Effect of temperature of annealing below 900 °C on structure, properties and tool life of an AlTiN coating under various cutting conditions

In this study the cemented carbide cutting tools with a nano-crystalline Al_0.67Ti_0.33N hard PVD coating deposited by cathodic arc evaporation were annealed within a range of temperatures 700-800 °C during 2 h in vacuum. The changes in structure and properties of the coating vs. temperature have been analyzed using TEM as well as high temperature nano-indentation methods. Cutting tools with the annealed AlTiN coating have been run through a number of cutting tests with varying conditions. The conditions were as following: 1) continuous cutting: turning of annealed 1040 steel (HB 220); 2) interrupted cutting: turning of 4340 steel (HRC 40); 3) end milling: ball nose end milling of hardened H13 steel (HRC 50). The cutting tool life has been investigated before and after annealing of the Al_0.67Ti_0.33N coatings at different temperatures. The relations between high temperature hardness and plasticity of the Al_0.67Ti_0.33N coating and tool life under varying cutting conditions was outlined.     

Characterization of nanocrystalline AlTiN coatings synthesized by a cathodic-arc deposition process

Graded and multilayered Al_xTi_1−xN nanocrystalline coatings were synthesized by using cathodic-arc evaporation (CAE) process. Ti₃₃Al₆₇ and Ti₅₀Al₅₀ alloy cathodes were used for the deposition of Al_xTi_1−xN nanocrystalline coatings with different Al/(Ti+Al) ratios. Optical emission spectra of the plasma species including atomic and ionized Ti, atomic Al, excited and ionized nitrogen (N₂ and N₂⁺) revealed that the excitation, ionization and charge transfer reactions of the Al-Ti-N plasma occurred during the Al_xTi_1−xN coating process. A preferred (111) orientation was shown in the Al_0.67Ti_0.33N with high Al/(Ti+Al) atomic content ratio (0.63) and small grain size (29 nm). The graded Al_0.67Ti_0.33N/TiN possessed the highest hardness of Hv_25 g 3850 ± 180. However, the multilayered Al_0.67Ti_0.33N/TiN coating supported a longer tool life with lower residual stress. It has been found that the wear performance and mechanical properties of the films were correlated with the Al/(Ti+Al) content ratio and multilayered structure.     

Structural and mechanical properties of AlTiN/CrN coatings synthesized by a cathodic-arc deposition process

Monolayered AlTiN and Multilayered AlTiN/CrN coatings were synthesized by a cathodic-arc deposition process, using TiAl (with 50/50 and 33/67 at.%) and Cr elemental cathodes. The atomic ratio of Al/(Ti + Al) in the AlTiN coatings was reduced to 0.44 and 0.61, respectively, compared with the corresponding Ti₅₀Al₅₀ and Ti₃₃Al₆₇ cathode materials. The multilayered AlTiN/CrN films showed smaller crystallite size, larger lattice strain, higher hardness, higher residual stress, and better adhesion strength as well than the monolayered AlTi films. The multilayered Al_0.35Ti_0.22N_0.43/CrN coating exhibited the highest hardness of about 38 GPa and the highest H³/E*² ratio value of 0.188 GPa, indicating the best resistance to plastic deformation, among all the coatings studied.     

Investigating the correlation between nano-impact fracture resistance and hardness/modulus ratio from nanoindentation at 25-500 °C and the fracture resistance and lifetime of cutting tools with Ti1−xAlxN (x = 0.5 and 0.67) PVD coatings in milling operations

A novel laboratory technique, nano-impact testing, has been used to test Ti_1−xAl_xN (x = 0.5 and 0.67) PVD coated WC-Co inserts at 25-500 °C. Cutting tool life was studied under conditions of face milling of the structural AISI 1040 steel; the end milling of hardened 4340 steel (HRC 40) and TiAl6V4 alloy. A correlation was found between the results of the rapid nano-impact test and milling tests. When x = 0.67 improved resistance to fracture was found during milling operations and also in the nano-impact test of this coating compared to when x = 0.50. The coating protects the cutting tool surface against the chipping that is typical for cutting operations with intensive adhesive interaction with workpiece materials such as machining of Ti-based alloys. The results give encouragement that the elevated temperature nano-impact test can be used to predict the wear and fracture resistance of hard coatings during milling operations. At 500 °C nanoindentation shows there is a lower H/E_r ratio for the PVD coatings compared to room temperature, consistent with reduced fracture observed at this temperature in the nano-impact test.     

