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(W, Ti)C graded ceramic tool in high-speed turning iron-based superalloys
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Performance of Si3N4/(W, Ti)C graded ceramic tool in high-speed turning iron-based superalloys ⁎
Xianhua Tiana,b, , Jun Zhaoc, Xinya Wangd, Haifeng Yanga,b, Zhongbin Wanga,b a
School of Mechatronic Engineering, China University of Mining and Technology, Xuzhou 221116, PR China Jiangsu Key Laboratory of Mine Mechanical and Electrical Equipment, China University of Mining and Technology, Xuzhou 221116, PR China c School of Mechanical Engineering, Shandong University, Jinan 250061, PR China d Department of Industrial & Manufacturing Systems Engineering, Kansas State University, Manhattan, KS 66506, USA b
A R T I C LE I N FO
A B S T R A C T
Keywords: Graded ceramic Si3N4/(W Ti)C Cutting performance Iron-based alloys
A Si3N4/(W, Ti)C graded nano-composite ceramic tool was fabricated and its performance in high speed turning iron-based alloys GH2132 was investigated compared with homogeneous and commercial ceramic tools. The chip morphology, cutting forces, cutting temperature, tool life and failure mechanisms and machined surface roughness were recorded and analyzed. The results showed that with the increasing cutting speed the resultant cutting force shows a tendency to first increase and then decrease while the cutting temperature increases gradually. Straight continuous chips, bending continuous chips, twist continuous chips and snarled chips form in turn. Saw-tooth chips tend to form when the cutting speed is more than 200 m/min. The graded tool shows longer tool life especially at the cutting speed of 150 and 200 m/min compared with the homogenous and commercial ceramic tools. Tool failure modes mainly include grooving on the rake face, notching on the flank face, abrasion and adhesion. The grooving on the rake face tends to decrease while notching on the flank face tends to increase as cutting speed increases. Surface roughness of the machined iron-based super-alloys is relatively high due to the serious adhesion. Better surface roughness can be got using the graded tool.
1. Introduction
performance of ceramic tools can be improved a lot [15,16]. The cutting performance of ceramic tools can also be improved by coatings [17]. However, the coatings are easy to spall especially at high speed cutting conditions. FMG also shows some benefits in improving the bonding strength of coatings [6]. High temperature alloys, including nikel-based, iron-based and cobalt-based alloys, are widely applied in air-craft and nuclear fields for their excellent properties at high temperature [18]. On the contrary, the superiority also makes them difficult-to-cut materials. When using cemented carbide tools to cut them, the cutting speed is always limited to 50 m/min, which limits the machining efficiency greatly [18]. Ceramic tools provide another option to cut high temperature alloys at higher cutting speeds. Many researchers have studied the performance of ceramic cutting tools in high-speed cutting superalloys. Tian et al. [4] compared Al2O3 + SiCw and SiAlON ceramic tools in high-speed milling Inconel 718 and concluded that SiAlON ceramic tools show a better notch wear and thermal shock resistance, while Al2O3 + SiCw tools show a better machined surface roughness. Bushlya et al. [19] used Al2O3-SiCw ceramic tools in high-speed turning aged Alloy 718 and concluded that notching, adhesion and attrition are the main wear mechanisms and their formation mechanisms were analyzed as well.
Ceramics are good candidates for cutting tools due to their high heat and wear resistance and good chemical stability [1]. They can be utilized to machine hard-to-cut materials, like high temperature superalloys, especially at high cutting speed [2–4]. Alumina based and silicon nitride based ceramics are the most applied ceramic cutting tool material at the moment. Besides, TiB2 [5] and Cr2O3 [6] based ceramics have also been reported. However, due to lower fracture strength and thermal shock resistance, ceramic tools tend to chip and fracture in the cutting process which limits their application. These ceramics can be toughened by changing their microstructure through particulate toughening, fiber toughening, whisker toughening, and transformation toughening effect and so on. The added compositions include particles, fibers, whiskers, transformation phases and metal phases [7–11]. Besides, graphene and nanotube have also been incorporated into ceramic matrix [12,13]. Another way is to change their macrostructure by using the concept of functionally graded material (FGM). FGM is first proposed in aerospace area to fabricate heat insulation material by the metal/ceramic structure [14]. Using FGM or laminated structure, mechanical properties as well as cutting ⁎
Corresponding author at: School of Mechatronic Engineering, China University of Mining and Technology, Xuzhou 221116, PR China. E-mail address: [email protected] (X. Tian).
https://doi.org/10.1016/j.ceramint.2018.05.222 Received 27 April 2018; Received in revised form 24 May 2018; Accepted 25 May 2018 0272-8842/ © 2018 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Tian, X., Ceramics International (2018), https://doi.org/10.1016/j.ceramint.2018.05.222
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Fig. 1. The graded cutting tools, (a) sketch of the insert and (b) fabricated inserts.
After that, the side surfaces of the blocks were ground (universal tool grinder, type MQ6025A) and lapped and the edges were chamfered. The final dimensions of the inserts are 16 mm × 16 mm × 6 mm with 0.1 mm × (−15°) chamfer and 0.2 mm corner radius. The commercial KY1540 tool insert has a dimension of 12.7 mm × 12.7 mm × 4.76 mm with 0.1 mm × (−20°) chamfer and 0.8 mm corner radius.
Zheng et al. [20] studied the performance of Sialon-Si3N4 graded ceramic cutting tools in milling of Inconel 718 and found that the graded tool possessed a self-sharpening characteristic and exhibited higher cutting performance compared with the homogeneous ones. It can be seen that the former studies mainly focus on nikel-based superalloys, rarely on Iron-based alloys. In this paper, the cutting performance of a Si3N4/(W, Ti)C graded ceramic tool in high speed turning Iron-based superalloys GH2132 is studied compared with one homogeneous tool and one commercial tool. The graded tool was fabricated by hot-press sintering technology. The chip morphology, cutting force, cutting temperature and machining quality were recorded. Tool life and failure mechanisms were analyzed.
