Erosion wear of CrN,TiN, CrAlN,and TiAlN PVD nitride coatings

Four nitride coatings (CrN, ZrN, CrAlN, and TiAlN) were deposited on YT15 cemented carbide by cathode arc-evaporation technique. Microstructural and fundamental properties of these nitride coatings were examined. Erosion wear tests were carried out, the erosion wear of these nitride coatings caused by abrasive particle impact was compared by determining the wear depth and the erosion rates of the coatings. The wear surface features were examined by scanning electron microscopy. Results showed that the coatings with Al (CrAlN and TiAlN) exhibited higher erosion wear resistance over those without Al (CrN and TiN). The H³/E² of the coating seemed to play an important role with respect to its erosion wear in erosion tests. AlTiN and CrAlN coatings being with high H³/E² exhibited lower erosion rates, while CrN coating with low H³/E² showed higher erosion rates under the same test conditions. Analysis of eroded surface of the coatings demonstrated that the TiN and CrN coatings exhibited a typical brittle fracture induced removal process, while AlTiN and CrAlN coatings showed mainly micro cutting and cycle fatigue fracture of material removal mode.     

Cracking behaviour of PVD tungsten coatings deposited on steel substrates

Tungsten coatings have been deposited on steel substrates by magnetron sputtering. For the same processing conditions, the increase of the coating thickness enhances the (111) component of the crystallographic texture whereas the residual stress level decreases. Tensile and four-point bending tests, associated with an acoustic emission analysis, have been performed inside a SEM chamber in order to study the cracking mechanisms. When the residual stresses are taken into account, an intrinsic critical cracking stress and the associated energy release rate can be determined; the obtained values suggest an intergranular cracking mechanism. No debonding has been observed at the interface despite the large plastic deformation of the substrate at the crack tips. The observed strain localisation modes in the substrate near the interface have been shown to have a major influence on the limit crack density.     

Improvement of the tribological behaviour of PVD nanostratified TiN/CrN coatings — An explanation

A hard TiN/CrN multilayered coating, consisting of alternating nanometer scale TiN and CrN layers (bilayer period of 40 nm), was deposited by arc evaporation process on M2 tool steel. Monolayered TiN and CrN are also deposited in the same conditions, and used as references. In order to get a better understanding of the tribological behaviour of coated parts, two types of experiments were performed. The dry-sliding wear resistance was evaluated with a ball-on-disk tribometer, while surface fatigue resistance was determined by a cyclic multi-impact test. The architecture of layers is measured by XRD and observed by TEM. The residual stress field was characterised using XRD and the sin²ψ method at a synchrotron radiation facility.All coatings present a columnar microstructure. TiN demonstrated better wear resistance than CrN and this characteristic is still increased two times by using the nanostratified coating. In the same way, the results of surface oligo-cyclic fatigue test confirm the high performance of the nanostructured coating with respect to the monolayered ones. The differences in mechanical properties of coatings evaluated through nanoindentation measurements do not lead to a direct correlation with the tribological results, and therefore cannot explain such differences. Moreover, a microscopic analysis of the samples after both tribological tests reveals two opposite cracking mechanisms. Monolayered TiN and CrN are subjected to a transversal crack propagation until the peeling of the coating, whereas the multilayered coating only undergoes cohesive cracks deviated in the TiN/CrN interface zones. Both opposite behaviours are the consequence of the distribution of stresses along the thickness of the film.     

An interface study of various PVD TiN coatings on plasma-nitrided austenitic stainless steel AISI 304

The adhesion between a TiN coating and a plasma-nitrided austenitic stainless steel is influenced by using different process steps. In order to obtain some information about the effects of various parameters, different process steps are used during the coating of austenitic stainless steel AISI 304. The deposition of a TiN layer with a Ti intermediate layer results in bad adhesion, especially when a thicker TiN coating has been deposited. X-Ray diffraction measurements indicate the presence of a martensitic phase on top of the plasma-nitrided surface after deposition of the TiN coating. This martensitic phase is also observed if after plasma nitriding only an additional heat treatment is carried out. A transmission electron microscopy study is also performed to reveal the microstructure.     