Machining performance and decomposition of TiAlN/TiN multilayer coated metal cutting inserts

The wear resistance of metal cutting inserts coated with metastable Ti_0.34Al_0.66N/TiN multilayers was tested in continuous turning of an AISI 316L stainless steel. The multilayers had periods of 25 + 50, 12 + 25 and 6 + 12 nm (Ti_0.34Al_0.66N + TiN) with a total multilayer stack thickness of 2 μm. Inserts coated with monolithic TiN and Ti_0.34Al_0.66N deposited under similar conditions were used as references. The multilayer coated inserts show a decrease of wear with decreased multilayer period, both on the rake and flank face. The wear on the rake face was lower on all the multilayer coated tools compared to the references. Scanning transmission electron imaging and energy dispersive spectroscopy elemental mapping of a worn multilayer coating show decomposition of the Ti_0.34Al_0.66N to domains rich of Al and Ti. High resolution transmission electron micrography shows preserved epitaxy between the TiN and Ti_0.34Al_0.66N layers. The improved wear resistance of the multilayer coated inserts is discussed in terms of an improved thermal stability of the multilayer stacks.     

Wettability and machinability study of pure aluminium towards uncoated and coated carbide cutting tool inserts

An investigation has been conducted to study wetting characteristics of aluminium towards different cutting tool materials for assessing the compatibility for dry machining of aluminum. For this purpose uncoated carbide (94%WC + 6%Co) and mono or multi-layer coated carbide tools with top coating of TiC, TiN, Al₂O₃ and diamond have been used. It was observed that aluminium had a tendency to wet uncoated carbide (94%WC + 6%Co) inserts. However, wetting was more pronounced when surface was enriched with cobalt. In contrast, wetting of aluminium was less when the WC content of the carbide tool surface increased. Coatings like TiC, TiN or Al₂O₃ could not show pure non-wetting characteristics for aluminium. The aluminium appeared to dissolve the coatings in different degrees. On the other hand, coating of diamond exhibited inertness towards aluminum leading to non-wetting behaviour. Turning test with aluminium indicated heavy material built up on uncoated (94%WC + 6%Co) tool. Built up edge formation could not be avoided when carbide inserts with a top coating of TiC, TiN, Al₂O₃ were engaged in machining of aluminium. However, the non-wetting characteristic of diamond coating was reflected during machining of aluminium. The chips slided smoothly over the rake face leaving no trace of edge built up.     

Temperature driven evolution of thermal, electrical, and optical properties of Ti-Al-N coatings

Monolithic single phase cubic (c) Ti_1−xAl_xN thin films are used in various industrial applications due to their high thermal stability, which beneficially effects lifetime and performance of cutting and milling tools, but also find increasing utilization in electronic and optical devices. The present study elucidates the temperature-driven evolution of heat conductivity, electrical resistivity and optical reflectance from room temperature up to 1400 °C and links them to structural and chemical changes in Ti_1−xAl_xN coatings. It is shown that various decomposition phenomena, involving recovery and spinodal decomposition (known to account for the age hardening phenomenon in c-Ti_1−xAl_xN), as well as the cubic to wurtzite phase transformation of spinodally formed AlN-enriched domains, effectively increase the thermal conductivity of the coatings from ∼3.8 W m⁻¹ K⁻¹ by a factor of three, while the electrical resistivity is reduced by one order of magnitude. A change in the coating color from metallic grey after deposition to reddish-golden after annealing to 1400 °C is related to the film structure and discussed in terms of film reflectivity.     

