Al2O3-ZrO2 mixed oxide composite incorporated aluminium rich zinc coatings for high wear resistance

Corrosion resistance and wear resistance are the two important parameters for high performance of zinc galvanic coating. In the present work, the improvement of these two characteristics was achieved by the incorporation of Al₂O₃-ZrO₂ mixed oxide composite in the coating. Al₂O₃-ZrO₂ mixed oxide composite was synthesized from ZrOCl₂·8H₂O. Aluminium rich zinc coatings with high sliding wear resistance was developed from a galvanic bath containing the mixed oxide. Based on the performance of the coating during physicochemical and electrochemical characterization, the concentration of mixed oxide composite in the bath was optimized as 0.50 wt% Al₂O₃-0.50 wt% ZrO₂. While rich in Al-metal content in the coating caused high corrosion resistance, the incorporation of the mixed oxide improved structural characteristics of the coating resulting in high wear resistance also. The coating was nonporous in nature and even the interior layers had high stability. The coatings have potential scope for high industrial utility.     

Wear Behavior of Plasma-Sprayed Al-Si/TiB2/h-BN Composite Coatings

In this study, mechanically alloyed Al-12Si/TiB₂/h-BN composite powder was deposited onto aluminum substrates by atmospheric plasma spraying. Wear performance of the coating was investigated with respect to the structural evolution of the composite powder coating. Non-lubricated ball-on-disk tests were used to examine the wear resistance of the coatings. The worn surfaces were examined using scanning electron microscopy and energy dispersive spectroscopy to elucidate the wear mechanisms operating at the sliding interface. It has been observed that TiB₂ and in situ formed AlN and Al₂O₃ phases in combination with h-BN solid lubricant strongly affect the wear performance of the coating.     

Fabrication and Properties of Plasma-Sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript> Composite Coatings

Al₂O₃ /xZrO₂ (where x = 0, 3, 13, and 20 wt.%) composite coatings were deposited onto mild steel substrates by atmospheric plasma spraying of mixed α-Al₂O₃ and nano-sized monoclinic-ZrO₂ powders. Microstructural investigation showed that the coatings comprised well-separated Al₂O₃ and ZrO₂ lamellae, pores, and partially molten particles. The coating comprised mainly of metastable γ-Al₂O₃ and tetragonal-ZrO₂ with trace of original α-Al₂O₃ and monoclinic-ZrO₂ phases. The effect of ZrO₂ addition on the properties of coatings were investigated in terms of microhardness, fracture toughness, and wear behavior. It was found that ZrO₂ improved the fracture toughness, reduced friction coefficient, and wear rate of the coatings.     

Dry sliding wear behavior of ceramic-metal composite coatings prepared by plasma spraying of self-reacting powders

Ceramic-metal composite (CMC) coatings were deposited on the surface of Fe-0.14–0.22 wt.% C steel by plasma spraying of self-reacting Fe₂O₃−Al composite powders. The dry sliding friction and wear character of the CMC coatings are investigated in this paper. The wear resistance of the CMC coatings was significantly better than that of Al₂O₃ coatings under the same sliding wear conditions. The tough metal, which is dispersed in the ceramic matrix, obviously improved the toughness of the CMC coatings. Wear mechanisms of the CMC coatings were identified as a combination of abrasive and adhesive wear.     

Tribological Behavior of Plasma-Sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-20 wt.%TiO<Subscript>2</Subscript> Coating

Al₂O₃-20 wt.% TiO₂ ceramic coatings were deposited on the surface of Grade D steel by plasma spraying of commercially available powders. The phases and the microstructures of the coatings were investigated by x-ray diffraction and scanning electron microscopy, respectively. The Al₂O₃-20 wt.% TiO₂ composite coating exhibited a typical inter-lamellar structure consisting of the γ-Al₂O₃ and the Al₂TiO₅ phases. The dry sliding wear behavior of the coating was examined at 20 °C using a ball-on-disk wear tester. The plasma-sprayed coating showed a low wear rate (~4.5 × 10^?6 mm³ N^?1 m^?1), which was <2% of that of the matrix (~283.3 × 10^?6 mm³ N^?1 m^?1), under a load of 15 N. In addition, the tribological behavior of the plasma-sprayed coating was analyzed by examining the microstructure after the wear tests. It was found that delamination of the Al₂TiO₅ phase was the main cause of the wear during the sliding wear tests. A suitable model was used to simulate the wear mechanism of the coating.     