Wear of PVD Ti/TiN multilayer coatings

The wear characteristics of PVD Ti/TiN multilayer coatings subjected to two-body abrasion and particle erosion have been studied using diamond slurry and silicon carbide particles as abrasive medium and erodant, respectively. The abrasive wear rate of the Ti/TiN multilayer coatings was found to increase with the relative amount of metallic Ti in the coatings. In erosion, the lowest wear rate was recorded for the homogeneous TiN coating. For the Ti/TiN multilayer coatings the erosion rate was found to decrease with an increasing relative amount of metallic Ti in the coatings. It is concluded that the concept of multilayered coatings offers a potent means to tailor the properties of tribological coatings. In particular, demands of different applications can be met by adjusting the relative thickness of metallic Ti in Ti/TiN coatings. The amount of metallic Ti can, for example, be used to control the coating residual stress state. Multilayered Ti/TiN coatings seem promising for combined wear and corrosion protection.     

Hydrothermal corrosion of TiAlN and CrN PVD films on stainless steel

Hydrothermal corrosion of thin TiAlN and CrN PVD films (of 3μm thickness) in 100 MPa water over a temperature range of 20-950 °C is compared to the behavior of TiN films over the same T-P conditions. Corrosion resistance increases in the sequence TiN → TiAlN → CrN. A FeTiO₃ (ilmenite) layer on the surface of the TiAlN film is almost chromium-free and provides protective properties up to 700 °C, whilst ülvospinel formation leads to spallation of oxide scale due to high level growth stresses. Formation of a very stable spinel scale on the surface of the CrN films provides long-term corrosion protection in 100 MPa water up to 800 °C. Nitride films on low-alloyed steel can substitute for expensive super alloy in wet air oxidation systems, with working temperatures up to 700 °C in the case of TiAlN, or 800 °C in the case of CrN coatings.     

Characterisation of corrosion and wear behaviour of nanoscaled e-beam PVD CrN coatings

The present paper analyses the performance of CrN single-layers produced by electron beam PAPVD (EBPAPVD), finding that both corrosion and wear resistance are directly dependant on the structure and stoichiometry of the nitride. The nanolayer structure of the coatings is formed by periodically varying the nitrogen pressure during deposition resulting in layers with higher and lower N-content. This fact, which has not been described in the literature, causes different structure and morphology of the individual films providing excellent properties to the coating. For corrosion resistance, the CrN layer's greater compactness impedes penetration of the electrolyte and thus prevents the formation of a galvanic couple between the coating and the substrate. Moreover, a good wear resistance is obtained, retarding its delamination.     

PVD hard coatings on prenitrided low alloy steel

The combination of traditional surface treatments such as nitriding with modern plasma-enhanced surface technologies reveals the possibility, particularly in the application to low alloy steels, of obtaining mechanical properties comparable with those of high alloy steels. Gas-nitrided samples of the hardened and tempered low alloy steels 30CrMoV9 and 17CrMoV10 were TiN coated by r.f. magnetron sputtering and ion plating. The requirements to obtain a nitrided substrate that can be coated were given special consideration. For this, various surface modifications of the nitrided substrates were realized by bright nitriding, nitriding with a compound layer and additional steps before coating, such as polishing, grinding and sputter cleaning.

The properties of prenitrided coated steels essentially depend on the structure and properties of the outer part of the nitrided case. TiN on bright nitrided and nitrided substrates with the compound layer removed has a better adherence than on compound layers. The decomposition of the iron nitride during the plasma sputter cleaning of compound layers results in a lower surface hardness and lower adherence of TiN. The highest wear resistances in the Timken test were registered on samples where the compound layer had been removed before TiN coating.     

Effects of titanium-implanted pre-treatments on the residual stress of TiN coatings on high-speed steel substrates

This investigation examined how titanium ion implantation pre-treatment affects the residual stress of TiN coatings on M2 high-speed steel. Ions were implanted by metal plasma ion implantation. The adhesion strength of the TiN coatings was enhanced by pre-treatment that implanted Ti into the M2 tool steel substrate. The implanted substrate functioned as a buffer layer between the deposited TiN and the tool steel substrate, resulting in variations of the residual stress. The residual stress determined by glancing-angle XRD demonstrates that the deposited TiN films on ion-implanted substrates exhibited reduced compressive stress, from − 3.95 to − 2.41 GPa, which corresponded to a decrease in the grain size of the TiN films. The texture of the TiN film was clearly transformed from the preferred orientation of (220) to (111), subsequently enhancing wear resistance against a tungsten ball.     

