JOURNAL OF MATERIALS SCIENCE 40 (2 0 0 5 ) 785 – 787 LETTERS Cutting performance of Al 2 O 3 -SiC nanocomposite tools YOUNG-MOK KO, WON TAE KWON ∗ Department of Mechanical and Information Engineering, The University of Seoul, 90 Jeonnong-Dong, Dongdaemoon-Ku, Seoul 130-743, South Korea E-mail: kwon@uos.ac.kr YOUNG-WOOK KIM Department of Materials Science and Engineering, The University of Seoul, Seoul 130-743, South Korea Since the initial work of Niihara [1], the superior prop- erties of ceramic nanocomposites have been exten- sively investigated. A system of particular interest is the Al 2 O 3 -SiC system because it has been reported to have the most improved properties; Al 2 O 3 ceramics containing 5% SiC particles of size 300 nm showing strengths of more than 1 GPa [1]. Compared to mono- lithic Al 2 O 3 ceramics, an increase in strength accompa- nied by a modest toughness increase has been reported [2, 3]. The effects of varying the volume fraction and the particle size of the SiC on mechanical properties have been studied elsewhere [4–6]. However, very few investigations of the wear and cutting performance of Al 2 O 3 -SiC composites have been published, and those were focused on the erosive and sliding wear of the composites [7, 8]. This paper presents the preliminary results of an in- vestigation on the cutting performance of Al 2 O 3 -SiC nanocomposites in machining a gray cast iron. Partic- ular attention has been given to the study of the effect of SiC particle size on tool life of the composite tools. Commercially available α-Al 2 O 3 powder (∼200 nm, AKP50, Sumitomo Chemical Co., Osaka, Japan) and two different β -SiC powders were used as starting pow- ders; SiC with an average particle size of 280 nm (Ul- trafine, Ibiden Co., Nagoya, Japan) and 30 nm (Material Institute Tech. Inc., Richmond, CA, USA). Batch com- position and sintering conditions of each homemade ceramic tool are given in Table I. Monolithic Al 2 O 3 tools were fabricated from α-Al 2 O 3 for comparison purposes. Each batch was ball-milled in ethanol for 24 hrs using SiC balls in a polyethylene jar. The mixed slurry was dried, subsequently sieved through a 60- mesh screen and hot-pressed at 1550–1700 ◦ C under a pressure of 25 MPa in an argon atmosphere. Sinter- ing time was 1 hr for monolithic Al 2 O 3 and 2 hrs for the Al 2 O 3 -SiC nanocomposites. Sintered density was measured using the Archimedes method. The sintered specimens were cut and polished to a 1 μm finish, then etched thermally. The microstructures were observed by inspecting both thermally etched and fractured sur- faces of the manufactured tools using scanning electron microscopy (SEM). SEM micrographs of the polished and etched surfaces were quantitatively analyzed by image analysis (Image-Pro Plus, Media Cybernetics, ∗ Author to whom all correspondence should be addressed. Maryland, U.S.A.), using the procedure introduced in the previous studies [9, 10]. The hardness was mea- sured using a Vickers indenter with a load of 500 g. The fracture toughness was measured by the indenta- tion method with a load of 49 N [11]. Turning experiments were carried out on a CNC lathe (Hyundai HiT-15, Ulsan, Korea) under dry cutting conditions. The sintered nanocompos- ites were cut and ground to make SNGN120408 (12.7 × 12.7 × 4.76 mm, 0.8 mm nose radius and 0.2 mm × 20 ◦ chamfer). A CSRNR tool holder (offset shank with 75 ◦ side cutting edge angle, 0 ◦ insert nor- mal clearance and 25 × 25 × 150 mm) was used for the cutting experiments. Cutting performance of the com- posite tools was tested by machining gray cast iron. The cutting tests for machining the gray cast iron 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 dimensions of the work piece were 110 mm in diam- eter and 350 mm in length. The wear of the tools was determined by measuring the wear depth on the flank face. The wear depth was measured by using a tool mi- croscope (Hanra Precision Engineering, Micro Vision System SV-2000, Seoul, Korea) at more than four points on the flank face and the average of them was taken as a nominal flank wear depth. The tool life was considered to be finished when the wear depth on the flank face reached 0.3 mm. For comparison, two kinds of com- mercial ceramic composite tools, made of Al 2 O 3 -TiC composites, and Al 2 O 3 -SiC whisker composites (Ta- ble II), were selected and tested under the same cutting conditions with the homemade cutting tools. The grain size, sintered density, hardness, and frac- ture toughness of the materials are given in Table III. The grain size of Al 2 O 3 matrix decreased on adding the SiC particles and the addition of smaller SiC particles led to a smaller grain size in the composites. The den- sity of the materials decreased on adding SiC particles because the theoretical density (3.218 g/cm 3 ) of β -SiC is lower than that (3.987 g/cm 3 ) of α-Al 2 O 3 . Almost full density (≥99% of theoretical) was achieved in all materials. Fig. 1 shows the SEM micrographs of the fracture surfaces of monolithic Al 2 O 3 (designated as AO) and Al 2 O 3 -SiC nanocomposites (designated as AOS and 0022–2461 C  2005 Springer Science + Business Media, Inc. 785