Microstructure and Tribological Properties of WC-Ni Matrix Cermet Coatings Prepared by Electrospark Deposition on H13 Steel Substrate

In order to study the effect of coating deposition on cermets and cemented carbides properties, Ti(C,N)-based cermets and YT15 cemented carbides were prepared by powder metallurgy technique, and then coated by CVD and PVD. The microstructure and elemental contents of the coatings were analyzed by SEM and EDS. The scratches, friction coefficient and cutting performance of the coatings were tested. The results show that the CVD coatings and PVD coatings are well bonded by the combined CVD+PVD technologies. For both the cermets or cemented carbides substrate, both the adhesion force and friction coefficient are the highest for the CVD coatings, while lowest for the PVD coatings, and moderate for the combined CVD+PVD coatings. As to the substrate cermets and cemented carbides, the cutting performance is the best for the combined CVD+PVD coatings, while is worst for the CVD coatings, and moderate for the PVD coatings. The wear mechanism during cutting is mainly oxidative and abrasive wear.

TRIBOLOGICAL PROPERTIES AND WEAR MECHANISM OF HARD COATINGS

Ni398 and Ni818 base alloy coatings were deposited on 1045 steel by electrospark deposition technique (ESD). Forming properties, thickness, microhardness and wear resistance of the coatings were investigated. The chemical composition and crosssection morphology were analyzed through energy dispersive spectrum (EDS) and metalloscope. The results show that the technological parameter window of Ni398 is larger than that of Ni818 electrode. However, other properties of the Ni818 coating, such as thickness and microhardness, were better than those of the Ni398 coating. Especially the wornout volume of Ni818 coating is only 1/6 of that for 1045 steel and 1/3 for Ni398 coating. Chemical composition analysis indicated that the addition of Mo promoted grain reflnement of nickel alloy. Metallographic analysis shows that the molten droplets of Ni398 coatings have an average structure thickness of 20{40 „m while the microstructure of Ni818 coatings is ∞at with width of 5{20 „m.

Effects of process parameters on microstructure and wear resistance of TiN coatings deposited on TC11 titanium alloy by electrospark deposition

Microstructure and tribological properties of Zr-based amorphous-nanocrystalline coatings deposited on the surface of titanium alloys by Electrospark Deposition

AlCoCrFeNi coatings were electrospark-deposited (ESD) on H13 steel substrates, and their nano-mechanical and tribological properties under a load of 2 N, 4 N, 6 N, 8 N, and 10 N were investigated by utilizing a nanoindentation instrument and a reciprocating friction and wear tester, respectively. The morphologies, composition, and phase structure of the as-deposited and worn AlCoCrFeNi coating were characterized using SEM (Scanning electron Microscope), EDS (Energy dispersive spectrometer), and XRD (X-Ray Diffraction). The results showed that the as-deposited AlCoCrFeNi coating with a nanocrystalline microstructure mainly consists of a BCC and B2 phase structure, and a gradient transition of elements between the coating and the substrate ensures an excellent bond between the coating and the substrate. The hardness of the AlCoCrFeNi coating exhibits an 8% increase, while its elastic modulus is reduced by 16% compared to the H13 steel. The AlCoCrFeNi coating remarkably increased the tribological property of the H13 steel under various loads, and its wear mechanism belongs to micro-cutting abrasive wear whilst that of the H13 steel can be characterized as severe adhesive wear. The friction coefficient and weight loss of the AlCoCrFeNi coating decrease with increasing load, both following a linear relationship with respect to the applied load. As the load intensifies, the work hardening sensitivity and oxidation degree on the worn surface of the coating are significantly enhanced, which collectively contributes to the improved tribological performance of the AlCoCrFeNi coating.

In recent decades, CrAlN coatings have been widely used for cutting tools due to their high hardness, good wear resistance, especially excellent thermal stability and oxidation resistance. However, the rapid development in high speeds and dry cutting applications demands further improvement in hardness and wear properties of CrAlN coatings. Mo nitrides coatings are commonly used as protective surface layers against wear and corrosion. The combination of CrAlN and Mo may lead to the development of new composite coatings with superior wear properties. In this study, the CrMoAlN multilayer coatings with different Mo contents were deposited on M2 tool steel and silicon wafers substrates by closedfield unbalanced magnetron sputtering ion plating (CFUMSIP) technique in a gas mixture of Ar+N2. The chemical composition, surface and cross sectional morphologies, microstructure, mechanical and tribological properties of coatings were studied by EDS, SEM, XRD, XPS, nano-indentation and pin-on-disk tribometer, respectively. The results indicate that the CrMoAlN coatings exhibit fcc structure. Mo atoms substitute Cr and/or Al atoms in CrAlN lattice forming the solid solution CrMoAlN coatings. The surface and cross-sectional morphologies of the CrMoAlN coatings show that the grain size and the column width decrease with the increasing of Mo content. Nano-indentation result reveals a promoted hardness and elastic modulus *浙江省自然科学基金资助项目Y15E050060 收到初稿日期: 2015-09-21,收到修改稿日期: 2016-03-09 作者简介:楼白杨,女, 1958年生,教授,博士 DOI: 10.11900/0412.1961.2015.00493 第727-733页 pp.727-733