Combustion synthesis and development of Ti-O-C aluminium composites

Aluminium matrix composite reinforced with Ti compounds was successfully fabricated by SHS combustion synthesis and squeeze casting course. Prepared samples from mixture containing Ti, C and Al₂O₃ fibres were heated in microwave reactor to ignite synthesis and produce porous preform for subsequent infiltrating with liquid metal. Studies showed that synthesizing temperature has been remarkably increased by applying higher magnetron power and addition of graphite. Synthesis of specimens prepared from preliminary ball milled Ti and C powders proceeded at the highest propagation wave velocity. Microwave heating of metal Ti powder in the stream of CO₂ resulted in formation of corrugated precipitates composed of titanium oxide with carbon inclusions TiO(C) and Ti₂O₃. The produced preforms were impregnated by squeeze casting with the aluminium alloy AlSi7Mg. Proper interface with slight reduction of Ti oxide between the reinforcement and the matrix was developed. Subsequently, the samples were annealed at 500 and 1000 °C. Annealing at the lower temperature induced creation of Ti₃O₂(C) and Al₂O₃. This process was continued at 1000 °C, and additionally some Ti(Al_0,8Si_0,2)₃ pellets appeared in the matrix. With prolonged annealing, oxygen was completely removed from Ti compound and oval grains of Ti(C) were created, enveloped with Al₂O₃. In the matrix, larger and numerous Ti₃AlSi₅ pellets were formed. Hardness examination showed that the best strengthening effect was achieved after annealing at 1000 °C.     

Effect of Hf on structure and age hardening of Ti-Al-N thin films

Protective coatings for high temperature applications, as present e.g. during cutting and milling operations, require excellent mechanical and thermal properties during work load. The Ti_1 − xAl_xN system is industrially well acknowledged as it covers some of these requirements, and even exhibits increasing hardness with increasing temperature in its cubic modification, known as age hardening. The thermally activated diffusion at high temperatures however enables for the formation of wurtzite AlN, which causes a rapid reduction of mechanical properties in Ti_1 − xAl_xN coatings. The present work investigates the possibility to increase the formation temperature of w-AlN due to Hf alloying up to 10 at.% at the metal sublattice of Ti_1 − xAl_xN films. Ab initio predictions on the phase stability and decomposition products of quaternary Ti_{1 − x − y}Al_xHf_yN alloys, as well as the ternary Ti_1 − xAl_xN, Hf_1 − xAl_xN and Ti_1 − zHf_zN systems, facilitate the interpretation of the experimental findings. Vacuum annealing treatments from 600 to 1100 °C indicate that the isostructural decomposition, which is responsible for age hardening, of the Ti_{1 − x − y}Al_xHf_yN films starts at lower temperatures than the ternary Ti_1 − xAl_xN coating. However, the formation of a dual phase structure of c-Ti_1 − zHf_zN (with z = y/(1 − x)) and w-AlN is shifted to ~ 200 °C higher temperatures, thus retaining a film hardness of ~ 40 GPa up to ~ 1100 °C, while the Hf free films reach the respective hardness maximum of ~ 38 GPa already at ~ 900 °C. Additional annealing experiments at 850 and 950 °C for 20 h indicate a substantial improvement of the oxidation resistance with increasing amount of Hf in Ti_{1 − x − y}Al_xHf_yN.     

Cutting performance and failure mechanisms of an Al2O3/WC/TiC micro- nano-composite ceramic tool

An Al₂O₃-based composite ceramic tool material reinforced with WC microparticles and TiC nanoparticles was fabricated by using hot-pressing technique. The cutting performance, failure modes and mechanisms of the Al₂O₃/WC/TiC ceramic tool were investigated via continuous and intermittent turning of hardened AISI 1045 steel in comparison with those of an Al₂O₃/(W, Ti)C ceramic tool SG-4 and a cemented carbide tool YS8. Worn and fractured surfaces of the cutting tools were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results of continuous turning revealed that tool lifetime of the Al₂O₃/WC/TiC ceramic tool was higher than that of the SG-4 and YS8 tools at all the tested cutting speeds. As for the intermittent turning, tool life of the Al₂O₃/WC/TiC ceramic tool was equivalent to that of YS8, but shorter than that of the SG-4 at lower cutting speed (110 m/min). However, tool life of the Al₂O₃/WC/TiC ceramic tool increased when the cutting speed increased to 170 m/min, becoming much longer than that of the SG-4 and YS8 tools. The longer tool life of the Al₂O₃/WC/TiC composite ceramic tool was attributed to its synergistic strengthening/toughening mechanisms induced by the WC microparticles and TiC nanoparticles.     

