火焰重熔合金粉末等离子喷涂层

1 前言近年来,Ni-Cr-B-Si合金粉末作为热喷涂材料得到了广泛应用,对其工艺性、耐磨性已有了较深入的了解。然而,喷涂层在服役过程中与酸碱盐等腐蚀介质发生作用时,易产生腐蚀导致零件的失效。这个问题还没有得到应有的重视。为此,我们通过实验研究了Ni-Cr-B-Si合金粉末等离子喷涂层经火焰重熔处理后的耐腐蚀性能。

Tribological properties of nanostructured Al_2O_3-40%TiO_2 multiphase ceramic particles reinforced Ni-based alloy composite coatings

The Ni-based alloy composite coatings reinforced by nanostructured Al2O3-40%TiO2 multiphase ceramic particles were prepared on the surface of 7005 aluminum alloy by plasma spray technology. The microstructure and tribological properties of the composite coatings were researched. The results show that the composite coatings mainly consist of γ-Ni, α-Al2O3, γ-Al2O3 and rutile-TiO2 etc, and exhibit lower friction coefficients and wear losses than the Ni-based alloy coatings at different loads and speeds. The composite coating bears low contact stress at 3 N and its wear mechanism is micro-cutting wear. As loads increase to 6-12 N, the contact stress is higher than the elastic limit stress of worn surface, and the wear mechanisms change into multi-plastic deformation wear, micro-brittle fracture wear and abrasive wear. With the increase of speeds, the contact temperature of worn surface increases. The composite coating experiences multi-plastic deformation wear, fatigue wear and adhesive wear.

Effects of Ce in novel bronze and its plasma sprayed coating

A novel aluminum bronze over the Cu-Al binary alloy eutectoid Cu-14Al-4.5Fe was prepared by a jointly-charging one-melting technique and conventional sand casting. The bronze coatings were atmospherically plasma sprayed on the 45# medium carbon steel substrate. The effect of rare earth Ce on the microstructures and Vickers hardness of the cast alloy and coatings were characterized by scanning electron microscopy, X-ray diffraction, electronic probe microanalysis, transmission electron microscopy and microhardness measurements. The results indicate that the hardness of both as-cast alloy and coating are enhanced by the addition of 0.6% Ce due to the refinement of κ phases which are well distributed in the matrix. The rapid solidification in the plasma spray processing retains Fe-supersaturated in the Al-bronze alloy coatings, which avoids the formation of eutectoid （α＋γ2） phase and stacking faults are found in the coatings with Ce added, accordingly improves the mechanical properties.

Tribological properties of Ni-base alloy composite coating modified by both graphite and TiC particles

In order to reduce the friction coefficient of Ni-base alloy coating and further improve its wear resistance,Ni-base alloy composite coatings modified by both graphite and TiC particles were prepared by plasma spray technology on the surface of 45 carbon steel.The results show that friction coefficient of the composite coating is 47.45% lower than that of the Ni-base alloy coating,and the wear mass loss is reduced by 59.1%.Slip lines and severe adhesive plastic deformation are observed on the worn surface of the Ni-base alloy coating,indicating that the wear mechanisms of the Ni-base alloy coating are multi-plastic deformation wear and adhesive wear.A soft transferred layer abundant in graphite and ferric oxide is developed on the worn surface of the composite coating,which reduces the friction coefficient and wear loss in a great deal.The main wear mechanism of the composite coating is fatigue delamination of the transferred layer.

Tribological behavior and mechanisms of graphite/CaF_2/TiC/Ni-base alloy composite coatings

In order to reduce the friction coefficients and improve the wear resistance of mechanical parts, which work in the severe friction and wear conditions at heavy loads, the graphite/CaFg/TiC/Ni-base alloy composite coatings were prepared by plasma spray and their tribological behavior and mechanisms were investigated. The results show that the friction coefficients of the composite coatings are in the range of 0.22-0.288, which are reduced by 25.9% to 53% compared with those of the pure Ni-base alloy coatings, and the wear rates of the former are 18.6%-70.1% less than those of the latter. When wear against GCr15 steel balls, a transferred layer mainly composed of ferric oxides, graphite and CaF2 may gradually develop on the worn surface of the composite coatings, which made the friction and wear between GCr15 steel ball and the composite coatings change into that between the former and the transferred layer. So the friction coefficients and the wear lubrication effect of the transferred layer. The main wear layer in friction process. rates of the composite coatings are greatly reduced because of the solid mechanism of the composite coatings is delamination of the transferred

Effects of graphite content on microstructure and tribological properties of graphite/TiC/Ni-base alloy composite coatings

