7A52铝合金-钢异种结构CMT熔钎焊接头组织及镀镍层的行为与影响

以ER4043铝硅焊丝为填充金属,研究了Q235钢螺柱与7A52铝合金板CMT焊接工艺,在焊接电流115~135 A,电弧电压14.5~16.5 V,焊接速度0.3 m/min条件下,焊接过程稳定,焊缝成形连续美观.结果表明,7A52铝合金侧熔合区界面为熔焊特征,铝母材发生熔合,熔合良好;钢螺柱侧熔合区为钎焊特征,界面存在反应层,由靠近钢螺柱的Fe₂Al₅层和靠近焊缝侧的FeAl₃层组成,整体反应层厚度由根趾向焊趾方向逐渐减小.焊趾部位出现富镍区,主要由Al₃Ni的共晶组织及少量Al₃Ni₂组成.与无镀镍层焊缝比较表明,镀镍层在焊接过程的行为降低了界面反应层厚度,且通过形成富镍区,降低了接头的脆性,使接头抗剪切强度提高了15%~19%,最高达到146.9 MPa,满足了高强铝合金螺柱焊接的质量要求.     

Microchemical and microstructural studies in a PTA weld overlay of Ni-Cr-Si-B alloy on AISI 304L stainless steel

Ni-Cr-Si-B alloy coatings deposited on AISI 304L stainless steel substrate using plasma transferred arc welding process were studied with respect to the microchemical and microstructural modifications that take place during the process. The coating was characterized for (1) interface integrity and dilution (2) type, morphology and distribution of secondary phases in the coating (3) elemental redistribution between substrate and coating and (4) different phases that form during the deposition process. Formation of a transition zone of only 760 μm width was understood in terms of interdiffusion of Fe and Ni across the interface. Preferential redistribution of carbon to the surface of the coating was observed. It was explained on the basis of difference in thermodynamic activity. Apart from γ-Ni solid solution, the other primary phases identified in Ni-Cr-Si-B alloy were Cr₂B, Cr₇C₃ and Cr₃C₂. The observed changes in microstructure, microchemistry and hardness have been understood based on the phase transitions of the Ni rich alloy during solidification and cooling on the substrate.     

Formation of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Diffusion Barrier Between Cr-Contained Stainless Steel and Cold-Sprayed Ni Coatings at High Temperature

A novel approach to prepare a coating system containing an in situ grown Cr₂O₃ diffusion barrier between a nickel top layer and 310SS was reported. Cold spraying was employed to deposit Ni(O) interlayer and top nickel coating on the Cr-contained stainless steel substrate. Ni(O) feedstock was prepared by mechanical alloying of pure nickel powders in ambient atmosphere, acting as an oxygen provider. The post-spray annealing was adopted to grow in situ Cr₂O₃ layer between the substrate and nickel coating. The results revealed that the diffusible oxygen can be introduced into nickel powders by mechanical alloying. The oxygen content increases to 3.25 wt.% with the increase of the ball milling duration to 8 h, while Ni(O) powders maintain a single phase of Ni. By annealing the sample in Ar atmosphere at 900 °C, a continuous Cr₂O₃ layer of 1-2 μm thick at the interface between 310SS and cold-sprayed Ni coating is formed. The diffusion barrier effect evaluation by thermal exposure at 750 °C shows that the Cr₂O₃ oxide layer effectively suppresses the outward diffusion of Fe and Cr in the substrate effectively.     

Thermal shock resistance of FeMnCrAl/Cr3C2-Ni9Al coatings deposited by high velocity arc spraying

FeMnCrAl/Cr₃C₂ and FeMnCrAl/Cr₃C₂-Ni9Al coatings were deposited onto low-carbon steel substrates by high velocity arc spraying. The cross-section and interface microstructures of the coatings were analyzed by optical microscopy (OM). The thermal shock resistance of the coatings was investigated. The characteristics of the coatings after the thermal cycling test were studied by OM, field emission scanning electron microscopy, and energy dispersion spectrometry. The results show that laminated structures with pores, oxide phases, and unmelted particles were found on all the prepared coatings. The FeMnCrAl/Cr₃C₂ coating with a Ni9Al interlayer registered the best thermal shock resistance, which may be attributed to the interdiffusion between the low-carbon steel substrates and the Ni9Al arc-sprayed coating that converted the mechanical bond between the substrates and the coatings to a metallurgical one.     

