Multilayer PVD Coatings Research Articles

TiN/ZrN Multilayer PVD Coatings on Titanium Alloys Produced by Powder Metallurgy

Multilayer coatings are synthetic structures constituted by alternate layers of different materials. The technological applications of the multilayer coatings can involve optical, electromagnetism and wear areas. The target of this work is the production of multilayer TiN/ZrN coatings by Electron Beam Physical Vapor Deposition (EB-PVD) over titanium alloys produced by powder metallurgy. P/M-Ti-35Nb-7Zr-5Ta cylindrical samples used as substrates were produced by mixing of the elemental powders with subsequent cold pressing steps and sintering at 1400°C, in high vacuum. TiN/ZrN coatings were obtained by evaporation of alternating Ti and Zr cylindrical targets. The multilayers were characterized by optical and scanning electron microscopy (SEM), chemical analysis via energy dispersive spectrometry (EDS) and Vickers indentation. Besides the possibility of obtaining several layers, the results show coatings with coherent columnar structure, low discontinuity, large and homogenous thickness and high adhesion to substrate.

Rolling‐sliding, scuffing and tribocorrosion behaviour of PVD multilayer coatings for gears application

PurposeThe aim of this work is the study the tribological behaviour and tribocorrosion resistance of newly developed multilayer PVD coatings Cr/CrN and CrN/ZrCN applied on nitrided F1272 steel for gear applications.Design/methodology/approachTribological characterization has been completed by several tribological tests performed under ball‐on‐disc configuration, extreme pressure tests to determine the maximum load before the films failure and rolling‐sliding tests under line‐contact conditions (35‐40 per cent of sliding). The response of the different coatings to sodium chloride aggressive environment has been simulated by accelerated tribocorrosion tests, combining simultaneously chemical and mechanical factors. The synergistic effect of wear on corrosion behaviour and vice versa, has been studied in order to compare the protective properties of the different PVD coatings developed.FindingsCr/CrN PVD coating improves wear in almost a 90 per cent compared to the nitrided substrate, presenting a similar behaviour to this one under extreme pressure conditions. CrN/ZrCN coating also improved substrate wear and especially good behaviour for this coating was observed under extreme pressure conditions. Cr/CrN coating strongly decreases micropitting and scuffing effect when it is tested under rolling‐sliding configuration. Under micro‐pitting conditions, coating protects the substrate and reduces the fatigue of uncoated discs. When adhesive wear (scuffing) is studied also Cr/CrN improves notable the nitrided steel performance. Under simultaneously corrosion‐wear conditions, Cr/CrN coating registered the lowest material loss because in this case only corrosion effect contributed to the coated surface degradation being the mechanical contribution inappreciable.Originality/valueNew multilayer coatings with improved wear performance and tribocorrosion resistance have been developed and comprehensively characterized. These coatings can be used in advanced gears for corrosive environmental conditions as well as with biodegradable lubricants.

Characterisation of tribocorrosion behaviour of multilayer PVD coatings

The effect of repassivation on tribocorrosion behaviour of two multilayer coatings of different structures is studied experimentally by measuring the variation of instantaneous open-circuit potential during friction. One coating consists of alternating Cr and CrN layers, while another consists of alternated layers of CrN and ZrN. Analysis of the results showed that friction force, i.e. the rate of the mechanical energy supplied to the material in the contact zone, has no direct influence on the tribocorrosion behaviour; however, the wear rate does strongly influence the tribocorrosion. A simple phenomenological model of repassivation of the multilayer coating is developed assuming "surface coverage" approach. This model establishes the relationship between the rate of mechanical activation of material by friction and the behaviour of the open-circuit potential.