In order to reduce the friction coefficients and further improve the anti-wear properties of Ni-base alloy coatings reinforced by TiC particles,graphite/TiC/Ni-base alloy（GTN） coatings were prepared on the surface of 45 carbon steel.The effects of graphite content on the microstructure and tribological properties of the GTN coatings were investigated.The results show that the addition of graphite to the GTN coatings may greatly reduce the friction coefficients and improve their wear resistance.The 6.56GTN and 12.71GTN coatings exhibit excellent integrated properties of anti-friction and wear resistance under low and high loads,respectively.Under a low load,the wear mechanisms of the GTN coatings are mainly multi-plastic deformation with slight abrasive wear and gradually change into mixture of multi-plastic deformation,delamination and micro-cutting wear with the increase of graphite fraction.As the load increases,the main wear mechanisms gradually change from micro-cracks,micro-cutting and adhesive wear to micro-cutting and micro-fracture with the increase of graphite fraction.

Tribological behavior and mechanism of NiCrBSi-Y_2O_3 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.

Effect of TiO_2 content on properties of Al_2O_3 thermal barrier coatings by plasma spraying

Al2O3 thermal barrier coatings with different TiO2 contents were deposited on 6061 aluminum alloy by plasma spraying. The corrosion resistance, thermal insulation property and phase composition of these coatings were investigated. The results indicate that all the feedstock powders exhibit phase transformation during the spray process. With the increase of the TiO2 content in the powder, the corrosion resistance of the coating is enhanced but the thermal insulation property is decreased. This can be attributed to the higher thermal conductivity but lower melting point and brittleness of TiO2 than those of Al2O3, so it is easy for TiO2 to disperse in the brittle Al2O3 substrate during spraying, in which these dispersively distributed TiO2 play the role of hole sealing, releasing stress and reducing cracks.

Thermal stability and mechanical properties of thick thermal barrier coatings with vertical type cracks

The thermal stability and failure mechanism of thick thermal barrier coatings(TBCs) with and without vertical type cracks were investigated through the cyclic thermal exposure and thermal-shock tests. The TBC systems with thickness of about 2000 μm in the top coat were prepared by an air plasma spray(APS) on the bond coat of about 150 μm in thickness prepared by APS. The adhesive strength values of the as-prepared TBCs with and without vertical type cracks were determined to be 24.7 and 11.0 MPa, respectively, indicating the better interface stability in the TBC with vertical type cracks. The TBC with vertical type cracks shows a better thermal durability than that without vertical type cracks in the thermal cyclic exposure and thermal-shock tests. The hardness values of the as-prepared TBCs with and without vertical type cracks were found to be 6.6 and 5.3 GPa, respectively, which were increased to 9.5 and 5.5 GPa, respectively, after the cyclic thermal exposure tests. These results indicate that the vertical type cracks developed in the top coat are important in improving the lifetime performance of thick TBC in high temperature environment.

Ultrasonic characterization of modified Cr_2O_3 coatings by reflection coefficient spectroscopy

Pores,microcracks and density of plasma sprayed Cr2O3 coatings before and after high-intensity pulsed ion beam(HIPIB) irradiation were investigated using the ultrasonic reflection coefficient spectroscopy(URCS).The URCS was analyzed based on an acoustic transmission model for the multi-layered structure.The longitudinal velocity in the coatings was calculated from the experimental URCS,and the attenuation coefficient expression was deduced by comparing the experimental and numerical fitting amplitude spectral lines.The longitudinal velocity of as-sprayed Cr2O3 coating is 2 002 m/s,and increases to 2 099 and 2 148 m/s after being irradiated by HIPIB with 1 and 5 shots.Correspondingly,the factor A changes from 0.046 to 0.026 and 0.020 and n from 1.702 to 1.658 and 1.649 in the attenuation coefficient expression of α=Af n.It is observed that the surface morphology of Cr2O3 coatings changes from rough and porous to smooth and uniform with the increase of shot number,which accords with the ultrasonic analyses reasonably.The URCS seems to provide a convenient and nondestructive method to characterize surface modification of the plasma sprayed coatings.

Effect of MoSi_2 content on dielectric and mechanical properties of MoSi_2/Al_2O_3 composite coatings

Molybdenum disilicide （MoSi2） sheath and aluminum oxide （Al2O3） core blended powders were fabricated by spray drying. A derived coating material was produced for the application as microwave absorbers using the as prepared powders by atmospheric plasma spray （APS） technology. The effects of MoSi2/Al2O3 mass ratio on the dielectric and physical mechanical properties of the composite coatings were investigated. When the MoSi2 content of the composites increases from 0 to 45%, the flexure strength and fracture toughness improve from 198 to 324 MPa and 3.05 to 4.82 MPa-m1/2 then decline to 310 MPa and 4.67 MPa-m1/2, respectively. The dielectric loss tangent increases with increasing MoSi2 content, and the real part of permittivity decreases conversely over the frequency range of 8.2-12.4 GHz. These effects are due to the agglomeration of early molten MoSi2 particles and the increase of the electrical conductivity with increasing MoSi2 content.