Wear Behavior of Plasma-Sprayed Carbon Nanotube-Reinforced Aluminum Oxide Coating in Marine and High-Temperature Environments

Wear behavior of plasma-sprayed carbon nanotube (CNT)-reinforced aluminum oxide (Al₂O₃) composite coatings are investigated at room temperature (298 K), elevated temperature (873 K), and in sea water. Lowest wear volume loss was observed in the sea water as compared to dry sliding at 298 and 873 K. Relative improvement in the wear resistance of Al₂O₃-8 wt.% CNT coating compared to Al₂O₃ was 72% at 298 K, 76% at 873 K, and 66% in sea water. The improvement in the wear resistance of Al₂O₃-CNT coatings is attributed to (i) larger area coverage by protective film on the wear surface at room temperature and in sea water, (ii) higher fracture toughness of Al₂O₃-CNT coatings due to CNT bridging between splats, and (iii) anti-friction effect of sea water. The average coefficient of friction (COF) was the lowest (0.55) in sea water and the highest (0.83) at 873 K for Al₂O₃-8 wt.% CNT coating.     

Tribological behavior and mechanism of NiCrBSi–Y2O3 composite coatings

The NiCrBSi–Y₂O₃ composite coatings were prepared on the surface of 45 carbon steel by plasma spray, the microstructure and tribological properties of the coatings were investigated. The results show that the NiCrBSi–Y₂O₃ composite coatings are mainly composed of γ-Ni, CrB, Cr₇C₃ and Y₂O₃. With addition of Y₂O₃, hard phases such as CrB, Cr₇C₃ emerge in composite coating, and the density of the composite coatings also increases. The NiCrBSi–0.5Y₂O₃ composite coating presents excellent tribological properties. Its friction coefficient is 0.175, which is about 37% of that of the pure NiCrBSi coating. The mass wear loss is 1.2 mg, which is reduced by 43% compared with the pure NiCrBSi coating. When the loads are 6–10 N, the NiCrBSi–0.5Y₂O₃ composite coating suffers from slight wear and the wear mechanisms are mainly adhesive wear accompany with slight micro-cutting wear and micro-fracture wear. As the load increases to 12 N, the wear mechanisms are adhesive wear and severe micro-cutting wear.     

Microstructure Characterization of the FeAl<Subscript>2</Subscript>O<Subscript>4</Subscript>-Based Nanostructured Composite Coating Synthesized by Plasma Spraying Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al Powders

The microstructure of the coating prepared by reactive plasma spraying Fe₂O₃/Al composite powders was characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicated that the coating exhibited nanostructured microstructure which consisted of FeAl₂O₄, Fe or Fe solid solution, Al₂O₃ and a little FeAl. In the composite coating, spherical Fe particles (tens of nanometers to hundreds of nanometers) were distributed uniformly within the equiaxed and columnar nanograins FeAl₂O₄ matrix. There were two kinds of Al₂O₃ phases present in the composite coating. One kind was nano-sized Al₂O₃ particles uniformly dispersed within the matrix, forming eutectic structure of (FeAl₂O₄ + γ-Al₂O₃); the other was 1-1.5 μm Al₂O₃ particles embedded individually within the matrix. The composite coating had higher toughness than the conventional microstructured Al₂O₃ coating.     

Mechanical and tribological properties of plasma-sprayed Cr3C2-NiCr, WC-Co, and Cr2O3 coatings

Mechanical properties such as Young’s moduli and fracture toughness of plasma-sprayed Cr₃C₂-NiCr, WC-Co and Cr₂O₃ coatings were measured. The tribological properties of the three kinds of coatings were investigated with a block-on-ring self-mated arrangement under water-lubricated sliding. Furthermore, the influences of the mechanical properties on the tribological properties of the coatings were also examined. It was found that the Young’s moduli, bend strengths and fracture toughness of the coatings were lower than the corresponding bulk materials, which may be attributed to the existence of pores and microcracks in the coatings. Among the three kinds of coatings, the magnitude of wear coefficients, in decreasing order, is Cr₃C₂-NiCr, WC-Co and Cr₂O₃, and the wear coefficient of Cr₂O₃ coating was less than 1 × 10⁻⁶mm³N⁻¹m⁻¹. The wear mechanisms of the coatings were explained in terms of microcracking and fracturing, and water deteriorated wear performance of the coatings. The higher the fracture toughness and the lower the porosity and length of microcracking of the coating, the more the wear-resistance of the coating.     