Oxidation behavior of arc-sprayed FeMnCrAl/Cr3C2-Ni9Al coatings deposited on low-carbon steel substrates

FeMnCr/Cr₃C₂ and FeMnCrAl/Cr₃C₂ coatings, using Ni9Al arc-sprayed coating as an interlayer on low-carbon steel substrates, were deposited by high velocity arc spraying (HVAS) on the cored wires. The high temperature oxidation behavior of the arc-sprayed FeMnCrAl/Cr₃C₂-Ni9Al and FeMnCr/Cr₃C₂ coatings on the low-carbon steel substrates was studied during isothermal exposures to air at 800 °C. The surface and interface morphologies of the coatings after isothermal oxidation after 100 h were observed and characterized by optical microscopy, field emission scanning electron microscope, energy dispersion spectrum, and X-ray diffraction. The results showed that the oxidation weight gains of the coatings were significantly lower than that of the low-carbon steel substrate. Moreover, the FeMnCrAl/Cr₃C₂-Ni9Al coating registered the lowest oxidation rate. This favorable oxidation resistance is due to the Al and Cr contents of the aforementioned coating that inhibits the generation of Fe and Mn oxides. This is attributed to the interdiffusion between the substrates and the Ni9Al arc-sprayed coating, which can convert the mechanical bonding between substrates and coatings into a metallurgical one, thereby inhibiting the oxidation of interface between the low-carbon steel and the coating.     

Microstructure and abrasive wear performance of chromium carbide reinforced Ni3Al matrix composite coating

A Ni-Al-Cr₃C₂ welding wire was produced by metal-powder-core technique. When the welding wires were welded on the surface of carbon steel, under the effect of the physical heat of arc, Ni reacted with Al to form Ni₃Al and carbide particles reinforced Ni₃Al matrix composite was formed. Cr₃C₂ was decomposed during welding and dispersed Cr₇C₃ with stripe shape formed, which strengthened the matrix significantly. The Cr₇C₃-Ni₃Al interface has broadened into a zone of interdiffusion and a new phase M₂₃C₆, which indicates that a good bond has been formed. The pin-abrasion wear test showed that the abrasion resistance of Cr₇C₃/Ni₃Al composite is six times higher than that of Stellite12 alloy at room temperature. The good wear resistance of Cr₇C₃/Ni₃Al composite coating can be attributed to large volume fraction of carbides, high hardness, and good phases interface bond.     

A comparative study of laser cladding high temperature wear-resistant composite coating with the addition of self-lubricating WS2 and WS2/(Ni–P) encapsulation

In order to inhibit its decomposition and improve its compatibility with the metal matrix during laser cladding, WS₂ powder was encapsulated with a layer of micro Ni–P by electroless plating. The microstructure and tribological properties of the NiCr–Cr₃C₂/30%WS₂ and NiCr–Cr₃C₂/30%WS₂(Ni–P) high temperature self-lubricating wear-resistant composite coatings at RT (room temperature), 300 °C and 600 °C were investigated, respectively. It was found that the NiCr–Cr₃C₂/30%WS₂(Ni–P) coating had a microstructure consisting of primary Cr₇C₃ dendrite, γ-(Fe,Ni)/Cr₇C₃ eutectic and solid lubricant particles WS₂ and CrS, Ni–P electroless plating had decreased the decomposition of WS₂ to some extent, the WS₂ solid lubricant particles dispersed in the ductile γ-(Fe,Ni)/Cr₇C₃ matrix. Friction and wear experiments indicated that the tribological properties of the NiCr–Cr₃C₂/30%WS₂(Ni–P) coating was better than that of NiCr–Cr₃C₂/30%WS₂ coating, the NiCr–Cr₃C₂/30%WS₂(Ni–P) coating presents lower friction coefficient at RT and 300 °C and lower wear rate from RT to the elevated temperature of 600 °C.     

Preparation and hot corrosion behaviour of a MCrAlY + AlSiY composite coating

A MCrAlY + AlSiY composite coating was prepared by arc ion plating. Hot corrosion behaviours of the composite coating and the reference NiCoCrAlYSiB coating were investigated. The results indicate that the composite coating consisted of β-(Ni,Co)Al with dispersed σ-NiCoCr and Cr₃Si in outer layer and Cr-rich phases in inner layer after annealing. As being corroded for 200 h, the composite coating proved better corrosion resistance than that of reference NiCoCrAlYSiB coating. The enhanced corrosion resistance of the composite coating was due to the gradient distribution of Al-enriched outer layer and Cr-enriched inner layer.     

