AlTiN Coatings Research Articles

Effects of Ni content on microstructure, mechanical properties and Inconel 718 cutting performance of AlTiN-Ni nanocomposite coatings

AlTiN-Ni coatings with various Ni contents (0–3 at%) were deposited using cathodic arc evaporation. X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, a nanohardness tester, scratch-adhesion tester, and cutting tester were used to examine the microstructure, mechanical properties, and cutting performance of the coatings. The AlTiN coatings exhibited a columnar structure, while the AlTiN-Ni coatings exhibited a nanocrystal structure due to the formation of nc-AlTiN/Ni nanocomposite coatings. The nanohardness of the AlTiN-Ni coatings decreased from 26.2 GPa to 20.9 GPa as the Ni content increased from 0 to 3 at%. At an Ni content of 1.5 at%, the coating possessed a high toughness and sufficient adhesion strength; however, these dropped drastically for the AlTiN-Ni coating with 3 at% Ni owing to the presence of amorphous Ni. The results for the Inconel 718 turning indicated that the wear mode is adhesion at the rake face, abrasion and adhesion (built-up edge) at the flank face, and chipping at the cutting edge. Compared to AlTiN-Ni3 and AlTiN-coated tools, the lifetime of the AlTiN-Ni1.5 coated tool increased to 160% at a cutting speed of 40 m/min. This was attributed to less adhesion at the rake face and chipping at the cutting edge, due to the nanocrystal structure and higher toughness of the AlTiN-Ni1.5 coating.

Characterization of advanced coating architectures deposited by an arc-HiPIMS hybrid process

We describe advanced coating architectures achieved by a novel combined vacuum arc evaporation/HiPIMS PVD-system which permits us to exploit the advantages of both processes. This system combines three highly ionized processes - arc evaporation, classical HiPIMS and Arc Enhanced Glow Discharge (AEGD). The process technology is commercially named HI3 (High Ionization Triple). The ion cleaning is based on the AEGD process. The tailoring of coating architectures is driven by the advantages of the individual techniques. Vacuum arc evaporation has limitations concerning the materials which can be evaporated, but is characterized by high process stability and high deposition rates, while sputter-deposition is implemented to provide a more complex composition and to achieve multilayer architectures with enhanced properties. Magnetron sputtering processes can be used to atomize materials which are difficult to evaporate by vacuum arc evaporation e.g. Si, SiC, WC, TiB2 and others. The high ionization of the HiPIMS process results in a dense coating structure even for nitride top coatings (e.g. VZrN). Both deposition methods can be run as individual process steps, and also in a hybrid mode. This hybrid process opens a window to generate multilayer as well as nanomultilayers down to sub-nanometer layers. Functional top layers with outstanding properties can be deposited in addition. Selected advanced coating architectures are highlighted. TiB2, SiBC and VZr targets were used to generate individual hybrid coating architectures in combination with arc deposited AlTiN coatings. Every coating started with an AlTiN base coating, followed by a hybrid coating and a HiPIMS top coating. Also classical arc coatings using AlTi and TiSiX cathodes were deposited and investigated to work out the differences to the hybrid coatings. TEM preparations were done for each coating type and investigation of nano beam diffraction were made for the top coating deposited by pure classical HiPIMS. Structural evolutions are discussed.

Friction and Wear Behavior of AlTiN-Coated Carbide Balls Against SKD11 Hardened Steel at Elevated Temperatures

