SialonSi3N4系梯度纳米复合陶瓷刀具的切削性能.docx

1、SialonSi3N4系梯度纳米复合陶瓷刀具的切削性能Cutting performance of Sialon-Si3N4 graded nano-composite ceramic cutting tools#ZHENG Guangming, ZHAO Jun, GAO Zhongjun, ZHOU Yonghui*5 (Key Laboratory of High Efficiency and Clean Mechanical Manufacture of MOE, School of Mechanical Engineering, Shandong University, JiNan

2、250061) Foundations: the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20090131110030), the National Basic Research Program of China (No. 2009CB724402), the National Natural Science Foundation of China (No. 50875156) Brief author introduction:ZHENG Guangming, (1986), Ma

3、le, Postgraduate student for doctor degree, Research on high effciency cutting and tool materials Correspondance author: ZHAO Jun, (1967), Mail, Ph.D., Professor. Research on high effciency cutting and tool materials. E-mail: zhaojun Abstract: Sialon-Si3N4 graded nano-composite ceramic tool material

4、s were fabricated by using hot-pressing technique. The cutting performance of the graded tools were investigated via turning of Inconel 718 alloy in comparison with common reference tools. The results showed that graded 10 structure in Sialon-Si3N4 graded ceramic tool materials can induce residual c

5、ompressive stresses in the surface layer during fabrication. Tool lifetime of graded ceramic tool was higher than that of the common reference tool. The longer tool life of the graded nano-composite ceramic tool was attributed to its synergistic strengthening and toughening mechanisms induced by the

6、 optimum graded compositional structure of the tool and the addition of nano-sized particles. Wear mechanisms 15 identified in the machining tests involved adhesive wear and abrasive wear. The mechanisms responsible for the higher tool life were determined to be the formation of compressive residual

7、 stress in the surface layer of the graded tools, which led to an increase in resistance to fracture. Keywords: Graded ceramic cutting tools; Wear mechanisms; Residual stress; Inconel 718 20 0 Introduction Si3N4 ceramics and Sialon ceramics are considered to be the ideal tool materials for machining

8、 of Nickel-based super alloys at higher speed conditions because of their relatively high strength and fracture toughness1,2. Whereas, the characteristics of Si3N4 and Sialon ceramic limiting their applications are their relatively lower hardness and wear resistance 3,4. 25 Conventionally, Si3N4-bas

9、ed and Sialon-based ceramic tool materials were strengthened and toughened by the addition of particles like SiC, TiCN, TiC, etc. to improve the mechanical properties 5-7. The matrix grains of the composite were also refined by adding nano-Si3N4particles, because the addition of nano-Si3N4 particles

10、 could promote the formation of the duplex distribution characteristic. The optimum flexural strength and fracture toughness were obtained when the volume fraction ratio of nano-sized Si3N4 to micro-sized Si3N4 is fixed at 1:3830 . In addition, The introduction of the concept of functionally graded

11、material (FGM) into the fabrication of ceramic cutting tool materials provided a new approach to improve their thermal and mechanical properties 9. Functionally graded cutting ceramics with symmetrical structure have been developed to perform high speed intermittent machining of hard metals, with hi

12、gher tool lives than those of homogeneous cutting ceramics1035 . The understanding of the wear mechanisms in cutting processes is the prerequisite for not only the proper application but also the development of graded ceramic tool materials. In turning of Inconel 718, the typical wear types of ceram

13、ic tools are crater wear, flank wear and depth of cut notch wear which are sometime accompanied by chipping 11-13. The typical wear mechanisms of 40 ceramic tools in turning of Inconel 718 are adhesive wear, abrasive wear, plastic deformation, diffusion wear and micro-breakout1,11,14. The wear mecha

14、nisms vary with the location of worn area. For example, adhesive wear is the main wear mechanisms in the rake face, while abrasive - 2 - 中国科技论文在线wear is the main wear mechanisms in the flank face. The characteristic of the depth of cut notch wear is very severe when machining Inconel 718 with cerami

15、c tools 2,15. Additionally, the 45 diffusion elements of Inconel 718 alloy to the tool rake face such as Ni and Co might accelerate the tool wear rate 11. In the present paper, Sialon-Si3N4 graded nano-composite ceramic tool materials were fabricated by the optimum graded compositional structure of

16、the tool and the addition of nano-sized particles. The cutting performance and wear mechanisms of graded ceramic tools were 50 investigated via turning of Inconel 718, with common reference tools used as competitors. Worn surfaces of the tools were characterized by scanning electron microscopy (SEM)