Novel CrAlYN/CrN nanoscale multilayer PVD coatings produced by the combined High Power Impulse Magnetron Sputtering/Unbalanced Magnetron Sputtering technique for environmental protection of γ-TiAl alloys

CrAlYN/CrN coatings utilising nanoscale multilayer structure with a typical bi-layer thickness of 4.2 nm have been deposited on light-weight Ti–45Al–8Nb alloys known as γ-TiAl. The surface pre-treatment was carried out by bombardment with Cr1+ ions generated by High Power Impulse Magnetron Sputtering, (HIPIMS) discharge, whereas the nanoscale multilayer CrAlYN/CrN coating was deposited by Unbalanced Magnetron Sputtering (UBM). Scanning Transmission Electron Microscopy (STEM), revealed that the coating/substrate interface was extremely clean and sharp. Large areas of coating growing epitaxially were observed. STEM–Energy Dispersive Spectroscopy (EDS) profile analyses further showed that, during the HIPIMS ion bombardment, Cr was implanted into the substrate to a depth of 5 nm. Adhesion critical load values as high as LC = 37 N have been measured in scratch adhesion tests. Impact tests brought further evidence for strong bonding. For coated γ-TiAl alloys, thermogravimetric quasi-isothermal oxidation tests in air at 750 °C after 1000 h exposure showed four times smaller weight gain compared to the uncoated material. In sulphidation tests after 1000 h exposure to aggressive H2/H2S/H2O atmosphere the CrAlYN/CrN protected γ-TiAl alloys showed a weight gain reduced by factor of four as compared to the uncoated substrate. High temperature pin-on-disc tests revealed that the friction coefficient reduces from 0.56 at room temperature to 0.4 at 630 °C.

CrN/NbN coatings deposited by HIPIMS: A preliminary study of erosion–corrosion performance

Nanoscale CrN/NbN multilayer PVD coatings have exhibited resistance to erosion–corrosion. However growth defects (under dense structures and droplets) in the coating produced by some deposition technologies reduce the ability to offer combined erosion–corrosion resistance. In this work a novel High Power Impulse Magnetron Sputtering (HIPIMS) technique has been utilised to pretreat substrates and deposit dense nanoscale CrN/NbN PVD coatings (HIPIMS–HIPIMS technique). This new technique, rich with metal ion plasma, deposits very dense structures and offers virtually defect free coatings (free of droplets as observed in cathodic arc technique and under-dense structures observed in standard dc sputtering). Plasma diagnostic studies revealed a high metal ion-to-gas ion ratio (Cr:Ar) of 3:1 for HIPIMS pretreatment conditions with the detection of 14% Cr 2+ and 1% Cr 3+ ions and J s of 155 mAcm − 2 . For deposition conditions the metal ion-to-gas ratio was approximately 1:4 which is significantly higher compared to DC at 1:30. Characterisation results revealed a high adhesion of L C 80 N, high hardness of 34 GPa and Young's modulus of 381 GPa. Low friction coefficient (0.46) and dry sliding wear coefficient, K C (1.22 × 10 − 15 m 3Nm − 1 ) were recorded. The effect of deposition technique (droplet defect and intergranular void free coatings) on erosion–corrosion resistance of CrN/NbN coatings has been evaluated by subjecting the coatings to a slurry impingement (Na 2CO 3 + NaHCO 3 buffer solution with Al 2O 3 particles of size 500–700 µm) at 90° impact angle with a velocity of 4 ms − 1 . Experiments have been carried at − 1000 mV, + 300 mV and + 700 mV representing 3 different corrosion conditions.

Simulation of a multilayer structure in coatings prepared by magnetron sputtering

Multilayer PVD coatings are obtained when substrates rotate along the targets of different materials. In order to deposit a uniform coating on the substrate with a complicated geometry (e.g., tools), the substrates need to rotate around two, three or even four axes in a manner similar to planetary rotation. The trajectories of the substrates are therefore rather complex and the multilayer structure depends on the number of rotational axes, the initial position of substrates and the geometrical parameters of the deposition system. The properties of multilayer coatings are influenced by the thickness and the sequence of layers. A convenient approach to predicting the multilayer structure is to use a computer simulation. Using the simulation we can calculate the deposition rate, the sequence and the thickness of the individual layers for any particular rotation of the sample. In present paper we verify the accuracy of a simulation which we developed in our previous work. The simulated multilayer structures were compared to deposited TiAlN/CrN multilayer coatings. Samples with a different number of rotational axes and different initial positions were prepared for transmission electron microscopy and compared to the simulation. The simulated multilayer structures agree well with the deposited structures.