Effect of Nd2O3 Additive on Microstructure and Tribological Properties of Plasma-Sprayed NiCr-Cr2O3 Composite Coatings

Four types of NiCr-Cr₂O₃ composite coatings doped with different mass fraction of Nd₂O₃ were deposited by atmospheric plasma spraying. The microstructure and phase composition of as-sprayed coatings were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). Furthermore, their friction and wear behaviors at 20 and 600 °C under unlubricated condition were evaluated using CSM high temperature tribometer. The results showed that Nd₂O₃ could refine microstructure of NiCr-Cr₂O₃ composite coating and make Cr₂O₃ distribution more uniform in the coating, which leads to the increase of average microhardness. In addition, NiCr-Cr₂O₃ composite coatings doped with Nd₂O₃ had better wear resistance than that without Nd₂O₃ at experimental temperatures. Especially, the coating containing 8 wt.% Nd₂O₃ showed the best wear resistance at 20 and 600 °C, which was attributed to the refined microstructure and improved microhardness. At 20 °C, the wear mechanism of the coating was abrasive wear, brittle fracture and splat detachment. At 600 °C, the wear mechanism was adhesion wear and plastic deformation.     

High temperature friction and wear behaviour of Ni–P–Ag–Al2O3 hybrid nanocomposite coating

Abstract

Codeposition of silver and alumina particles has been performed within an Ni–P coating on carbon steel samples by electroless deposition to form an Ni–P–Ag–Al₂O₃ hybrid nanocomposite coating. The structure of heat treated coatings was evaluated by XRD analysis. Tribological properties of the coatings were investigated by a pin-on-disc test method using a 52100 steel pin as counter body at high temperature. A 3D optical profiler was employed to measure the wear rate of the deposits. Surface morphology, cross section and wear scars of the coatings were studied by using SEM equipped with EDS analysis. The results showed that tribological properties of Ni–P–Ag–Al₂O₃ hybrid coating are similar to Ni–P–Ag conventional composite coating. Moreover, friction coefficient and wear resistance of the hybrid coating are strongly influenced by self-lubricating silver thin layers formed between mating surfaces during high temperature sliding wear.     

Fabrication and Tribological Evaluation of Vacuum Plasma-Sprayed B4C Coating

B₄C coating was fabricated by vacuum plasma spraying and the tribological properties of the coating against WC-Co alloy were evaluated by sliding wear tests. Al₂O₃ coating, one of the most commonly used wear-resistant coatings, was employed as comparison in the tribological evaluation. The results obtained show that, the B₄C coating is composed of a large amount of nanostructured particles along with some amorphous phases. Both of the friction coefficient and wear rate of the B₄C coating are much lower than those of the Al₂O₃ coating, and the tribological evaluation reveals a decreasing trend for the B₄C coating in friction coefficient as well as wear rate with increasing normal load, which is explained in terms of the formation of a protective transfer layer on its worn surface. Tribofilm wear is found to be the dominant wear mechanism involved in the B₄C/WC-Co alloy friction pair.     

Effect of Feedstock Size and its Distribution on the Properties of Detonation Sprayed Coatings

The detonation spraying is one of the most promising thermal spray variants for depositing wear and corrosion resistant coatings. The ceramic (Al₂O₃), metallic (Ni-20 wt%Cr) , and cermets (WC-12 wt%Co) powders that are commercially available were separated into coarser and finer size ranges with relatively narrow size distribution by employing centrifugal air classifier. The coatings were deposited using detonation spray technique. The effect of particle size and its distribution on the coating properties were examined. The surface roughness and porosity increased with increasing powder particle size for all the coatings consistently. The feedstock size was also found to influence the phase composition of Al₂O₃ and WC-Co coatings; however does not influence the phase composition of Ni-Cr coatings. The associated phase change and %porosity of the coatings imparted considerable variation in the coating hardness, fracture toughness, and wear properties. The fine and narrow size range WC-Co coating exhibited superior wear resistance. The coarse and narrow size distribution Al₂O₃ coating exhibited better performance under abrasion and sliding wear modes however under erosion wear mode the as-received Al₂O₃ coating exhibited better performance. In the case of metallic (Ni-Cr) coatings, the coatings deposited using coarser powder exhibited marginally lower-wear rate under abrasion and sliding wear modes. However, under erosion wear mode, the coating deposited using finer particle size exhibited considerably lower-wear rate.     

