TiN and CrN PVD coatings on electroless nickel-coated steel substrates

Plasma-assisted (PA) PVD ceramic coating such as TiN have so far achieved only very limited use on cheap low-alloy steels, owing to problems relating to both corrosion resistance and the need for load support from the underlying material. Here we report tests to asses the wear and corrosion performance of TiN and CrN PAPVD coatings on phosphorus-doped electroless nickel (ENiP)-coated steels. It is shown that this route offers a potentially cost-effective means of utilizing PAPVD ceramic films on lower grade steels. In particular, CrN/ENiP on AISI 304 stainless steel is shown to exhibit a promising combination of wet abrasion resistance with good corrosion properties.     

Corrosion behaviour of nanocomposite TiSiN coatings on steel substrates

Nanocomposite TiSiN coatings were deposited on tool steels. Detailed mechanisms that govern the corrosion of these coated steels were revealed, following immersion tests in a 70% nitric acid solution. Pitting originated preferentially from coating defect sites and expanded with increasing immersion time. Both Young’s modulus and hardness measured by nanoindentation decreased as the corrosion damage intensified. A thin oxide layer formed from the thermal annealing of the as-deposited samples at 900 °C was found to be effective against corrosive attack. In addition, compressive residual stress was noted to suppress the propagation of corrosion-induced cracks. The role of residual stress in controlling the corrosion resistance of these ceramic-coated steels is clarified by finite element analysis.     

电镀锌钢材表面物理气相沉积Zn-Mg合金镀层的电化学性能(英文)

锌合金镀层由于具有较强的耐腐蚀性能而得到广泛的关注,特别是Zn-Mg合金镀层,其耐腐蚀性能能得到显著提高。采用气相沉积方法制备不同镁含量的Zn-Mg合金镀层,研究Zn-Mg合金镀层中镁含量对其耐腐蚀性能的影响。在3%NaCl溶液中进行浸泡试验、动电位测试和电偶腐蚀试验,研究不同Mg含量镀层的耐腐蚀性能。结果表明,Zn-Mg合金镀层的耐腐蚀性能与Mg含量显著相关,镀层的腐蚀电位随着Mg含量的增加而降低,但是腐蚀电流密度却升高,直至15%Mg含量;在Zn-Mg合金镀层中存在钝化区。     

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.     

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.     

Characterisation of organic-inorganic hybrid coatings deposited on aluminium substrates

Optically transparent silica-based single amorphous phase organic-inorganic hybrid coating materials with differing organic/inorganic ratios have been prepared by a novel patented sol-gel process and deposited using a simple angled flow coating method on commercially pure aluminium substrates. Transmission electron microscopy and scanning electron microscopy were used to characterise the microstructures of the hybrid materials and the quality of the interfaces between the coatings and the aluminium substrates. The scratch resistance, critical load to failure and failure modes of these hybrid coating materials were studied using a simple scratch test. The coatings produced were all shown to adhere well to the aluminium substrates and exhibit good levels of scratch resistance.     

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.     

Characteristics of tungsten coatings deposited by molten salt electro-deposition and thermal fatigue properties of electrodeposited tungsten coatings

Tungsten coatings were obtained on a tungsten substrate by molten salt electrodeposition (MSE) at 50 mA/cm² for 60 min in a NaCl-KCl-NaF-WO₃ (0.3385:0.3385:0.25:0.0 73mol) melt at 800 °C. The MSE tungsten coatings have rough rectangular pyramid surface and special columnar grains structure. Thermal fatigue tests have shown that the damage factor of MSE tungsten coatings was smaller than that of rolled tungsten under the same thermal loads and MSE tungsten coatings displayed better thermal fatigue properties compared to that of rolled tungsten, which was attributed to high purity, special columnar grains and rectangular pyramid surface morphology.     

Cracking investigation of W and W(C) films deposited by physical vapor deposition on steel substrates

This paper presents the investigation of the cracking of coatings deposited on steel substrates. The coating on substrate systems consisted on pure tungsten films (W) and films of solid solutions of carbon in tungsten [W(C)], which were deposited by direct current reactive magnetron sputtering on stainless steel substrates. The systems were strained uniaxially with a microtensile device adapted to a scanning electron microscope. The mechanical response was analyzed from the experimental results: the straining of the samples showed an evolution of the density of cracks in the coating, which was described trough an empirical equation based on the Weibull distribution function. The density of cracks, which corresponds to the crack saturation of the coating, appeared to vary inversely with coating thickness. Critical parameters relative to their mechanical stability were also determined from the experimental results: the strain energy release rate for crack extension through the film, G^f_c, and the fracture toughness, K^f_Ic, of the coatings. These values are included between 0.2 and 14 J m⁻², and between 0.1 and 2.5 MPa m^−1/2. The fracture resistance of W and W(C) coatings was found to be correlated to their thickness and microstructure.     

Impact toughness of tungsten films deposited on martensite stainless steel

Tungsten films were deposited on stainless steel Charpy specimens by magnetron sputtering followed by electron beam heat treatment. Charpy impact tests and scanning electron microscopy were used to investigate the ductile-brittle transition behavior of the specimens. With decreasing test temperature the fracture mode was transformed from ductile to brittle for both kinds of specimens with and without W films. The data of the crack initiation energy, crack propagation energy, impact absorbing energy, fracture time and deflection as well as the fracture morphologies at test temperature of-70 ℃ show that W films can improve the impact toughness of stainless steel.     

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.     

