Tool wear mechanisms of PcBN in machining Inconel 718: Analysis across multiple length scale

Recently, PcBN tooling have been successfully introduced in machining Ni-based superalloys, yet our knowledge of involved wear mechanisms remains limited. In this study, an in-depth investigation of PcBN tool degradation and related wear mechanisms when machining Inconel 718 was performed. Diffusional dissolution of cBN is an active wear mechanism. At high cutting speed oxidation of cBN becomes equally important. Apart from degradation, tool protection phenomena were also discovered. Oxidation of Inconel 718 resulted in formation of γ-Al₂O₃ and (Al,Cr,Ti)₃O₄ spinel that were deposited on the tool rake. Also on the rake, formation of (Ti,Nb,Cr)N takes place due to cBN-workpiece interaction. This creates a sandwich tool protection layer forming continuously as tool wear progresses. Such in operando protection enabled counterbalancing tool wear mechanisms and achieved high performance of PcBN in machining.     

Cutting temperature of ceramic tools in high speed machining of difficult-to-cut materials

This paper deals with an experimental and analytical investigation into the different factors which influence the temperature distribution on Al₂O₃---TiC ceramic tool rake face during machining of difficult-to-cut materials, such as case hardened AISI 1552 steel (60–65 Rc) and nickel-based superalloys (e.g. Inconel 718). The temperature distribution was predicted first using the finite element analysis. Temperature measurements on the tool rake face using a thermocouple based technique were performed and the results were verified using the finite element analysis. Experiments were then performed to study the effect of cutting parameters, different tool geometries, tool conditions, and workpiece materials on the cutting edge temperatures. Results presented in this paper indicate that for turning case hardened steel, increasing the cutting speed, feted, and depth of cut will increase the cutting edge temperature. On the other hand, increasing the tool nose radius, and angle of approach reduces the cutting edge temperature, while increasing the width of the tool chamfer will slightly increase the cutting ege temperature. As for the negative rake angle, it was found that there is an optimum value of rake angle where the cutting edge temperature was minimum. For the Inconel 718 material, it was found that the cutting edge temperature reached a minimum at a speed of 510 m/min, and feed of 1.25 mm/rev. However, the effect of the depth of cut and tool nose radius was almost the same as that determined in the turning of case hardened steel. It was also observed in turning Inconel 718 with ceramic tools that, cutting forces and different types of tool wear were reduced with increasing the feed.     

Evaluation of layer adhered on PCBN tools during turning of AISI D2 steel

Polycrystalline cubic boron nitride (PCBN) tools have high abrasion resistance and are thus suitable for application in the machining of steels with a high volume fraction of primary carbides in their microstructure. These tools are usually applied in the machining of steels with hardness above 45–50 HRC and in the case of application to steels with hardness below 45 HRC, the formation of an adhered layer on the rake face of the tools often occurs. This paper reports a study on the impact of the layer adhered on PCBN tools during the turning of AISI D2 steel, with 35 and 50 HRC. The microhardness and microstructure of the adhered material were determined, as well as the tool wear based on volumetric wear parameters. The layer adhered on the PCBN tool rake face has the same chemical elements as the machined steel alloy. Its microstructure is oriented in the direction of the chip flow and the primary carbides were fragmented. For the sample with 35 HRC the amount of material adhered (W_AM) on the rake face of the PCBN tool was approximately 360% higher than the steel with 50 HRC. The material layer adhered on the PCBN tool rake surface in the case of the 35 HRC steel acts as an edge (assuming the cutting function), while for the 50 HRC steel, the adhered layer intensifies the adhesion wear mechanism through spalling on the tool rake face. The results obtained provide important information for the selection of materials and grades for the development of new cutting tools.     

Wear behavior of Al2O3/Ti(C,N)/SiC new ceramic tool material when machining tool steel and cast iron

Design, fabrication and application of ceramic cutting tools are one of the important research topics in the field of metal cutting and advanced ceramic materials. In the present study, wear resistance of an advanced Al₂O₃/Ti(C,N)/SiC multiphase composite ceramic tool material have been studied when dry machining hardened tool steel and cast iron under different cutting conditions. Microstructures of the worn materials were observed with scanning electronic microscope to help analyze wear mechanisms. It is shown that when machining hardened tool steel at low speed wear mode of the kind of ceramic tool material is mainly flank wear with slight crater wear. The adhesion between tool and work piece is relatively weak. With the increase of cutting speed, cutting temperature increases consequently. As a result, the adhesion is intensified both in the crater area and flank face. The ceramic tool material has good wear resistance when machining grey cast iron with uniform flank wear. Wear mechanism is mainly abrasive wear at low cutting speed, while adhesion is intensified in the wear area at high cutting speed. Wear modes are dominantly rake face wear and flank wear in this case.     