CrAlYCN/CrCN nanoscale multilayer PVD coatings deposited by the combined High Power Impulse Magnetron Sputtering/Unbalanced Magnetron Sputtering (HIPIMS/UBM) technology

CrAlYCN/CrCN coating combining high hardness (H p = 36 GPa) and low friction coefficient ( µ = 0.42 against Al 2O 3) has been developed for machining of Si containing Al-alloys. The coating was deposited by the combined High Power Impulse Magnetron Sputtering/Unbalanced Magnetron sputtering, (HIPIMS/UBM) technology. Macroparticle free Cr + ion flux was generated by HIPIMS discharge to sputter clean the substrates prior to the coating deposition. The use of HIPIMS for surface pre treatment resulted in excellent adhesion, scratch test adhesion critical load value of Lc = 55 N on HSS and Lc = 68 N due to the local epitaxial growth and extremely smooth coating surface, Ra = 0.012 μm due to the elimination of growth defects. The coating crystallised in fcc structure with a preferred {220} orientation. XTEM analysis revealed a nanoscale multilayer structure of the coating with carbon segregated at the column boundaries but also vertically to form a lateral phase at the interfaces between the individual nanolayers. Addition of C to CrAlYN/CrN increased the chemical inertness between cutting tool and workpiece material without deteriorating the oxidation resistance of the coating. Thermo gravimetric analysis showed that the temperature for the onset of rapid oxidation was as high as 940 °C. In dry milling of AlSi9Cu1 alloy, CrAlYCN/CrCN coated 8 mm diameter cemented carbide end mills outperformed non coated end mills by factor of 2.5 with effective hindered built up edge formation mechanism.

Novel TiAlCN/VCN nanoscale multilayer PVD coatings deposited by the combined high-power impulse magnetron sputtering/unbalanced magnetron sputtering (HIPIMS/UBM) technology

A new TiAlCN/VCN coating combining high hardness, low friction coefficient and chemical inertness has been developed for dry machining of “Sticky” (Al-, Ti- and Ni-based) alloys as well as advanced Metal-Matrix-Composite (MMC) materials used in aerospace and automotive industries. Excellent performance was achieved due to the synergy between V and C as main coating elements and the nanoscale multilayer structure of the coating. TiAlCN/VCN was deposited by the combined High-Power Impulse Magnetron Sputtering/Unbalanced Magnetron sputtering (HIPIMS/UBM) technology. Macroparticle free V + ion flux generated by HIPIMS discharge was used to sputter clean the substrates prior to the coating deposition. A 0.4 μm thick TiAlN base layer followed by 3 μm thick TiAlCN/VCN nanoscale multilayer coating was deposited by unbalanced magnetron sputtering. The sputtering was carried out in a mixed CH 4, N 2 and Ar atmosphere. In dry milling of Al7010–T7651 alloy, TiAlCN/VCN nanoscale multilayer PVD coating outperformed state of the art Diamond Like Carbon (DLC, Cr/WC/a-CH) coating by factor of 4. In drilling Al-alloy enforced MMC materials, cemented carbide drills coated with TiAlCN/VCN produced 130 holes compared to 1–2 holes with uncoated drills.

Microstructure and mechanical properties of Ti(C,N) and TiN/Ti(C,N) multilayer PVD coatings

Abstract Magnetron sputtered Ti(C, N) and TiN/Ti(C, N) multilayer coatings are deposited onto cemented carbide substrates at 350 °C. The crystal structure and microstructure of the deposited coatings are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), nanoindentation and scratch test. XRD examination indicates that both coatings are of fcc structure. In accordance with SEM observation, both coatings are columnar crystallites structures and the TiN/Ti(C, N) multilayer coating forms the modulation structure with alternating TiN and Ti(C, N) layers. As for TiN/Ti(C, N) multilayer coating, the hardness and adhesion with substrate are improved due to interface effect between TiN and Ti(C, N) layers. Ti(C, N) and TiN/Ti(C, N) multilayer coatings exhibit approximately identical performance and different failure forms in machining carbon steel. But the performance of TiN/Ti(C, N) multilayer coating inserts in machining stainless steel is superior to Ti(C, N) coating inserts due to the better thermal stability of TiN/Ti(C, N) multilayer coating.

