Wear-Resistant Layered Electrospark Coatings Based on ZrB2

We have studied the composition and tribological parameters (coefficient of friction and wear rate) of coatings obtained in electrospark alloying (ESA) of steel 45 with the composite ceramic ZrB₂ – SiC – B₄C based on zirconium diboride. We have shown that layer-by-layer electrospark alloying using Ti – Al – N composites to form an undercoat reduces the coefficient of friction of the coating down to 0.12-0.20 while maintaining a rather low wear level (7-11 μm/km). We have analyzed the effect of the composition of the secondary structures which are formed during tribo-oxidation under dry friction conditions.     

电弧喷涂高性能防腐耐磨涂层

垃圾焚烧厂工件表面通常暴露在含HCl/KCl的高温气氛中,这些高腐蚀性高温气氛是造成焚烧厂高额维护费用的主要原因。使用热喷涂技术对部件表面进行涂层防护可明显提高传统钢材的表面耐腐蚀性能。电弧喷涂由于其易于操作性和低成本,已成为最为成熟的技术之一。要得到可观的腐蚀防护能力,涂层必须有很高的致密度。因此,电弧喷涂必须做出适当调整以适应垃圾焚烧厂的特殊需求。虽然镍基合金和钴基合金代表了当今腐蚀防护的技术水平,但是这些合金非常昂贵。属于同一系列的铁基合金将成为一种经济效益更为可观的防腐蚀材料。最近的研究表明,与铁铬基合金和镍铬基合金相比,铁基合金中加入硅后其耐腐蚀性能得到显著提高。鉴于这一原因,本文开展了对不同成分的铁-铬-硅系合金的研究,重点讨论了该合金的最新研究结果。     

Foundations of the Fabrication Technology of Wear-Resistant Coatings Made of Mixtures of Chromium Carbide Powders with a Metallic Binder by Explosive Pressing

Experimental data on the explosive compaction of powder mixtures of chromium carbide (Cr₃C₂) with metals (Ti, Ni, Cu) are presented, their theoretical explanations are given, and scientifically substantiated principles of the composition selection and development of the explosive fabrication of wear-resistant antifriction chromium carbide hard alloys and coatings are formed on this basis. The explosive pressing of powder mixtures was performed according to the scheme with the use of a plane normally incident detonation wave in a broad range of loading parameters (the powder heating temperature in shock waves was varied in experiments from 200 to 1000°C, while the maximal pressure of the shock-wave compression varied from 4 to 16 GPa). To analyze the phase transformations, the numerical thermodynamic simulation of the phase equilibrium was performed applying the Thermo-Calc software complex. The microstructure and the chemical and phase compositions were investigated using an Axiovert 40 MAT optical microscope (Carl Zeiss, Germany), Versa 3d and Quanta 3D FEG scanning electron microscopes (FEI, United States), BS 540 (Tesla, Czech Republic) and Titan 80–300 and Techai G2 20F (FEI, United States) transmission electron microscopes, and a Solver Pro atomic force microscope (OOO NT-MDT, Zelenograd). The temperature stability and oxidation resistance at elevated temperatures of materials formed by the explosion were investigated by thermogravimetric analysis using an STA 449 F3 Jupiter device (NETZSCH, Germany) in synthetic air upon heating to 1500°C. Tribotechnical tests were performed using an MI-1M friction machine (MEZIMiV, Moscow) according to the pin–ring scheme with digging in distilled water. Mechanisms of compaction and formation of strong boundaries between the particles of powder materials during the explosive pressing are described. It is shown that chromium carbide hard alloys with a titanium binder formed by explosion retain their phase composition invariable, do not oxidize to 600°C, and have considerably better antifriction properties and wear resistance when compared with SGP-0.5 and KKhN-20 materials lubricated with water, which have been applied in friction pairs until now.     