Microstructure and corrosion properties of plasma-sprayed NiCr-Cr3C2 coatings comparison with different post treatment

The effects of laser and plasma arc remelting on the microstructure and properties of plasma-sprayed NiCr-Cr₃C₂ coatings on steel substrates have been investigated. The microstructure of the coatings has been analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). It is found that the Cr₃C₂, δ-(Cr,Ni), Cr₇C₃ and Cr₂₃C₆ phases were obtained for both coatings, before and after remelting treatment. The laser remelting was operated in a continuous way with 800 W power in different scan speed, while the plasma arc remelting was operated with a plasma cladding machine under different scan currents. However, the denser microstructure of both remelted coatings can be obtained, especially for the plasma arc remelted coating. The Vickers microhardness measurement showed certain enhancement values for both remelted coatings. The corrosion behavior was evaluated through salt spray corrosion (SSC) method. Energy-dispersive spectroscopy (EDS) showed that the chloride was produced during SSC process. The higher corrosion resistance for plasma arc remelted coating may be due to the more compact microstructure, less porosity rate and tensile residual stress. Compared with laser remelting method, plasma arc remelting is a cheap, convenient and effective remelting method.     

Chromium-nitride in situ composites with a compositional gradient formed by reactive DC plasma spraying

Nitrides of transition metals have good wear- and corrosion-resistant properties because of their high hardness and chemical stability. Chromium-nitride coatings can be deposited by ion plating; however, the thin thickness due to the slow deposition rate must be improved for severe wear-resistant applications. The main objective in this paper is to realize good structural control in the processing of chromiumnitride in situ composite coatings formed at a high deposition rate. They were synthesized by reactive low-pressure plasma spraying using elemental chromium powder as a spray material. The transferred arc between the gun electrode and the substrate was used to accelerate the nitriding reaction. The sprayed coatings consist of chromium, Cr₂N, and CrN, which have a composition gradient from the substrate interface to the surface. The volume fraction of Cr₂N increases with transferred arc current, and nonreacted chromium concurrently decreases, except close to the substrate. The CrN phase, however, only exists as a surface layer of 20 to 30 μm because it is decomposed to Cr₂N above 1420 K. The hardness of the composite coatings depends on the volume fraction of Cr₂N, and it increases to 1300 HV at a Cr₂N volume fraction of 0.98. The seizure stress with lubricant depends on the coating hardness. The maximum seizure stress of 24.9 MPa is obtained at a hardness of 1300 HV. The composite coatings also show a superior wear resistance. Hence, the Cr₂N in situ composite coatings synthesized by reactive plasma spraying with transferred arc are expected to be good candidates for wear-resistant applications.     

Corrosion properties of materials coated with Cr2O3/NiCr and with Cr2O3+NiCr functionally gradient materials

This paper studied the corrosion properties of five kinds of Cr₂O₃ coated materials: the SUS316L austenitic stainless steels respectively coated with the Cr₂O₃ layer (Cr₂O₃/316), Cr₂O₃ and 80Ni‐ 20Cr layers (Cr₂O₃/80NiCr/316), Cr₂O₃ and 50Ni‐ 50Cr layers (Cr₂O₃/50NiCr/316), Cr₂O₃ + 80Ni‐ 20Cr functionally gradient materials (Cr₂O₃ + 80NiCr FGM), and Cr₂O₃ + 50Ni‐ 50Cr FGM (Cr₂O₃ + 50NiCr FGM). All the coatings were made by atmospheric pressure plasma spraying method (APPS). The corrosion resistance of the coated materials was analyzed by immersion tests and electrochemical evaluations. A mechanism of the corrosion failures for these kinds of coated structures was proposed. The different coating structures for improving the adhesion between ceramics and substrates were assessed, and the effect of Cr content in the NiCr coatings on the corrosion property was discussed. The ceramic coatings with the 50Ni‐ 50Cr intermediate layer possessed a better corrosion resistance than that with 80Ni‐ 20Cr. The FGM structures appeared to offer weaker resistance to corrosion attack than that with the intermediate layer in general. Under corrosion test conditions, the corrosion‐proof abilities of the coated structures were, respectively: the Cr₂O₃/50NiCr/316 in the best rank; the Cr₂O₃/316, Cr₂O₃/80NiCr/316, and Cr₂O₃ + 50NiCr FGM in the second rank; and the Cr₂O₃ + 80NiCr FGM in the last rank. This means that applying the 50NiCr intermediate layer under the Cr₂O₃ ceramic coating can further improve the corrosion resistance of Cr₂O₃/316. Porosity analysis was used to explain the difference of corrosion resistance between the Cr₂O₃/50NiCr coated material and the Cr₂O₃ + 50NiCr FGM. The porosity in each layer of the Cr₂O₃ + 50NiCr FGM was higher than that in the Cr₂O₃/50NiCr coating, and as a result the corrosion resistance of Cr₂O₃/50Ni Cr/316 is better than Cr₂O₃ + 50NiCr FGM.     