Performances of micro-textured WC-10Ni3Al cemented carbides cutting tool in turning of Ti6Al4V

Cutting performances of micro-textured WC-10Ni₃Al cutting tools compared with micro-textured WC-8Co cutting tools in turning of Ti6Al4V was investigated in this study. Cutting forces, cutting temperature, and tool life based on the criterion of a 300 μm flank wear were measured. The wear tracks of the rake face and flank face for micro-textured WC-10Ni₃Al cutting tools were analyzed. It is found that WC-10Ni₃Al cutting tools had smaller heat damages during LST compared with WC-8Co cutting tools, which was benefit for avoiding premature tool failure during Ti6Al4V machining process. Micro-textures on the rake face could effectively reduce cutting forces, cutting temperature, adhesion on the rake face, and hence increase tool life, especially at higher cutting speed.     

Self-lubrication of sintered ceramic tools with CaF2 additions in dry cutting

An Al₂O₃/TiC ceramic cutting tool with the additions of CaF₂ solid lubricant was produced by hot pressing. The fundamental properties of this ceramic cutting tool were examined. Dry machining tests were carried out on hardened steel and cast iron. The tool wear, the cutting forces, and the friction coefficient between the tool–chip interface were measured. It was shown that the friction coefficient at the tool–chip interface in dry cutting of hardened steel and cast iron with Al₂O₃/TiC/CaF₂ ceramic tool was reduced compared with that of Al₂O₃/TiC tool without CaF₂ solid lubricant. The mechanisms responsible were determined to be the formation of a self-lubricating film on the tool–chip interface, and the composition of this self-lubricating film was found to be mainly CaF₂ solid lubricant, which was released and smeared on the wear track of the tool rake face, and acted as lubricating additive between the tool–chip sliding couple during machining processes. The appearance of this self-lubricating film contributed to the decrease of the friction coefficient. Cutting speed was found to have a profound effect on this self-lubricating behavior.     

Failure mechanisms of TiB2 particle and SiC whisker reinforced Al2O3 ceramic cutting tools when machining nickel-based alloys

In this paper, Al₂O₃/TiB₂/SiC_w ceramic cutting tools with different volume fraction of TiB₂ particles and SiC whiskers were produced by hot pressing. The fundamental properties of these composite tool materials were examined. Machining tests with these ceramic tools were carried out on the Inconel718 nickel-based alloys. The tool wear rates and the cutting temperature were measured. The failure mechanisms of these ceramic tools were investigated and correlated to their mechanical properties. Results showed that the fracture toughness and hardness of the composite tool materials continuously increased with increasing SiC whisker content up to 30 vol.%. The relative density decreased with increasing SiC whisker content, the trend of the flexural strength being the same as that of the relative density. Cutting speeds were found to have a profound effect on the wear behaviors of these ceramic tools. The ceramic tools exhibited relative small flank and crater wear at cutting speed lower than 100 m/min, within further increasing of the cutting speed the flank and crater wear increased greatly. Cutting speeds less than 100 m/min were proved to be the best range for this kind of ceramic tool when machining Inconel718 nickel-based alloys. The composite tool materials with higher SiC whisker content showed more wear resistance. Abrasive wear was found to be the predominant flank wear mechanism. While the mechanisms responsible for the crater wear were determined to be adhesion and diffusion due to the high cutting temperature.     

Refrigerated cooling air cutting of difficult-to-cut materials

One approach to enhance machining performance is to apply cutting fluids during cutting process. However, the use of cutting fluids in machining process has caused some problems such as high cost, pollution, and hazards to operator's health. All the problems related to the use of cutting fluids have urged researchers to search for some alternatives to minimize or even avoid the use of cutting fluids in machining operations. Cooling gas cutting is one of these alternatives. This paper investigates the effect of cooling air cutting on tool wear, surface finish and chip shape in finish turning of Inconel 718 nickel-base super alloy and high-speed milling of AISI D2 cold work tool steel. Comparative experiments were conducted under different cooling/lubrication conditions, i.e. dry cutting, minimal quantity lubrication (MQL), cooling air, and cooling air and minimal quantity lubrication (CAMQL). For this research, composite refrigeration method was adopted to develop a new cooling gas equipment which was used to lower the temperature of compressed gas. The significant experimental results were: (i) application of cooing air and CAMQL resulted in drastic reduction in tool wear and surface roughness, and significant improvement in chip shape in finish turning of Inconel 718, (ii) in the high-speed milling of AISI D2, cooling air cutting presented longer tool life and slightly higher surface roughness than dry cutting and MQL. Therefore, it appears that cooling air cutting can provide not only environment friendliness but also great improvement in machinability of difficult-to-cut materials.     