The influence of age-hardening on turning and milling performance of Ti-Al-N coated inserts

Ti-Al-N coatings are well known for their excellent properties and age-hardening abilities. Here we show that the life-time of coated inserts during turning of stainless steel can be increased to 200% by post-deposition vacuum annealing at 900 °C combined with a ~ 1 K/min vacuum furnace cooling. During milling of 42CrMo steel an increase in tool life-time to 140% is only obtained if the cooling condition after annealing at 900 °C contains a fast segment with 50 K/min from 800 to 700 °C. Thereby, the Co-binder in cemented carbide exhibits a retarded phase transformation from cubic to hexagonal. Consequently, the fracture toughness of the cemented carbide is reduced only from ~ 10.8 to 10.4 MPa√m while the coating still has an adhesive strength of ~ 65 N.Our results indicate that best machining performances of coated inserts are obtained after annealing at 900 °C where the supersaturated Ti_0.34Al_0.66N coating undergoes spinodal decomposition to form nm-sized cubic TiN and AlN domains resulting in a hardness increase from 34.5 to 38.7 GPa. Additionally, we demonstrate that careful attention needs to be paid on the influence of annealing conditions on adhesive strength and fracture toughness of coated inserts.     

Design and performance of AlTiN and TiAlCrN PVD coatings for machining of hard to cut materials

Machining of hard to cut materials such as hardened steels and high temperature strong aerospace materials is a challenge of modern manufacturing. Two categories of the aluminum-rich TiAlN-based Physical Vapor Deposited (PVD) coatings, namely AlTiN and TiAlCrN, are commonly used for this area of application. A comparative investigation of the structural characteristics, various micro-mechanical properties, oxidation resistance and service properties of the both coatings has been performed.Crystal structure has been studied using High Resolution Transmission Electron Microscopy (HR TEM). Electronic structure has been investigated using X-ray Photoelectron Spectroscopy (XPS). Micro-mechanical properties (microhardness, plasticity index, impact fatigue fracture resistance) have been evaluated using a Micro Materials Nano-Test System. Short-term oxidation resistance has been studied at 900 °C in air. The tool life of the coating was studied during ball nose end milling of hardened H 13 tool steel as well as end milling of aerospace alloys such as Ni-based superalloy (Waspalloy) and Ti alloy (TiAl₆V₄).It was shown that the set of characteristics that control wear performance strongly depend on specific applications. For machining of hardened tool steels, when heavy loads/high temperatures control wear behavior, the coating has to possess a well-known combination of high hot hardness and improved oxidation resistance at elevated temperatures. To achieve these properties, crystal structure for TiAlN-based coatings should be mainly B1, and elemental composition of the coating should ensure formation of strong inter-atomic bonds such as Al-Cr metal-covalent bonds in the TiAlCrN coating. Nano-crystalline structure with grain size of around 10-30 nm enhances necessary properties of the coating.In contrast, for machining of aerospace alloys, when elevated load/temperature combined with intensive adhesive interaction with workpiece material results in unstable attrition wear with deep surface damage, the coating should possess a different set of characteristics. Crystal structure for TiAlN-based coatings is basically B1; but due to a high amount of aluminum, the AlTiN coating contains AlN domains. The coating has a very fine-grained nano-crystalline structure (grains sized around 5 nm). Electron structure of energy levels indicates formation of metallic bonds. This results in plasticity increase at the cost of hot hardness reduction. The surface is able to dissipate energy by means of plastic deformation (instead of crack formation) and in this way, surface damage is reduced.     

Characterisation of HVOF sprayed Cr3C2-50(Ni20Cr) coating and the influence of binder properties on solid particle erosion behaviour

The coating Cr₃C₂ with 50 wt.% Ni20Cr deposited by high velocity oxy-fuel (HVOF) spray process was characterized in detail to investigate the effect of annealing on the solid particle erosion behaviour and understand the influence of the binder properties. Systematic characterization of the coating was carried out using electron microscopy (scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA)), X-ray diffraction (XRD), microindentation and nanoindentation techniques. The solid particle erosion tests were done on the as-sprayed coating and coatings annealed at 400 °C, 600 °C and 800 °C using silica erodent particles. The coefficient of restitution of the coated samples was also measured by WC ball impact tests to simulate dynamic impacts. The as-sprayed coating consisted of primary carbides and binder that was a mixture of amorphous and nanocrystalline phases. Annealing leads to recrystallisation of binder phase and precipitation of secondary carbides. The coating hardness and binder ductility change with annealing temperature. The erosion resistance improves with annealing up to 600 °C. In the as-sprayed coating, the amorphous phase, inter-splat boundaries and the elastic rebound characteristics affect the erosion response. While in the case of the coating annealed at 600 °C, the presence of ductile crystalline binder, fine carbide precipitates and embedment of erodent particles together improve solid particle erosion resistance.     