Preparation and properties of supersonic atmospheric plasma sprayed TiB2−SiC coating

With the TiB2−SiC powders after spray granulation and vacuum calcination as raw materials,the TiB2−SiC coating was prepared by supersonic atmospheric plasma spraying(SAPS).The effects of spraying power and spraying distance on the properties of the TiB2−SiC coating were investigated and the fabrication processing of SAPS was optimized.The results show that the sprayed powders after calcination have a uniform particle size distribution,good sphericity and enhanced fluidity.The coating prepared by the calcined powders has a dense structure and high deposition efficiency.When the calcined TiB2−SiC powders are used and the spraying power is 95 kW and the spraying distance is 150 mm during supersonic plasma spraying,the obtained TiB2−SiC coating behaves the best comprehensive performance with the porosity,microhardness,bonding strength and resistivity equal to 5.6%,3.57 GPa,18.3 MPa and 10.8 mΩ·cm,respectively.

Comparative study on corrosion behavior of plasma sprayed Al_2O_3, ZrO_2, Al_2O_3/ZrO_2 and ZrO_2/Al_2O_3 coatings

ZrO2, Al2O3, ZrO2/Al2O3 and Al2O3/ZrO2 coatings were fabricated on low carbon steel using atmospheric plasma spraying technique. The microstructure and phase composition of the as-sprayed coatings were examined by scanning electron microscopy （SEM） and X-ray diffraction （XRD）, respectively. The polarization test, salt spray test and immersion test were used to investigate the corrosion behavior of the coatings in 3.5% NaCl solution. The results suggested that the bilayered Al2O3/ZrO2 coating exhibits superior corrosion resistance when compared with the other coatings. This is ascribed to the presence of very few interconnected pores and stable phases in the coating.

Influence of heat treatment on nanocrystalline zirconia powder and plasma-sprayed thermal barrier coatings

Nanostructured zirconia top coat was deposited by air plasma spray and NiCoCrAlTaY bond coat was deposited on Ni substrate by low pressure plasma spray.Nanostructured and conventional thermal barrier coatings were heat-treated at temperature varying from 1050 to 1 250oC for 2-20 h.The results show that obvious grain growth was found in both nanostructured and conventional thermal barrier coatings(TBCs)after high temperature heat treatment.Monoclinic/tetragonal phases were transformed into cubic phase in the agglomerated nano-powder after calcination.The cubic phase content increased with increasing calcination temperature.Calcination of the powder made the yttria distributed on the surface of the nanocrystalline particles dissolve in zirconia when grains grew.Different from the phase constituent of the as-sprayed conventional TBC which consisted of diffusionlesstransformed tetragonal,the as-sprayed nanostructured TBC consisted of cubic phase.

Oxidation resistance of Si-coated TZM alloy prepared through combined process of plasma spray and laser surface melting

Plasma thermal spraying ofSi coating layer ontitanium-zirconium-molybdenum （Ti-Zr-Mo）,TZM alloy,was conducted for the surface protection of the Mo substrate that is unstable in air at high temperatures. Although the plasma thermal spraying alone could protect the Mo alloy from oxidation at a high temperature for a short time, the post laser surface melting process further improved the oxidation resistance of Si-coated alloy. In the case of the post laser treated specimen,MoSi compounds, mainly MoSi2 phases, were formed during the additional annealing process, and the oxidation resistance could be even further enhanced. The corrosion behaviors of Si-coated specimens in 3.5%NaCl solution were also investigated;however,nosignificant variations with respect to the post treatment procedure were found.

The influence of MoS_2 on tribology characteristic parameter of Ni60A/MoS_2 composite lubricating coating

The influence of MoS2 on the tribology characteristic parameter of Ni60A/MoS2 composite lubricating coating was researched on the UMT-2 fretting abrasion tester （USA） The result shows that with increasing content of MoS2, the hardness curve of the composite coating decreases and the trend accelerates. Under the same experimental conditions, the mass loss of plasma spray composite coating without adding MoS2 iS 1.27×10^-2 mg. When the amount of MoS2 reaches 35%, the mass loss is 0.96×10^-2 mg. It can be seen that adding MoS2 phase can improve the wear resistance, the amplitude of which is close to 30%. The friction coefficient of plasma spray composite coating without adding MoS2 is 0.23. Adding MoSz could decrease the friction coefficient of the coating and presents a downtrend. When the mass fraction is 35%, the friction coefficient is the smallest （0.13）, and the range is doubled.