Advanced coated ceramic tools for machining superalloys

The main limitation on the use of nickel-base superalloys, such as INCONEL 718, is the difficulty in conventional-type machining. The use of high cutting speed to achieve both machining adiabatic conditions and high productivity is necessary for their applications. This non-conventional type machining results in a short life-span of tools, even for those expensive ceramic ones with reinforced SiC whiskers (SiC_w) suitable for use at high cutting speeds. The aim of the paper is to present the results of a new idea proposed by the authors to obtain an increase in tool life at high cutting speed by minimizing the temperature effects on composite reinforcement mechanisms. The 2090 SiC whiskers reinforced A1₂O₃ tools were CrN and (Ti,AI)N coated using the PVD technique, and comparative machining tests on INCONEL 718 were carried out using uncoated and coated tools. After machining, the tools were observed with a scanning electron microscope (SEM), and EDAX (X-ray) semiquantitative analyses were performed. The behaviour of the CrN and (Ti,AI)N layers using various cutting conditions was analysed and different wear mechanisms along the tool chip contact length were observed. The cause and the mechanisms of wear were deduced and mathematic models linking tool life with process parameters were suggested.     

Tool wear mechanism in turning of novel wear-resisting aluminum bronze

1　ＩＮＴＲＯＤＵＣＴＩＯＮＡｌｕｍｉｎｕｍｂｒｏｎｚｅｉｓａｎｉｍｐｏｒｔａｎｔｅｎｇｉｎｅｅｒｉｎｇｍａｔｅｒｉ ａｌｄｕｅｔｏｉｔｓｅｘｃｅｌｌｅｎｔｐｈｙｓｉｃａｌ ,ｍｅｃｈａｎｉｃａｌ,ａｎｔｉ ｃｏｒｒｏ ｓｉｏｎａｎｄｗｅａｒｒｅｓｉｓｔｉｎｇｐｒｏｐｅｒｔｉｅｓ .Ｏｕｒｒｅｓｅａｒｃｈｇｒｏｕｐｄｅ ｖｅｌｏｐｅｄａｓｐｅｃｉａｌｔｙｐｅｏｆｈｉｇｈｓｔｒｅｎｇｔｈ ,ｗｅａｒ ｒｅｓｉｓｔｉｎｇａ ｌｕｍｉｎｕｍｂｒｏｎｚｅ(ＫＫ ) ,ｗｈｉｃｈｉｓｅｘｃｅｐｔｉｏｎａｌｌｙｇｏｏｄｆｏｒ…     

Wear mechanisms of the rough form tools in the automatic screw machine test

Tool wear mechanisms of the rough form tools in the automatic screw machine test during machining of bismuth-bearing low carbon resulfurized free machining steel under practical machining conditions were investigated. Four mechanisms, namely mild adhesive wear, abrasive wear, continuous wear, and plastic deformation have been observed to play some roles simultaneously. Mild adhesive wear, which is a wear process taking place during detachment of an adhered chip, is believed to be enhanced by fatigue. Abrasive wear could take place either by oxide inclusions in the workpiece or by the primary carbide particles of the tool freed by some wear mechanisms. Continuous wear has been attributed to some type of atomic process, most probably dissolution of tool material into the chip. On the flank face, continuous, abrasive, and mild adhesive wear are believed to be the major wear mechanisms. On the rake face, continuous wear appears to be the predominant tool wear mechanism. Based on this investigation and consideration of the effect of built-up edge (BUE), reduction of cutting force, optimization of BUE size, stabilization of BUE, and reduction of oxide inclusions are found to be important for reduction of tool wear under practical machining conditions.     

