WEAR ELSEVIER wear208(1997)220-225 Failure mechanisms of a whisker-reinforced ceramic tool when machining nickel-based alloys Zhao Jun, Deng Jianxin, Zhang Jianhua, Ai Xing Department of Mechanical Engineering, Shandong University of Technology, Jinan 250061, People's Republic of china Received 11 September 1996; accepted 15 November 1996 Abstract Cutting behavior and failure mechanisms of the SiC-whisker-reinforced Al2O3 ceramic cutting tool JX-1 in turning nickel-based alloys ave been investigated in comparison with those of other kinds of ceramic and carbide tools. The resistance to depth-of-cut notch wear of the JX-1 has been found to be greater than that of other Al2O3based ceramic tools because of the toughening effect of the whiskers, and its higher nose and fiank wear resistance than that of Sialon tools has been attributed to its better chemical stability Wear and fracture mechanisms have been studied in terms of microstructure, mechanical and chemical properties and thermal shock resistance of tool materials. Take the machining of a nickel-based alloy GH169, for example. At lower cutting speeds(180 m min ) catastrophic fracture of the edge due to plastic deformation may occur. Similar results were obtained whenmachining GH761 and GH49. It is also found that cutting fluid influences the high-speed cutting behavior of JX-1 to a great extent. Elsevier Science Keywords: Microstructure; Turning; Mechanical properties; Thermal shock resistance 1. Introduction ductivity, thermal shock resistance and lower thermal expan sion coefficient, seems to be ideal [2, 3] To solve the problem of high-speed machining of nickel- A nickel-based alloy is generally a difficult material to based alloys, arising from economical considerations, much machine since it has low thermal conductivity and high work has been carried out to machine nickel-based alloys at con gth. It is composed of nickel, nickel-iron and other hard higher cutting speeds with various ceramic tools including stituents widely employed at high temperatures for long TIC-A12O3, Si, N4, Al2O3-SiCw and Sialon tools, as well as periods of time. The difficulties in machining nickel-based carbide ones. Among these studies, one of the most severe loys are usually its high cutting temperature, high resistance failure modes found to control tool life in machining nickel to plastic deformation and severe work hardening. The requi- based alloys is depth-of-cut notch wear, especially at lower ents for tool material for machining nickel-based alloys cutting speeds. According to these authors, depth-of-cut are regarded as high strength and toughness at high temper- notch wear, along with radius and rake face wear, is mainly atures, especially high thermal conductivity and resistance to induced by microcrack propagation and thermal fatigue thermal shock [4, 5]. Plastic deformation, diffusion and drastic attrition con The tools generally selected to machine nickel-basedalloys tribute much to flank wear and catastrophic fracture of the are K-grade(wC-Co type)carbide, CBN and ceramic tools. edge at higher cutting speeds because of high stresses, remov Nickel-based alloys are therefore usually machined at rela- ing aggregates of grains [4, 6] tively low cutting speeds, such as less than 50 m min,with In this paper, the SiC-whisker-reinforced A12O3 ceramic K-grade carbide tools [1]: CBn tools are not widely used tool JX-1 was used for machining GH169 and other nickel cause of their high cost. From this viewpoint, ceramic tools based alloys in comparison with other ceramic and candide appear to be the most suitable as regards tool materials, tools The failure characteristics of the tools are discussed in among which the SiC-whisker-reinforced Al2O3 ceramic terms of microstructure, mechanical and chemical propertie tool, characterized by higher fracture toughness, thermalcon- and thermal shock resistance of the tool materials. The cutting 0043-16487977$17.00@ 1997 Elsevier Science S.A. All rights reserved S0043-1648(96)07476-5