2.2. Cutting tests setup The experiments layout is shown in Fig. 2. The cutting performance of the graded ceramic cutting tools was studied via high-speed dry turning age-strengthened-type iron-based supperalloys GH2132. Its chemical composition is shown in Table 2 [22]. The tensile strength can reach about 1035 MPa at room temperature, 799 MPa at 600 °C and 402 MPa at 800 °C. The alloy bar was with a dimension of 122 mm diameter × 380 mm long. The graded cutting tool compared with one homogeneous tool and one commercial tool are used in the tests as shown in Table 3, and their mechanical properties are also presented. Indentation method was used to measure the hardness and fracture toughness [23] while the flexural strength was measured by three-point bending test. It can be concluded that the graded structure is beneficial for improving mechanical properties of ceramic tools especially the flexural strength and fracture toughness. The cutting geometry parameters are as follows, rake angle γo = −5°, clearance angle αo = 5°, inclination angle λs = 0°, and side cutting edge angle κr = 45°. The cutting parameters are shown in Table 4. To ensure the measurement repeatable and comparable, every test was repeated at least three times with a new cutting edge. The tool failure criterions are as follows, (1) average flank wear VBave = 0.30 mm, (2) maximum flank wear VBmax ≥ 0.60 mm, or (3) catastrophic fracture of the cutting edge. Cutting forces were recorded by a three-component piezoelectric Kistler dynamometer (type 9265A) with a sampling frequency of 4000 Hz. Cutting temperature was obtained by NEC thermal infrared imager (type TH5140R). An AM413ZT Dino-Lite digital microscope
2. Experimental procedure 2.1. Design and fabrication of graded ceramic tools Considering the ease of fabrication, compositional distribution of the graded ceramic tools changes only along z direction as shown in Fig. 1(a). To make the top and bottom surfaces could be used as rake faces, a five-layer symmetric graded structure is used. The thickness ratio (that is h1/h2 = h2/h3) is fixed at 0.2 according to our former research [21]. The finally fabricated inserts are shown in Fig. 1(b). To avoid fracture and spalling between layers, the composition between layers is gradually changed. Three kinds of homogeneous ceramic materials were developed to construct the graded structure as listed in Table 1. They were named after the adding amount of reinforcing phase (W, Ti)C. Some nano-Si3N4 particles, weight ratio to micro-Si3N4 being set to be 1/3, were added. The graded material is built as SWT15/ SWT20/SWT25/SWT20/SWT15 and named as GSWT52. Since thermal expansion coefficient of the reinforcing phase is larger than that of the base material, residual compressive stress was introduced in the surface layers during the cooling down process after complete sintering. Besides, the higher hardness of the surfaces layers and the higher strength of inner layers are also ensured. The raw materials and the detailed fabrication process of the mixed powers in Table 1 are presented elsewhere [21]. After that, the mixed powers were cold prepressed into the graphite mold layer by layer and then hot-pressed sintering at 1700 °C for 45 min under a pressure of 30 MPa in vacuum condition. The sintering plates were first surface ground (surface grinder, type M7120D/H) to specified size and then cut into square blocks (inside diameter slice machine, type J5060C-1). Table 1 Composition of different homogeneous composites (vol%). Composites
Nano (25 nm) and micro (0.5 µm) Si3N4
(W, Ti)C (1 µm)
Sintering adds (0.5 µm)
SWT15 SWT20 SWT25
77 72 67
15 20 25
8 8 8
Fig. 2. Cutting experiments layout. 2
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chips (vc ≤ 100 m/min) to bending continuous chip (vc ≤ 150 m/min), twist continuous chips (vc ≤ 200 m/min) and snarled chips (vc ≤ 300 m/min). Even some segmental chips (Fig. 3(e)) appear at the cutting speed of 300 m/min. This should be attributed to the high strain rates and thermal softening effect which makes the chip easier to deform under higher cutting speeds [24]. Fig. 4 shows the micro free surface morphologies of chips at different cutting speeds. The shearing mechanisms give rise to the jagged and rough appearances [25]. With the increasing cutting speed, the extrusion deformation intensifies. When the cutting speeds are more than 200 m/min, the larger lamella structure means that the saw-tooth chips forms and the saw-tooth pitch increases considerably with the further increase of cutting speed. The formation of saw-tooth chips will decrease the contact length between chip and rake face [26]. Chip morphologies have an evident effect on wear morphology of tool flank face as discussed in Section 3.4.
Table 2 Chemical composition of GH2132 (wt%) [22]. Fe
Ni
Cr
Ti
Mo
V
Al
Bal
24.00～ 27.00 Mn ≤ 2.00
13.50～ 16.00 Si ≤ 1.00
1.75～2.30
1.00～1.50
0.10～1.50
0.40
C ≤ 0.08
P ≤ 0.03
S ≤ 0.02
B 0.001～ 0.01
Table 3 Materials and mechanical properties of cutting tools. Material
Grade
Hardness
Flexural strength
Fracture toughness
Sialon Si3N4/(W, Ti)C Graded
KY1540 SWT20 GSWT52
16.36 17.72 17.64
– 979 1080
8.4 8.5 10.9
3.2. Cutting forces and cutting temperature
Table 4 Cutting parameters. Depth of cut (mm)
Feed rate (mm/r)
Cutting speed (m/min)
0.1
0.1
50, 100, 150, 200, 250, 300
The measurement of cutting force is essential to assess performance of cutting tools since it has great effect on the machined surface quality and productivity. Cutting forces are usually influenced by friction in the tool/chip interface and shear strength of workpiece material in the shear areas [27]. Fig. 5(a) shows the resultant cutting forces under different cutting speeds. It can be got by the equation Fr = F2x + F2y + F2z , where Fx, Fy and Fz are the recorded cutting force components in x-, y-, and z- directions by the dynamometer. They are recorded at the initial cutting stage. In general, the resultant cutting forces show a tendency to increase first and then decrease, while that of SWT20 increases once again after 200 m/min. The first increase of cutting force is mainly due to serious friction between the chips and tool. With further increasing cutting speed, the cutting heat generated in the shear area cannot be effectively conducted and diffused and cutting temperature rises and thus the thermal softening effect, which decreases the hardness and shear strength of workpiece material, leads to the decrease of cutting forces. The subsequent increase of the cutting force of SWT20 is maybe due to the serious adhesive wear. Infrared imager can only provide an assessment of temperature values due to the interference of some factors [27]. It still provides
(AnMo Co., Taiwan) was utilized to measure the tool wear values periodically, and a JSM-6510 LV scanning electron microscope (SEM) equipped with an energy X-ray spectrometer (EDS) was used to identify the tool failure patterns and wear mechanisms. The surface roughness value Ra is the arithmetic mean value of at least three measurements per sample, which were got by a portable surface roughometer (model TR200, China).