In this study, AlTiN coatings were deposited on YT14 cemented carbide balls by arc ion plating technique. The friction and wear behavior of the AlTiN-coated balls against SKD11 hardened steel was investigated by sliding tests using a ball-on-disk tribometer at various temperatures from 25 to 700 °C in air. The results showed that the friction and wear behavior was significantly influenced by the testing temperature. Obvious fluctuations were observed in the friction curves at elevated temperatures, which could be attributed to the formation and rupture of unstable Fe and Cr oxide layers. As the temperature increased from 25 to 500 °C, the wear rate of the coated balls increased from the scale of 10−21–10−20 m3/N m, and then decreased to 10−22 m3/N m as the temperature further increased to 700 °C. It was also found that the friction and wear behavior of the coated balls was directly dependent on the counterpart materials. As the temperature increased, the main wear mechanism of the coated balls changed from mild abrasive wear and adhesive wear to abrasive wear failure at 500 °C, and then transferred to adhesive wear and mild oxidation wear at 700 °C. For SKD11 hardened steel, the primary wear mechanism changed from delamination wear to abrasive wear and then transferred to plastic deformation and fatigue wear, accompanied by adhesive wear and tribo-oxidation wear.

Tribological and Wear Performance of Nanocomposite PVD Hard Coatings Deposited on Aluminum Die Casting Tool.

In the aluminum die casting process, erosion, corrosion, soldering, and die sticking have a significant influence on tool life and product quality. A number of coatings such as TiN, CrN, and (Cr,Al)N deposited by physical vapor deposition (PVD) have been employed to act as protective coatings due to their high hardness and chemical stability. In this study, the wear performance of two nanocomposite AlTiN and AlCrN coatings with different structures were evaluated. These coatings were deposited on aluminum die casting mold tool substrates (AISI H13 hot work steel) by PVD using pulsed cathodic arc evaporation, equipped with three lateral arc-rotating cathodes (LARC) and one central rotating cathode (CERC). The research was performed in two stages: in the first stage, the outlined coatings were characterized regarding their chemical composition, morphology, and structure using glow discharge optical emission spectroscopy (GDOES), scanning electron microscopy (SEM), and X-ray diffraction (XRD), respectively. Surface morphology and mechanical properties were evaluated by atomic force microscopy (AFM) and nanoindentation. The coating adhesion was studied using Mersedes test and scratch testing. During the second stage, industrial tests were carried out for coated die casting molds. In parallel, tribological tests were also performed in order to determine if a correlation between laboratory and industrial tests can be drawn. All of the results were compared with a benchmark monolayer AlCrN coating. The data obtained show that the best performance was achieved for the AlCrN/Si3N4 nanocomposite coating that displays an optimum combination of hardness, adhesion, soldering behavior, oxidation resistance, and stress state. These characteristics are essential for improving the die mold service life. Therefore, this coating emerges as a novelty to be used to protect aluminum die casting molds.

Effect of Hexagonal Phase Content on Wear Behaviour of AlTiN Arc PVD Coatings

In this study, the effect of increasing aluminum content and magnetic steering field strength on the structure and wear behavior of arc PVD AlTiN coatings is discussed. Deposition was done by means of an industrial-scale PVD unit for tool coating. The aluminium content in the AlTi source material was increased from 67 to 73 at.%. We applied two settings of the magnetic field that steers the arc across the cathode surface thereby evaporating the AlTi alloy differently. The resulting coating thickness ranged from 3.5 to about 7 µm. Cemented tungsten carbide was used as substrate material. Coating properties like hardness, adhesion, and crystal phases were analyzed by indentation and X-ray diffraction, respectively. The wear behaviour of the different AlTiN hard coatings were investigated in two ways. In a first idealized test, cyclic impacting was done applying a constant force. The resulting wear pattern was quantified by an Alicona multi-focus microscope. A second wear test was done by metal cutting under realistic conditions. Fly milling of ductile cast iron (EN-GJS-700) was performed with regular interruptions in order to measure the increasing wear mark. As expected, aluminium contents above 67 at.% (in the metal fraction of the coating) lead to a decreased wear resistance as the soft hexagonal phase exceeds values of a few vol.%. However, it was found that the formation of the hexagonal phase can be effectively influenced and delayed by increasing the magnetic steering field at the cathode. The wear behavior observed in cyclic impact testing corresponds well to results obtained with the more complex loading situation encountered in milling.