Microstructure and defect characterization at interfaces in TiN/CrN multilayer coatings

Microstructures of TiN/CrN multilayer coatings deposited on austenite steel (Cr Ni 18 8) by pulsed laser deposition (PLD) are characterized using transmission electron microscopy while their mechanical properties were assessed in a ball-on-disk test. All coatings have the same total thickness of about 1 μm. The individual layers show a highly defective columnar structure, which is characterized by conventional electron microscopy (TEM) as well as by high resolution TEM. These techniques, combined with measurements of the local chemical composition through EDS prove that PLD allows to produce fully separated CrN and TiN layers. The friction, and consequently the wear, are lowered by increasing the total number of layers in the coating.     

Tribological behavior of TiN and CrN coatings sliding against an epoxy molding compound

TiN and CrN coatings were deposited by unbalanced magnetron sputtering, and then rubbed against an epoxy molding compound (EMC). In sliding against an EMC, TiN exhibited an extremely high wear rate and a low friction coefficient, while the CrN-coated sample showed the opposite behavior. To understand this difference, Raman spectroscopy and thermal testing were used to study both coatings. Combining the results of oxidation, Raman spectroscopy and tribological testing, it can be concluded that the oxidation and pore generation occurring in the TiN coating during sliding deteriorated the mechanical properties of the coating and therefore its wear resistance. The excellent wear performance of the CrN coating against EMC was related to its good oxidation resistance, and adhesion to the substrate at high temperature.     

Electrolytic removal of chromium rich PVD coatings from hardmetals substrates

The electrochemical behaviour of AlCrSiN coatings deposited on WC–Co substrates has been studied using potentiodynamic and potentiostatic polarization techniques in solutions consisting of 0.5 M H₂SO₄ and different concentrations of oxalic and citric acids. Polarization curves show that coatings are efficiently removed by applying current densities around 70 mA/cm² for 5 to 10 min. Both oxalic and citric acids act as corrosion inhibitors protecting the hardmetal substrate after the coating removal. In both cases the maximum inhibition efficiency is obtained for concentrations around 0.1 M. Corrosion protection can be associated to the adsorption of carboxylic groups onto the hardmetal substrate. The free energies calculated by applying the Langmuir equation to the corrosion currents are in the range of those found for physisorption phenomena. Electrolytes based on citric additions lead to higher adsorption constants (K_ads), which could explain their higher inhibition efficiency.     

不同PVD技术沉积TiN涂层的形貌和力学性能研究

本文采用阴极弧沉积、中频磁控溅射及二者的复合技术在GCr15基底上制备了TiN涂层。通过扫描电镜、XRD谱、微米划痕测试、硬度测试以及摩擦磨损测试对涂层的组织结构和力学性能进行了表征及对比。结构表明,采用复合磁控阴极弧技术制备的TiN涂层具有较好的综合性能,如较光滑的表面、较高的结合力和硬度,故磨损率较低。     

Processing of hardmetal coatings on steel substrates

The possibility to coat steel substrates with a WC–Co hardmetal coating by means of electrophoretic deposition and subsequent microwave heating is reported. A fully densified coating with a final thickness up to 200 μm was achieved. Vickers hardness measurements revealed a difference of 600 H_V between the bulk material and the coating.     

Wear and corrosion behavior of CrCN/CrN coatings deposited by cathodic arc evaporation on nitrided 42CrMo4 steel substrates

In the paper, the results of wear and corrosion tests of the CrCN/CrN multilayer coatings, formed by cathodic arc evaporation on 42CrMo4 (AISI 4140) steel substrates are presented. The substrates were subjected to thermo-chemical treatment–nitriding with various nitriding potential. The results of nitriding were determined by XRD and the hardness profile in the samples cross-section. The morphology of thin coatings was examined with SEM. A Vickers FV-700 and Fisherscope HM2000 hardness testers enabled to investigate hardness of steel substrates and CrCN/CrN coatings respectively. A pin-on-disc wear tests were used to determine the hardness and tribological parameters of the coatings: the coefficient of the friction and wear rate. The scratch test and Rockwell test were applied to assess the adhesion of the coatings to the substrates. The corrosion properties of coating–steel substrate systems were investigated using potentiodynamic polarisation tests. Corrosion potential, corrosion current density and polarization resistance were determined. It was found that that the nitriding of steel substrates improves properties of the coating–substrate system. The nitriding 42CrMo4 steel substrate with low nitriding potential enable to obtain substrates without surface “white layer” what favours good adhesion of the coating to the substrate. The CrCN/CrN multilayer coating–steel substrate systems show good mechanical and tribological properties and corrosion resistance.     

