Investigation of wear and corrosion resistance of nanocomposite coating formed on AZ31B Mg alloy by plasma electrolytic oxidation

Ceramic-WC coatings were prepared on AZ31 B Mg alloy by plasma electrolytic oxidation (PEO) from a phosphate based bath containing suspended tungsten carbide nanoparticles at various process times. Scanning electron microscope results indicated that increase of coating time and incorporation of tungsten carbide into the ceramic coating during the PEO process led to a decrease in the number and diameter of coating pores. Phase analysis showed that the nanocomposite coating was composed of MgO, Mg₃(PO₄)₂ and WC. Tribological properties and corrosion behaviour of uncoated AZ31 B Mg alloy and ceramic coatings were evaluated using a pin-on-disc tribometer and potentiodynamic polarisation technique in 3.5% NaCl solution, respectively. The wear and electrochemical tests showed that wear and corrosion resistance of ceramic-WC nanocomposite coatings were better than ceramic only ones. In addition, wear and corrosion behaviour of coatings improved with increasing the coating time.     

直流基体偏压对Al-Cr-Si-N涂层结构和力学性能的影响

采用电弧离子镀技术在不同直流偏压下沉积Al-Cr-Si-N涂层,研究基体偏压对涂层成分、微观结构和性能的影响。结果表明:Al-Cr-Si-N涂层以密排六方结构和面心立方结构的AlN相为主,随着基体负偏压增加,涂层的衍射峰整体向小角度方向偏移:涂层内残余压应力逐渐增加,最大值为-0.77 GPa;涂层硬度和摩擦系数变化不明显。当基体负偏压为-40V时,Al-Cr-Si-N涂层的特征参数H/E和H~3/E~(*2)均达最大值,分别为0.15和0.37GPa,此时涂层具有最佳的耐磨性能,摩擦系数亦最低。     

Properties and Tribological Performance of Vanadium Carbide Coatings on AISI 52100 Steel Deposited by Thermoreactive Diffusion

Vanadium carbide coatings were formed on AISI 52100 steel specimens by thermoreactive diffusion and characterized using nanoindentation, x-ray diffraction, and chemical analysis. The deposition process formed a 4-µm coating of vanadium carbide (V₄C₃) with an average grain size of 33 nm and a [200] crystallographic texture. The hardness and elastic modulus of the coatings were determined to be 35 ± 7.5 GPa and 334 ± 67 GPa, respectively. Friction and wear of the coatings were examined in reciprocating sliding contact against tungsten carbide (WC) balls in dry and in an abrasive environment. It was determined that in the abrasive environment, the V₄C₃ coating provided wear protection comparable to WC.     

Mechanical and tribological evaluation of PVD WC/C coatings

Five different WC/C coatings deposited by physical vapour deposition (PVD) on high speed-steel (HSS) have been evaluated with respect to their mechanical and tribological properties. For all coatings a chromium layer was deposited first to enhance coating adhesion. The carbide phase (WC) and the carbon (C) phase were deposited simultaneously by direct-current magnetron sputtering of a WC target and plasma-assisted chemical vapour deposition using hydrocarbon gas, respectively. The influence of the chromium interface layer thickness, the amount of WC phase and the flow of hydrocarbon gas on the mechanical and tribological properties of the coatings have been investigated. The coatings have been characterised with respect to their chemical composition (glow discharge optical emission spectroscopy), hardness (Vickers microhardness), morphology (scanning electron microscopy, SEM), roughness (profilometry), residual stress (beam bending), critical load (scratch testing) and abrasive wear resistance (the “dimple grinder test”). Furthermore, a ball-on-plate test was employed to obtain information about the frictional properties and sliding wear resistance of the coatings. The wear mechanisms and wear debris were analysed by SEM, Auger electron spectroscopy and electron spectroscopy for chemical analysis. All WC/C coatings displayed a thickness between 2 and 4 μm and a surface roughness in the range of 10 to 70 nm. The hardness varied between 1500 and 1800 HV. The coating residual stress was found to range from −2.5 to −0.5 GPa. The scratch test revealed a relatively high critical normal load, i.e., a relatively good adhesion of the WC/C coatings to the HSS. The abrasive wear resistance was found to be very high, in fact equally as high as that of PVD TiN. In the sliding wear test it could be seen that the coating containing the lowest amount of carbide phase (WC), i.e., the highest amount of carbon phase (C), and which had the highest compressive residual stress yielded the lowest friction and wear rate against steel. In addition, this coating was also found to yield the lowest wear rate of the counter material. In summary, a WC/C coating with overall good mechanical and tribological properties was obtained provided a relatively thin chromium layer was deposited first and if a relatively high acetylene gas flow was utilised during deposition of the WC/C layer.     

