High temperature behaviors of high velocity arc sprayed Fe-Al/Cr_3C_2 composite coatings

Fe-Al/Cr3C2 composite coatings were manufactured using high velocity arc spraying （HVAS） technology. The high temperature erosion, wear and corrosion resistance of the coatings were investigated. The coating properties such as bonding strength, porosity, hardness as well as microstructures were characterized. The results show that the coatings have relatively high heat tremble bond strength, hardness, and typical layer-shaped coatings＇ microstructures. With the rise of temperature, the coating erosion resistance increases too; the impingement angel does effects on erosion properties, and the erosion mechanism changes from ductile to brittle behaviors at 450℃. The coatings have good room temperature wear resistance and relatively good high temperature resistance. The wear mechanism of the coatings is peeling wear behavior. The coatings have excellent high temperature corrosion resistance because of the produce of oxides during corrosion.

Thermal Shock Resistances of FeMnCr/Cr_3C_2 Coatings Deposited by Arc Spraying

Arc spraying with the cored wires was applied to deposit FeMnCr/Cr3C2 coatings on low carbon steel substrates, namely FM1, FM2 and FM3. Thermal shock resistances of the coatings were investigated to assess the influence of Cr3C2 content on thermal shock resistance. Characteristics of the coatings under thermal cycling test were studied by optical microscopy, field emission scanning electron microscope （FE-SEM） and energy dispersion spectrum （EDS）, X-ray diffraction （XRD）. The experimental results show that hardness of the coatings increases, bonding strength decreases slightly with increase of the Cr3C2 content of the coatings. As a result, FM2 coating possesses the best thermal shock resistance, attributing to its better thermal expansion matches and wettability than those of FM3 coating, less oxide rate than that of FM1 coating restraining from cracks formation and propagation in coatings.

高速电弧喷涂FeAlCrNi/Cr_3C_2复合涂层的腐蚀性能研究

采用涂盐热腐蚀法研究了高速电弧喷涂(HVAS)FeA lCrN i/Cr3C2复合涂层的腐蚀特性,并用SEM、TEM、X射线衍射等手段分析了涂层的组织与性能、腐蚀表面和截面的形貌与成分。结果表明,复合涂层具有典型的层状结构和较高的力学性能;随着热腐蚀时间的增加,涂层的腐蚀速率呈现抛物线变化;随着热腐蚀温度升高,涂层的腐蚀增重增加较缓慢;腐蚀后涂层表面生成了氧化物和硫化物,其腐蚀机理为内氧化。

高速电弧喷涂FeAlCrNi/Cr_3C_2复合涂层的组织及高温性能

使用高速电弧喷涂技术制备FeAlCrNi/Cr3C2复合涂层,采用Philips Quant 200扫描电镜、德国D8 AdvanceX射线衍射仪、日立H800扫描电镜、GM/CS-MS高温冲蚀磨损试验装置,以及其它多种检测设备,对涂层的显微组织、相结构、机械性能、高温冲蚀、腐蚀和磨损性能进行研究。结果表明,复合涂层具有相对较好的抗热震性能和较高的硬度,良好的高温冲蚀、磨损和抗腐蚀性能。涂层的结合方式为机械结合为主;涂层主要由扁平组织、小颗粒和细小的氧化物与分散相、以及不足2%的孔隙组成。涂层的相结构复杂,且存在一些平行相如(001)FeAl//(111)AlFe3C0.5。

Wear resistance of surface metal matrix composite produced by gas tungsten arc melt injection of Cr3C2 -NiCr particles into low carbon steel

Cr3 C2-NiCr particles were injected into the melted surface of Q235 low carbon steel to make a surface metal matrix composite （MMC） layer by gas tungsten are melt injection （GTAMI） process. Hardness of the surface MMC layer was tested. Wear resistance of the surface MMC was investigated with a ball-on-disk dry sliding setup. Microstrnetures of the surface MMC layer and morphology of the worn surfaces were investigated with scanning electron microscopy （SEM）. The results showed that the hardness of the MMC was as high as 1 960. 7 HV. Wear loss of the upper part of the MMC layer is onlyO. 8% of that of the substrate under the dry sliding condition given. Wear loss of the bottom part is 2. 5 % of that of the substrate.