Effect of Electron-Beam Treatment on Wear-Resistant Coatings Applied by Electroexplosive Sputtering

TiC–Mo, TiC–Ni, TiB₂–Mo, and TiB₂–Ni coatings applied to the surface of Hardox 450 steel by electroexplosive sputtering are subjected to electron-beam treatment, After electroexplosive application, the surface relief of the coatings includes features such as deformed solidifying microglobules, buildup, microcraters, microcracks, and peeling. After electron-beam treatment, the microglobules, buildup, microcraters, and microcracks disappear from the coating surface. A polycrystalline structure containing cellular elements is formed. After electron-beam treatment, the surface roughness is 1.1–1.2 μm. The thickness of the layers modified by the electron beam in the electroexplosive coatings depends linearly on the surface energy density. The greatest coating thickness is observed when using the TiB₂–Mo system; the coating thickness is least for the TiC–Ni system. That may be attributed to the thermophysical properties of the coatings. The following substructures are observed in the coatings: cellular, striated, fragmented, and subgranular. Grains with chaotically distributed dislocations and reticular dislocations are also observed. Electron-beam treatment leads to the formation of composite filled structure over the whole cross section of the remelted layer. The structure formed in this layer is more disperse and uniform than in coatings formed without electron-beam treatment. The inclusions of titanium carbide or titanium diboride in the molybdenum or nickel matrix are 2–4 times smaller than immediately after electroexplosive sputtering. Within the molybdenum or nickel grains and at their boundaries, rounded particles of secondary phase (titanium carbide or titanium diboride) are observed. They may be divided into two classes by size: particles of the initial powder (80–150 nm) that have not dissolved on irradiation; and particles formed on solidification of the melt (10–15 nm). In the electroexplosive powder coatings, the structure is mainly formed by dynamic rotation of the sprayed particles, which form a vertical structure both in the coating and in the upper layers of the substrate. The coatings have excellent operational properties: nano- and microhardness, elastic modulus of the first kind, and wear resistance in dry slipping friction.     

Structure and Properties of Wear-Resistant Detonation Coatings Based on Titanium Carbonitride

An investigation was made of the composition, structure and wear rate of detonation coatings on steel 30KhGSNA deposited from composite powders based on TiC_0.5N_0.5 with refractory additions of SiC, AlN, and a Ni – Cr metallic binder. It was shown that at a load of 10 MPa coatings based on titanium carbonitride exhibit substantially less wear and a larger range of sliding velocities with a stable value of wear than coatings of the hard alloy VK15 (WC – 15% Co). The physico-chemical reactions in the process of tribo-oxidation were analyzed.     

新型高强耐磨复杂黄铜及其生产技术

以β相为基的高强耐磨多元复杂黄铜是新近发展起来的并得到广泛应用的新型高技术含量、高附加值的铜合金品种，具有广阔的市场发展空间。本文系统地阐述了具有市场需求前景的高强耐磨复杂黄铜的种类及特性，重点介绍了典型合金产品的生产加工技术，希望对该类合金的生产及新品种的开发起到建设性的指导作用。     

用六价铬还原产物电镀铬

研究了不同还原剂与六价铬的还原反应和各种反应条件对还原率的影响。讨论了反应历程,确定了最佳反应条件。这种还原产物可以做为无毒性电镀铬的铬源。使用这种三价铬化合物进行了电镀试验,获得了厚度超过100μm的镀层。     

Optimization of Characteristics of Pyrolytic Chromium Carbide Coatings

Russian Journal of Non-Ferrous Metals - The optimization of characteristics of pyrolytic chromium carbide coatings (PCCCs) for various fields of industry is discussed. The scope of PCCC application...     

Effect of Cooling Rate on Structure and Properties of Wear-Resistant Low Chromium Cast Iron after Hot Deformation

Thereismuchinterestinwear resistantlow chromiumcastironforitshighhardnessandgood abrasionresistance.However,itstoughnessisvery lowduetothecontinuousnet shapeddistributionof carbide.Hotplasticdeformationcanbreakdownthe netcarbideandimprovecomprehensivemech…     

Effect of Chromium on the Structure and Properties of Boride Diffusion Coatings

We have studied the effect of the chromium concentration in an impregnating borochromating powder mixture on the change in the lattice parameters of the rhombic FeB phase of boride coatings on carbon steels, their microhardness, and the BK _α energy spectra. An increase in the microhardness of the boride phases for chromium concentration 3.5-6 mass% in powder boron-impregnating mixtures is accompanied by a decrease in the FeB lattice parameters. Interpretation of the BK _α spectra has allowed us to establish that this fact is due to an increase in the covalent component of the Fesd ― Bp bond.     

