G Model MSA-25534: No of Pages 9 ARTICLE IN PRESS D Jianxin et aL Materials Science and Engineering A xxx(2009)xxx-XXx (b) Fig. 13. SEM micrographs at the wear track of (a)LT-2 layered tool, (b)LT-4 layered tool, and(c)Lt-5 layered tool after 20 min of cutting. oppressive stresses in AWT surface layers while with the low residual stresses are compressive in the awt outer layer and tensile ones at AT internal layers tensile in the AT internal layer. Thickness ratios were found to can be seen the awr stress-free tool is more sensitive to rake have a profound effect on the residual stresses. Increasing thick face fracture and cutting edge chipping compared with that of the ness ratio can result in a strong decrease of the tensile stresses in layered tools. Since the tools in machining process suffer severe AT internal layers together with a greatly rise of the compressive stress, which may cause the subsurface lateral cracks and facilitate stresses in Awr external ones the removal of the material chips, and the failure of the tool always 2. The fracture toughness at the outer layer of the AWT+AT mul depends on the stress distribution. Once the maximum tensile tilayered ceramic materials is greatly improved compared with stress exceeds the ultimate strength of the tool material, fracture that of the stress-free one will occur. As calculated above, compressive residual stresses can 3. These multilayered ceramic tools can minimize the flank wear be introduced at the outer layer of the AwT+ at layered tools dur- and edge chipping compared with the stress-free one Th ing fabrication. The higher resistance to fracture of the layered tools anisms responsible were determined to be the form compared with the stress-free one can be analysed in terms of these compressive residual stress on the outer layer of the compressive residual stresses, which may partially counteract the tools, which led to an increase in resistance to fracture. tensile stresses generated during cutting process at the outer layer 4. Thickness ratios were found to have a profound effect on the cut- and decrease in the crack-driving force, consequently, the pro ting performance of the layered ceramic tools. The Lt-4 layere gation of a crack generated in the outer layer can be considerably tool with thickness ratio of 8 between adjacent layers exhibited hindered(see Fig 8), and thus led to an increase in resistance to higher flank wear resistance over the LT-2 and LT-5 layered tools fracture. Therefore these compressive residual stresses are benefi r the increase of the resistance to fracture at the outer layer of Acknowledgement the layered materials, which is also reported by other researchers This work was supported by the"Taishan Scholar Program of In addition, layered structure in ceramic tool can also result in a Shandong Province", the"Outstanding Young Scholar Science Foun- little hardness increase at the outer can be seen in Table 4. dation of Shandong Province", and the"National Basic Research The mechanical hardness depends on both the elastic and the plas- Program of China(2009CB724402)". ticresponse of the material. As can b I that layered structures in AWT+ AT multilayered ceramic material can form large compres- References sive residual stress at the outer layer during fabricating process Such internal stresses can greatly influence the elastic and the plas- [1] G. Brandt, Mater. Technol. 14(1999)17-22. tic response of the material in hardness tests, and are benefit for [2] X Ai, Z.Q. Li, JX. Deng. Key Eng Mater. 108 (1995)53-66 the increase of hardness at the outer layer of the layered materi 3] I. Barry.G.Byne,Wear247(2001)139-151. als, which is also reported by other researchers 50-53]. This effect X Deng, x A,wear195(1996)128-132. lJx. Deng, LL Liu, J.H. Liu, ]L Zhao, Int J. Mach. Tool Manuf. 