微弧氧化处理原位颗粒增强铝基复合材料的磨损性能(英文)

采用微弧氧化工艺来改善原位颗粒增强铝基复合材料的表面性能。通过向铝熔体中加入15%CuO来制备CuAl2增强铝基复合材料。所制备的材料经过热压、均匀化处理、淬火和人工时效处理,然后在含KOH、KF和Na2SiO3的电解液中进行微弧氧化处理。经微弧氧化处理,复合材料的表面生成了有效厚度约15μm的Al2O3膜层。洛氏硬度测试后,在压痕边缘部位没有出现裂纹或明显的剥离现象,表明Al2O3膜层与基底结合良好。干摩擦试验结果表明,Al2O3膜层对Al2O3球的破坏性作用具有明显的抑制,Al2O3膜层的磨损性能比基体提高15倍以上。     

Preparation of nanostructured Ni/Al2O3 composite coatings in high magnetic field

Ni/Al₂O₃ composite coatings were prepared by a novel method from a modified Watt's type electrolyte containing nano-Al₂O₃ particles, where a high magnetic field was imposed in the direction parallel to an electrolytic current instead of mechanical agitation. Effects of magnetic field on the content of particles, surface morphology, microhardness and wear resistance of plating layer were investigated. It was found that the high magnetic field played an important role in the formation of composite coatings. The amounts of nano-Al₂O₃ particles in the composite coating increased with increasing of magnetic flux density and reached a maximum value at 8 T, then reduced slightly. The microhardness and wear resistance of the nanocomposite coatings also enhanced with increasing of magnetic flux density as compared to that of pure Ni coating fabricated in the absence of magnetic field. That was because the co-deposited nano-Al₂O₃ particles were uniformly distributed in the Ni matrix and contributed to greatly increase the microhardness and wear resistance of the composite coatings. Moreover, the mechanism of action of high magnetic field was discussed preliminarily.     

Effect of reinforcement,compact pressure and hard ceramic coating on aluminium rock dust composite performance

Aluminium 6061T6 is reinforced with naturally available rock dust particles to fabricate low cost aluminium rock dust composite through powder metallurgy technique. Reinforcement ratio was varied from 0% to 50% whereas size of the particles was kept constant as 20 μm. Mixed powders were compacted at three different pressures from 100 to 200 MPa. Al₂O₃ ceramic coating was given over the novel composite material by Type III Sulphuric acid hard coating method. Developed composites were tested for microstructure, micro-hardness and wear resistance. SEM micrograph confirms uniform distribution of reinforcement in matrix and a fine ceramic hard coating is observed through optical microscopic images. Micro-hardness increases as reinforcement level increases up to 10%. Wear properties were analysed using pin on disc setup without lubricant and by maintaining three parameters viz load, sliding velocity and sliding distance being unchanged. It was found that composite with 10% rock dust gives better wear resistance than any other compositions. Also incrementing figure is notified for hardness and subsequently wear resisting property too when compacting pressure gets increased. Coated sample exhibits better performance than uncoated composite samples at all compositions and at different levels of compacting pressure.     

Intermediate temperature tribological behavior of carbon nanotube reinforced plasma sprayed aluminum oxide coating

Tribological behavior of plasma sprayed carbon nanotube (CNT) reinforced aluminum oxide (Al₂O₃) composite coatings was examined at room temperature, 573 K and 873 K using tungsten carbide (WC) ball-on-disk tribometer. The weight loss due to wear of Al₂O₃ coating was found to be increasing with the temperature while Al₂O₃-CNT coating showed a decreasing trend in the weight loss with the temperature. Relative improvement in the wear resistance of Al₂O₃-CNT coating compared to Al₂O₃ coating was found to be 12% at room temperature which gradually increased to ∼ 56% at 573 K and ∼ 82% at 873 K. Protective layer as a result of tribo-chemical reaction was observed on the wear track of both of the coatings. The improvement in the wear resistance of Al₂O₃-CNT coating was attributed to three phenomena viz. (i) higher hardness at the elevated temperature as compared to Al₂O₃ coating, (ii) larger area coverage by protective film on the wear surface at the elevated temperature and (iii) CNT bridging between splats. The coefficient of friction (COF) of Al₂O₃ coating was nearly constant at room and elevated temperature whereas COF for Al₂O₃-CNT coating decreased at the elevated temperature (873 K).     