Heat-Resisting Aluminized Coatings Modified by Chromium Addition Produced on Nickel-Based Alloys

Aluminizing process is an important technology in which aluminum is introduced into the surface of base material. In this work, aluminized layers were produced by the pack cementation process on Inconel 600, Inconel 625 and Nimonic 90 nickel-based alloys. Powder mixture contained 80% of Al and 20% of Fe–Cr. Microstructure, hardness, chemical composition and heat resistance were investigated. The microstructure consisted of intermetallic phases near the surface, and below them, the solid solution was observed. The oxidation resistance at elevated temperature of alloys with the layer was compared with pure alloys. After 20-h annealing at 1000 °C, the phase analysis was carried out. On the Nimonic 90 with aluminized coatings, a lot of Cr₂O₃ and Al₂O₃ oxides were produced, whereas on the pure Nimonic 90, a lot of NiO oxides were observed. It was found that the best heat resistance was obtained for the layer produced on the Nimonic 90.     

Effect of Chromium on the Structure and Properties of Boride Diffusion Coatings

We have studied the effect of the chromium concentration in an impregnating borochromating powder mixture on the change in the lattice parameters of the rhombic FeB phase of boride coatings on carbon steels, their microhardness, and the BK _α energy spectra. An increase in the microhardness of the boride phases for chromium concentration 3.5-6 mass% in powder boron-impregnating mixtures is accompanied by a decrease in the FeB lattice parameters. Interpretation of the BK _α spectra has allowed us to establish that this fact is due to an increase in the covalent component of the Fesd ― Bp bond.

     

Features of the Formation of Wear-Resistant Coatings from Powders Prepared by a Micrometallurgical Process of High-Speed Melt Quenching

Metallurgist - Development of compositions and application of coatings by cold gas-dynamic deposition from powders prepared by means of a micrometallurgical method is studied. In addition, use of...     

粉末冶金法制高纯溅射铬靶材的方法

通过试验重点对粉末冶金法制备高纯溅射铬靶材的传统烧结工艺进行了分析和优化研究。试验结果表明,采用"模压+烧结"或者"冷等静压+烧结"的方式加工靶材,并合理控制烧结温度,能够有效保证靶材的密度。     

高纯氧化钇复合涂层的研制

本文采用等离子喷涂方法制备了氧化铝—氧化钇复合陶瓷涂层,研究涂层的制备工艺。通过SEM对涂层的微观组织进行分析研究。通过对涂层结合强度、孔隙率、沉积率和表面粗糙度的测试,研究涂层的综合性能。对单层氧化钇涂层和双层结构复合涂层进行性能对比,研究表明双层结构复合涂层具有更好的力学性能,在满足使用性能的同时,具有易清除再加工、易修复的特点。     

Preparation of Superconcentrate and Chromium Powder from Chromite Ore

Metallurgist - Non-traditional metallurgical technology of comprehensive processing of Sevan chromite (with a 43–46% Cr2O3 content) is developed allowing chromium extraction from local...     

Microstructure, Chemical and Phase Composition of Chromium Silicide Diffusion Coatings on Carbon Steels

The microstructure, chemical and phase composition of chromium silicide diffusion coatings on steels 20, 45, U8, and U10 are studied. It is established that the phases Cr²³C⁶ and Cr⁷C³ with a silicon content in them of up to 0.25 at.% form at the surface of chromium silicide coatings. The maximum silicon content at 7% in steels 20 and 45 is observed beneath the carbide layer at a depth of 40–50 µm, but for steel U10 it is 1.9% at the carbide layer-matrix boundary. It is shown that the corrosion resistance of chromium silicide diffusion coatings increases markedly compared with uncoated specimens: by a factor of 15–30 depending on the acid used (H₂SO₄, HCl, H₃PO₄, HNO₃, CH₃COOH). There is also an increase in the cavitation resistance of articles with chromium silicide coatings in water and 3% NaCl solution.__________Translated from Poroshkovaya Metallurgiya, Nos. 1–2(441), pp. 23–30, January–February, 2005.     

金属表面防腐用含聚四氟乙烯复合涂膜的研制

聚苯硫醚(PPS)和聚酰亚胺(PI)具有高温熔流性以及与金属表面良好的粘接性,将其与PTFE制成混合涂膜,即可以保持PTFE的耐腐蚀、耐高温和固体润滑的特点,又可与金属表面有良好的粘结强度。试制了PTFE PPS、PTFE PPS以及PTFE PPS PI三种复合涂料,经比较得知,PTFE PPS PI复合涂膜的性能最好,其附着力为1级,柔韧性达到1mm,冲击强度大于500N.cm。还考察了涂膜的耐腐蚀性和抗热震性。