Bias voltage optimum adjustment considering coatings’ strength and adhesion requirements when cutting various steels

PVD coatings were deposited at various bias voltages on cemented carbide inserts. The coating’s mechanical properties, fatigue and adhesion were determined via FEM-supported evaluation of nanoindentation, perpendicular and inclined impact test results. The coated inserts were applied in milling hardened and normalized steel. For explaining the wear evolution based on the cutting loads and stress fields developed in the coating and its substrate, FEM calculations were performed considering among others the films’ strength and adhesion. According to the workpiece properties, certain coating’s parameters become prevailing for the tool life. These depend on the bias voltage and facilitate its optimum adjustment.     

Hard and wear-resistant titanium nitride coatings for cemented carbide cutting tools by pulsed high energy density plasma

Hard and wear-resistant titanium nitride coatings were deposited by pulsed high energy density plasma technique on cemented carbide cutting tools at ambient temperature. The coating thickness was measured by an optical profiler and surface Auger microprobe. The elemental and phase compositions and distribution of the coatings were determined by Auger microprobe, x-photon electron spectroscope, and X-ray diffractometer. The microstructures of the coatings were observed by scanning electron microscope and the roughness of the sample surface was measured by an optical profiler. The mechanical properties of the coatings were determined by nanoindentation and nanoscratch tests. The tribological properties were evaluated by the cutting performances of the coated tools applied in turning hardened CrWMn steel under industrial conditions. The structural and mechanical properties of the coatings were found to depend strongly on deposition conditions. Under optimized deposition conditions, the adhesive strength of TiN film to the substrate was satisfactory with the highest critical load up to more than 90 mN. The TiN films possess very high values of nanohardness and Young’s modulus, which are near to 27 GPa and 450 GPa, respectively. The wear resistance and edge life of the cemented carbide tools were improved dramatically because of the deposition of titanium nitride coatings.     

Chemical Vapor Deposition and Atomic Layer Deposition of Coatings for Mechanical Applications

Chemical vapor deposition (CVD) of films and coatings involves the chemical reaction of gases on or near a substrate surface. This deposition method can produce coatings with tightly controlled dimensions and novel structures. Furthermore, the non-line-of-sight-deposition capability of CVD facilitates the coating of complex-shaped mechanical components. Atomic layer deposition (ALD) is also a chemical gas phase thin film deposition technique, but unlike CVD, it utilizes “self-limiting” surface adsorption reactions (chemisorption) to control the thickness of deposited films. This article provides an overview of CVD and ALD, discusses some of their fundamental and practical aspects, and examines their advantages and limitations versus other vapor processing techniques such as physical vapor deposition in regard to coatings for mechanical applications. Finally, site-specific cross-sectional transmission electron microscopy inside the wear track of an ALD ZnO/ZrO₂ 8 bilayers nanolaminate coating determined the mechanisms that control the friction and wear.     

激光熔覆制备Fe-Ti-Mo-C系复合涂层

采用钛铁、钼铁和石墨为激光熔覆粉末,利用激光多道搭接熔覆技术在碳钢基体上制备Fe-Ti-Mo-C复合涂层.利用X射线衍射仪、场发射扫描电镜、电子探针对涂层的相结构和显微组织进行了研究.用显微硬度计和滑动磨损试验机,对涂层的硬度和耐磨性能进行测试.结果表明,涂层中原位生成了(Ti,Mo)C复合碳化物.(Ti,Mo)C呈面心立方结构,晶格常数略小于TiC晶粒.随着原材料中钼铁加入量的增加,涂层显微组织由铁素体、珠光体向马氏体转变,显微硬度和耐磨性增加,但抗裂性能降低.     