高速电弧喷涂FeAlCrNi/Cr_3C_2复合涂层的摩擦学特性

使用T11以及THT07-135型高温磨损试验机对高速电弧喷涂(HVAS)FeAlCrNi/Cr3C2复合涂层进行了滑动摩擦磨损特性的研究,并用SEM,TEM,X-ray等手段观察分析了磨痕的形貌和成分、涂层截面的组织和相结构。结果表明:FeAlCrNi/Cr3C2复合涂层具有典型的层状结构且有较高的结合强度和硬度;在常温和高温下,涂层的摩擦系数在开始阶段存在“跑合”现象;随着温度的升高,涂层的摩擦系数降低,耐磨损性能提高;剥层磨损是FeAlCrNi/Cr3C2复合涂层的主要磨损形式;Cr3C2增强相的加入,大大提高了涂层的耐磨损性能。

空气等离子喷涂NiCr/Cr2C3涂层的制备及抗热震性能

采用等离子喷涂技术制备了NiCr/Cr2C3涂层,并采用SEM、XRD、马弗炉和高温热膨胀仪对涂层的结构、物相和热震性能进行了表征。结果表明:等离子喷涂NiCr/Cr2C3涂层呈层状结构,涂层的主晶相为NiCr和Cr2C3相,涂层在700℃、800℃和850℃时抗热震性能良好,均满足使用要求。

Powder Extrusion Molding of Nanocrystalline WC-10Co Composite Cemented Carbide

The rods that were shaped from nanocrystalline WC- 10.21 Co-0.42 VC/ Cr3 C2 （ wt% ） composite powders by using powder extrusion molding （PEM） were investigated. The nanocrystalline WC- 10.21 Co- 0. 42 VC/ Cr3 C2 （ wt% ） composite powders were prepared by the spray thermal decomposition-continuous reduction and carburization technology. In order to improve the properties of rods shaped by using powder extrusion molding, the cold isostatic pressing （CIP） technology was used before or after debinding. Specimens were siutered by vacuum siutering and hot isostatic pressing （HIP）. The density, Rockwell A hardness, magnetic coercivity , and magnetic saturation induction of siutered specimen were measured. The microstructure of the green bodies and the siutered specimens was studied by scanning electron microscopy （SEM）. Results show that the rod formed by using powder extrusion molding after debinding and followed by cold isostatic pressing can be siutered to 99.5% density of composite cemented carbide rods with an average grain size of about 200- 300 nm, magnetic coercivity of 30.4 KA / m, Rockwell A hardness of 92.6 and magnetic saturation induction of 85% . Superfine WC- 10 Co cemented carbide rods with excellent properties were obtained.

Enhanced wetting and properties of carbon/carbon-Cu composites with Cr_3C_2 coatings by Cr-solution immersion method

A facile ammonium-dichromate solution immersion method was introduced to synthesize the copperwettable Cr3C2 coating on and inside the carbon-carbon （C/C） preform. The formation mechanism and the microstructures of the Cr3C2 coatings were studied. The contact angle between molten copper and the C/C decreased from 140°to 60°, demonstrating the significant improvement in the wettability. The Cr3C2- coated C/C-Cu composite with only 4.2% porosity and 3.69 gcm^-3 density was manufactured through copper infiltration. As a result, the thermal and electrical conductivity of the modified C/C-Cu increased significantly due to the infiltrated copper. Also the mechanical properties of the composites including both the flexural and compressive strengths were enhanced by over 100%. The modified C/C-Cu composite exhibited lower friction coefficients and wear rates for different load levels than those of the commercial C/Cu composite. These results demonstrate the potential of the modified C/C-Cu material for use in electrical contacts.

Microstructure and wear-resistant properties of NiCr–Cr_3C_2 coating with Ni45 transition layer produced by laser cladding

NiCr–Cr3C2 metal–ceramic composite coating is commonly produced on metal substrate by laser cladding to be used as wear-resistant coating under medium- or high-temperature working conditions.The coating has high hardness, generally over three times that of the substrate.In order to make the hardness increase gradually from substrate to coating surface, the nickel-based alloy Ni45 was chosen as the transition layer and Ni Cr–Cr3C2 coating was indirectly cladded on 20Cr2Ni4 A substrate.Microstructure and composition of the coating were characterized by scanning electron microscope(SEM), energy-dispersive spectroscopy(EDS) and X-ray diffraction(XRD).Microhardness of the cross section of the coating was measured.Friction and wear behavior of Ni Cr–Cr3C2coating and substrate were investigated through sliding against the Si C ball at 20, 100 and 300 °C.The morphologies of worn surfaces were analyzed by SEM and EDS.The results show that the hardness of Ni45 transition layer is between that of the substrate and Ni Cr–Cr3C2coating, which avoids hardness jump and stress concentration of the coating.Ni Cr–Cr3C2coating contains hard phases of Cr3C2 and Cr7C3which enhance the wear resistance.With thetemperature increasing, friction coefficient and wear rate of the substrate increase significantly.Compared with the substrate, Ni Cr–Cr3C2coating has lower friction coefficient and wear rate at 100 and 300 °C, which verifies the good wear resistance of NiCr–Cr3C2 coating.