Study on High-Frequency Fatigue Properties of PVD AlTiN Coating of Cutting Tool

Based on ultrasonic vibration-assisted mode, high-frequency impacting tests with diamond indenter at different amplitudes on AlTiN coating of cutting tool are carried out. The microstructure and morphology are obtained by scanning electron microscopy (SEM) and 3D profiler. The failure mechanism of coating under impact is analyzed. The high frequency fatigue property of the coating is analyzed. The results show that: lateral crack could be seen under impact test; the maximum tensile stress occurs close the edge of the contact zone of impact center; AlTiN coating is easy to emerge the fatigue damage under the high-frequency impact loading, and the adhesion strength of the coating and substrate interface affects the impact fatigue strength of cutting tool coating.

Performance analysis and comparative assessment of nano-composite TiAlSiN/TiSiN/TiAlN coating in hard turning of AISI 52100 steel

The present study investigates the machining performance of coatings deposited by cathode arc evaporation (CAE) and DC reactive magnetron sputtering (DCRMS) process with different structures and deposition layers on Al2O3/TiCN ceramic inserts in turning of hardened steel under dry cutting environment. Mono-layered AlCrN and multi-layered AlTiN were deposited using CAE process whereas nano-structured TiAlSiN/TiSiN/TiAlN coating was deposited using DCRMS process. The coated tools resulted in improved machining performance when compared to uncoated cutting tool. The CAE process resulted in surface defects like droplets and pores whereas the sputtering process generated droplet free surface that helped in superior performance of TiAlSiN/TiSiN/TiAlN coating when compared with AlTiN and AlCrN coatings. Moreover, nanostructure in TiAlSiN/TiSiN/TiAlN coating prevented coating flaking or peeling and ensured superior anti-abrasive behaviour due to its amorphous structure.

Characterization and machining performance of laser-textured chevron shaped tools coated with AlTiN and AlCrN coatings

Owing to increased demands of more efficient cutting tools for machining difficult to cut materials and environment friendly cutting operations, laser textured tools have become necessary. The characterization and machining studies with such laser textured tools coated with hard ceramic coatings are the prime motivation for this present work. The main aspect of the study is to evaluate two different PVD coated (AlTiN and AlCrN) laser textured tools. In the first stage, laser textured tools were prepared with novel chevron shaped textures on tool rake face using nanosecond pulse laser. This stage is followed by PVD coatings of AlTiN and AlCrN coatings by cathodic arc evaporation (CAE) technique. Coating characterization studies were conducted considering coating morphology, surface roughness, coating elemental analysis and phase analysis of coated and coated textured tools. The performance of the different tools thus manufactured was evaluated by carrying out suitable turning experiments on cylindrical Ti6Al4V work material under dry cutting environment. Machining results were evaluated in terms of cutting force, flank wear progress, rake surface analysis, and chip underside study. Further, static diffusion couple test (SDCT) has been conducted to understand diffusion wear mechanism in plain and textured tools. A new concept of derivative cutting or interfacial multipoint micro-cutting (IMP-μC) on chip underside surface due to texture patterns and a reduction of derivative cutting due to coatings on the textured tools have been proposed.

Influence of the Al content on mechanical properties of CVD aluminum titanium nitride coatings

Fcc-AlTiN coatings deposited by PVD are widely used in the market. Fcc-AlTiN is a metastable phase with excellent properties such as high hardness, high oxidation resistance and high cutting performance. The deposition of single phase fcc-AlxTi(1−x)N with higher than x=0.7 by PVD have not been reported, because AlTiN coatings with higher x-values contained softer hexagonal wurtzite phase. Al-rich fcc-AlxTi(1−x)N(x>0.7) coatings deposited by thermal CVD process have been developed in the last decade. It was reported that these fcc-AlxTi(1−x)N(x>0.7) coatings were much superior to PVD-AlTiN coatings in cutting tests. In this work, influence of x value (x=0, 0.31, 0.62, 0.73, 1.0) on mechanical properties of AlxTi(1−x)N coatings by thermal CVD process was investigated. The deposited CVD-AlxTi(1−x)N coatings were characterized by X-ray diffraction, scanning electron microscopy, nano-indentation and adhesion measurements. Except for CVD-AlxTi(1−x)N with x=1.0, CVD-AlxTi(1−x)N coatings (x=0, 0.31, 0.62, 0.73) with single phase fcc-AlTiN were obtained and every deposited coating was composed of fine-grained granular structure. CVD-AlxTi(1−x)N with x=0.73 showed the highest hardness and adhesion property.