Aluminum-rich TiAlCN coatings by Low Pressure CVD

Ti_1 − xAl_xN is a well established material for cutting tool applications exhibiting a high hardness and an excellent oxidation resistance. A main route for increasing the performance of Ti_1 − xAl_xN is the incorporation of further elements. Therefore the main objective of this work is to improve the properties and wear resistance of aluminum-rich CVD-TiAlN coatings by incorporating carbon. A new Low Pressure CVD process was employed for the deposition of a very aluminum-rich TiAlCN layers. The process works with a gas mixture of TiCl₄, AlCl₃, NH₃, H₂, N₂, Ar and ethylene as carbon source. In this work microstructure, composition, properties and cutting performance of CVD-TiAlCN coatings were investigated.Hard aluminum-rich TiAlCN coatings were obtained at 800 °C and 850 °C consisting of a composite of fcc-Ti_1 − xAl_xN and minor phases of TiN, h-AlN and amorphous carbon. WDX analysis indicates only a low carbon content < 2 at.%. Lattice constant calculations suggest that carbon atoms should not be incorporated in the Ti_1 − xAl_xN lattice. From TEM analysis and Raman spectroscopy it is evident that carbon is mainly located at the grain boundaries as a-C phase. Therefore these fcc-Ti_1 − xAl_xN(C) coatings with low carbon content are rather a composite of fcc-Ti_1 − xAl_xN and an amorphous carbon phase (a-C). At 900 °C the metastable fcc-Ti_1 − xAl_xN nearly disappears and co-deposition of TiN and h-AlN occurs. The layers deposited at 800 °C and 850 °C possess a high hardness around 3000 HV and compressive stress. CVD-TiAlCN coatings prepared at 850 °C shows also an amazing thermal stability under high vacuum conditions up to 1200 °C. Aluminum-rich composites fcc-Ti_1 − xAl_xN/a-C with x > 0.8 exhibit a superior cutting performance in different milling tests.     

Phase constituents and microstructure of laser cladding Al2O3/Ti3Al reinforced ceramic layer on titanium alloy

Laser cladding of the Fe₃Al + TiB₂/Al₂O₃ pre-placed alloy powder on Ti-6Al-4V alloy can form the Ti₃Al/Fe₃Al + TiB₂/Al₂O₃ ceramic layer, which can greatly increase wear resistance of titanium alloy. In this study, the Ti₃Al/Fe₃Al + TiB₂/Al₂O₃ ceramic layer has been researched by means of electron probe, X-ray diffraction, scanning electron microscope and micro-analyzer. In cladding process, Al₂O₃ can react with TiB₂ leading to formation of amount of Ti₃Al and B. This principle can be used to improve the Fe₃Al + TiB₂ laser cladded coating, it was found that with addition of Al₂O₃, the microstructure performance and micro-hardness of the coating was obviously improved due to the action of the Al-Ti-B system and hard phases.     

Thermal stability and oxidation resistance of laser clad TiVCrAlSi high entropy alloy coatings on Ti-6Al-4V alloy

TiVCrAlSi high entropy alloy coatings were deposited on Ti-6Al-4V alloy by laser cladding. SEM, XRD and EDS analyses show that, the as-clad coating is composed of (Ti,V)₅Si₃ and a BCC solid solution. After annealing at 800 °C for 24 h under vacuum, the coating is composed of (Ti,V)₅Si₃, Al₈(V,Cr)₅, and a BCC solid solution. The temperature-dependent phase equilibrium for the coating material calculated by using the CALPHAD method, indicates that above 880 °C the stable phases existing in the coating material are a BCC solid-solution and (Ti,V)₅Si₃. When the temperature is below 880 °C, the stable phases are (Ti,V)₅Si₃, Al₈(V,Cr)₅, and a BCC solid solution. In order to validate the calculation results, they were compared with TiVCrAlSi alloy samples prepared by arc melting, encapsulated in quartz tubes under vacuum, annealed at 400-1100 °C for 3 days and water-quenched. XRD analysis shows that the experimental phase composition agrees with the thermodynamic calculations. After vacuum annealing, there is a small increase of hardness for the laser clad TiVCrAlSi coating, which is due to the formation of Al₈(V,Cr)₅. The oxidation tests show that the TiVCrAlSi coating effectively improves the oxidation resistance of Ti-6Al-4V at 800 °C in air. The formation of a dense and adherent scale consisting of SiO₂, Cr₂O₃, TiO₂, Al₂O₃ and a small amount of V₂O₅ is supposed to be responsible for the observed improvement of the oxidation resistance.     