Wear mechanisms of PVD ZrN coated tools in machining

Medium-frequency magnetron sputtered PVD ZrN coatings (ZrN, ZrN/Zr) were deposited on YT15 (WC + 15%TiC + 6%Co) cemented carbide. Microstructural and fundamental properties of these ZrN coatings were examined. Dry machining tests on hardened steel were carried out with these coated tools. The wear surface features were examined by scanning electron microscopy. Results showed that deposition of the PVD ZrN coatings onto the YT15 cemented carbide causes great increase in surface hardness. The ZC-1 coated tool (ZrN/YT15 without interlayer) has the highest surface hardness; while the ZC-2 (ZrN/Zr/YT15 with a Zr interlayer) shows the highest adhesion load for the coatings to the substrate. The ZrN coated tools exhibit improved rake and flank wear resistance to that of the YT15 tool. The coated tools with a Zr interlayer (ZC-2) have higher wear resistance over the one without Zr interlayer (ZC-1). The rake wear of the ZrN coated tools at low cutting speed was mainly abrasive wear; while the mechanism responsible for the rake wear at high cutting speed was determined to be adhesion. Extensive abrasive wear accompanied by small adhesive wear were found to be the predominant flank wear mechanisms for the ZrN coated tools.     

Design,fabrication and properties of a self-lubricated tool in dry cutting

Micro-holes were made using micro-EDM on the rake and flank face of the cemented carbide (WC/Co) tools. Molybdenum disulfide (MoS₂) solid lubricants were filled into the micro-holes to form self-lubricated tools (ML-1 and -2). Dry cutting tests on hardened steel were carried out with these self-lubricated tools and conventional tools (ML-3). The cutting forces, the tool wear, and the friction coefficient between the tool–chip interface were measured. It was shown that the cutting forces with ML-1 and -2 self-lubricated tools were greatly reduced compared with that of ML-3 conventional tool, the ML-1 self-lubricated tool with one micro-hole in its rake face possessed the lower friction coefficient at the tool–chip interface; while the ML-2 self-lubricated tool with one micro-hole in its flank face revealed more flank wear resistance. The mechanism responsible was explained as the formation of a self-lubricating film between the sliding couple, and the composition of this lubricating film was found to be MoS₂ solid lubricant, which was released from the micro-hole and smeared on the rake or flank face, and can be acted as lubricating additive during dry cutting processes.     

Effects of environmental atmospheres on tribological behaviors of sintered polycrystalline diamond sliding against silicon nitride

To explore the effect of various atmosphere the tribological behaviors of the sintered polycrystalline diamond compacts (PDCs), the friction and wear behaviors of PDCs sliding against Si₃N₄ balls were evaluated by a ball-on-disk tribometer under nitrogen, argon, oxygen and air (10% relative humidity) environments, respectively. The energy dispersive X-ray spectrum (EDS), Raman spectroscopy, scanning electron microscopy (SEM) and atomic force microscope (AFM) were conducted to investigate the microstructure evolution of worn surface. The results demonstrated that the low friction appeared in argon and nitrogen environment. The formations of consecutive carbonaceous transfer films on wear scars contributed to decrease the friction during sliding process. The wear of PDCs and Si₃N₄ balls were serious in argon and nitrogen environment, but slight in oxygen and air conditions. There is a direct relationship between material removal and running-in period. The passivation effect of dangling bond under oxygen and air conditions can shorten the running in period thus weaken the wear.     

Cutting wear,microstructure and mechanical properties of (Ti0.5,W0.5)C-based cermet inserts containing Mo2C

(Ti_0.5,W_0.5)C-15 wt%Co cermets containing Mo₂C were prepared and used for cutting tool inserts. The microstructure and mechanical properties were characterized, and cutting wear was compared during machining VDEH 90CrSi5 alloy steel. Tool wear mechanism was analyzed by SEM and EDS. The Mo₂C-added inserts possess refined ceramic grains and solid-solution strengthened binder, and further they have higher coercive force, hardness, fracture toughness, and transverse rupture strength. Owing to these factors, obvious superiority for them is displayed on the flank wear over non-Mo₂C one in continuously machining VDEH 90CrSi5 alloy steel. It is also found that wearing of the inserts is the integrated results of abrasive wearing, adhesive wearing, oxidative wearing and diffusive wearing. After introducing Mo₂C to the inserts, the abrasive wear resistance, adhesive wearing and diffusive wearing are all hindered effectively, still oxidative wearing is not reduced yet.     

Microstructure and tribological characteristics of nitrided layer on 2Cr13 steel in air and vacuum

A 2Cr13 steel was gas nitrided in pure NH₃ gas atmosphere at 793 K for 20 h. The microstructure, composition and microhardness of the nitrided samples were examined. The tribological behaviour of the nitrided 2Cr13 steel in air and vacuum was investigated in order to analyse effects of the nitriding on wear resistance of the 2Cr13 steel. The results show that the nitrided layer consists of a compound layer and diffusion zone. The nitriding increases both the surface hardness and wear resistance of 2Cr13 steel in air and vacuum, and the anti-wear characteristic of the nitrided 2Cr13 steel in vacuum is much higher than that in air. The nitrided layer exhibits a mild wear in air, and avoids the severe wear that happens on the unnitrided steel. While the adhesion dominates the wear process in vacuum. The material transfer between the wear couples helps to improve the tribological characteristics of the nitrided layer in vacuum.     