超音速火焰喷涂Cr3C2/NiCr涂层抗加沙空蚀性分析

采用HVOF技术在1Cr18Ni9Ti不锈钢基体上制备了Cr3C2/NiCr涂层,借助XRD,TEM,SEM等方法分析了涂层的组织形貌及相组成.以1Cr18Ni9Ti奥氏体不锈钢作为对比材料,用磁致伸缩空蚀仪配备扬沙装置测试了涂层在清水以及含沙水中抗空蚀性能.结果表明,涂层呈层状结构,含有未熔颗粒和少量孔隙,涂层由Cr3C2,Cr7C3,Cr23C6及NiCr等相组成;在清水试验中,1Cr18Ni9Ti不锈钢抗空蚀性能良好,与空蚀过程中1Cr18Ni9Ti奥氏体不锈钢产生加工硬化有直接关系;在含沙40 kg/m3试验水中,Cr3C2/NiCr涂层呈现出较好的抗空蚀性能,与涂层自身相组成以及较高硬度有关.Cr3C2/NiCr涂层破坏总是从孔隙等薄弱环节开始,而1Cr18Ni9Ti奥氏体不锈钢的破坏起始于晶界和孪晶界.     

Mechanical and Tribological Properties of HVOF-Sprayed (Cr<Subscript>3</Subscript>C<Subscript>2</Subscript>-NiCr+Ni) Composite Coating on Ductile Cast Iron

The aim of the investigations was to compare the microstructure, mechanical, and wear properties of Cr₃C₂-NiCr+Ni and Cr₃C₂-NiCr coatings deposited by HVOF technique (the high-velocity oxygen fuel spray process) on ductile cast iron. The effect of nickel particles added to the chromium carbide coating on mechanical and wear behavior in the system of Cr ₃ C ₂ -NiCr+Ni/ductile cast iron was analyzed in order to improve the lifetime of coated materials. The structure with particular emphasis of characteristic of the interface in the system of composite coating (Cr ₃ C ₂ -NiCr+Ni)/ductile cast iron was studied using the optical, scanning, and transmission electron microscopes, as well as the analysis of chemical and phase composition in microareas. Experimental results show that HVOF-sprayed Cr₃C₂-NiCr+Ni composite coating exhibits low porosity, high hardness, dense structure with large, partially molten Ni particles and very fine Cr₃C₂ and Cr₇C₃ particles embedded in NiCr alloy matrix, coming to the size of nanocrystalline. The results were discussed in reference to examination of bending strength considering cracking and delamination in the system of composite coating (Cr ₃ C ₂ -NiCr+Ni)/ductile cast iron as well as hardness and wear resistance of the coating. The composite structure of the coating provides the relatively good plasticity of the coating, which in turn has a positive effect on the adhesion of coating to the substrate and cohesion of the composite coating (Cr₃C₂-NiCr+Ni) in wear conditions.     

Microstructures and mechanical properties of AZ91D/0Cr19Ni9 bimetal composite prepared by liquid-solid compound casting

The liquid-solid compound casting technology was used to produce the AZ91D/0Cr19Ni9 bimetal composite without and with hot dipping aluminium, respectively. The influences of Al coating on microstructures and mechanical properties of AZ91D/0Cr19Ni9 interface were investigated. The results showed that the mechanical bonding was obtained between AZ91D and bare steel 0Cr19Ni9 where a gap existed at the interface; the metallurgical bonding was formed between AZ91D and Al-coated 0Cr19Ni9, which could be divided into two different intermetallic layers: layer I was mainly composed of α-Mg+β-Mg₁₇Al₁₂ eutectic structure and a small amount of MgAl₂O₄, and layer II mainly comprised of Fe₂Al₅ intermetallic compound. Furthermore, the hardness value of interface was obviously higher than that of AZ91D matrix, and the average hardness values of layers I and II were HV 158 and HV 493, respectively. The shear strength of AZ91D/Al-coated 0Cr19Ni9 interface was higher than that of AZ91D/bare 0Cr19Ni9 interface, which confirmed that Al coating could improve the adhesive strength between AZ91D and 0Cr19Ni9 during liquid-solid compound casting process.     