TBCs for Gas Turbines under Thermomechanical Loadings： Failure Behaviour and Life Prediction

The present contribution gives an overview about recent research on a TBC （thermal barrier coating） system consisted of （I） an intermetallic MCrAIY-alloy BC （bond coat） applied by VPS （vacuum plasma spraying） and （2） an YSZ （yttria stabilised zirconia） top coat APS （air plasma sprayed） at Forschungszentrum Juelich, Institute of Energy and Climate Research （IEK-2）. The influence of high temperature dwell time, maximum and minimum temperature on crack growth kinetics during thermal cycling of such plasma sprayed TBCs is investigated using scanning electron microscopy and AE （acoustic emission） analysis. Thermocyclic life in terms of accumulated time at maximum temperature decreases with increasing high temperature dwell time and increases with increasing minimum temperature. AE analysis proves that crack growth mainly occurs during cooling at temperatures below the ductile-to-brittle transition temperature of the BC. Superimposed mechanical load cycles accelerate delamination crack growth and, in case of sufficiently high mechanical loadings, result in premature fatigue failure of the substrate. A life prediction model based on TGO growth kinetics and a fracture mechanics approach has been developed which accounts for the influence of maximum and minimum temperature as well as of high temperature dwell time with good accuracy in an extremely wide parameter range.

Microstructure,formation mechanism and properties of plasma-sprayed Cr_(7)C_(3)−CrSi_(2)−Al_(2)O_(3)coatings

The Cr_(7)C_(3)−CrSi_(2)−Al_(2)O_(3)composite coatings were prepared by plasma spraying Cr_(7)C_(3)−CrSi_(2)−Al_(2)O_(3)and Al−Cr2O3−SiC composite powders,respectively.The microstructure,formation mechanism and properties of the two Cr_(7)C_(3)−CrSi_(2)−Al_(2)O_(3)composite coatings obtained by plasma spraying were investigated,and the reaction mechanism of the Al−Cr_(2)O_(3)−SiC system was explored.The results show that the coating obtained by plasma spraying Al−Cr_(2)O_(3)−SiC composite powders had thinner lamella and more tortuous interlayer interface,and the in-situ synthesized Cr_(7)C_(3),CrSi_(2) and Al_(2)O_(3) in the coating were all nano-crystallines.Compared with the Cr_(7)C_(3)−CrSi_(2)−Al_(2)O_(3)coating prepared by plasma spraying Cr_(7)C_(3)−CrSi_(2)−Al_(2)O_(3)composite powders,the plasma-sprayed Cr_(7)C_(3)−CrSi_(2)−Al_(2)O_(3)coating obtained from Al−Cr_(2)O_(3)−SiC composite powders had higher density,higher microhardness(increased by 20%),better fracture toughness and lower wear rate(reduced by 28%).

Development of Solid Oxide Fuel Cell Technology at the Institute of Nuclear Energy Research

This paper shows the development of solid oxide fuel cell （SOFC） technology at the Institute of Nuclear Energy Research. In the development, fabrication processes for planar anode-supported-cell （ASC） by conventional methods and metal-supported-cell （MSC） by atmospheric plasma spraying are well established. Procedures and techniques for stacking and cell/stack performance tests are continuously improved to enhance the quality and reliability. Innovative nano-structured catalysts, in which reduced Pt and CeOz particles dispersed onto the A120~ carriers can effectively prevent the migration and coalescence of the metal crystallites, are thermal stable and possess a conversion ratio higher than 95% for reforming of natural gas. A non-premixed after-burner/reformer is designed and fabricated, and it has passed the prerequisite functional tests. Layouts including stacks, components of BOP, power conditioning and control as well as gases and water supply, are designated for a 1-kW SOFC power system. In compliance with system requirements, operating modes, data acquisition, power conditioning, instrumentations, and control logics have been identified and settled. After successive system validation tests, two modules of 18-cell stacks are allocated into the SOFC system. Test results indicate a thermal self-sustaining system on natural gas is achieved with a power output of around 760 watts.

Development of an Emulator for the Plasma Process Control

This work aims at developing an automatic system for the control of the APS （air plasma spraying） plasma process in which some instability phenomena are present. APS is a versatile technique to produce coatings of powder material at high deposition rates. Using this technique, powder particles are injected into a plasma jet, where they are melted and accelerated towards a substrate. The coating microstructures and properties depend strongly on the characteristics of the plasma jet, which can be controlled by the adjustment of the process parameters. However, the imeractions among the spray variables, render optimization and control of this process are quite complex. Understanding relationships between coating properties and process parameters is mandatory to optimize the process technique and the product quality. We are interested in this work to build an on-line control model for the APS process based on the elements of artificial intelligence and to build an emulator that replicates the dynamic behavior of the process as closely as possible.