MSA-25534: No of Pages 9 ARTICLE IN PRESS D Jianxin et aL. Materials Science and Engineering A xxx(2009)xxx-xXX Fig 13 shows the SEM micrographs at the wear track of the Lt ●LT4 layered tool 2, LT-4, and LT-5 layered ceramic tools after 20 min of cutting. It is 05 evident that the flank wear of LT-4 layered tool is smaller than that -LT-2 layered tool of the LT-2 and LT-5 tools It seems that the flank wear of the layered -o-LT-5 layered tool tools is also influenced by the thickness ratio. The lt-4 layered tool -CH AwT stress-free tool with thickness ratio of 8 between adjacent layers exhibited higher flank wear resistance over the LT-2 and LT-5 layered tools. 3.5. Discussion As calculated above, layered structures in AWT+ AT multilay ered ceramic materials can form excess residual stresses during fabrication. These residual stresses are compressive in AWT outer yer and tensile in AT internal layer. Both the compressive resid stress in AwT outer layer and the tensile stress in aT inner layer are far lower than the fracture strength of the Awt and at unstressed 50010001500200025003000 materials [41]. That is to say the differences in CTE of AWT and Cutting distan AT are sufficient to induce residual stresses in awr+at multilay ered ceramics, but these residual stresses do not exceed the values Fig 10. Flank wear of LT-2, LT-4, and LT-5 layered ceramictools and AWTstress-free which can cause micro-cracking and interface delamination of the AWT+ AT multilayered ceramic materials The residual stresses in AWT+AT multilayered ceramic mate both the rake face and the cutting edge of the AwT stress-free tool als exhibit an alternate compressive-tensile, their magnitudes and ere broken down completely under these test conditions. While distribution are significantly dependent on the thickness ratios. the layered tools are less sensitive to this kind of wear Increasing thickness ratio can result in a strong decrease of the ten- There are quite a number of and ridges and mechanical plowing sile stresses in at internal layers together with a greatly rise of rooves on the flank face of the Awr stress-free tool and the lt- compressive stresses in AwT external ones(see Figs 5-7). From a 4 layered tool (see Fig 12), and it is indicative of typical abrasive residual stress viewpoint, LT-4 multilayered ceramic material with wear. It appears the tool wear mechanism at the flank face of the thickness ratio of 8 would be the best candidate for structural appl layered tool is no different from that of the stress-free one. cations among the ones studied here, since it combines the high (b) Fig. 11. SEM micrographs of the worn tool-tip profiles of (a)AWT stress-free tool and (b)LT-4 layered tool after 25 min of cutting. (a) Fig. 12. SEM micrographs of the flank face of (a)AWT stress-free tool and ( b)LT-4 layered tool after 25 min of cutting. 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 D. Jianxin et al. / Materials Science and Engineering A xxx (2009) xxx–xxx 7 Fig. 10. Flank wear of LT-2, LT-4, and LT-5 layered ceramic tools and AWT stress-free tool in dry cutting of nodular cast iron. both the rake face and the cutting edge of the AWT stress-free tool were broken down completely under these test conditions. While the layered tools are less sensitive to this kind of wear. There are quite a number of and ridges and mechanical plowing grooves on the flank face of the AWT stress-free tool and the LT- 4 layered tool (see Fig. 12), and it is indicative of typical abrasive wear. It appears the tool wear mechanism at the flank face of the layered tool is no different from that of the stress-free one. Fig. 13 shows the SEM micrographs at the wear track of the LT- 2, LT-4, and LT-5 layered ceramic tools after 20 min of cutting. It is evident that the flank wear of LT-4 layered tool is smaller than that of the LT-2 and LT-5 tools. It seems that the flank wear of the layered tools is also influenced by the thickness ratio. 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. 3.5. Discussion As calculated above, layered structures in AWT + AT multilay￾ered ceramic materials can form excess residual stresses during fabrication. These residual stresses are compressive in AWT outer layer and tensile in AT internal layer. Both the compressive residual stress in AWT outer layer and the tensile stress in AT inner layer are far lower than the fracture strength of the AWT and AT unstressed materials [41]. That is to say the differences in CTE of AWT and AT are sufficient to induce residual stresses in AWT + AT multilay￾ered ceramics, but these residual stresses do not exceed the values which can cause micro-cracking and interface delamination of the AWT + AT multilayered ceramic materials. The residual stresses in AWT + AT multilayered ceramic materi￾als exhibit an alternate compressive-tensile, their magnitudes and distribution are significantly dependent on the thickness ratios. Increasing thickness ratio can result in a strong decrease of the ten￾sile stresses in AT internal layers together with a greatly rise of the compressive stresses in AWT external ones (see Figs. 5–7). From a residual stress viewpoint, LT-4 multilayered ceramic material with thickness ratio of 8 would be the best candidate for structural appli￾cations among the ones studied here, since it combines the high Fig. 11. SEM micrographs of the worn tool-tip profiles of (a) AWT stress-free tool and (b) LT-4 layered tool after 25 min of cutting. Fig. 12. SEM micrographs of the flank face of (a) AWT stress-free tool and (b) LT-4 layered tool after 25 min of cutting