Wear resistance and solid lubricity of molybdenum-containing nitride coatings deposited by cathodic arc evaporation

Molybdenum-containing MoTiN, MoAlTiN, MoCrN and MoZrN coatings were deposited on the 17-4 PH stainless steel substrate by the cathodic arc evaporation technique. Pin-on-disc dry sliding tests were performed to investigate their wear resistance and the solid lubricity of the coatings. All of these coatings, with MoTiN and MoAlTiN in particular, demonstrated superior wear resistance and a significantly lower coefficient of friction against WC-6Co ball material when compared to their corresponding Mo-free TiN, AlTiN, CrN and ZrN monolithic coatings. For example, the specific wear rate of the MoAlTiN coating is only 0.14% of the wear rate of the AlTiN coating, and its coefficient of friction is only 0.28 compared to 0.60 of AlTiN. The excellent tribological performance of the Mo-containing coatings is attributed to the formation of a MoO3 surface layer on the wear tracks through the tribo-oxidation process. Further wear tests of the MoTiN and MoAlTiN coatings against Al2O3 ball material revealed less improvement in wear resistance and reduction of the coefficient of friction. When tested against Si3N4 ball material, both coatings, though still showing noticeably better wear resistance than their corresponding Mo-free coatings, did not demonstrate any beneficial effect of Mo on lowing the coefficient of friction. The scanning electron microscopy and energy dispersive X-ray spectroscopy analyses of the wear track surfaces illustrated the importance of retaining a stable and sufficiently thick MoO3 surface layer in order to maintain the beneficial effect of Mo on the tribological performance of the coatings.

Effects of tailored nitriding layers on comprehensive properties of duplex plasma-treated AlTiN coatings

Duplex-treated AlTiN coatings were deposited by advanced plasma assisted arc (APA-Arc) technology on pre-plasma nitrided AISI-H13 steel substrates using different N2/H2 flow ratios. The microstructures and properties of the AlTiN coatings were comprehensively characterized and analyzed. The results show that the N2/H2 flow ratios can tailor the thickness of compound layer during plasma nitriding process and the bright nitriding layer without compound layer is achieved. The properties of duplex-treated AlTiN coatings are well improved compared with monolayer AlTiN coating. The adhesion of the AlTiN coating is well enhanced by duplex treatment process, and adhesion grade increases from HF3-4 for monolayer AlTiN coating to HF1 for composite coatings. Moreover, the composite coatings with various thickness compound layers show different load-bearing capacities, and the interfacial adhesion force of the composite coating without compound layer reaches 61 N. The hardness of AlTiN coating is also enhanced by duplex treatment with the highest hardness of 2935 HV0.05. Meanwhile, tribological properties of AlTiN coatings are also slightly improved by duplex treatments.

Frictional and wear performance of hard coatings during machining of superduplex stainless steel

In this work, machining of the superduplex stainless steel was investigated using cemented carbide turning inserts with chemical vapor deposited (CVD) TiCN + Al2O3 as well as physical vapor deposited (PVD) TiCN and AlTiN coatings. These three coating system were tested during finish turning operation of superduplex stainless steel. It has been found that unfavorable friction and wear conditions were observed when TiCN- and TiCN + Al2O3-coated tools were used. On the other hand, the AlTiN-coated tool showed a self-adaptive behavior through the formation of tribo-film of aluminum oxide that improves frictional conditions and, consequently, wear resistance during machining of SDSS. This behavior shows that the tool life for inserts coated with PVD AlTiN was approximately two times higher than CVD TiCN + Al2O3. Another important result that can be observed in this work is related with the surface integrity that was improved when machined with cutting inserts coated with PVD AlTiN.