Microstructure and mechanical properties of gradient Ti(C, N) and TiN/Ti(C, N) multilayer PVD coatings

Magnetron sputtered homogeneous TiN, gradient Ti(C, N) and TiN/Ti(C, N) multilayer coatings are deposited onto cemented carbide substrates at 350 °C. The microstructure and mechanical properties of the deposited coatings are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), typical secondary ion mass spectroanalyzer (SIMS), nanoindentation, and scratch test. XRD examination indicates that three coatings are of fcc structure. SEM observation indicates that three coatings are characterized by columnar grain structures. The relative concentration of C increases and the concentration of N decreases with increasing gradient Ti(C, N) coating thickness according to SIMS testing. The TiN/Ti(C, N) multilayer coating forms the modulation structure with alternating TiN and Ti(C, N) layers. The gradient Ti(C, N) and TiN/Ti(C, N) multilayer coating exhibit higher nano-hardness compared with homogeneous TiN coating. Gradient Ti(C, N) and TiN/Ti(C, N) multilayer coatings exhibit better adhesion with the substrate compared with homogeneous TiN coating.

VmeCN Based Nanoscale Multilayer PVD Coatings Deposited by the Combined High Power Impulse Magnetron Sputtering/Unbalanced Magnetron Sputtering Technology

TiAlCN/VCN has been deposited by the combined high power impulse magnetron sputtering/unbalanced magnetron sputtering (HIPIMS/UBM) technology using a Hauzer HTC 1000-4 PVD system. V+ ion flux has been generated by HIPIMS discharge to sputter-clean the substrates prior to the coating deposition. The sputtering was carried out in a mixed CH4, N2 and Ar atmosphere. Coatings phase and nanoscale structure were characterised using a variety of surface analysis techniques. In dry milling of Al 7010-T 7651 alloy, a TiAlCN/VCN nanoscale multilayer PVD coating outperformed state-of-the-art diamond-like carbon (DLC, Cr/WC/a-CH) coating by a factor of four. In drilling Al-alloy enforced MMC materials, cemented carbide drills coated with TiAlCN/VCN produced 130 holes compared to one to two holes with uncoated drills.

Structure and properties of the multi-component TiAlSiN coatings obtained in the PVD process in the nitride tool ceramics

Comprehensive structure and properties investigation results of the multilayer, multi-component PVD coatings developed on the Si 3N 4 nitride tool ceramics substrate are presented in the paper. The detailed results are presented of examinations carried out on the transmission and scanning electron microscopes, as well as of the mechanical properties and tribological tests of the investigated coatings. Examinations of the chemical compositions of the deposited coatings were also carried out using the X-ray energy dispersive spectrograph EDS, glow-discharge optical emission spectroscope GDOS, and using the X-ray diffractometer. The inserts made from Si 3N 4 were multilayer coated in the PVD process with the TiN, TiN + multiTiAlSiN + TiN, TiN + TiAlSiN + TiN, and TiN + TiAlSiN + AlSiTiN coatings. Additional investigations were carried out to compare coatings obtained in this way on inserts from various manufacturers offering the nitride tool ceramics with the CVD coatings based on the Al 2O 3 and TiN layers. Basing on the metallographic examinations results it was found out that the multilayer PVD and CVD coatings were uniformly put down onto the substrate and the particular layers adhere closely to each other. It was found out in the microhardness tests of the coatings that the TiN + multiTiAlSiN + TiN one has the highest hardness. It was demonstrated also that all CVD coatings are characterised by very good adhesion to the substrate compared to the PVD coatings. Results of the X-ray qualitative phase analysis confirm occurrences of phases coming from coatings and the substrate. Analyses of the chemical composition – EDS and GDOS confirm presence of both titanium, aluminium, silicon, nitrogen, and oxygen in the investigated coatings and of silicon and nitrogen in the investigated substrate.

A multilayer coating architecture to reduce heat checking of die surfaces

The primary reason for thermal fatigue cracking in die casting is the thermal load and its cycling during the operation. Conventional single and multiplayer coatings have been found to at best equal the thermal fatigue lives of hot working steels used for die casting dies. This paper presents a new approach to fatigue resistance that uses a three-layer coating architecture to reduce the heat transfer and chemical diffusion to the die steel substrate. In this, the outer layer consists of a thermal barrier coating of rare-earth oxide, the middle layer a TiAlN diffusion barrier coating and the inner layer a thin adhesive Ti layer. Thermal cycling tests in liquid aluminum up to 4000 cycles using this architecture and conventional commercial multi-layer PVD coatings confirm that the new coating significantly improves the thermal fatigue resistance of the substrate.