Phase transformations in face centered cubic (Al0.32Cr0.68)2O3 thin films

Face centered cubic (Al_0.32Cr_0.68)₂O₃ thin films have been annealed in the temperature range of 500–1000 °C during 2–8 h. The fcc structure of the film remains intact when annealed at temperatures up to 700 °C for 8 h. X-ray diffraction and transmission electron microscopy show the onset of phase transformation to corundum phase alloys in the sample annealed at 900 °C for 2 h, where annealing at 1000 °C for 2 h results in complete phase transformation to α-(Al_0.32Cr_0.68)₂O₃. In-plane and out-of-plane line scans performed in EDX TEM and θ/2θ XRD patterns did not show any phase separation into α-Cr₂O₃ and Al₂O₃ prior and after the annealing. The apparent activation energy of this process is 380–480 kJ/mol as determined by the Johnson–Mehl–Avrami model.     

Proposal of self-healing coatings for nuclear fusion applications

Avoiding cracks in ceramic coatings is one of the most important problems to be solved for the thermally sprayed tritium permeation barriers in fusion reactor. In this paper, a self-healing composite coating composed of TiC + mixture (TiC/Al₂O₃) + Al₂O₃ was developed to address this problem. The coating was deposited on certain martensitic steel by plasma spraying. The morphology and phase of the coating were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) while the porosity was analyzed by using Image Pro software. The thermal shock resistance test and residual stress measurement of the coating were also performed. In the experiment, NiAl + TiC + mixture (TiC/Al₂O₃) + Al₂O₃ and mixture (TiC/Al₂O₃) + Al₂O₃ films were also fabricated and studied respectively. The results showed that the TiC + mixture (TiC/Al₂O₃) + Al₂O₃ coating exhibited the best mechanical integrity and self-healing ability among the three samples with the porosity decreased by 90% after heat-treatment under normal atmosphere. The oxidation/expansion of TiC in the coating played an important role in the sealing of pores. This self-healing coating made by thermal spraying is proposed as a good candidate for tritium permeation barrier in fusion reactors.     

Atom probe specimen preparation and 3D interfacial study of Ti-Al-N thin films

3D-atom probe tomography is used to study the atomistic morphology of Ti-Al-N thin films in the as-deposited and annealed states. We present results on modification of a focused ion beam based lift-out technique to meet the challenges for specimen preparation of substrate-free thin film material, which allows to avoid substrate interference during post-deposition annealing. We further emphasize the influence of doped silicon and low-carbon steel posts on the measurement performance during atom probe tomography of Ti_0.46Al_0.54N films. Pre-sharpened silicon posts ensure the preparation of equally shaped specimens, whereas steel posts reach a better mass resolution. Taking these results into account, we moreover examined the decomposition of Ti_0.46Al_0.54N towards TiN and AlN with respect to determination and distribution of oxygen impurities as a function of temperature. Thereby we observe an enrichment of these oxygen impurities in AlN with increasing annealing temperature to 1350 °C, from an originally random distribution in the as-deposited state.     

Workpiece surface integrity when slot milling γ-TiAl intermetallic alloy

Slot milling is presented as a potential manufacturing route for aerospace component feature production when machining γ-TiAl intermetallic alloy Ti–45Al–2Mn–2Nb + 0.8 vol.% TiB₂XD using 2 mm diameter AlTiN coated WC ball nose end milling cutters. When operating with flood cutting fluid at v = 88 m/min, f = 0.05 mm/tooth, d = 0.2 mm, maximum flank wear was ∼65 μm after 25 min. SEM micrographs of slot surfaces show re-deposited/adhered and smeared workpiece material to a length of ∼50 μm. Brittle fracture of the slot edges was restricted to <10 μm with sporadic top burr formation observed up to ∼20 μm. Cross sectional micrographs of the slot sidewalls showed bending of the lamellae limited to within 5 μm.