17、 and energy dispersive X-ray spectroscopy (EDS) to reveal the wear mechanisms. Surface roughness of the finish hard turning of Inconel 718 and microstructures of the chips were also analyzed. 1 Experimental methods 55 The design and fabrication of SialonSi3N4 graded nano-composite ceramic tool mater

18、ials was discussed in our previous study 16. In the present study, Sialon-Si3N4 graded nano-composite ceramic tool materials were fabricated by the optimum graded compositional structure of the tool and the addition of nano-sized particles. The graded materials have a five-layered with symmetrical s

19、tructure. GSS1 (the outer layer and the inner layer were Si3N4-based material) was 60 sintered with the thickness ratio of 0.3 at 1700 for 60 min under a fixed uniaxial pressure of 35 MPa. GSS2 (the outer layer was Sialon-based material and the inner layer was Si3N4-based material) was sintered with

20、 the thickness ratio of 0.3 at 1750 for 60 min under a fixed uniaxial pressure of 35 MPa. For the purpose of comparison, homogeneous reference ceramic materials SAAT10 (Sialon-based material) and ST10 (Si3N4-based material) were also manufactured by 65 hot-pressing. The cutting performance of the Si

21、alon-Si3N4 graded nano-composite ceramic tools (GSS1 and GSS2) were tested in comparison with that of the reference ceramic tools (SAAT10 and ST10) and a commercially available Sialon ceramic tool (Kennametal, type is SNGN120408T01020, grade is KY1540). The mechanical properties of the five tool mat

22、erials are listed in Table 1. The 70 tools have the following geometry parameters: rake angle 0=-5, clearance angle 0=5, inclination angle s=0, side cutting edge angle r=45. Tab. 1 Averages and standard deviations of mechanical properties of the tool materials. Tools f/MPa KI C /MPam1/2 HV /GPa GSS1

23、 98060 9.540.52 a 16.910.30 aGSS2 81030 9.330.46 a 16.980.24 aST10 86090 8.190.91 16.290.23 SAAT10 64595 7.800.55 16.590.31 KY1540 7.450.61 18.240.25 Note: a the property of the surface lay 75 A computer numerically controlled (CNC) centre lathe PUMA200MA with maximum speed of 6000 r/min was used fo

24、r the machining trials. Machining trials were conducted using 120 mm diameter 380 mm long Inconel 718 alloy bars. All tests were carried out with the following parameters: depth of cut ap=0.1 mm, feed rate f=0.1 mm/rev, cutting speed v=80, 120 and 200 80 m/min. Average flank wear VBave=0.30 mm was u

25、sed as the tool life criterion. The condition of the cutting edge was examined periodically, and any apparent change in the edge surface was closely examined with an optical microscope. A scanning electron microscope (SEM) (JSM-6380LA, Japan) equipped with an energy-dispersive X-ray spectrometer (ED

26、S) was used to examine the - 3 - 中国科技论文在线85 nature of the worn tools and observe morphological features of chips. The surface roughness of the Inconel 718 was measured by a portable surface roughness tester (Model TR200, China). The surface roughness measures used in the paper is the arithmetic mean

27、 value of the surface roughness of profile, Ra. 2 Results and discussion 90 2.1 Cutting performance of Sialon-Si3N4 graded nano-composite ceramic tools Fig. 1 Average flank wear curves of the five tools at f=0.1 mm/r and ap=0.1 mm, (a) v=80 m/min, (b) v=120 m/min, (c) v=200 m/min. 95 Fig. 1 shows th

28、e variation of average flank wear width with cutting time of the five tools in turning of Inconel 718, tested at different speeds with 0.1 mm/r feed rate and 0.1 mm depth of cut. As can be seen from Fig. 1a-c, among the five cutting tools, graded nano-composite ceramic tools (GSS1 and GSS2) showed b

29、etter performance than that of homogeneous reference tools (ST10 100 and SAAT10), especially at lower cutting speeds 80 m/min and 120 m/min. Furthermore, the graded ceramic tool GSS1 showed better cutting performance than that of the commercially available Sialon ceramic tool KY1540 at lower cutting

30、 speeds 80 and 120 m/min. The tool life of SAAT was the shortest because of its relatively low flexural strength and fracture toughness (see Table 1). 105 From the cutting experiments, the results have shown that tool life was affected by cutting speeds significantly. It was found that the ceramic t

31、ool exhibited a relative long cutting life at cutting speed 120 m/min under this experiment conditions. As can be seen from Fig. 1a, the ceramic tools were not suitable for low speed cutting of nickel-based alloys because of the shorter tool life of the five tools at cutting speed 80 m/min, at least in this experiment conditions. 110 Increasing in cutting speed caused a lager increment in cutting temperature at the cutting edge of the tools. The higher temperature caused the tools to lose their strength. Therefore, the tools lives were shortest at cutting speed