Study of wettability test of pure aluminum against uncoated and coated carbide inserts

The wide application of aluminum in different industries has increased the need for finding the suitable cutting tool. In contrast to ferrous materials, the dry machining of aluminum is a great challenge. Wetting test is widely used to find out the chemical affinity of aluminum with different tool materials before proceeding for actual machining. Wettability tests were carried out in a high vacuum brazing chamber to find out the spreadability of aluminum on cutting tools. Mono or multilayer coated carbide tools with a top coating of TiC, TiN, Al₂O₃, TiB₂, MoS₂ and diamond on cemented carbide (WC-Co) cutting tool inserts were used in the experiment. The results revealed that diamond/graphite is the most inert for aluminum.     

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.     

Experimental investigation of the cutting temperature when turning with coated indexable inserts

This paper deals with an experimental investigation into the different factors which influence the temperature which occur at the coating/substrate–chip interface when machining a medium carbon steel and an austenitic stainless steel. Both flat-faced and grooved inserts coated with TiC, TiC/TiN and TiC/Al₂O₃/TiN were used. A standard K-type thermocouple embedded in the workpiece was used to convert measured efms to the interfacial temperature. Some optimal coating structures for high speed machining of these steels corresponding to the minimum interface temperature were selected. In particular, it was observed that by the proper selection of the thermal properties of the coating and the workpiece materials, which result in a substantial increase in the interface temperature, the effect of a thermal barrier in the top layer of the coating can occur.     

Finite element modelling of the thermo-mechanical behavior of coatings under extreme contact loading in dry machining

During metal cutting processes, intensive friction and high temperature generated at the tool chip interface affect the cutting zone of the tool, by inducing damage and wear. To improve the cutting tool's life, thin hard coatings, synthesized by physical or chemical vapor deposition (PVD or CVD) techniques, are often used as protective layers. In this work, numerical/theoretical analysis of dry machining has been performed to study the impact of different coating layers on the machining process. Four cases are considered: an uncoated tool made of tungsten carbide (WC-Co) and coated tungsten carbides in three different configurations. The first one is made of one layer namely TiN, the second one (hypothetical carbide insert) is composed of two layers (Al₂O₃ and TiN), and the last one has three layers (TiCN, Al₂O₃ and TiN). The workpiece material is an AISI 316L stainless steel. All cutting conditions are fixed in order to highlight the effect of coatings independently from others influencing parameters. The analysis has shown the impact of the different configurations of coatings on the temperature level inside the tool and on its surface, on the pressure and also on the cutting and feed forces.     

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.     

Model of quality management of hard coatings on ceramic cutting tools

For the development and introduction of new coated cutting tools (i.e. new combinations of cutting materials and hard coatings), it is necessary to carry out a number of studies with the purpose of optimizing the coatings composition and processing procedures, and also to test new tools under working conditions. The aim of this paper is to establish a common model for environmentally oriented quality management in the use and development of coated ceramic cutting tools with new coating systems. The paper also presents an investigation of the results of tribological and cutting properties of the coatings deposited with the PVD and CVD techniques on cutting inserts made from (Al₂O₃ + TiC) tool ceramics. Tests were carried out on ceramic inserts, uncoated and PVD or CVD-coated, with gradient, mono-, multi- (nano) layers and multicomponent hard wear resistant coatings composed of TiN, Ti(C, N), (Ti, Al)N, (Ti, AlSi)N and Al₂O₃ layers.     

Effect of pretreatment, seeding and interlayer on nucleation and growth of HFCVD diamond films on cemented carbide tools

The direct deposition of diamond on carbide tools is difficult because formation of graphitization and thus leading to poor adhesion, due to presence of cobalt on the surface. Various methods were adopted to suppress the effect of cobalt during deposition. One of them was by putting an interlayer. In this study, carbide substrates with coatings of Ti, TiN and TiC were used. Ti coating has a strong tendency to form intermediate carbide leading to the highest nucleation density of diamond. A comparison was made on nucleation and growth of diamond crystals on various interlayers by hot filament CVD method. At the same time, the variations of diamond film growth morphology have been studied on unseeded and seeded carbide inserts. The SEM pictures revealed that among interlayer, Ti coating gave highest nucleation density compared to TiN and TiC coatings. At the same time, diamond seeded inserts, pretreated by Treat 1 [HCl + HNO₃ + H₂O (1:1:1)] for 15 min ultrasonically resulted in the highest nucleation density, compared to Treat 2 [K₃[Fe(CN)₆] + KOH + H₂O] solution in (1:1:10) for 15 min, at constant process parameters.     