Fine platelet-like grained WC–Co cemented carbides: Preparation, characterization, properties and application in PVD coating substrates

Strengthening of the adhesion strength and its stability of PVD coated cemented carbides has always been the focus of attention. Commercial ultrafine WC–12Co composite powder by spray conversion processing was used as the raw material. WC–12Co–0.05La2O3, WC–12Co–0.9Cr3C2–0.05La2O3, WC–12Co–0.5Cr3C2–0.4VC–0.05La2O3 and WC–12Co–0.9Cr3C2–0.4VC–0.05La2O3 alloys were prepared by a conventional long-time ball-milling. The results show that fine platelet-like grained WC–12Co–0.9Cr3C2–0.4VC–0.05La2O3 alloy is characterized with a homogenous microstructure, the best property combination of high strength, high hardness and high toughness and the highest WC (0001) texture coefficient. By using fine platelet-like grained WC–Co cemented carbides as the substrates, larger than 100N adhesion strength expressed by critical load LC2 for AlCrN, AlTiN and (AlCrSiWN+AlCrN) PVD coatings is achieved. The related strengthening mechanisms are discussed.

Effect of HPPMS Pulse-Frequency on Plasma Discharge and Deposited AlTiN Coating Properties

Coatings like TiAlN (titanium content more than 50%) or AlTiN (aluminium content more than 50%) are well established as hard and wear-resistant tool coatings, often prepared by physical vapour deposition (PVD) like arc evaporation or direct current magnetron sputtering (dcMS). With increasing challenges of operating conditions, there is a constant need for improvement of mechanical properties to withstand extreme loading conditions. This can be obtained by a higher amount of ionized sputtered metal atoms during the deposition process. To increase the metal ion flux a high-power pulse magnetron sputtering (HPPMS) was developed. In order to understand the relation between HPPMS process parameters and mechanical properties of the AlTiN coatings, the present study discusses how different pulse-frequencies (for a constant pulse length) influence AlTiN coating structure growth and their mechanical properties. In addition, film deposition rate and phase formation are influenced by altering process parameters like pulse length and frequency. Hence, different pulse-frequencies produce specific coatings with corresponding properties for functional requirements. Based on the established findings, answers to new scientific queries along with the demand to further optimize these coatings for tool applications are required.

Microstructure, mechanical properties and cutting performance of AlTiN coatings prepared via arc ion plating using the arc splitting technique

In this work, an arc ion plating (AIP) setup equipped with an arc splitting system was used to prepare AlTiN coatings (s-AlTiN). For comparison, AlTiN coatings were also deposited via conventional AIP (c-AlTiN). The chemical composition, microstructure, hardness and wear properties of the two different coatings were studied by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, glow discharge optical emission spectrometry, nanoindentation tests and pin-on-disk tests. The cutting performance of end mill tools coated with the two different AlTiN coatings was investigated by dry milling hardened steel and the wear mechanisms are discussed. The results showed that the s-AlTiN coating exhibited a much smoother coating surface and a denser microstructure instead of the typical columnar structure of the c-AlTiN coating. Furthermore, the s-AlTiN coating exhibited a higher hardness, a lower friction coefficient and a better wear resistance compared with the c-AlTiN coating fabricated through conventional AIP. The application of the s-AlTiN coating was found to significantly improve the tool life.

Microstructure and Corrosion Resistance of the AlTiN Coating Deposited by Arc Ion Plating

A new type of AlTiN coating containing about 29.13 at.% Al,16.02 at.% Ti and 54.85 at.% N was prepared by arc ion plating technology. The coating is composed of singular fcc-(Al, Ti)N phase and has no hcp-AlN phase to be formed. Due to the high content of beneficial element Al, the hardness and effective elastic modulus of the coating are up to 33.9 and 486.1 GPa, respectively. The adhesion strength between the coating and substrate is about 39.7 N. Electrochemical test shows that the corrosion current density of the AlTiN coating is nearly one-sixth of the substrate, and the charge transfer resistance R ct of the AlTiN coating is much larger than that of the substrate, which means that the coating could act as a protective barrier between the substrate and corrosive electrolyte, enhancing the corrosion resistance.