镁合金表面非平衡磁控溅射CrN镀层结合性能和摩擦磨损性能

采用不同偏压闭合场非平衡磁控溅射技术在镁合金表面沉积Cr-N镀层,分别对镀层的组织结构、厚度、结合性能和摩擦磨损性能进行了表征和分析。结果表明,镀层主要由Cr(N)相和少量Cr2N相组成。在偏压为60V时镀层具有较高的硬度、良好的结合性能和摩擦磨损性能。偏压进一步升高,虽然镀层硬度有所提高,但结合性能和抗磨性能均下降。     

Structure-property relations of arc-evaporated Al-Cr-Si-N coatings

The addition of silicon to the widely used aluminum-containing transition metal nitrides is promising for the synthesis of hard and thermally stable films with good oxidation resistance. For that reason, Al-Cr-Si-N coatings were deposited by reactive cathodic arc-evaporation under industrial conditions from Al₇₀Cr_30 − xSi_x (x = 0, 1, 2, 5 at.%) targets at substrate bias voltages ranging from − 40 V to − 150 V. The structure of the well adherent coatings was investigated by X-ray diffraction and Raman spectroscopy, which indicated at higher Al/Cr ratio > 1.9 an increased tendency of the metastable face-centered cubic solid solution of AlN in CrN to separate into a cubic-hexagonal phase mixture. At higher bias voltages, this effect is gradually inverted and the single cubic phase can be retained. X-ray photoelectron spectroscopy revealed dominant Si-N bonds suggesting either a substitutional solid solution or a separate Si-N phase. Mechanical properties, i.e. hardness and elastic modulus, measured by indentation together with stress evolution demonstrate the beneficial effect of the conservation of the metastable cubic phase.     

Post-treatment of thermal spray coatings on magnesium

Magnesium alloys have a beneficial combination of high strength to weight ratio, good machinability and high recycling potential. Despite this, the application of magnesium still is behind that of other constructive materials mainly due to low wear and corrosion resistance. For more demanding applications, a large amount of surface treatment methods are developed to overcome this problem. Thermal spraying is an efficient and flexible method of coating deposition and is widely used for protection of different materials against corrosion and wear. Nevertheless, the bonding of thermal spray coatings on magnesium alloys is not sufficient, so the following post-treatment processes are needed. One of such possibilities is high energy beam treatment of thermally sprayed coatings. During the heat treatment of magnesium substrates with coating the remelting of coating and a thin surface layer of substrate occurs. Depending on the combination of applied coating system and treatment method, different processes can be realised in modified layers: the alloying of magnesium substrate with other elements to improve corrosion properties, redistribution of hard particles from composite coating and new phases formation during the processing to improve the wear resistance of magnesium alloys. In the present work some examples concerning the laser and electron beam treatment of aluminium based composite coatings as well as infra red irradiation of zinc based coatings are described. Coatings are deposited on magnesium substrates (AM20, AZ31, AZ91) by arc spraying with Zn, ZnAl4 and ZnAl15 solid wires and cored wires in aluminium core with powder filling containing different hard particles, such as boron, silicon and tungsten carbide or titanium oxide. Remelting of thermal spray coatings is carried out by means of continuous irradiation of СО₂-laser in nitrogen or argon atmosphere, electron beam in vacuum and focused tungsten halogen lamp line heater in atmosphere. Microstructure of sprayed coatings as well as that of modified surface layers is investigated by metallographic methods. Corrosion properties are estimated by electrochemical measurements. Abrasion wear resistance of the modified layers is determined by scratch test, corundum grinding disk test and Rubber wheel test. It is shown that all methods applied for processing of thermal spray coatings lead to formation of modified surface layers in magnesium substrate with improved wear and corrosion properties. Different mechanisms of microstructure formation such as redistribution of chemical composition of composite coating components, partial remelting of hard phase particles, and new phases formation are discussed. Electrochemical behaviour of modified surface layers is mostly improved due to alloying, homogenization of element distribution and strong decrease of as-sprayed coating porosity. Abrasion wear resistance of processed magnesium substrates strongly depends on the microstructure and usually is 5 to 20 times higher compared with base material.     