Adhesion phenomena in the secondary shear zone in turning of austenitic stainless steel and carbon steel

This paper aims to increase the understanding of the adhesion between chip and tool rake face by studying the initial material transfer to the tool during orthogonal machining at 150 m/min. Two types of work material were tested, an austenitic stainless steel, 316L, and a carbon steel, UHB 11. The tools used were cemented carbide inserts coated with hard ceramic coatings. Two different CVD coatings, TiN and Al₂O₃, produced with two different surface roughnesses, polished and rough, were tested. The influences of both tool surface topography and chemistry on the adhesion phenomena in the secondary shear zone were thus evaluated. Extensive surface analyses of the inserts after cutting were made using techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM). As expected, cutting in the stainless steel resulted in a higher amount of adhered material, compared to cutting in the carbon steel. Remnants of built-up layers were found on the surfaces of the 316L chips but not on the UHB 11 chips. Moreover, it was shown that for both materials the tool roughness had a profound effect, with the rougher surfaces comprising much higher amounts of adhered material than the polished ones. Non-metallic inclusions from both types of workpiece steels accumulate in the high temperature area on the inserts. The general tendency was that higher amounts of transferred material were found on the TiN coating than on the Al₂O₃ coating after cutting.     

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.     

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.     

Using coated ceramic particles to increase wear resistance in high-speed steels

The use of chemical-vapor-deposition (CVD)-coated ceramic particle reinforcements in metal-matrix composites allows the control of reactivity at the particle/matrix interface. Wear-resistant, high-speed, steel-based composites containing uncoatedAl₂O₃ uncoated TiC, and CVD-coated A1₂O₃ were liquid-phase sintered and characterized using pin-on-disk wear testing. TiC or TiN CVD coating of Al₂O₃ resulted in a porosity decrease at the particle/matrix interface in addition to better ceramic/metal cohesion due to improved wettability. Lower wear rates were obtained with the composites containing TiC-or TiN-coated Al₂O₃.     

Machining performance of pearlitic–ferritic nodular cast iron with coated carbide and silicon nitride ceramic tools

This paper concerns the fundamental cutting characteristics obtained in the turning of the pearlitic–ferritic nodular iron (EN-GJS-500-7 grade with UTS=500 MPa) when using carbide tools coated with single TiAlN and multilayer TiC/Ti(C,N)/Al₂O₃/TiN coatings, as well as silicon nitride (Si₃N₄) based ceramic tools. As a competitor, a P20 uncoated carbide grade was selected. The fundamental process readings include cutting and feed forces, the tool–chip interface temperature, Peclet number, friction coefficient and the tool–chip contact length as functions of cutting parameters. In particular, the measurements of cutting temperature were carried out using conventional tool–work thermocouple method and IR thermography. It is concluded based on many process characteristics that multilayer coated and ceramic tools can substantially improve the performance of nodular iron machining.     

The history of hard CVD coatings for tool applications at the University of Technology Vienna

The history of chemical vapour deposition (CVD) started in the 19th century with the production of lamp filaments and by the Mond process for the nickel production. In the 20th century Van Arkel deposited metals from the gas phase for application in lamp industry.TiC was the first hard coating deposited by CVD in the 1950s. Nearly 20 years later Krupp Widia introduced the first commercial TiC coating on hardmetal tools.Prof. Richard Kieffer started with TiN deposition by the CVD process in the 1970s at the “Technischer Hochschule Wien” and Prof. Benno Lux continued with Al₂O₃- and diamond coatings.In the following years CVD processes for TiN, Ti(C,N), ZrC, (Ti,Zr)C, TiB₂, Al₂O₃, Ta_xC, Cr_xC_y, diamond, BN and BCN were investigated at the University of Technology Vienna.The depositions of new crystalline solid solutions (mixed crystals), nano-crystalline materials and nano-crystalline mixtures of phases have been research topics so far.     

Wetting phenomena in the TiC/(Cu–Al) system

The wetting behavior in the TiC/(Cu–Al) system was studied by the sessile drop method over the entire Cu–Al alloy concentration range. The experimental results show that the wetting evolution in the TiC/Cu system is controlled by partial dissolution of the titanium carbide phase. The presence of oxygen on the TiC surface strongly inhibits the interaction between the ceramic and molten Cu, thus leading to non-wetting conditions. The improved wetting of the oxygen-free TiC substrate by Cu–Al alloys is due to the enhanced transfer of titanium from the carbide phase into the melt, and results from its increased solubility in the Al-containing molten alloy. The wetting of TiC substrates covered with an oxygen-containing layer by a molten Cu–Al alloy is affected by the reduction of this layer and transfer of the released Ti into the molten metal. Enhanced wetting may also result from in situ deoxidization of the surface of the Cu–Al liquid drop and of the TiC substrate due to the evaporation of the Al₂O sub-oxide at elevated temperature. A thermodynamic analysis of the systems under consideration is in good agreement with the experimental observations.     

Surface integrity generated by oblique machining of steel and iron parts

In this study the surface integrity produced by oblique turning of a range of iron-based materials including C45 carbon, 41Cr4 low-alloy hardened, X6CrNiTi18-10 stainless steels and EN-GJS-500-7 spheroidal iron was quantified by means of 2D and 3D surface roughness parameters, strain-hardening effects and associated residual stresses. Surfaces were produced by a special straight-edged cutting tool with large inclination angle of 55° equipped with carbide and mixed Al₂O₃–TiC ceramic cutting tool inserts. It was documented that oblique machining performed with relatively higher feed rate allows obtaining lower surface roughness and, in general, better bearing characteristics. Moreover, compressive stresses with the maximum value located close to the machined surface and parabolic profile can be induced into the surface layer. The magnitude of stresses depends on the strain-hardening rate of the surface layer.     