Silt Erosion Characteristics of a Cr_3C_2-NiCr Coating Fabricated by High Velocity Oxy-Fuel (HVOF) Thermal Spray

A Cr3C2-NiCr coating was prepared by high velocity oxy-fuel(HVOF)thermal spray on 1Cr18Ni9Ti stainless steel.Phases and microstructures of the coating were investigated by X-ray diffraction(XRD),optical microscopy(OM)and scanning election microscopy(SEM),respectively.The cavitation erosion resistance and silt erosion resistance of the coating were evaluated using a GB/T6383-2009 standard method in two experimental conditions(fresh water and water contained fine silt),compared with the coatings hydro machine material 1Cr18Ni9Ti stainless steel.The coating shows a layered structure and has a significantly higher microhardness(11.97 GPa)than that of the 1Cr18Ni9Ti stainless steel(2.1 GPa),which results in less mass losses both in cavitation erosion and silt erosion experiment.The HVOF coating has a predominant performance in the cavitation erosion and silt erosion resistance.The higher microhardness of the coating is the main cause which results in a less mass losses in the erosion experiments.And the mass loss usually happens at the edges of the pores.

Microstructure evolution of nanostructured ferritic alloy with and without Cr3C2c oated SiC at high temperatures

This work focuses on fundamental understanding of microstructure evolution of nanostructured ferritic alloy(NFA) and 25 vol.% Cr3C2 coated Si C(Cr3C2@Si C)-NFA composite during spark plasma sintering at950°C and the following thermal treatment at 1000°C. A unique bi-phase microstructure with distinct Cr-rich and Si-rich phases has been observed for the 25 vol.% Cr3C2@Si C-NFA composite, while for the NFA sample, the traditional large grain microstructure remains. Grain sizes are significantly smaller for the25 vol.% Cr3C2@Si C-NFA composite compared to those for the pure NFA, which can be attributed to the presence of grain boundary phases in the composite sample. During the thermal treatment, microstructure features can be directly correlated with the dissolution kinetics and phase diagrams calculated using Thermo-Calc/DICTRA/PRISMA~?.

Wear-resistant coating spraying technique for wear-proofing cover of coke dry quenching furnace

During the operation of a coke dry quenching system of coking plant, wear-proofing cover of the boiler was seriously eroded, and even the ceiling tube of the boiler was worn and torn. Thus, attentions were paid to the research, development and application of the wear-resistant coating spraying technique for wear-proofing cover of the coke dry quenching furnace. The Cr3C2–NiCr coatings for wear-proofing cover were fabricated via supersonic arc spraying process, and the residual coating of wear-proofing cover would be sampled for being analyzed after two years. The coating presents a dense microstructure with few pores and micro-cracks (the porosity is 4.65%). After thermal spraying of the wear-proofing cover, the hardness and the wear resistance of the surface are improved. The remaining coating is continuous and compact, with an average thickness of about 147μm. Transverse micro-cracks parallel to the spreading direction of the coating surface are displayed on different areas of the coating, which demonstrates its serious erosion wear effect. The main chemical component of white zone is Fe–18Cr–Ni. The Cr level of light gray phase is about 77.57 wt.% and the O level is 22.43 wt.%. And the main chemical components of dark gray phase are C, O, Al, Si and Ca. X-ray diffraction patterns were adopted to implement phase analysis on the surface of coating sample, which indicated that the coating was composed of a large amount of Cr3O2 and a small amount of metal Cr.

炉底辊环防积瘤激光熔覆涂层的制备及应用

针对炉底辊表面结瘤的现象,利用激光熔覆方法在Ni基炉底辊环表面制备NiCr-Cr3C2涂层,通过试验分析了熔覆涂层的显微组织及硬度,研究其可行性,并通过实际上机使用,分别下机检验中温和高温段的使用状况。结果表明,该熔覆涂层具有高硬度、良好的高温抗氧化性和耐磨性,实际使用效果良好,用该方法制备的辊环较好的解决了炉底辊积瘤现象,延长了其使用寿命。