3. Results and discussions 3.1. Chip analysis Fig. 3(a)-(d) shows the macro chip morphology under different cutting speeds. Obviously, with the increasing cutting speed, the chip deformation becomes more severe. It changes from straight continuous
Fig. 3. Macro chip morphologies under different cutting speed (f = 0.1 mm/r, ap = 0.1 mm), (a) vc = 100 m/min, (b) vc = 150 m/min, (c) vc = 200 m/min, (d) vc = 300 m/min, (e) Fragmental chips, vc = 300 m/min, and (f) Screw shape chips, vc = 100 m/min. 3
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Fig. 4. Micro free surface morphologies of chips under different cutting speed (f = 0.1 mm/r, ap = 0.1 mm), (a) vc = 50 m/min, (b) vc = 100 m/min, (c) vc = 150 m/ min, (d) vc = 200 m/min and (e) vc = 300 m/min.
(b)
200 KY1540
SWT20
Cutting temperature T ( )
Resultant cutting force Fr (N)
(a)
GSWT52
150 100 50
600
KY1540
SWT20
GSWT52
400
200
0
0 50
100 150 200 Cutting speed vc (m/min)
50
300
100 150 200 300 Cutting speed vc (m/min)
Fig. 5. (a) Resultant cutting force and (b) Cutting temperature under different cutting speeds.
the five different cutting conditions. While tool life of the newly developed tools increases first up to 150 m/min, and then decrease. The graded tool shows some advantage especially at the cutting speed of 100 and 150 m/min. And it shows the typical initial-normal-acutely worn stages. Fig. 7 shows the evolution of some cutting parameters of the graded tool versus cutting time at the cutting speed of 150 m/min. It can be seen that the tool life is about 17.5 min and flank tool wear increases gradually as the cutting process goes on. Machined surface roughness shows the same changing trend, which means that tool wear has a great influence on machined surface quality. At the normal worn stage, cutting force and cutting temperature show a trend to slowly increase with slight fluctuation. At the acutely worn stage, cutting force increases greatly while cutting temperature increases to a certain level and maintain stable. The increasing cutting force will lead to more serious friction between tools and workpiece and in turn lead to faster tool wear.
some helpful information by comparing the measured temperatures of different tools. As shown in Fig. 5(b), the cutting temperature rises gradually with the increasing cutting speed. When the cutting speed is more than 150 m/min, tool wear of KY1540 becomes seriously in a short time and it makes the highest cutting temperature. The graded tool shows smaller cutting forces and lower cutting temperature because of its longer tool life and less tool wear values. Because of the reasonable composition distribution of the graded tool, compressive residual stress will be induced in the surface layers of it. The residual stress can alleviate the external thermal-mechanical stress and reduce tool wear and thus reduces the cutting force and cutting temperature. It is also beneficial to the machined surface quality of workpiece. 3.3. Tool life and progressive failure Fig. 6 shows the change process of flank wear versus cutting distance under different cutting speeds. Tool life of KY1540 is limited for 4
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(a)
(b) 0.5
0.7
Flank wear VB (mm)
Flank wear VB (mm)
0.6 0.4
0.3 0.2 KY1540 SWT20 GSWT52
0.1
SWT20 0.4
GSWT52
0.3 0.2 0.1 0
0 0
500 1000 Cutting distance L (m), vc=50m/min
0
1500
(c)
500 1000 1500 2000 Cutting distance L (m), vc=100m/min
2500
(d) 0.5
0.5
0.4
0.4
Flank wear VB (mm)
Flank wear VB (mm)
KY1540
0.5
0.3 0.2 KY1540 SWT20 GSWT52
0.1
0.3 0.2 KY1540 SWT20
0.1
GSWT52 0
0 0
500 1000 1500 2000 Cutting distance L (m), vc=150m/min
2500
0
200 400 600 800 Cutting distance L (m), vc=200m/min
1000
(e) 0.6
Flank wear VB (mm)
0.5 0.4 0.3
0.2
KY1540 SWT20
0.1
GSWT52 0 0
200 400 600 800 Cutting distance L (m), vc=300m/min
1000
Fig. 6. Flank wear vs. cutting distance, (a) vc = 50 m/min, (b) vc = 100 m/min, (c) vc = 150 m/min, (d) vc = 200 m/min and (e) vc = 300 m/min.
Fig. 7. Evolution of some cutting parameters versus cutting time (GSWT52, vc = 150 m/min), (a) flank wear and surface roughness and (b) resultant cutting force and cutting temperature. 5
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Fig. 8. Progressive tool wear patterns of the graded tool (vc = 150 m/min).
Fig. 9. Failure morphologies of the graded tool under different cutting speeds, (a) vc = 50 m/min, (b) vc = 100 m/min, (c) vc = 150 m/min, (d) vc = 200 m/min and (e) vc = 300 m/min.
machined surface quality becomes worse (Fig. 7(a)) due to the aggravated tool wear, combining with the hard particles, tool wear happens on the minor cutting edge (Fig. 8(d)).
Fig. 8 shows the progressive tool wear patterns around the cutting nose. The serious friction between tool nose and machining workpiece material leads to dark brown marks on the flank faces (Fig. 8(a)). After 5 min cutting, adhesive wear becomes serious and some bonded chips on the cutting nose was found at 15 min (Fig. 8(e)). After 7.5 min cutting, notching wear on the flank face forms (Fig. 8(d)) and finally leads to the failure of the tool (Fig. 8(f)). With the cutting process,
3.4. Tool failure mechanisms Failure morphologies of the graded tool are shown in Fig. 9, and it 6
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Fig. 10. Magnified failure morphology of the graded tool at vc = 50 m/min, (a) SEM images, and the EDS analysis of (b) areas 1 and (c) area 2.
Fig. 11. Back surface morphologies of chips (vc = 150 m/min), (a) SEM image, and (b) EDS analysis of area 3.
