools(C1-C3). In contrast, the composite tool commercial tools during machining gray cast iron as a func (AOS1-AOS4)have very good wear resistance, as shown in tion of the machining time is shown in Fig. 5. The cutting Fig.3. AOS2 showed the longest tool life among the tools tests were performed at a cutting speed of 330 m/min with sted for machining heat-treated AISI 4140. The tool life a feed rate of 0.2 mm/rev and a depth of cut of 0.5mm of aos2 was seven times longer than that of a commer- The monolithic Al2O3 tool(Ao) was worn out rapidly as cial tool(C2)(see Fig 4). As shown in Fig. 2, the addition it did during machining heat-treated AISI 4140. AOSI with of sic made the transformation of fracture mode from in- tergranular fracture for Al2 O3 to intragranular fracture for tested for machining gray cast iron(Fig. 6). AOS4 showed Al2O3-SiC composites. The improved cutting performance the shortest tool life among the home-made composite tools, but it was still longer than those of commercial tools. The granular fracture mode of the composites. Generally, the tool tool life of AosI was 1.5 times longer than the longest life shortened with increasing the sic content in the com- tool life of selected commercial tool(C1). Generally, the posites. The microfracture was also observed in AOS4 and tool life shortened with increasing the Sic content in the it was considered to be the reason for the shorting of tool composites. This may attribute to the chemical reactions be life in Aos4 tween SiC and Fe in the work-material during machining 4 4. Conclusions The introduction of hard Sic grains into monolithic Al2O3 increased the hardness and decreased the grain size of the material, thereby greatly improving its cutting performance, compared to the commercial tools made of monolithic Al2O3, Al2O3-TiC composites, and Al2O3-SiC whisker composites. The Al2O3-5 wt SiC composites and the Al2O3-l0 wt. SiC composites showed the best cutting performance for machining gray cast iron and heat-treated AISI 4140 steel, respectively. The tool life of the Al2O3-5 wt %SiC and Al2O3-10 wt %SiC composite 0200400 tools was 1.5 times and 7 times longer than those of com- Cutting Time(sec) mercial tools in machining gray cast iron and heat-treated Fig. 5. Flank wear of various cutting tools as a function of cutting tir AISI 4140, respectively. The present results indicate that during machining gray cast iron at a cutting speed of 330 m/min with a the Al2O3-SiC composites are a promising material for feed rate of 0. 2 mm/rev and a depth of cut of 0.5mm machining applicationsY.M. Ko et al. / Ceramics International 30 (2004) 2081–2086 2085 AO AOS1 AOS2 AOS3 AOS4 C1 C2 C3 0 200 400 600 800 * * * Tool Life (sec) Tool Materals Fig. 4. Tool life of various cutting tools during machining heat-treated AISI 4140 at a cutting speed of 160 m/min with a feed rate of 0.2 mm/rev and a depth of cut of 0.25 mm (asterisk (∗) denotes tools broken during machining). mercially tools (C1–C3). In contrast, the composite tools (AOS1–AOS4) have very good wear resistance, as shown in Fig. 3. AOS2 showed the longest tool life among the tools tested for machining heat-treated AISI 4140. The tool life of AOS2 was seven times longer than that of a commer￾cial tool (C2) (see Fig. 4). As shown in Fig. 2, the addition of SiC made the transformation of fracture mode from in￾tergranular fracture for Al2O3 to intragranular fracture for Al2O3–SiC composites. The improved cutting performance of the Al2O3–SiC composite tools attributed to the intra￾granular fracture mode of the composites. Generally, the tool life shortened with increasing the SiC content in the com￾posites. The microfracture was also observed in AOS4 and it was considered to be the reason for the shorting of tool life in AOS4. 0 200 400 600 800 1000 1200 1400 1600 1800 2000 0 200 400 Flank wear ( mm) Cutting Time (sec) AO AOS1 AOS2 AOS3 AOS4 C1 C2 C3 Fig. 5. Flank wear of various cutting tools as a function of cutting time during machining gray cast iron at a cutting speed of 330 m/min with a feed rate of 0.2 mm/rev and a depth of cut of 0.5 mm. AO AOS1 AOS2 AOS3 AOS4 C1 C2 C3 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Tool Life (sec) Tool Materals Fig. 6. Tool life of various cutting tools during machining gray cast iron at a cutting speed of 330 m/min with a feed rate of 0.2 mm/rev and a depth of cut of 0.5 mm. The variation of the flank wear of the homemade and commercial tools during machining gray cast iron as a func￾tion of the machining time is shown in Fig. 5. The cutting tests were performed at a cutting speed of 330 m/min with a feed rate of 0.2 mm/rev and a depth of cut of 0.5 mm. The monolithic Al2O3 tool (AO) was worn out rapidly as it did during machining heat-treated AISI 4140. AOS1 with 5 wt.% SiC showed the longest tool life among the tools tested for machining gray cast iron (Fig. 6). AOS4 showed the shortest tool life among the home-made composite tools, but it was still longer than those of commercial tools. The tool life of AOS1 was 1.5 times longer than the longest tool life of selected commercial tool (C1). Generally, the tool life shortened with increasing the SiC content in the composites. This may attribute to the chemical reactions be￾tween SiC and Fe in the work-material during machining [2,4]. 4. Conclusions The introduction of hard SiC grains into monolithic Al2O3 increased the hardness and decreased the grain size of the material, thereby greatly improving its cutting performance, compared to the commercial tools made of monolithic Al2O3, Al2O3–TiC composites, and Al2O3–SiC whisker composites. The Al2O3–5 wt.% SiC composites and the Al2O3–10 wt.% SiC composites showed the best cutting performance for machining gray cast iron and heat-treated AISI 4140 steel, respectively. The tool life of the Al2O3–5 wt.%SiC and Al2O3–10 wt.%SiC composite tools was 1.5 times and 7 times longer than those of com￾mercial tools in machining gray cast iron and heat-treated AISI 4140, respectively. The present results indicate that the Al2O3–SiC composites are a promising material for machining applications