Micro-blasting effect on fracture resistance of PVD-AlTiN coated cemented carbide cutting tools

The dry micro-blasting effects on the fracture resistance of PVD-AlTiN coated cemented carbide cutting tools were studied. The AlTiN coatings with the composition of (Al0.60Ti0.40)N were deposited using cathodic arc evaporation method. The two types of coatings, which had a compressive residual stress of 0.1GPa (Low-σ) and 2.6GPa (High-σ), were prepared. The coated samples were subjected to the dry micro-blasting treatment by Al2O3 grains at pressures of 0.11MPa, 0.14MPa, and 0.17MPa. A milling test using AISI 4140 (42CrMo4) steel as the workpiece material was carried out for evaluating the fracture resistance of the prepared samples. The tool life cutting distance of Low-σ sample micro-blasted at 0.14MPa and 0.17MPa was 2.9m and 7.2m, respectively, largely extended as compared to that of as-deposited Low-σ sample, 1.0m. On the other hand, the tool life of High-σ sample micro-blasted at 0.14MPa was 8.6m, almost same with that of as-deposited High-σ one, 8.8m. Those results indicate that the dry micro-blasting effect on the fracture resistance is larger for the Low-σ coating than for the High-σ one.

Load sensitivity in repetitive nano-impact testing of TiN and AlTiN coatings

A key step in optimisation of coating behaviour is to understand the relationship between a range of parameters that can easily be obtained in the repetitive nano-impact test and ultimate coating performance in demanding applications. In this study we have performed a statistical analysis of multiple repetitive impact tests on advanced nitride coating systems and have identified the key parameters that can be used to assess durability and wear resistance. At lower load the coating mechanical properties and microstructure are beneficial in providing improved impact resistance. At higher load the initial impact resistance is also enhanced in non-columnar coatings with higher resistance to plastic deformation but their limited ductility can affect their damage tolerance under continued impact.

Stabilization of cubic phase in AlTiN coatings using anode configurations

In this study, the effects of residual stress and hardness in view of producing thick PVD AlTiN coatings are investigated. The compressive residual stress in the coatings results in coating delamination at the cutting edges. Coatings produced at lower stress overcome the delamination issue, however lack the required hardness for metal cutting applications. We found that reduction in hardness is closely related to stability of cubic AlTiN phase. We present an anode configuration ‘annular extension’ to stabilize cubic phase and produce thick PVD coatings. The usefulness and limitations of thick PVD coatings are also discussed.

Effects of Loadings on Friction and Wear Behaviors of Cathodic Arc Ion Plating AlTiN Coating at High Temperature

ABSTRACTA layer of AlTiN coating was deposited on YT14 cutting tool by cathodic arc ion plating (CAIP) and the coefficients of friction (COFs) of the AlTiN coating under different loads at a temperature of 800°C were investigated with a high-temperature wear tester. The wear morphologies, chemical elements, and phases of the coating after wear were analyzed with scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD), respectively, and the contours of wear tracks were investigated with a comprehensive measurement tester for material surface performance. The effects of loads on COFs and wear resistance of the AlTiN coating were analyzed, and the wear mechanism of the AlTiN coating at high temperature is discussed. The results show that the mixed oxides of Al2O3 and TiO2 are produced under high temperature to improve the lubrication performance and wear resistance of the AlTiN coating. The average COFs of the coating under loads of 5, 7, and 9 N are 0.6495, 0.5897, and 0.3898, respectively. The COFs of the coating decrease with increasing load; as a result, the AlTiN coating is suitable for heavy loads at high temperature. The friction and wear mechanisms of the AlTiN coating are primarily composed of oxidation wear and abrasive wear, accompanied by fatigue wear and adhesive wear.