When the chip flows through the rake face, the serious extrusion and friction effect will lead to adhesion wear. As shown in Fig. 10, EDS analysis of areas 2, compared with area 1, means many elements coming from the workpiece material and confirms the happening of adhesion. The adhesive chip on the rake face is not stable and will be taken away by the following flowing chip. As a result, some tool materials are also taken away by the flowing chip. Fig. 11(a) shows back surface morphologies of chips at the cutting speed of 150 m/min. According to the EDS analysis of area 3 (Fig. 11(b)), some elements (Ni, Si) from cutting tools were found and it confirms the conclusion. The
can be seen that tool failure modes include grooves on the rake face, notches on the flank face, chipping, adhesive and abrasive wear. With the increasing of cutting speed, the grooving on the rake face shows a tendency to reduce while notching on the flank face shows a tendency to increase. Adhesive wear becomes considerably serious when the cutting speeds are more than 150 m/min. When the cutting speeds are lower than 150 m/min, the chips are in straight and bending continuous forms (Fig. 3(b) and (c)). The continuous chips will make the cutting process smooth and steady while they are hard to break and will scrape the tool rake faces severely. 7
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Fig. 12. Magnified failure morphology of the graded tool at vc = 300 m/min.
first increase of the surface roughness is mainly due to the serious friction between tools and workpiece material in the cutting area. Besides, under relatively low cutting speed, built-up edge tends to form and makes the cutting process unstable [29]. It also tends to deposit on the machined surface and increases the surface roughness as well. The subsequent decrease is due to thermal softening effect, which makes workpiece material easier to cut. Theoretically, for the same kind of cutting tools, the smaller nose radius always results in higher values of roughness [30]. While in this paper, as for KY1540, the larger corner radius increases the contact length between tool nose and machined surface and induces more serious friction. In addition, more serious tool wear of KY1540 (Fig. 6), also makes the surface roughness higher. The graded tool shows a comparative advantage due to its higher hardness and lower tool wear.
4 Surface Roughness Ra (μm)
KY1540
SWT20
GSWT52
3
2
1
0 50
100 150 200 Cutting speed vc (m/min)
300
Fig. 13. Surface roughness vs. cutting speed.
4. Conclusions adhesion and taken-away process repeats and leads to the formation of small pits as illustrated by white arrows in Fig. 10(a) and then finally groove wear on the rake face. With the increasing cutting speed, the higher cutting temperature makes the chip more easily to deform. Besides, the formation of saw-tooth chips (Fig. 4(d) and (e)) decrease the tool-chip contact length. These effects reduce the groove, and the wear mode transforms from groove to pit. It is worth to note that after the groove forms when the cutting speed is less than 150 m/min, it acts as chip evacuation slot and lead to the formation of the screw shape chip (Fig. 3(f)). Notch wear on the flank face becomes the dominant failure mode as the cutting speed is more than 150 m/min and limits the tool life greatly. At the depth of cut, there exists great temperature gradient and thus high thermal stress. The hardened layer of the workpiece material will make it hard to cut and high mechanical stress exists. When the external thermal-mechanical stress exceeds the tensile strength of the tool materials, microcracks as shown in Fig. 12 appear and propagate. Microcracks then coalesce into macrocrack and lead to the fracture of tool and finally notch wear happens. Besides, adhesion and oxidation wear also accelerate notch wear. The higher cutting temperature with the increased cutting speed leads to higher thermal stress and more serious notch wear. Adhesive wear is rather serious as shown in Fig. 12.
In this paper, cutting performance of newly developed Si3N4/(W, Ti)C graded ceramic tool in turning iron-based super-alloys was studied. According to the experimental findings, the following conclusions can be drawn. (1) Chip formation changes from straight continuous chips (vc ≤ 100 m/min) to bending continuous chip (vc ≤ 150 m/min), and twist continuous chips (vc ≥ 200 m/min). Saw-tooth chips tend to form when the cutting speed is more than 200 m/min. The chip formation has evident influence on tool wear morphology. (2) The resultant cutting force tends to increase first and then decrease while the cutting temperature rises gradually with the increasing cutting speed. The graded tool shows smaller cutting forces and lower cutting temperature since the induced compressive residual stress alleviates the thermal-mechanical stress and reduces tool wear. (3) The graded tool shows longer tool life especially at the cutting speed of 100 and 150 m/min. Tool failure modes include grooving wear on the rake face, notching wear on the flank face, chipping, adhesive and abrasive wear. With the increasing of cutting speed, the groove wear on the rake face shows a tendency to reduce while notch wear on the flank face shows a tendency to increase. (4) The surface roughness of iron-based superalloys machined by the ceramic tools under the given cutting conditions is relatively high. With the increase of cutting speed, surface roughness shows a trend to first increase and then decrease and the graded tool shows comparative advantage.
3.5. Surface roughness Surface roughness is one of the most widely used parameter to evaluate the machined surface integrity [28]. As shown in Fig. 13, the surface roughness of iron-based superalloys machined by the ceramic tools, which is parallel to the feed direction and recorded at the beginning cutting process, is relatively high due to the serious adhesion effect. Like the cutting force, with the increase of cutting speed, surface roughness shows a trend to initially increase and then decrease. The
Acknowledgements This work is supported by the Fundamental Research Funds for the 8
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Central Universities (2017QNA15), and the Priority Academic Program Development of Jiangsu Higher Education Institution (PAPD).