Z. Jun et al./Wear208(1997)220-225 Table 1 Mechanical properties of nickel-based alloys 07}…+ n0.3mm Ni alloys Yield strength Percentage Thermal Flank wear g(MPa) elongation conductivity k HRC 1100 v=62.5m/min GH1691497 212 1340 conditions for machining nickel-based alloys with the JX-1 ≠=280mmin tool were determined appropriately on the basis of under- anding of the factors controlling wear Fig. 1. Flank wear of JX-1 tool vs time 2. Experimental techniques as0,3nm The work materials are solution-treated and aged GH169 f013mr素 equivalent to Inconel 718)containing 53. 46% Ni, 18.79% = Cr; aged GH761 containing 432%Ni, 13. 31% Cr; and aged GH49 containing 57. 4% Ni, 10. 25% Cr. The mechanica properties of GH169, GH761 and GH49 are shown Table 1. In addition to the hot-pressed 25 vol% SiCw -AlO ceramic tool JX-1, ceramic tools SG-4(Al,Ox-(WTi)C) ddIr LT55(AL2Og-TiC-Mo-Ni), Sialon and carbide tool YG6 (WC-Co, equivalent to K10) were each employed under the ame cutting conditions as those of JX-1. Their mechanical roperties are shown in Table 2. Nitrogen and food coolant Fig 2, Wear of JX-l tool in GH169 machining (a chlorinated soluble oil, 10: 1 concentration with water) used to investigate the effect of various atmospheres on profiles between nickel-based alloys and JX tool life and failure modes under similar conditions. y energy-dispersive X-ray spectroscopy(EDX) All the machining experiments were carried out on a CA6140 lathe equipped with a 45 lead angle, 5"negative inclination, 8 negative rake tool holder. The geometry of the 3. Machining results tool inserts was SNG15083, with an edge chamfer of 0.2 mm at 20 The work materials were in the form of round bars The average flank wear rate at various cutting speeds when Cutting forces were measured with a Kistler piezoelectric turning GH169 with the JX-1 tool and flood coolant is shown quartz dynamometer, and cutting temperatures were meas- in Fig. 1. Cutting speeds around 100 m min seem to be the ured by means of a technique for non-conducting ceramics best range for the JX-1 tool when turning GH169. Plots of developed in our laboratory tool wear at various cutting speeds after 300 m of cutting Scanning electron microscopy(SEM)was used to exam- distance, shown in Fig. 2, reveal that the JX-1 tool is prone ine wear and fracture surfaces, and transmission electron to depth-of-cut notching, with minimal damage to the tool microscopy(TEM)was undertaken on specimens for high- fank face and nose at lower speeds; an increase of speed, temperature mechanical property tests. Elemental diffusion however, leads to a reduction in depth-of-cut notching and Table 2 Mechanical properties of selected cutting tools Fracture Flexural strength Thermal Thermal Elastic Thermal shock Hardness HRA or(MPa resistance R(K) (mK)-1) coefficient a (GPa) 71 94.5 95. 8.27 4.5 895
tially as the cutting speed increases. Experiments of changing the feed rate when machining at 100 m min reveal that 0. 1-0.2 mm rev-I seems to be the suitable range above which tool wear increases. Nitrogen was found to have no -1 obvious effect on tool life because it is very difficult for nitrogen to enter into the tool/chip inter Trace f0.1snmmurev ting fluid (a chlorinated soluble oil)was proven to lengthe tool life effectively as a result of the formation of chemically v=62.3m/min D LTS5 adsorbed film which can decrease the friction between the tool and the workpiece or chip [7]. Similar results were obtained when machining GH761 and GH49. T(min) 4. Tool failure modes and failure mechanism studies Tool failure of JX-1 is found to be caused by wear and fracture. Rake face cratering, flank wear, nose wear and depth-of-cut notching are the main modes of wear, while chipping flaking, spalling, catastrophic fracture of the edge as well as collapsing due to plastic deformation contribute to tool fracture T(min) 4. 