45(2005) may be another reason for the increase in flank wear resistance of layered tools over the stress-free one [6 KA Senthil, D A. Raja, T. Sornakumar, Int ] Refrac Hard Mater. 21(2003) ong all the layered tools tested, the Lr-4 layered tool wit [7]0. Prakash, P. Sarkar, P.S. Nicholson. ]. Am. Ceram. (4)(1995)1125-1137 wear resistance. It seems that the flank wear resistance of the lay ered tools was influenced by the thickness ratio among constituent 91 w. clegg K. Kendall, N Alford, T. Button, J.D. Birchall, Nature 347(1990) layers. As can be seen from Table 4, the layered tool with high [101 D.B. Marshall, JJ. Ratto, F.F. Lange. J Am Ceram Soc. 74(1991)2979-2987 thickness ratio has higher fracture toughness and surface hardness. 111] B.F. Sorensen, A Horsewell,. Am. Ceram Soc. 84(9)(2001)2051-205 Therefore, the high flank wear resistance of LT-4 layered tools may I D Green, P.Z. Cai, G L Messing, J. Eur. Ceram Soc. 19(1999)2511-2 ergo, D M. Lipkin, De G Portu, DR Clarke, J Am Ceram Soc. orresponds to its high mechanical properties at its outer layer 1633-163 [14] De G. Portu, L. Micele, Y. Sekiguchi, G. Pezzotti, Acta Mater. 53(2005) [15]S Ho, C. Hillman, F F. Lange, Z Suo, ]. Am. Ceram Soc. 78(9)(1995)2353-2357 [16] M. Lugovy, V. Slyunyayev, N. Orlovskaya. G. Blugan, J Kuebler, M. Lewis, Acta with different thickness ratios among constituent layers were pro- [181 H. ToSm anew s,,. t We: Arz. A.wea: e. c. Bo,:., Kalinski L. Eur. Ceram. duced by hot pressing. The following conclusions were obtained Soc27(2007)1373-1377 oran. J Am Ceram Soc. 83(4) red structure in AWT+ At layered ceramic materials Nagliati, C. Melandri, G. Pezzotti, D. Sciti, ]. Eur. Ceram Soc. ce excess residual stresses during fabrication. These [21] P.Z. Cai, D ). Green, G L Messing. ].Eur.Ceram Soc. 5(1998)2025-2034 Please cite this article in press as: D Jianxin, et al, Mater. Sci. Eng. A(2009). doi: 10. 1016/j. msea. 2009.09.020Please cite this article in press as: D. Jianxin, et al., Mater. Sci. Eng. A (2009), doi:10.1016/j.msea.2009.09.020 ARTICLE IN PRESS GModel MSA-25534; No. of Pages 9 8 D. Jianxin et al. / Materials Science and Engineering A xxx (2009) xxx–xxx Fig. 13. SEM micrographs at the wear track of (a) LT-2 layered tool, (b) LT-4 layered tool, and (c) LT-5 layered tool after 20 min of cutting. compressive stresses in AWT surface layers while with the low tensile ones at AT internal layers. As can be seen, the AWT stress-free tool is more sensitive to rake face fracture and cutting edge chipping compared with that of the layered tools. Since the tools in machining process suffer severe stress, which may cause the subsurface lateral cracks and facilitate the removal of the material chips, and the failure of the tool always depends on the stress distribution. Once the maximum tensile stress exceeds the ultimate strength of the tool material, fracture will occur. As calculated above, compressive residual stresses can be introduced at the outer layer of the AWT + AT layered tools dur￾ing fabrication. The higher resistance to fracture of the layered tools compared with the stress-free one can be analysed in terms of these compressive residual stresses, which may partially counteract the tensile stresses generated during cutting process at the outer layer and decrease in the crack-driving force, consequently, the propa￾gation of a crack generated in the outer layer can be considerably hindered (see Fig. 8), and thus led to an increase in resistance to fracture. Therefore, these compressive residual stresses are benefit for the increase of the resistance to fracture at the outer layer of the layered materials, which is also reported by other researchers [7–11]. In addition, layered structure in ceramic tool can also result in a little hardness increase at the outer layer as can be seen in Table 4. The mechanical hardness depends on both the elastic and the plas￾tic response of thematerial. As can be seen that layered structures in AWT + AT multilayered