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References [1] D. Dudzinski, A. Devillez, A. Moufki, et al., A review of developments towards dry and high speed machining of Inconel 718 alloy, Int. J. Mach. Tools Manuf. 44 (4) (2004) 439–456. [2] A. Altin, M. Nalbant, A. Taskesen, The effects of cutting speed on tool wear and tool life when machining Inconel 718 with ceramic tools, Mater. Des. 28 (9) (2007) 2518–2522. [3] X.H. Tian, J. Zhao, J.B. Zhao, et al., Effect of cutting speed on cutting forces and wear mechanisms in high-speed face milling of Inconel 718 with Sialon ceramic tools, Int. J. Adv. Manuf. Technol. 69 (9–12) (2013) 2669–2678. [4] X.H. Tian, J. Zhao, Y. Dong, et al., A comparison between whisker-reinforced alumina and SiAlON ceramic tools in high-speed face milling of Inconel 718, Proc. Inst. Mech. Eng. Part B: J. Eng. Manuf. 228 (8) (2014) 845–857. [5] M.L. Gu, C.Z. Huang, B. Zou, et al., Effect of (Ni, Mo) and TiN on the microstructure and mechanical properties of TiB2 ceramic tool materials, Mater. Sci. Eng.: A 433 (1–2) (2006) 39–44. [6] A.A. Vereschaka, S.N. Grigoriev, M.A. Volosova, et al., Nano-scale multi-layered coatings for improved efficiency of ceramic cutting tools, Int. J. Adv. Manuf. Technol. 90 (1–4) (2017) 27–43. [7] J. Zhao, X.L. Yuan, Y.H. Zhou, Cutting performance and failure mechanisms of an Al2O3/WC/TiC micro-nano-composite ceramic tool[J], Int. J. Refract. Met. Hard Mater. 28 (3) (2010) 330–337. [8] J. Zhao, X. Ai, Z.J. Lü, Preparation and characterization of Si3N4/TiC nanocomposite ceramics, Mater. Lett. 60 (23) (2006) 2810–2813. [9] J.X. Deng, L.L. Liu, J.H. Liu, et al., Failure mechanisms of TiB2 particle and SiC whisker reinforced Al2O3 ceramic cutting tools when machining nickel-based alloys, Int. J. Mach. Tools Manuf. 45 (12–13) (2005) 1393–1401. [10] R.H.J. Hannink, P.M. Kelly, B.C. Muddle, Transformation toughening in zirconia‐containing ceramics, J. Am. Ceram. Soc. 83 (3) (2000) 461–487. [11] X.H. Tian, J. Zhao, Y.T. Wang, et al., Fabrication and mechanical properties of Si3N4/(W, Ti)C/Co graded nano-composite ceramic tool materials, Ceram. Int. 41 (3) (2015) 3381–3389. [12] P. Rutkowski, L. Stobierski, D. Zientara, et al., The influence of the graphene additive on mechanical properties and wear of hot-pressed Si3N4 matrix composites, J. Eur. Ceram. Soc. 35 (1) (2015) 87–94. [13] S. Wang, G. Wang, D. Wen, et al., MechAnical Properties And Thermal Shock Resistance Analysis of BNNT/Si3N4 composites, Appl. Compos. Mater. 25 (2) (2018) 415–423. [14] M. Koizumi, FGM activities in Japan, Compos. Part B: Eng. 28 (1–2) (1997) 1–4.
9
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Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Performance of Si3N4/(W, Ti)C graded ceramic tool in high-speed turning iron-based superalloys ⁎
Xianhua Tiana,b, , Jun Zhaoc, Xinya Wangd, Haifeng Yanga,b, Zhongbin Wanga,b a
School of Mechatronic Engineering, China University of Mining and Technology, Xuzhou 221116, PR China Jiangsu Key Laboratory of Mine Mechanical and Electrical Equipment, China University of Mining and Technology, Xuzhou 221116, PR China c School of Mechanical Engineering, Shandong University, Jinan 250061, PR China d Department of Industrial & Manufacturing Systems Engineering, Kansas State University, Manhattan, KS 66506, USA b
A R T I C LE I N FO
A B S T R A C T
Keywords: Graded ceramic Si3N4/(W Ti)C Cutting performance Iron-based alloys
A Si3N4/(W, Ti)C graded nano-composite ceramic tool was fabricated and its performance in high speed turning iron-based alloys GH2132 was investigated compared with homogeneous and commercial ceramic tools. The chip morphology, cutting forces, cutting temperature, tool life and failure mechanisms and machined surface roughness were recorded and analyzed. The results showed that with the increasing cutting speed the resultant cutting force shows a tendency to first increase and then decrease while the cutting temperature increases gradually. Straight continuous chips, bending continuous chips, twist continuous chips and snarled chips form in turn. Saw-tooth chips tend to form when the cutting speed is more than 200 m/min. The graded tool shows longer tool life especially at the cutting speed of 150 and 200 m/min compared with the homogenous and commercial ceramic tools. Tool failure modes mainly include grooving on the rake face, notching on the flank face, abrasion and adhesion. The grooving on the rake face tends to decrease while notching on the flank face tends to increase as cutting speed increases. Surface roughness of the machined iron-based super-alloys is relatively high due to the serious adhesion. Better surface roughness can be got using the graded tool.
1. Introduction
performance of ceramic tools can be improved a lot [15,16]. The cutting performance of ceramic tools can also be improved by coatings [17]. However, the coatings are easy to spall especially at high speed cutting conditions. FMG also shows some benefits in improving the bonding strength of coatings [6]. High temperature alloys, including nikel-based, iron-based and cobalt-based alloys, are widely applied in air-craft and nuclear fields for their excellent properties at high temperature [18]. On the contrary, the superiority also makes them difficult-to-cut materials. When using cemented carbide tools to cut them, the cutting speed is always limited to 50 m/min, which limits the machining efficiency greatly [18]. Ceramic tools provide another option to cut high temperature alloys at higher cutting speeds. Many researchers have studied the performance of ceramic cutting tools in high-speed cutting superalloys. Tian et al. [4] compared Al2O3 + SiCw and SiAlON ceramic tools in high-speed milling Inconel 718 and concluded that SiAlON ceramic tools show a better notch wear and thermal shock resistance, while Al2O3 + SiCw tools show a better machined surface roughness. Bushlya et al. [19] used Al2O3-SiCw ceramic tools in high-speed turning aged Alloy 718 and concluded that notching, adhesion and attrition are the main wear mechanisms and their formation mechanisms were analyzed as well.
Ceramics are good candidates for cutting tools due to their high heat and wear resistance and good chemical stability [1]. They can be utilized to machine hard-to-cut materials, like high temperature superalloys, especially at high cutting speed [2–4]. Alumina based and silicon nitride based ceramics are the most applied ceramic cutting tool material at the moment. Besides, TiB2 [5] and Cr2O3 [6] based ceramics have also been reported. However, due to lower fracture strength and thermal shock resistance, ceramic tools tend to chip and fracture in the cutting process which limits their application. These ceramics can be toughened by changing their microstructure through particulate toughening, fiber toughening, whisker toughening, and transformation toughening effect and so on. The added compositions include particles, fibers, whiskers, transformation phases and metal phases [7–11]. Besides, graphene and nanotube have also been incorporated into ceramic matrix [12,13]. Another way is to change their macrostructure by using the concept of functionally graded material (FGM). FGM is first proposed in aerospace area to fabricate heat insulation material by the metal/ceramic structure [14]. Using FGM or laminated structure, mechanical properties as well as cutting ⁎
Corresponding author at: School of Mechatronic Engineering, China University of Mining and Technology, Xuzhou 221116, PR China. E-mail address: [email protected] (X. Tian).
https://doi.org/10.1016/j.ceramint.2018.05.222 Received 27 April 2018; Received in revised form 24 May 2018; Accepted 25 May 2018 0272-8842/ © 2018 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Tian, X., Ceramics International (2018), https://doi.org/10.1016/j.ceramint.2018.05.222
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Fig. 1. The graded cutting tools, (a) sketch of the insert and (b) fabricated inserts.