1. Analysis of wear mechanisms Fig. 3. Wear of various tools in GH169 machining Adhesive and attrition wear are the main mechanisms of an increase in nose and flank wear. Comparative tests with the JX-l tool when machining nickel-based alloys at lower different tools show that the JX-1 tool exhibits less advantage speeds. Adhesive wear was found to play an important role over the carbide tool Y G6 when machining GH169 at a very in rake face cratering, especially when machining dry at a low speed (62.5 m min-l), as is shown in Fig 3(a). How- very low speed(20 m min -), as is shown in Fig.5.Depth ever, the cutting behavior of the JX-I tool is much better than of-cut notch wear of the JX-1 tool after machining GH169 at that of other ceramic and carbide tools when the cutting speed a speed of 62.5 m min is shown in Fig. 6. The depth-of- increases to 100 m min(Fig 3(b)), with its resistance to cut contact line is a location of severe thermal and stress is also found that the Sialon tool is less susceptible to depth- erties of the workpiece, cutting conditions and tool geometry of-cut notching than Al2O3-based ceramic tools, but its VB etc [8] and vC are greater than that of the JX-1 tool Fig. 4 shows the cutting temperature of the JX-1 tool as a nction of speed when machining GH169 with flood coolant. It is found that the cutting temperature increases exponen 88347628Ky38:::5 Fig. 4. Cuting temperatur o mini e s ating sped Fig. 5. Crater wear of JX-1 tool after machining GH169 v= m min a=0.3mm,f=0.15 mm rev-,t=100s
Z. Jun et al../Wear208(1997)220-225 decreases as the cutting speed increases can also be explained as the softening effect of the workpiece at higher tempera tures. Evidence of attrition can be observed at both lower and higher cutting speeds. Fig. 7 shows the underside of the chip (generated at a cutting speed of 20 m min )where particl of intrusive JX-I were found, these particles of JX-1 tool having been removed from the tool faces and carried away with the chip. This suggests that attrition is the dominant wear mechanism leading to depth-of-cut notching of the JX-1 tool EDX analysis of the section between the JX-1 tool and GH169, done at higher cutting speeds, indicates thattwo ways of diffusion take place and the zone is actually a diffusion band. Nickel and iron diffusing into the tool material react ly with Sic whiskers, producing FeSi and NiSi. This decreases the strength and hardness of the tool material. Fur- thermore, partial SiC whiskers are oxidized, leading to the 99358928K85:的面 formation of glassy phase silicon dioxide across the Al2O3/ Fig.6.Notch wear of JX-1 tool after machining GH169 U=62.5 m min-1 SiCw interface. This oxidation could be aggravated by a=0.3mm,f=0.15mrev-,r=318 increasing the cutting speed and feed rate, causing severe wear to the tool According to the thermomechanical property parameter of GH169 provided by the manufacturer, 850"C is a yield 4.2. Analysis of fracture mechanisms point above which the workpiece begins to soften The cutting temperature curve, as a function of cutting speed, reveals that The fracture of JX-I when machining nickel-based alloys 100-110 m min"is the relevant speed range up to 850C. When machining GH169 at speeds lower than this range, the was found to be caused by either brittle fracture mechanisms strength of the workpiece remains very high. It was envisaged or plastic deformation. Generally, brittle fracture takes place that the process of chip separation from the workpiece and flaking (rake face near the nose of the tool, shown in Fig. 6) sliding contact with hard constituents could create attrition wear conditions in the notch region, especially at a very low High mechanical and thermal load resulting from the plastic speed.850C is also a temperature at which the x-i tool deformation of the chip is applied continuously on the rake ce, initiating microcracks at the whisker/matrix interface material still keeps very high hardness and strength. How- as a result of the interaction with microstructural defects and ever, the tool material begins softening at temperatures above residual stresses in the interior of the tool 10]. Microcrack around 100 m min- is the best range of JX-1 for turning propagation, along with pulling up of particles, may lead to GH169. From this viewpoint, the fact that notch wear chipping flaking in the rake face and nose. Fracture of the edge and nose may occur in the event of extreme mechanical and thermal shock A macrocrack perpendicular to the edge in the flank face nd the collapse of the edge were observed when machining GH169 at a speed of 230 m min with the JX-1 