Solid particle erosion is an important material degradation process. One way of improving the erosion resistance of a material is to suitably modify the surface. Electrospark deposition (ESD) is a well-known surface modification process. Operational simplicity, low capital cost, and low operational cost of the ESD process have made it attractive for high-technology areas in engineering industries. Tungsten carbide (WC) is considered a potential hard material for erosion-resistant application. This material can be deposited by ESD. The present investigation has been undertaken to evaluate the room-temperature erosion response of WC coating deposited by ESD and to compare the erosion behavior of this coating with that of detonation-sprayed WC-Co coating. WC coatings were deposited on mild steel (MS) and aluminum substrate by ESD. Similarly, WC-12% Co coatings were deposited on MS and Al by detonation spraying. The microstructural features and mechanical properties of these coatings were characterized using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction, and microhardness testing. The solid particle erosion rate was determined using an erosion test rig. The morphology of the eroded surfaces and the areas beneath the eroded surfaces were examined by means of SEM. The results showed that the WC coating by ESD improves erosion resistance. Although most coatings exhibit a ductile erosion response, WC coating by ESD on Al substrate exhibits a brittle erosion response. Material loss from ESD coating on Al occurs due to the joining of preexisting cracks and the removal of chunk of material.

Wear and corrosion resistant properties of high entropy alloy coatings (HEAC) on H13 steel are of particular interest for industrial applications. The CoCrFeNi HEA/WC composite coatings (HEACC) developed in this study were successfully prepared by incorporating 10–40 wt.% WC into a matrix of CoCrFeNi HEA using laser cladding on an H13 steel substrate. Phase transformation, microstructure evolution, microhardness, wear and corrosion resistance of CoCrFeNi HEACC were investigated. According to the results, all CoCrFeNi HEACC exhibited higher wear and corrosion resistance than the H13 steel substrate. Wear resistance of CoCrFeNi HEACC first increases and then decreases with an increase in the concentration of WC particles, and the lowest coefficient of friction and the shallowest depth of wear groove were observed after adding 30 wt.%. Grain refinement strengthening and second-phase particle strengthening may contribute to enhanced hardness and wear resistance of coatings with WC additions. In addition, all the CoCrFeNi HEACC exhibited improved corrosion resistance. In particular, an addition of 10 wt.% WC helped to significantly improve the corrosion resistance and ease of passivation of CoCrFeNi HEACC.

This thesis presents the Additive Manufacturing (Direct Laser Deposition) of Tungsten Carbide (WC) cermets, a material that has long been used for wear applications. This alternative route of fabrication allows the expensive yet wear-resistant materials to be placed at locations where the wear resistance is required. This thesis illustrates the effects of different print parameters, presents the optimal parameters that result in a dense and successful deposition without Carbon loss or Cobalt binder evaporation, and examines the microstructure and wear mechanisms. With our unique microstructures, the wear performance of our WC coatings exceeds that of the commercial WC cermets by more than 1 order of magnitude.

Tungsten disulphide (WS2) is one of the widely used intrinsic low friction materials, which is commonly used in the form of coating. WS2 offers very low coefficient of friction only in non humid conditions. Presence of humidity destroys this property and restricts its utility. Modifying the structure of WS2 by adding certain metals helps in overcoming this limitation and in addition improves the mechanical properties. Further, deposition technique and processing parameters play a critical role in deciding the properties of a coating. In this work, Cr-WS2 coatings were deposited on silicon and stainless steel substrates using a fourcathode direct current (DC) unbalanced magnetron sputtering system. Effect of substrate bias and WS2 top layer on the lubricating behavior of coatings has been studied. Deposited coatings were characterized using X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), nanoindentation, and tribometry techniques to analyze the structure, morphology, mechanical and tribological properties. Optimized coating showed a sharp reflection from (101) hexagonal WS2 phase along with broad (002) and (103) reflections, which signifies a combination of nanocrystalline and amorphous behavior. Surface morphology of the coating revealed typical acicular features along with small clusters of cauliflower-like microstructure. For the coating without top WS2 layer, only cauliflower-like features were observed. It has been found that the applied substrate bias significantly affects the lubricating properties. The coating which consists of top WS2 layer deposited at zero bias voltage exhibited the best lubricating properties with co-efficient of friction (COF) of 0.07 till 1300 cycles and an average value of 0.10 till 1800 cycles for the tests conducted in ambient air atmosphere. Keywords: Magnetron sputtering, solid lubricant coating, Cr-WS2, Co-efficient of friction Cite this Article: M. Jeevitha, Srinivas G., Praveen Kumar V., Jakeer Khan G.H., Siju, K. Niranjan, Harish C. Barshilia. Nanostructured CrWS2 Solid Lubricant Coating for Space Applications. Journal of Instrumentation Technology & Innovations. 2019; 9(1), 12– 18p