After that, the side surfaces of the blocks were ground (universal tool grinder, type MQ6025A) and lapped and the edges were chamfered. The final dimensions of the inserts are 16 mm × 16 mm × 6 mm with 0.1 mm × (−15°) chamfer and 0.2 mm corner radius. The commercial KY1540 tool insert has a dimension of 12.7 mm × 12.7 mm × 4.76 mm with 0.1 mm × (−20°) chamfer and 0.8 mm corner radius.
Zheng et al. [20] studied the performance of Sialon-Si3N4 graded ceramic cutting tools in milling of Inconel 718 and found that the graded tool possessed a self-sharpening characteristic and exhibited higher cutting performance compared with the homogeneous ones. It can be seen that the former studies mainly focus on nikel-based superalloys, rarely on Iron-based alloys. In this paper, the cutting performance of a Si3N4/(W, Ti)C graded ceramic tool in high speed turning Iron-based superalloys GH2132 is studied compared with one homogeneous tool and one commercial tool. The graded tool was fabricated by hot-press sintering technology. The chip morphology, cutting force, cutting temperature and machining quality were recorded. Tool life and failure mechanisms were analyzed.
2.2. Cutting tests setup The experiments layout is shown in Fig. 2. The cutting performance of the graded ceramic cutting tools was studied via high-speed dry turning age-strengthened-type iron-based supperalloys GH2132. Its chemical composition is shown in Table 2 [22]. The tensile strength can reach about 1035 MPa at room temperature, 799 MPa at 600 °C and 402 MPa at 800 °C. The alloy bar was with a dimension of 122 mm diameter × 380 mm long. The graded cutting tool compared with one homogeneous tool and one commercial tool are used in the tests as shown in Table 3, and their mechanical properties are also presented. Indentation method was used to measure the hardness and fracture toughness [23] while the flexural strength was measured by three-point bending test. It can be concluded that the graded structure is beneficial for improving mechanical properties of ceramic tools especially the flexural strength and fracture toughness. The cutting geometry parameters are as follows, rake angle γo = −5°, clearance angle αo = 5°, inclination angle λs = 0°, and side cutting edge angle κr = 45°. The cutting parameters are shown in Table 4. To ensure the measurement repeatable and comparable, every test was repeated at least three times with a new cutting edge. The tool failure criterions are as follows, (1) average flank wear VBave = 0.30 mm, (2) maximum flank wear VBmax ≥ 0.60 mm, or (3) catastrophic fracture of the cutting edge. Cutting forces were recorded by a three-component piezoelectric Kistler dynamometer (type 9265A) with a sampling frequency of 4000 Hz. Cutting temperature was obtained by NEC thermal infrared imager (type TH5140R). An AM413ZT Dino-Lite digital microscope
2. Experimental procedure 2.1. Design and fabrication of graded ceramic tools Considering the ease of fabrication, compositional distribution of the graded ceramic tools changes only along z direction as shown in Fig. 1(a). To make the top and bottom surfaces could be used as rake faces, a five-layer symmetric graded structure is used. The thickness ratio (that is h1/h2 = h2/h3) is fixed at 0.2 according to our former research [21]. The finally fabricated inserts are shown in Fig. 1(b). To avoid fracture and spalling between layers, the composition between layers is gradually changed. Three kinds of homogeneous ceramic materials were developed to construct the graded structure as listed in Table 1. They were named after the adding amount of reinforcing phase (W, Ti)C. Some nano-Si3N4 particles, weight ratio to micro-Si3N4 being set to be 1/3, were added. The graded material is built as SWT15/ SWT20/SWT25/SWT20/SWT15 and named as GSWT52. Since thermal expansion coefficient of the reinforcing phase is larger than that of the base material, residual compressive stress was introduced in the surface layers during the cooling down process after complete sintering. Besides, the higher hardness of the surfaces layers and the higher strength of inner layers are also ensured. The raw materials and the detailed fabrication process of the mixed powers in Table 1 are presented elsewhere [21]. After that, the mixed powers were cold prepressed into the graphite mold layer by layer and then hot-pressed sintering at 1700 °C for 45 min under a pressure of 30 MPa in vacuum condition. The sintering plates were first surface ground (surface grinder, type M7120D/H) to specified size and then cut into square blocks (inside diameter slice machine, type J5060C-1). Table 1 Composition of different homogeneous composites (vol%). Composites
Nano (25 nm) and micro (0.5 µm) Si3N4
(W, Ti)C (1 µm)
Sintering adds (0.5 µm)
SWT15 SWT20 SWT25
77 72 67
15 20 25
8 8 8
Fig. 2. Cutting experiments layout. 2
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chips (vc ≤ 100 m/min) to bending continuous chip (vc ≤ 150 m/min), twist continuous chips (vc ≤ 200 m/min) and snarled chips (vc ≤ 300 m/min). Even some segmental chips (Fig. 3(e)) appear at the cutting speed of 300 m/min. This should be attributed to the high strain rates and thermal softening effect which makes the chip easier to deform under higher cutting speeds [24]. Fig. 4 shows the micro free surface morphologies of chips at different cutting speeds. The shearing mechanisms give rise to the jagged and rough appearances [25]. With the increasing cutting speed, the extrusion deformation intensifies. When the cutting speeds are more than 200 m/min, the larger lamella structure means that the saw-tooth chips forms and the saw-tooth pitch increases considerably with the further increase of cutting speed. The formation of saw-tooth chips will decrease the contact length between chip and rake face [26]. Chip morphologies have an evident effect on wear morphology of tool flank face as discussed in Section 3.4.