Single- and Two-Layer Coatings of Metal Blends onto Carbon Steel: Mechanical, Wear, and Friction Characterizations

Single- and two-layer coatings were deposited onto carbon steel using a high-velocity oxy-fuel deposition gun. The two-layer coating consisted of a top layer of tungsten carbide cobalt/nickel alloy blend that provides wear resistance and a bottom layer of iron/molybdenum blend that provides corrosion resistance. The morphological changes in the single- and two-layer coatings were examined using scanning electron microscopy. The residual stresses formed on the surface of various coatings were determined from x-ray diffraction data. Nanomechanical properties were measured using the nanoindentation technique. Microhardness and fracture toughness were measured incorporating the microindentation tests. Macrowear and macrofriction characteristics were measured using the pin-on-disk testing apparatus. The goal of this study was to ensure that the mechanical properties, friction, and wear resistance of the two-layer coating are similar to that of the single-layer coating.     

Mechanical and tribological properties evaluation of cathodic arc deposited CrN/ZrN multilayer coatings

Five nanostructured CrN/ZrN multilayer coatings were deposited periodically by cathodic arc evaporation. The bilayer periods of the CrN/ZrN multilayer coatings were controlled in the range of 5 to 30 nm. The structures and bilayer period of the multilayer coatings were characterized by an X-ray diffractometer. The microstructures of thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Nanoindentation, scratch tests, Daimler–Benz Rockwell-C (HRC-DB) adhesion tests, microhardness and pin-on-disk wear tests were used to evaluate the hardness, adhesion, indentation toughness and tribological properties of thin films, respectively. It was found that the hardness and tribological properties were strongly influenced by the bilayer period of the CrN/ZrN multilayer coatings. An optimal combination of mechanical properties and excellent tribological behavior was found for a coating with a critical bilayer period of 30 nm.     

Microstructures and mechanical properties evaluation of TiAlN/CrSiN multilayered thin films with different bilayer periods

The Ti_0.45Al_0.55N/Cr_0.75Si_0.25N nanoscale multilayered coatings were deposited periodically by a bipolar asymmetric pulsed DC reactive magnetron sputtering technique. The structures and bilayer period of multilayer coatings were characterized by an X-ray diffractometer. The surface and cross-sectional morphologies of thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The surface roughness of thin films was explored by atomic force microscopy (AFM). A nanoindenter, a micro Vickers hardness tester and pin-on-disk wear tests were used to evaluate the hardness, fracture toughness and tribological properties of the thin films, respectively. Six coatings with bilayer period ranges from 6 nm to 40 nm were produced in this work. It was observed that the hardness increased with increasing bilayer period and reached the maximum at 12 nm and then leveled off at periods larger than 12 nm. An optimal hardness, and plastic deformation resistance, as well as adequate tribological behaviors were found on the coating with a critical bilayer period of 12 nm.     

Effect of deposition temperature on properties of boron-doped diamond films on tungsten carbide substrate

Boron-doped diamond (BDD) films were deposited on the tungsten carbide substrates at different substrate temperatures ranging from 450 to 850 °C by hot filament chemical vapor deposition (HFCVD) method. The effect of deposition temperature on the properties of the boron-doped diamond films on tungsten carbide substrate was investigated. It is found that boron doping obviously enhances the growth rate of diamond films. A relatively high growth rate of 544 nm/h was obtained for the BDD film deposited on the tungsten carbide at 650 °C. The added boron-containing precursor gas apparently reduced activation energy of film growth to be 53.1 kJ/mol, thus accelerated the rate of deposition chemical reaction. Moreover, Raman and XRD analysis showed that heavy boron doping (750 and 850 °C) deteriorated the diamond crystallinity and produced a high defect density in the BDD films. Overall, 600–700 °C is found to be an optimum substrate temperature range for depositing BDD films on tungsten carbide substrate.     