Boroaluminide coatings on ferritic-martensitic steel deposited by low-temperature pack cementation

In this study, new boroaluminide protective coatings were deposited on ferritic-martensitic steel substrates (P91) using the pack cementation technique, at moderate temperatures in order not to influence the substrates' mechanical properties. Extensive thermodynamic calculations were performed initially, using the Thermocalc Computer program, so as to optimize the process parameters. The most important gas-precursors for successful deposition of the coatings were identified. The effect of pack composition on the formation and growth of boroaluminides at 715 °C, using pack powders containing Al and B as element depositing sources, two halide salts as activators, and Al₂O₃ as inert filler, was investigated. Three distinct regions were found in the coatings consisting of an outer Al-rich layer, a transition region containing Al, B and Fe and an inner layer containing mostly B, Cr and Fe. The layers were characterized by means of optical and Scanning Electron Microscopy (SEM) in terms of coating morphology and thickness. X-ray diffraction (XRD) was used in order to detect the phases formed and the presence of iron aluminide and boride phases in the coatings due to the boroaluminizing process.     

Hard AlTiN, AlCrN PVD coatings for machining of austenitic stainless steel

The austenitic stainless steels in general are considered to be difficult to machine materials. This is mainly due to the high plasticity and tendency to work-harden of the austenitic stainless steel, which usually results in severe cutting conditions. Additionally, austenitic stainless steels have much lower thermal conductivity as compared to structural carbon steels; this inflicts high thermal impact within the chip-tool contact zone, which significantly increase the cutting tool wear rate. The machineability of austenitic stainless steels can be improved due to application of coated cutting tools. Hard PVD coating with low thermal conductivity and improved surface finish should be used in this case. This can result in enhancement of frictional characteristics at the tool/workpiece interface as well as chip evacuation process. In this study the stainless steel plates were machined using cemented carbide finishing end mills with four high aluminum containing PVD coatings namely: AlCrN, AlCrNbN, fine grained (fg) AlTiN and nano-crystalline (nc) AlTiN. Both AlTiN and AlCrN-based coatings have high oxidation resistances due to formation of aluminum oxide surface layers. The influence of surface post-deposition treatment on tool wear intensity was investigated. The coating surface texture before and after post-deposition treatment was analyzed by means of the Abbot-Firestone ratio curves. Minimal wear intensity after length of cut 150 m was achieved for cutting tools with the nc-AlTiN coating.     

Corrosion behaviour of MoSx-based coatings deposited onto high speed steel by magnetron sputtering

MoS_x-based films were deposited using magnetron sputtering from a pure MoS₂ target. Alloying was accomplished by “co-deposition” from separate targets onto substrates having a two-fold rotation. An additional experiment had also a Cr⁺-ion etch for surface preparation, followed by a Cr adhesion layer, made using a Cr target mounted on a cathodic arc evaporation source. MoS_x and Al- and Ti-alloyed MoS_x coatings have been deposited onto high speed steel (HSS) and glass substrates for corrosion investigations.The coatings were characterised by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, hardness and adhesion measurements. The corrosion behaviour of the samples was electrochemically measured by open-circuit-potential (OCP) measurements and by potentiodynamic corrosion tests in 0.8 M NaCl solution (pH 7). Additionally the MoS_x-based coatings on HSS have been exposed to salt spray tests. The corrosion investigations revealed that the addition of Al and Ti to MoS_x shifts the open-circuit-potential of about 80 to 110 mV to lower values, i.e. the alloying elements make the MoS_x coating a little bit less noble. In agreement with the OCP measurements, the corrosion potential E_corr in potentiodynamic corrosion tests was the highest for non-alloyed MoS_x coatings on HSS substrates. After the potentiodynamic corrosion tests, a strong corrosive attack could be observed for all coated samples. In salt spray tests the lowest number of corrosion pits was found for the MoS_x-Al (Cr⁺) coating on HSS.     

Selected properties of Ti coatings deposited on ceramic AlN substrates by thermal spraying

This paper presents the results of an investigation of selected properties of Ti coatings deposited onto ceramic AlN substrates obtained by the detonation spraying method. It discusses and illustrates the microstructure of the coatings and joints among Ti coatings and AlN substrates. The results of linear distribution of Ti and Al in the cross section of the joint are also included, together with the stereometric patterns of the surface structure of Ti coatings deposited on AlN ceramic substrates. Finally, an finite element method modelling analysis of thermal residual stresses in the discussed coatings is presented.     

Measurement of residual stresses by X-ray diffraction techniques in MoN and Mo2N coatings deposited by arc PVD on high-speed steel substrate

Polycrystalline MoN and Mo₂N films have promising physical and mechanical properties, which made them candidates for wear- and corrosion-resistant coatings and diffusion barriers in microelectronics. The residual stresses in MoN and Mo₂N films consist of thermal and growth stresses or intrinsic stress generated during deposition. Residual stresses in the MoN and Mo₂N coatings deposited by arc PVD techniques on HSS substrate were measured by XRD using the Rocking and the Fixed Incidence Multiplane (FIM) techniques. Residual stresses measured by both techniques in Mo₂N (face center cubic, f.c.c.) and in MoN (hexagonal) films were about 5 and 10 GPa (compressive), respectively. These results indicated that residual stresses in the MoN film was two times greater than the residual stresses in the Mo₂N film.     

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.     

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.     

The effect of MEVVA ion implantation of Zr on the corrosion behaviour of PVD TiN coatings

The use of TiN coatings as corrosion barriers is limited by the presence of defects such as pin-holes. In this study Zr ions were implanted into PVD deposited TiN coatings at varying doses, to improve the corrosion resistance. The corrosion behaviour was assessed in saline environments using linear polarisation techniques and the corroded surface of the coatings characterised using XPS and SEM. Overall, ion implantation resulted in an increase in the coating’s corrosion resistance. Protection was attributed to closure of existing pin-holes and the formation of various nitrides, oxides and oxynitrides of Ti and Zr.