Table 2 Chemical composition of GH2132 (wt%) [22]. Fe
Ni
Cr
Ti
Mo
V
Al
Bal
24.00～ 27.00 Mn ≤ 2.00
13.50～ 16.00 Si ≤ 1.00
1.75～2.30
1.00～1.50
0.10～1.50
0.40
C ≤ 0.08
P ≤ 0.03
S ≤ 0.02
B 0.001～ 0.01
Table 3 Materials and mechanical properties of cutting tools. Material
Grade
Hardness
Flexural strength
Fracture toughness
Sialon Si3N4/(W, Ti)C Graded
KY1540 SWT20 GSWT52
16.36 17.72 17.64
– 979 1080
8.4 8.5 10.9
3.2. Cutting forces and cutting temperature
Table 4 Cutting parameters. Depth of cut (mm)
Feed rate (mm/r)
Cutting speed (m/min)
0.1
0.1
50, 100, 150, 200, 250, 300
The measurement of cutting force is essential to assess performance of cutting tools since it has great effect on the machined surface quality and productivity. Cutting forces are usually influenced by friction in the tool/chip interface and shear strength of workpiece material in the shear areas [27]. Fig. 5(a) shows the resultant cutting forces under different cutting speeds. It can be got by the equation Fr = F2x + F2y + F2z , where Fx, Fy and Fz are the recorded cutting force components in x-, y-, and z- directions by the dynamometer. They are recorded at the initial cutting stage. In general, the resultant cutting forces show a tendency to increase first and then decrease, while that of SWT20 increases once again after 200 m/min. The first increase of cutting force is mainly due to serious friction between the chips and tool. With further increasing cutting speed, the cutting heat generated in the shear area cannot be effectively conducted and diffused and cutting temperature rises and thus the thermal softening effect, which decreases the hardness and shear strength of workpiece material, leads to the decrease of cutting forces. The subsequent increase of the cutting force of SWT20 is maybe due to the serious adhesive wear. Infrared imager can only provide an assessment of temperature values due to the interference of some factors [27]. It still provides
(AnMo Co., Taiwan) was utilized to measure the tool wear values periodically, and a JSM-6510 LV scanning electron microscope (SEM) equipped with an energy X-ray spectrometer (EDS) was used to identify the tool failure patterns and wear mechanisms. The surface roughness value Ra is the arithmetic mean value of at least three measurements per sample, which were got by a portable surface roughometer (model TR200, China).
3. Results and discussions 3.1. Chip analysis Fig. 3(a)-(d) shows the macro chip morphology under different cutting speeds. Obviously, with the increasing cutting speed, the chip deformation becomes more severe. It changes from straight continuous
Fig. 3. Macro chip morphologies under different cutting speed (f = 0.1 mm/r, ap = 0.1 mm), (a) vc = 100 m/min, (b) vc = 150 m/min, (c) vc = 200 m/min, (d) vc = 300 m/min, (e) Fragmental chips, vc = 300 m/min, and (f) Screw shape chips, vc = 100 m/min. 3
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Fig. 4. Micro free surface morphologies of chips under different cutting speed (f = 0.1 mm/r, ap = 0.1 mm), (a) vc = 50 m/min, (b) vc = 100 m/min, (c) vc = 150 m/ min, (d) vc = 200 m/min and (e) vc = 300 m/min.
(b)
200 KY1540
SWT20
Cutting temperature T ( )
Resultant cutting force Fr (N)
(a)
GSWT52
150 100 50
600
KY1540
SWT20
GSWT52
400
200
0
0 50
100 150 200 Cutting speed vc (m/min)
50
300
100 150 200 300 Cutting speed vc (m/min)
Fig. 5. (a) Resultant cutting force and (b) Cutting temperature under different cutting speeds.
the five different cutting conditions. While tool life of the newly developed tools increases first up to 150 m/min, and then decrease. The graded tool shows some advantage especially at the cutting speed of 100 and 150 m/min. And it shows the typical initial-normal-acutely worn stages. Fig. 7 shows the evolution of some cutting parameters of the graded tool versus cutting time at the cutting speed of 150 m/min. It can be seen that the tool life is about 17.5 min and flank tool wear increases gradually as the cutting process goes on. Machined surface roughness shows the same changing trend, which means that tool wear has a great influence on machined surface quality. At the normal worn stage, cutting force and cutting temperature show a trend to slowly increase with slight fluctuation. At the acutely worn stage, cutting force increases greatly while cutting temperature increases to a certain level and maintain stable. The increasing cutting force will lead to more serious friction between tools and workpiece and in turn lead to faster tool wear.
some helpful information by comparing the measured temperatures of different tools. As shown in Fig. 5(b), the cutting temperature rises gradually with the increasing cutting speed. When the cutting speed is more than 150 m/min, tool wear of KY1540 becomes seriously in a short time and it makes the highest cutting temperature. The graded tool shows smaller cutting forces and lower cutting temperature because of its longer tool life and less tool wear values. Because of the reasonable composition distribution of the graded tool, compressive residual stress will be induced in the surface layers of it. The residual stress can alleviate the external thermal-mechanical stress and reduce tool wear and thus reduces the cutting force and cutting temperature. It is also beneficial to the machined surface quality of workpiece. 3.3. Tool life and progressive failure Fig. 6 shows the change process of flank wear versus cutting distance under different cutting speeds. Tool life of KY1540 is limited for 4
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(a)
(b) 0.5
0.7
Flank wear VB (mm)
Flank wear VB (mm)
0.6 0.4
0.3 0.2 KY1540 SWT20 GSWT52
0.1
SWT20 0.4
GSWT52
0.3 0.2 0.1 0
0 0
500 1000 Cutting distance L (m), vc=50m/min
0
1500
(c)
500 1000 1500 2000 Cutting distance L (m), vc=100m/min
2500
(d) 0.5
0.5
0.4
0.4
Flank wear VB (mm)
Flank wear VB (mm)
KY1540
0.5
0.3 0.2 KY1540 SWT20 GSWT52
0.1
0.3 0.2 KY1540 SWT20
0.1
GSWT52 0
0 0
500 1000 1500 2000 Cutting distance L (m), vc=150m/min
2500
0
200 400 600 800 Cutting distance L (m), vc=200m/min
1000
(e) 0.6
Flank wear VB (mm)
0.5 0.4 0.3
0.2
KY1540 SWT20
0.1
GSWT52 0 0
200 400 600 800 Cutting distance L (m), vc=300m/min
1000
Fig. 6. Flank wear vs. cutting distance, (a) vc = 50 m/min, (b) vc = 100 m/min, (c) vc = 150 m/min, (d) vc = 200 m/min and (e) vc = 300 m/min.
Fig. 7. Evolution of some cutting parameters versus cutting time (GSWT52, vc = 150 m/min), (a) flank wear and surface roughness and (b) resultant cutting force and cutting temperature. 5
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Fig. 8. Progressive tool wear patterns of the graded tool (vc = 150 m/min).
Fig. 9. Failure morphologies of the graded tool under different cutting speeds, (a) vc = 50 m/min, (b) vc = 100 m/min, (c) vc = 150 m/min, (d) vc = 200 m/min and (e) vc = 300 m/min.
machined surface quality becomes worse (Fig. 7(a)) due to the aggravated tool wear, combining with the hard particles, tool wear happens on the minor cutting edge (Fig. 8(d)).