Cemented carbide surface modifications using laser treatment and its effects on hard coating adhesion

A pulsed HyBrID copper laser (510 nm, 30 ns, 13.8 kHz) was used for the treatment of cemented carbide substrate before deposition of TiCN/Al₂O₃/TiN coating by the MT-CVD process. The influence of the laser treatment on the surface morphology, surface structure and coating adhesion was investigated based on the laser irradiation dynamics used here. The experimental results showed that a large variety of cemented carbide surface textures could be obtained, depending on the laser intensity and number of applied laser pulses. Moreover, this laser process was found to produce some less carbon non-stoichiometric WC phases such as β-WC_1 − x and α-W₂C. Finally, using the Rockwell C adhesion test as output criteria, two sets of laser parameters were identified that produced a surface with adhesion strength comparable to that of commercial tools pretreated by micro-sandblasting.     

Intermediate temperature tribological behavior of carbon nanotube reinforced plasma sprayed aluminum oxide coating

Tribological behavior of plasma sprayed carbon nanotube (CNT) reinforced aluminum oxide (Al₂O₃) composite coatings was examined at room temperature, 573 K and 873 K using tungsten carbide (WC) ball-on-disk tribometer. The weight loss due to wear of Al₂O₃ coating was found to be increasing with the temperature while Al₂O₃-CNT coating showed a decreasing trend in the weight loss with the temperature. Relative improvement in the wear resistance of Al₂O₃-CNT coating compared to Al₂O₃ coating was found to be 12% at room temperature which gradually increased to ∼ 56% at 573 K and ∼ 82% at 873 K. Protective layer as a result of tribo-chemical reaction was observed on the wear track of both of the coatings. The improvement in the wear resistance of Al₂O₃-CNT coating was attributed to three phenomena viz. (i) higher hardness at the elevated temperature as compared to Al₂O₃ coating, (ii) larger area coverage by protective film on the wear surface at the elevated temperature and (iii) CNT bridging between splats. The coefficient of friction (COF) of Al₂O₃ coating was nearly constant at room and elevated temperature whereas COF for Al₂O₃-CNT coating decreased at the elevated temperature (873 K).     

Effects of heating temperature and duration on the microstructure and properties of the self-healing coatings

The present work investigates how the heating temperature and duration affect the properties of the self-healing coating on martensitic steels. The coating composed of TiC + mixture (TiC/Al₂O₃) + Al₂O₃ is fabricated by means of air plasma spraying. The thermal shock test is performed at 600 °C, 700 °C and 800 °C, respectively, to evaluate the thermal-mechanical stability of the coating. The cross-section morphology of the samples after 1 h, 9 h, 18 h and 30 h of heat treatment shows that the porosity of the coating decreases with the increase of heating duration. The evaluation of electrochemical performance by electrochemical impedance spectroscopy shows that the corrosion resistance of the coating after being heated for 18 h is much better than the other samples due to the process of the inner layer being compacted in the coating. The adhesive tensile strength test between coating and substrate shows that the adhesive strength of the coatings is higher than 9 MPa within 40 h of heat treatment at 600 °C. The residual stress reaches a minimum value after the coating was heated for 9 h at 600 °C, then increases with the heating duration after 9 h. Energy dispersive X-ray analysis at the Vickers indentation indicates that the oxygen content at the crack position increases significantly after being heated for 30 h at 600 °C. These experimental results suggest that this coating can meet the requirement of application under the actual temperature conditions.     

Comparative studies on corrosion and tribological performance of multilayer hard coatings grown on WC-Co hardmetals

Multilayer TiN/TiCN/TiCN/TiC/TiN and TiN/TiCN/TiCN/TiC/Al₂O₃ hard coatings with total thicknesses of 15.7 μm and 9.3 μm were deposited on WC-10Co substrates using a chemical vapor deposition system. Evaluation of surface, cross-section morphologies, chemical composition and phases of coatings were analyzed by field emission scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) analyses respectively. Corrosion properties were evaluated in 3.5 wt% NaCl medium using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Tribological properties of fabricated multilayer hard coatings were evaluated using pin-on-disk tests. Results show that active dissolution of the WC-10Co occurred while the coated samples showed more anodic slopes as well as lower corrosion current densities. The corrosion current densities of 3.3 × 10⁻⁷ A/cm² and 7.5 × 10⁻⁸ A/cm² were obtained for the TiN/TiCN/TiCN/TiC/TiN and TiN/TiCN/TiCN/TiC/Al₂O₃ coated specimens which are much lower than 4 × 10⁻⁶ A/cm² of substrate. EIS analysis confirmed the results of potentiodynamic polarization curves. Delamination of the TiN coating and formation of titanium oxide compounds on the surface of the TiN/TiCN/TiCN/TiC/TiN coating revealed that oxidative wear mechanism is dominant for this sample, while adhesive wear mechanism was dominant for the TiN/TiCN/TiCN/TiC/Al₂O₃ coated sample.     

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.