ceramic material can form large compres￾sive residual stress at the outer layer during fabricating process. Such internal stresses can greatly influence the elastic and the plas￾tic response of the material in hardness tests, and are benefit for the increase of hardness at the outer layer of the layered materi￾als, which is also reported by other researchers [50–53]. This effect may be another reason for the increase in flank wear resistance of layered tools over the stress-free one. Among all the layered tools tested, the LT-4 layered tool with thickness ratio of 8 between adjacent layers exhibited more flank wear resistance. It seems that the flank wear resistance of the lay￾ered tools was influenced by the thickness ratio among constituent layers. As can be seen from Table 4, the layered tool with high thickness ratio has higher fracture toughness and surface hardness. Therefore, the high flank wear resistance of LT-4 layered tools may corresponds to its high mechanical properties at its outer layer. 4. Conclusions Al2O3/(W,Ti)C + Al2O3/TiC multilayered ceramic tool materials with different thickness ratios among constituent layers were pro￾duced by hot pressing. The following conclusions were obtained: 1. Multilayered structure in AWT + AT layered ceramic materials can induce excess residual stresses during fabrication. These residual stresses are compressive in the AWT outer layer and tensile in the AT internal layer. Thickness ratios were found to have a profound effect on the residual stresses. Increasing thick￾ness ratio can result in a strong decrease of the tensile stresses in AT internal layers together with a greatly rise of the compressive stresses in AWT external ones. 2. The fracture toughness at the outer layer of the AWT + AT mul￾tilayered ceramic materials is greatly improved compared with that of the stress-free one. 3. These multilayered ceramic tools can minimize the flank wear and edge chipping compared with the stress-free one. The mech￾anisms responsible were determined to be the formation of compressive residual stress on the outer layer of the layered tools, which led to an increase in resistance to fracture. 4. Thickness ratios were found to have a profound effect on the cut￾ting performance of the layered ceramic tools. The LT-4 layered tool with thickness ratio of 8 between adjacent layers exhibited higher flank wear resistance over the LT-2 and LT-5 layered tools. Acknowledgement This work was supported by the “Taishan Scholar Program of Shandong Province”, the “Outstanding Young Scholar Science Foun￾dation of Shandong Province”, and the “National Basic Research Program of China (2009CB724402)”. References [1] G. Brandt, Mater. Technol. 14 (1999) 17–22. [2] X. Ai, Z.Q. Li, J.X. Deng, Key Eng. Mater. 108 (1995) 53–66. [3] J. Barry, G. Byrne, Wear 247 (2001) 139–151. [4] J.X. Deng, X. Ai, Wear 195 (1996) 128–132. [5] J.X. Deng, L.L. Liu, J.H. Liu, J.L. Zhao, Int. J. Mach. Tool Manuf. 45 (2005) 1393–1401. [6] K.A. Senthil, D.A. Raja, T. Sornakumar, Int. J. Refract. Met. Hard Mater. 21 (2003) 109–117. [7] O. Prakash, P. Sarkar, P.S. Nicholson, J. Am. Ceram. Soc. 78 (4) (1995) 1125–1137. [8] R. Bermejo, Y. Torres, A.J. Sanchez-Herencia, C. Baudin, M. Anglada, L. Llanes, Acta Mater. 54 (18) (2006) 4745–4757. [9] W.J. Clegg, K. Kendall, N. Alford, T. Button, J.D. Birchall, Nature 347 (1990) 455–467. [10] D.B. Marshall, J.J. Ratto, F.F. Lange, J. Am. Ceram. Soc. 74 (1991) 2979–2987. [11] B.F. Sorensen, A. Horsewell, J. Am. Ceram. Soc. 84 (9) (2001) 2051–2059. [12] D.J. Green, P.Z. Cai, G.L. Messing, J. Eur. Ceram. Soc. 19 (1999) 2511–2517. [13] V. Sergo, D.M. Lipkin, De G. Portu, D.R. Clarke, J. Am. Ceram. Soc. 80 (7) (1997) 1633–1638. [14] De G. Portu, L. Micele, Y. Sekiguchi, G. Pezzotti, Acta Mater. 53 (2005) 1511–1520. [15] S. Ho, C. Hillman, F.F. Lange, Z. Suo, J. 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