Fig. 8 shows the progressive tool wear patterns around the cutting nose. The serious friction between tool nose and machining workpiece material leads to dark brown marks on the flank faces (Fig. 8(a)). After 5 min cutting, adhesive wear becomes serious and some bonded chips on the cutting nose was found at 15 min (Fig. 8(e)). After 7.5 min cutting, notching wear on the flank face forms (Fig. 8(d)) and finally leads to the failure of the tool (Fig. 8(f)). With the cutting process,
3.4. Tool failure mechanisms Failure morphologies of the graded tool are shown in Fig. 9, and it 6
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Fig. 10. Magnified failure morphology of the graded tool at vc = 50 m/min, (a) SEM images, and the EDS analysis of (b) areas 1 and (c) area 2.
Fig. 11. Back surface morphologies of chips (vc = 150 m/min), (a) SEM image, and (b) EDS analysis of area 3.
When the chip flows through the rake face, the serious extrusion and friction effect will lead to adhesion wear. As shown in Fig. 10, EDS analysis of areas 2, compared with area 1, means many elements coming from the workpiece material and confirms the happening of adhesion. The adhesive chip on the rake face is not stable and will be taken away by the following flowing chip. As a result, some tool materials are also taken away by the flowing chip. Fig. 11(a) shows back surface morphologies of chips at the cutting speed of 150 m/min. According to the EDS analysis of area 3 (Fig. 11(b)), some elements (Ni, Si) from cutting tools were found and it confirms the conclusion. The
can be seen that tool failure modes include grooves on the rake face, notches on the flank face, chipping, adhesive and abrasive wear. With the increasing of cutting speed, the grooving on the rake face shows a tendency to reduce while notching on the flank face shows a tendency to increase. Adhesive wear becomes considerably serious when the cutting speeds are more than 150 m/min. When the cutting speeds are lower than 150 m/min, the chips are in straight and bending continuous forms (Fig. 3(b) and (c)). The continuous chips will make the cutting process smooth and steady while they are hard to break and will scrape the tool rake faces severely. 7
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Fig. 12. Magnified failure morphology of the graded tool at vc = 300 m/min.
first increase of the surface roughness is mainly due to the serious friction between tools and workpiece material in the cutting area. Besides, under relatively low cutting speed, built-up edge tends to form and makes the cutting process unstable [29]. It also tends to deposit on the machined surface and increases the surface roughness as well. The subsequent decrease is due to thermal softening effect, which makes workpiece material easier to cut. Theoretically, for the same kind of cutting tools, the smaller nose radius always results in higher values of roughness [30]. While in this paper, as for KY1540, the larger corner radius increases the contact length between tool nose and machined surface and induces more serious friction. In addition, more serious tool wear of KY1540 (Fig. 6), also makes the surface roughness higher. The graded tool shows a comparative advantage due to its higher hardness and lower tool wear.
4 Surface Roughness Ra (μm)
KY1540
SWT20
GSWT52
3
2
1
0 50
100 150 200 Cutting speed vc (m/min)
300
Fig. 13. Surface roughness vs. cutting speed.
4. Conclusions adhesion and taken-away process repeats and leads to the formation of small pits as illustrated by white arrows in Fig. 10(a) and then finally groove wear on the rake face. With the increasing cutting speed, the higher cutting temperature makes the chip more easily to deform. Besides, the formation of saw-tooth chips (Fig. 4(d) and (e)) decrease the tool-chip contact length. These effects reduce the groove, and the wear mode transforms from groove to pit. It is worth to note that after the groove forms when the cutting speed is less than 150 m/min, it acts as chip evacuation slot and lead to the formation of the screw shape chip (Fig. 3(f)). Notch wear on the flank face becomes the dominant failure mode as the cutting speed is more than 150 m/min and limits the tool life greatly. At the depth of cut, there exists great temperature gradient and thus high thermal stress. The hardened layer of the workpiece material will make it hard to cut and high mechanical stress exists. When the external thermal-mechanical stress exceeds the tensile strength of the tool materials, microcracks as shown in Fig. 12 appear and propagate. Microcracks then coalesce into macrocrack and lead to the fracture of tool and finally notch wear happens. Besides, adhesion and oxidation wear also accelerate notch wear. The higher cutting temperature with the increased cutting speed leads to higher thermal stress and more serious notch wear. Adhesive wear is rather serious as shown in Fig. 12.
In this paper, cutting performance of newly developed Si3N4/(W, Ti)C graded ceramic tool in turning iron-based super-alloys was studied. According to the experimental findings, the following conclusions can be drawn. (1) Chip formation changes from straight continuous chips (vc ≤ 100 m/min) to bending continuous chip (vc ≤ 150 m/min), and twist continuous chips (vc ≥ 200 m/min). Saw-tooth chips tend to form when the cutting speed is more than 200 m/min. The chip formation has evident influence on tool wear morphology. (2) The resultant cutting force tends to increase first and then decrease while the cutting temperature rises gradually with the increasing cutting speed. The graded tool shows smaller cutting forces and lower cutting temperature since the induced compressive residual stress alleviates the thermal-mechanical stress and reduces tool wear. (3) The graded tool shows longer tool life especially at the cutting speed of 100 and 150 m/min. Tool failure modes include grooving wear on the rake face, notching wear on the flank face, chipping, adhesive and abrasive wear. With the increasing of cutting speed, the groove wear on the rake face shows a tendency to reduce while notch wear on the flank face shows a tendency to increase. (4) The surface roughness of iron-based superalloys machined by the ceramic tools under the given cutting conditions is relatively high. With the increase of cutting speed, surface roughness shows a trend to first increase and then decrease and the graded tool shows comparative advantage.
3.5. Surface roughness Surface roughness is one of the most widely used parameter to evaluate the machined surface integrity [28]. As shown in Fig. 13, the surface roughness of iron-based superalloys machined by the ceramic tools, which is parallel to the feed direction and recorded at the beginning cutting process, is relatively high due to the serious adhesion effect. Like the cutting force, with the increase of cutting speed, surface roughness shows a trend to initially increase and then decrease. The
Acknowledgements This work is supported by the Fundamental Research Funds for the 8
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Central Universities (2017QNA15), and the Priority Academic Program Development of Jiangsu Higher Education Institution (PAPD).
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