Effects of nitrogen flux on microstructure and tribological properties of in-situ TiN coatings deposited on TC11 titanium alloy by electrospark deposition

Determining the critical loads of V and Nb doped ternary TiN-based coatings deposited using CFUBMS on steels

NiCr-based self-lubricating PM304 coatings have been used successfully in many high- temperature, high-speed applications such as air cycle machines, bleed air turbo compressors and turbo expanders. However, coarse PM304 coatings are not fully dense, containing a few percentages of pores and cracks which are harmful not only to the coating's tribological properties but also to the coating's overall mechanical strength. Furthermore, fine IS304 was prepared by the methods of high energy ball milling and induction sintering. The size of self-lubricating phase was refined, with Ag particles of about 5 µm and BaF2/CaF2 of about 1 µm. The results show that temperature and microstructure have a great effect on wear properties of IS304 and PM304 coatings. At the temperature of 20— 340 , the friction coefficients of two types of coatings (IS304 andPM304) are higher, and the micro- scopic brittle fracture is the dominant wear mechanism. With the increase of the temperature, the coef- ficient of the coatings decreases rapidly due to the formation of self-lubricating film on the worn surfaces which consist of Ag and fluoride. At the temperature of 340—700 , since the self lubricating phase

Composite porcelain enamels are inorganic coatings for metallic components based on a special ceramic-vitreous matrix in which specific additives are randomly dispersed. The ceramic-vitreous matrix is made by a mixture of various raw materials and elements and in particular it is based on boron-silicate glass added with metal oxides(1) of titanium, zinc, tin, zirconia, alumina, ecc. These additions are often used to improve and enhance some important performances such as corrosion(2) and wear resistance, mechanical strength, fracture toughness and also aesthetic functions. The coating process, called enamelling, depends on the nature of the surface, but also on the kind of the used porcelain enamel. For metal sheets coatings two industrial processes are actually used: one based on a wet porcelain enamel and another based on a dry-silicone porcelain enamel. During the firing process, that is performed at about 870°C in the case of a steel substrate, the enamel raw material melts and interacts with the metal substrate so enabling the formation of a continuous varying structure. The interface domain between the substrate and the external layer is made of a complex material system where the ceramic vitreous and the metal constituents are mixed. In particular four main regions can be identified, (i) the pure metal region, (ii) the region where the metal constituents are dominant compared with the ceramic vitreous components, (iii) the region where the ceramic vitreous constituents are dominant compared with the metal ones, and the fourth region (iv) composed by the pure ceramic vitreous material. It has also to be noticed the presence of metallic dendrites that hinder the substrate and the external layer passing through the interphase region. Each region of the final composite structure plays a specific role: the metal substrate has mainly the structural function, the interphase region and the embedded dendrites guarantee the adhesion of the external vitreous layer to the substrate and the external vitreous layer is characterized by an high tribological, corrosion and thermal shock resistance. Such material, due to its internal composition, functionalization and architecture can be considered as a functionally graded composite material. The knowledge of the mechanical, tribological and chemical behavior of such composites is not well established and the research is still in progress. In particular the mechanical performances data about the composite coating are not jet established. In the present work the Residual Stresses, the Young modulus and the First Crack Failure of the composite porcelain enamel coating are studied. Due to the differences of the porcelain composite enamel and steel thermal properties the enamelled steel sheets have residual stresses: compressive residual stress acts on the coating and tensile residual stress acts on the steel sheet. The residual stresses estimation has been performed by measuring the curvature of rectangular one-side coated specimens. The Young modulus and the First Crack Failure (FCF) of the coating have been estimated by four point bending tests (3-7) monitored by means of the Acoustic Emission (AE) technique(5,6). In particular the AE information has been used to identify, during the bending tests, the displacement domain over which no coating failure occurs (Free Failure Zone, FFZ). In the FFZ domain, the Young modulus has been estimated according to ASTM D6272-02. The FCF has been calculated as the ratio between the displacement at the first crack of the coating and the coating thickness on the cracked side. The mechanical performances of the tested coated specimens have also been related and discussed to respective microstructure and surface characteristics by double entry charts.