Characterization of Microstructure and Wear Resistance of PEO Coatings Containing Various Microparticles on Ti6Al4V Alloy

Titania-based composite coatings were prepared by plasma electrolytic oxidation (PEO) treatment of Ti6Al4V alloy in electrolyte with α-Al₂O₃, Cr₂O₃ or h-BN microparticles in suspension. The microstructure, composition of PEO composite coatings were analyzed by SEM, EDS and XRD. The wear resistance of composite ceramic coatings was studied by ball-on-disk wear test at ambient temperature and 300 °C. The results showed that the addition of microparticles accelerated the growth rate of PEO coating and changed the microstructure and composition of PEO coating. PEO coating was porous and mainly composed of rutile-TiO₂, anatase-TiO₂ and Al₂TiO₅. PEO/α-Al₂O₃ (Cr₂O₃ or h-BN) composite coating only had small micropores and appeared some α-Al₂O₃ (Cr₂O₃ or h-BN) phase. Besides, the addition of α-Al₂O₃ (Cr₂O₃ or h-BN) microparticles greatly improved the wear resistance of PEO coating. At ambient temperature, abrasive wear dominated the wear behavior of PEO coating, but abrasive wear and adhesive peel simultaneously happened at 300 °C. Whether at ambient temperature or 300 °C, PEO composite coating had better wear resistance than PEO coating. Besides, PEO/h-BN composite coating outperformed other composite coatings regardless of the temperature.     

Characterization of Fe-Cr-B based coatings produced by HVOF and PTA processes

Two Fe-Cr-B based gas atomized powders, Armacor M and 16, were thermally sprayed on a low carbon steel substrate, using the HVOF (High Velocity Oxygen Fuel) process. Armacor M was also weld-surfaced with the PTA (Plasma Transferred Arc) process. The resultant deposits were subsequently characterized, using X-ray diffraction, scanning electron microscopy, and microhardness measurement. The effects of heat treatment were also studied for HVOF-sprayed coatings. The wear performance of the coatings was investigated by two-body abrasive wear tests. The results of microstructural analysis of as-sprayed deposits revealed oxide and boride phases such as Fe₃O₄ and Cr_1.65F_0.35B_0.96 in an α matrix for the HVOF-sprayed Armacor 16 coating, and only the boride phases (Cr_1.65F_0.35B_0.96 and Cr₂B) in an α matrix for the HVOFsprayed Armacor M coating. PTA weld-surfaced Armacor M coating contains needle-type long precipitates of Cr₂B) and Cr_1.65F_0.35B_0.96, in the α matrix. The hardness of the HVOF-sprayed Armacor 16 coating after heat treatment was substantially less than that of the as-sprayed coating due to the phase transformation from α to γ phase. Heat treatments of the HVOF-sprayed Armacor M coating did not produce changes in phase and its hardness decreased as compared to that of the as-sprayed coating. While HVOF-sprayed and PTA weld-surfaced Armacor M coatings have the same hardness, the latter shows better abrasive wear resistance because of the size and orientation of its boride phases. The broadening of the XRD patterns and the increase in hardness after wear testing suggest that the transformation from the crystalline to the amorphous structure occurred on the uppermost layer during wear testing.     

In situ nanostructured ceramic matrix composite coating prepared by reactive plasma spraying micro-sized Al-Fe2O3 composite powders

In situ nanostructured ceramic matrix composite coating was prepared by reactive plasma spraying micro-sized Al-Fe₂O₃ composite powders. The microstructure of the composite coating was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, respectively. The results indicated that the composite coating exhibited dense and crack-free microstructure with a number of spherical α-Fe and γ-Al₂O₃ nano-grains embedded within equiaxed and columnar FeAl₂O₄ nano-grains matrix. The composite coating showed markedly higher toughness and wear resistance than the conventional Al₂O₃ coating.