Microhardness and corrosion behavior in CrN/electroless Ni/mild steel complex coating

The electroless nickel–phosphorous (Ni–P) coating was chosen as an interlayer to improve the properties of the CrN/mild steel (MS) composite. A hypophosphite-reduced acid solution was used to first deposit electroless Ni–P onto MS substrates, and then the CrN overlayer was deposited by reactive r.f. magnetron sputtering onto the electroless Ni–P modified substrate. The electroless Ni–P layer crystallizes with the precipitation of a Ni₃P phase during r.f. sputtering, and thus a coating–substrate composite of CrN/Ni–Ni₃P/MS is formed. The electroless Ni–P coating increases the surface hardness of the steel substrate to more than three times. The surface hardness of the CrN coating modified by an electroless Ni–P interlayer exhibits a hardness higher than 2000 HK_0.015. The usual substrate effect on the microhardness of the coatings is nearly eliminated with the complex coating feature, and a significant enhancement of surface hardness in the coating assembly is achieved. The corrosion tests indicate that the Ni–Ni₃P/MS configuration exhibits a more positive E_corr value (i.e. less electronegative) than CrN/MS and the corresponding potential curve is shifted toward the low-current side, indicating a better anti-corrosion performance. Through comparison of the E_corr values and the polarization curves, it is demonstrated that the CrN/Ni–Ni₃P/MS composite exhibits significantly higher corrosion resistance than the Ni–Ni₃P/MS and CrN/MS coating configurations.     

Friction and wear properties of TiN,TiAlN, AlTiN and CrAlN PVD nitride coatings

Four nitride coatings, TiN, TiAlN, AlTiN and CrAlN were deposited on YG6 (WC + 6 wt.% Co) cemented carbide by cathodic arc-evaporation technique. The friction and wear properties were investigated and compared using ball-on-disc method at high speed with SiC ball as a counter material. The tests were evaluated by scanning electron microscopy, X-ray diffractometer, energy dispersive X-ray, micro hardness tester and an optical profilometer. The results showed that TiN and TiAlN coatings presented lower friction coefficient and lower wear rate, and that high Al content AlTiN and CrAlN coatings didn't present better anti-wear properties in this test. Oxidation and abrasive wear were the main wear mechanism of TiN coating. In spite of the observation of micro-grooves and partial fractures, TiAlN possessed perfect tribological properties compared with the other coatings. High Al content increased the chemical reactivity and aroused severe adhesive wear of AlTiN coating. CrAlN coating presented better properties of anti-spalling and anti-adhesion, but abundant accumulated debris accelerated wear of the coating under this enclosed wear environment.     

深振荡磁控溅射复合沉积CrN/TiN超晶格涂层的摩擦学性能

研究了IN718高温合金、WC-6%Co硬质合金和Si(100)基体上深振荡磁控溅射复合沉积CrN/TiN超晶格涂层的摩擦学性能。研究表明,涂层的生长对基体的类型没有选择性。随着基体硬度的升高,划痕结合力失效临界载荷增大,涂层结合力失效机制由翘曲失效转变为基体/涂层协同变形,未发现涂层的剥落失效。载荷为2N时,磨损机制由磨粒磨损和氧化磨损转变为轻微磨粒磨损。载荷为4 N时,IN 718基体上涂层的磨损机制为严重的氧化磨损,WC-6%Co基体上的涂层的磨损机制为磨粒磨损和氧化磨损,氧化物的产生、堆积和转移导致摩擦系数的波动。     

Microstructure and physical properties of PVD TiN/（Ti, Al）N multilayer coatings

Magnetron sputtered （Ti, Al） N monolayer and TiN/（Ti, Al） N multilayer coatings grown on cemented carbide substrates were studied by using energy dispersive X-ray spectroscopy （EDX）, scanning electron microscopy （SEM）, nanoindentation, Rockwell A indentation test, strength measurements and cutting tests. The results show that the （Ti, Al）N monolayer and TiN/（Ti, Al）N multilayer coatings perform good affinity to substrate, and the TiN/（Ti, Al）N multilayer coating exhibits higher hardness, higher toughness and better cutting performance compared with the （Ti, Al）N monolayer coating. Moreover, the strength measurement indicates that the physical vapour deposition （PVD） coating has no effect on the substrate strength.