Deposition, characterization and machining performance of multilayer PVD coatings on cemented carbide cutting tools

CrN/TiN and TiN/AlTiN multilayer coatings with different periods were deposited on cemented carbide cutting tools in an industrial-size cathodic arc evaporation device. Nanolayer coatings were particularly studied and the influence of the superlattice period on mechanical behaviors have been investigated. Mechanical properties were first correlated to the period of multilayer and nanolayer coatings. Machining performance of coated cutting tools were then evaluated by turning Inconel 718 superalloy. The decrease of layer periodicity leads to higher microhardness for both compositions. Adhesion tests and surface topography analyses indicate better adhesion and lower roughness for CrN/TiN than for TiN/AlTiN coatings. All these coatings, especially TiN/AlTiN nanolayers, favorably influence flank wear and cutting time for machining Inconel 718 in relatively severe cutting conditions. The relationship between physical properties, coatings compositions and wear mechanisms during machining Inconel 718 is discussed.

A New Tool for Evaluation of Intrinsic Mechanical Properties of Multilayered Coatings

A new tool is proposed for characterising intrinsic mechanical properties and wear mechanisms of multilayered coatings. In the present work multilayered coatings have been investigated with respect to their tendency to interlamella spalling in abrasion, i.e. the tendency for spalling within the coating at the lamella interfaces. This tendency is proposed to be caused by an excessive difference in the residual stress between the lamella materials and is triggered by the additional stresses imposed by abrasive diamond grits. Thick lamellae will have a stronger tendency for spalling than will thinner layers, as a result of a higher shear force in the lamella interfaces. The method is evaluated on a set of five multilayered PVD coatings, including both metallic/ceramic (Cr/CrN and Ti/TiB2) and ceramic/ceramic systems (TiN/CrN, TiN/NbN, and TiN/TaN). Each coating is represented by a number of different lamella thicknesses, ranging from approximately 50 to 900 nm.

Dissolution and soldering behavior of nitrided hot working steel with multilayer LAFAD PVD coatings

Soldering and corrosive dissolution are the primary causes of die non-performance in permanent mold and die casting production of net shape parts for the transportation industry. At worst, these corrosive reactions result in core pin or sprue dissolution, and at the least, some soldered cast metal remains behind when the casting is ejected. The objective of this work was to explore the possibility of surface engineering of the die steel surface to reduce the dissolution and soldering tendencies of the surface. This paper presents a duplex surface treatment approach for dissolution resistance that consists of nitrided hot working die steel substrate coated by multi-layer titanium-based coatings applied by the large area filtered arc deposition technique. The dissolution behavior of the coating candidates is evaluated by measuring weight loss after dipping them in molten aluminum for a predetermined time. Results are compared with those of single layer coatings and surface treatments. The chemisorption and adhesion behavior is evaluated by measuring ejection force of the soldered material. The duplex coating is found to significantly reduce both the dissolution and adhesion tendencies of the coated steel surface.

Nano Indentations Studies of WC/C and TiN/(Ti,Al)N Multilayer PVD Coatings Combined with Cross-sectional Electron Microscopy Observations

AbstractMultilayers of tungsten carbide/carbon (WC/C) with an amorphous structure and multilayers of titanium nitride/titanium-aluminum nitride (TiN/(Ti,Al)N) with a polycrystalline structure, prepared by physical vapor deposition, have been subjected to nanoindentation testing. The investigation has been aimed at establishing whether the load-displacement responses provides accurate information on the fracture mechanisms and whether such mechanisms can be characterized using a new technique for cross-sectional electron microscopy of the nanoindentations. Analysis of the load-displacement curves showed that they can be used to identify the cracking mechanisms occurring in the multilayers and that cross-sectioning of the nanoindentations is necessary if a more complete understanding of the multilayer coatings behavior is required.