Effect of Purging Gas on Wetting Behavior of Sn-3.5Ag Lead-Free Solder on Nickel-Coated Aluminum Substrate

The wetting characteristics of Sn-3.5Ag lead-free solder alloy on nickel-coated aluminum substrates in air (ambient), nitrogen, and argon atmospheres were investigated. The contact angles for the solder alloy obtained under air and argon atmospheres were in the range of 36°-38°. With nitrogen atmosphere the contact angle was found to be significantly lower at about 26°. Solder solidifying in air exhibited needle-shaped tin-rich dendrites surrounded by a eutectic matrix. The amount of tin dendrites decreased in argon atmosphere. However, the morphology of tin dendrites transformed from needle-shaped to nearly non-dendritic shape as the soldering atmosphere was changed from air to nitrogen. The interfacial microstructures revealed the presence of Ni₃Sn and Ni₃Sn₄ IMCs at the interface. The enhanced wettability observed under nitrogen atmosphere is attributed to the higher thermal conductivity of nitrogen gas and the formation of higher amount of Ni₃Sn IMCs at the interface compared to air and argon atmospheres.     

切削Inconel718时新型陶瓷刀具JX-2-Ⅰ的切削性能研究

JX－2－Ⅰ是最新研制的碳化硅晶须（SiCw）增韧和碳化硅颗粒（SiCp）弥散增强氧化铝（Al2O3）新型陶瓷刀具。本文详细研究了该刀具加工Inconel718时的切削性能，结果表明，在低速干切时的刀具抗磨损能力为YG8＞JX－2－Ⅰ＞JX－1＞JX－2－Ⅱ；在105m／min的高速湿式切削时，JX－2－Ⅰ的切削性能与JX－1差不多，但是在42m／min的速度时JX－2－Ⅰ的切削性能好于JX－1（Al2O3＋SiCw）。同时发现在用JX－2－Ⅰ中高速切削Inconel718时必须使用冷却液。由于切削温度对工件材料加工硬化的影响，以及对工件材料高温强度屈服拐点的影响而存在一个切削速度的最佳选取范围。SEM分析表明，刀具磨损的主要形式是后刀面磨损、边界磨损、切深沟槽磨损和前刀面月牙洼磨损；刀具磨损的主要机理是粘结磨损、磨粒磨损和塑性变形磨损。     

On the effects of cutting speed and cooling methodologies in grooving operation of various tempers of β-titanium alloy

High strength and its retention at elevated temperatures render titanium alloys highly difficult to cut. Of commonly used titanium alloys, β-alloys are the ones possessing highest values of strength. Higher productivity in machining demands higher cutting speed and its implementation generates even more heat at primary and secondary shear zones. Poor thermal conductivity of titanium causes concentration of excessive heat near the cutting edge, which in turn, leads to rapid damage of cutting tool. The situation, thus, demands application of an innovative cooling methodology that would cause effective removal of heat in order to make implementation of higher cutting speeds viable. The paper describes an experimental investigation carried out to quantify the effects of high levels of cutting speed and the influence of carbon dioxide snow (CO₂-snow) as an innovative cooling methodologies in machining of three tempers of β-titanium alloy. A comparison was made among various cooling techniques, which consisted of following: conventional flood emulsion; impingement of jet of CO₂-snow at the rake face, the flank face, the rake and flank faces together; and the combination of the CO₂-jet and MQL. The comparative effectiveness of each methodology was evaluated in terms of cutting forces, tool wear, and acoustic emission as an indicator to measure differences in terms of the chip morphology.     

New observations on tool wear mechanism in dry machining Inconel718

Tool wear is a problem in machining nickel-based alloy Inconel718, and it is thus of great importance to understand tool wear. Tool wear mechanism in dry machining Inconel718 with coated cemented carbide tools was analyzed in this paper. CCD and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDS) were used to study tool wear mechanism. The results show that the main reason which causes cutting tool wear was that the tool materials fall off from the tool substrate in the form of wear debris. In addition,, element diffusion between tool and workpiece and oxidation reaction all accelerate the formation and the peeling of the wear debris. According to analysis of tool wear mechanism, tool flank wear model was established. The optimal temperature in machining Inconel718 with PVD-coated (TiAlN) tool was obtained through the established model. Excellent experimental agreement was achieved in optimal temperature calculated by the established model.