Wear of CrC-coated carbide tools in dry machining

This paper discusses the tribological characteristics and cutting performance of chromium carbide (Cr_x%C)-coated carbide tool inserts and micron-drills in dry machining. Cr_x%C coatings have been deposited with different optical emission monitoring (OEM) set values, x%, of chromium target “poisoning” by unbalanced magnetron sputtering and OEM control. The microstructures and mechanical properties of Cr_x%C coatings have been measured by the experiments of scanning electron microscope (SEM), nanoindentation and adhesion. Experimental results indicate that the coating microstructure, mechanical properties and wear resistance vary according to OEM set values. Cr_10%C-coated inserts showed the best wear resistance in AISI 1045 steel turning test. Cr_50%C-coated tools have performed exceptionally well in both copper turning and printed circuit board (PCB) through-hole drilling tests. The service life of Cr_50%C-coated tool is four times higher than that of an uncoated tool in the PCB through-hole drilling test.     

Nanolayer (Ti,Cr)N coatings for hard particle erosion resistance

This paper discusses the synthesis and characterization of titanium chromium nitride ((Ti,Cr)N) thin films deposited onto AM355 stainless steel by multi-source cathodic arc physical vapor deposition (PVD) for improved erosion resistance. The effect of Cr evaporator current and substrate bias on the erosion resistance of the (Ti,Cr)N coating were investigated. The coatings were characterized using X-ray diffraction, scanning electron microscopy, electron probe microanalysis, scanning transmission electron microscopy, scratch adhesion testing and erosion testing. The (Ti,Cr)N coatings deposited using multisource mode were determined to be nanolayered structures consisting of TiN rich and CrN rich layers. EPMA showed that the atomic percentage of Cr within the coating increased (increased Cr:Ti ratio) with increasing Cr evaporator current and that the (Ti,Cr)N chemical composition did not appear to change with varying bias. Using XRD and STEM, it was determined that all nanolayer (Ti,Cr)N coatings were multi-phased consisting of a B1 NaCl crystal structure. XRD also revealed that as the Cr evaporator current was increased, there was an increase in the CrN phase volume. Macroparticle incorporation increased with an increase in Cr evaporator current and decreased with an increase in bias. The nanolayer (Ti,Cr)N coatings ranged in Vickers hardness from 1700 to 2800 VHN_0.050. Coating adhesion increased as Cr:Ti ratio increased. In regards to erosion, (Ti,Cr)N coatings with a high number of TiN/CrN interfaces performed poorly against alumina media. As the Cr evaporator current was varied, the coating deposited with the highest Cr:Ti ratio (evaporator current of 85 A) and when bias was varied, the lowest substrate bias of - 50 V had the best erosion performance.     

Electrospark WC–Co coatings with different iron concentration

The effect of the iron concentration in WC–Co electrode materials on the structure and properties of coatings produced by electrospark alloying (ESA) on low-carbon steel is investigated. The effect of the iron concentration on the mass transfer and thickness of the deposited coatings is described. The phase composition, surface roughness and wear resistance of the coatings in dry and microabrasive friction are investigated. It is shown that the rate of decarbidization of tungsten carbide in ESA with a higher iron concentration of the electrode materials increases.     

Bias Voltage-Dependent Impedance Spectroscopy Analysis of Hydrothermally Synthesized ZnS Nanoparticles

In this report, bias voltage-dependent dielectric and electron transport properties of ZnS nanoparticles were discussed. ZnS nanoparticles were synthesized by introducing a modified hydrothermal process. The powder XRD pattern indicates the phase purity, and field emission scanning electron microscope image demonstrates the morphology of the synthesized sample. The optical band gap energy (E_g?=?4.2 eV) from UV measurement explores semiconductor behavior of the synthesized material. The electrical properties were performed at room temperature using complex impedance spectroscopy (CIS) technique as a function of frequency (40 Hz-10 MHz) under different forward dc bias voltages (0-1 V). The CIS analysis demonstrates the contribution of bulk resistance in conduction mechanism and its dependency on forward dc bias voltages. The imaginary part of the impedance versus frequency curve exhibits the existence of relaxation peak which shifts with increasing dc forward bias voltages. The dc bias voltage-dependent ac and dc conductivity of the synthesized ZnS was studied on thin film structure. A possible hopping mechanism for electrical transport processes in the system was investigated. Finally, it is worth to mention that this analysis of bias voltage-dependent dielectric and transport properties of as-synthesized ZnS showed excellent properties for emerging energy applications.