Wear and failure mechanisms of multilayered PVD TiN/TaN coated tools when milling austenitic stainless steel

As compared to today's single layered coatings, multilayered PVD coatings offer improved mechanical and tribological properties. This work reports on milling austenitic stainless steel with cemented carbide tools coated with multilayered coatings. The purpose was to increase the understanding of wear and failure mechanisms during milling of austenitic stainless steel. Multilayered PVD TiN/TaN coatings deposited on cemented carbide substrates are presented and compared with single-layered TiN and TaN. It was found that the tool life was mainly limited by chipping of the cutting edge, caused by crack interaction. A mechanism for comb crack nucleation and growth is presented, which accounts for the beneficial effects of multilayered coatings on milling tools. Some additional mechanical and chemical wear mechanisms observed are also presented and discussed. Multilayered coatings made up of TiN and TaN proved to be suitable for milling austenitic stainless steel. TaN has shown to be too brittle to work well as a single-layer coating. However, by layering TaN with TiN, a tougher coating can be obtained. By doing so, a coating material with a small tendency to interact with the austenitic stainless steel is obtained. As a result of the smaller interaction, less comb cracks are formed.

Deposition and characterisation of multilayered PVD TiN/CrN coatings on cemented carbide

In laboratory as well as in application tests, multilayered PVD coatings have shown enhanced mechanical and tribological properties as compared to today's single layered PVD coatings. A coating which has shown very interesting properties, such as high temperature stability and high fracture toughness, is multilayered PVD TiN/CrN. Our knowledge about the connection between the growth dynamics and the properties of this coating is, however, rather poor. Therefore, to further develop and optimise this coating, it is necessary to study the correlations between on the one hand the growth process, and on the other the microstructure, composition and mechanical properties of the coating.In this work growth rate, morphology, microstructure, chemical and phase composition, together with coating hardness, Young's modulus and fracture toughness of different multilayered PVD TiN/CrN coatings have been evaluated. All coatings have been deposited on cemented carbide substrates using a combination of reactive electron beam evaporation (Ti) and reactive d.c. magnetron sputtering (Cr). The influence of lamella thickness and different deposition parameters: substrate bias, magnetron sputtering power and nitrogen flow, on the above mentioned characteristics has been examined. In addition to the multilayered TiN/CrN coatings, homogeneous TiN and CrN have been included and compared.The investigation showed that a dense, fully cubic NaCl phase, multilayered PVD TiN/CrN coating with high fracture toughness can be deposited provided that the lamella thickness is kept less than 14 nm and 5 nm of TiN and CrN respectively. Thin lamellae seem to inhibit transformation from growth of the cubic NaCl phase to new phases, e.g. hexagonal β-Cr2N and metallic Cr. Furthermore, thin lamellae yielded a (200) preferred growth orientation while thicker lamellae generated a mixture of growth orientations. In addition, very thin lamellae must be deposited to obtain good fracture toughness. It was also found that it was necessary to use a negative substrate bias in order to obtain a high quality coating.

The multilayer effect in abrasion — optimising the combination of hard and tough phases

In the present investigation it is shown that the wear resistance of multilayer PVD coatings, combining relatively soft but tough chromium (Cr) and harder but more brittle chromium nitride (CrN), exceeds that of both its phases. This striking exception to the simple rules of mixtures — the multilayer effect in abrasion — is investigated with respect to physical mechanisms, layer thickness dependence and implications for multilayer design for abrasive applications.Multilayers of Cr and CrN were deposited on high speed steel using reactive magnetron sputtering. The coatings were characterised with respect to microhardness and abrasive wear resistance against a slurry of 2.5 μm diamond abrasives. The abraded surfaces were investigated by scanning electron microscopy and optical profilometry to reveal the microscopic wear mechanisms. A physical model for the layer thickness dependence for wear resistance of multilayer coatings was developed. Despite its simplifications, the model agrees very well with the experimental results.The advantage of Cr layers is their tendency to deform plastically rather than becoming removed by wear; the drawback is lack of penetration resistance. The penetration resistance, however, is the main advantage of the CrN layers. It was concluded, both theoretically and experimentally, that the multilayer effect is explained by the reduction of abrasive penetration depth in the Cr layers due to the underlying harder CrN layer.