tool ( Fig. 8). Debonding, pulling out and bridging of whiskers which contribute to toughening were found in the crack ig. 9 shows a TEM of a specimen cooled from 1000C, prepared for high-temperature property tests, in which grain boundary sliding leading to plastic deformation was seen [11]. Under higher temperatures derived from higher cutting speeds, grain-boundary sliding, the viscosity effect of glassy phase, along with initiation of voids, decreases the clamping pressure and friction stress between the matrix and whiskers Plastic deformation is caused by high compressive stresses high temperature and their resultant grain-boundary sliding, and the viscosity effect of glassy phase. The crack caused by plastic deformation is found to have a tendency to open up 48c very quickly at high feedrates, which may lead to catastrophic Fig. 7. Underside of the chip. fracture of the edge
A Jun et a./Wear208(1997)220225 I tool than that of other Al2O3-based tools is attributed to its higher thermal shock resistance, derived from the toughening effect of whiskers along with decreased thermal expansion coefficient and elastic modulus. The more severe nose wear and fank wear of the Sialon tool than that of the jx-1 tool can be explained as more severe attrition, because high une- ven stresses imposed on the Sialon tool, resulting from irreg ular chip flow, generate microcracks through the glassy phase running along the B grain boundaries and this process con tinues until a lump of material is lifted off. Additionally, the JX-1 tool is more chemically stable to nickel-based alloys than the Sialon tool, so that the chemical aspects of wear are less serious than those of the Sialon tool 5. Conclusi 8日347128KV848:∵污的 The work has shown that the Sic-whisker-reinforced Fig 8. Failure mode of JX-1 tool after machining GH169. 0=230 m min Al2O3 ceramic tool JX-1 can be used to machine nickel-based a0. 3 mm, =0. 15 mm rev-,t=60 s alloys over a wide range of cutting conditions. The JX-1 tool shows less superiority in machining at a very low speed than the carbide tool. Its cutting behavior when cutting at higher speeds, however, is much better than that of other ceramic and carbide tools as result of its excellent wear resistance thermal conductivity and chemical stability 1) Take the machining of GH169, for example. At lower cutting speeds(180 m min"), catastrophic fracture of the edge due to plastic deformation may occur Similar results are obtained when machining GH761 and (2) Because severe thermal gradients pth-of-cut line, the thermal shock resistance of tool mate- 02体m rials influences depth-of-cut notching (3)The use of a cutting fluid could lengthen tool life greatly as a result of the formation of a chemically adsorbed film between tool and workpiece or chip 4.3. Analysis of comparative cutting performances of different tools References The influence of thermal shock resistance on depth-of-cut [l]NNarutaki, Y Yamane, K Hayashi, High-speed machiningofInconel notching has been described by some authors, because severe 718, in: C Dingchang, N. Narutaki, W. Xiaolu(Eds ) Progress of thermal gradients are present at the depth-of-cut line.The cutting and grinding with problems in CAD CAM FMS and nermal shock resistance of a material depends on the follow- Mechatronics, Beijing, China, 23-25 November 1992, pp. 19-24 ing: thermal conductivity/diffusivity, thermal expansion [2]A. Xing, L. Zhaoqian, D Jianxin, Development and perspective of coefficient, fracture strength/toughness, and elastic modulus advanced ceramic cutting tool material, Key engineering material, Tran Tech Publications, Switzerland, 1995 [8]. Thermal shock resistance can be expressed as Kic/(aE) [3]AG. Evans, Perspective on the development of high toughness (Kick)/(aE)orR(=or(1-v)/(aE)). That the Sialon ramics, J. Am. Ceram Soc. 73(2)(1990)187-195 tool has the highest thermal shock resistance among all tools [4] J.F. Huet, B M. Kramer, The wear of ceramic tools, Proc. NMARc Conf, SME, Toronto, May 1982, p. 297 the same reason, the higher notch wear resistance of the Jx- nickel alloys, Ann. CIRP 36(1)(1987)13-16
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