Effect of flow velocity on cavitation erosion behavior of HVOF sprayed WC-10Ni and WC-20Cr3C2–7Ni coatings

WC-10Ni and WC-20Cr₃C₂–7Ni coatings were deposited successively using high-velocity oxygen-fuel (HVOF) spraying. The microstructures and mechanical properties of the coatings were evaluated by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), Vickers microhardness tester, and Ultra nanoindentation tester. The cavitation erosion behaviors of the coatings at different flow velocities were investigated by a rotating disk rig facility with bolt cavitator and circulating system. The results showed that the main phases in the WC-10Ni and WC-20Cr₃C₂–7Ni coatings were WC, W₂C, W, and WC, (W,Cr)₂C, respectively. Both coatings were dense and well bonded to the steel substrate. Despite higher porosity and elastic modulus (E) as well as slightly lower hardness (H), the WC-10Ni coating showed lower H/E, H³/E² and η values as well as cavitation erosion resistance at each flow velocity compared to the WC-20Cr₃C₂–7Ni coating. Both coatings exhibited an increase in the volume loss rates with increasing flow velocity, and the critical flow velocity of the WC-20Cr₃C₂–7Ni coating was in the region of 33.5 to 41.9 m·s⁻¹. The cavitation erosion failure mechanism of the WC-10Ni coatings was the brittle detachment of the WC particles, while cavitation pinholes, pits, cracks, craters, and massive exfoliation contributed to the evolution of the cavitation erosion processes of the WC-20Cr₃C₂–7Ni coating with the increase of the flow velocity.     

Influence of Water Vapor on the Cyclic-Oxidation Behavior of a Low-Pressure Plasma-Sprayed NiCrAlY Coating

The oxidation of a low-pressure plasma-sprayed (LPPS) NiCrAlY coating on a nickel-base superalloy was studied at 1050 °C in flows of O₂, and mixture of O₂ and 5% H₂O under atmospheric pressure. Water vapor has an obvious effect on the cyclic oxidation of the NiCrAlY coating. There is more decrease in weight gain when exposure to O₂ is replaced by exposure to O₂ + 5% H₂O. The oxide formed on the LPPS NiCrAlY coating after cyclic oxidation in pure oxygen is composed mainly of Cr₂O₃, and a thin Al₂O₃-rich layer is formed at the interface between the Cr₂O₃-rich layer and the coating. The oxide formed on the LPPS NiCrAlY coating after cyclic oxidation in a mixture of O₂ + H₂O is composed of NiCr₂O₄, NiO and Cr₂O₃. The effect of water vapor on the oxidation of the NiCrAlY coating may be attributed to an increase in Ni and Cr cation transport, stress-corrosion cracking of Al₂O₃ and moisture-enhanced volatility of the Cr₂O₃ scale.     

Microstructure and wear resistance of TaC reinforced Ni-based coating by laser cladding

The in situ synthesized TaC particulate reinforced Ni-based composite coating was fabricated on a mild steel by laser cladding of powder mixture of Ni60 alloy powder with (Ta₂O₅ + C)-doping. The microstructure and wear resistance of the TaC/Ni60 composite coating were investigated. It is shown that the coating is bonded metallurgically to the substrate and has a homogeneous fine microstructure containing both approximate cubic TaC particle and acicular chromium carbide uniformly dispersed in the dual phase matrix of γ(Ni) solid solution and eutectic of Cr₃C₂, Fe₂B with γ(Ni). Compared to a Ni60 coating, the hardness of the TaC/Ni60 composite coating was enhanced by a factor of 1.38, could achieve a Vicker microhardness of Hv_0.31100. And the wear rate in a block on ring test against hardened steel was reduced by a factor of five. This is attributed to the presence of in situ synthesized TaC particles and their well distribution in the coating.     

Inconel617合金表面电子束熔覆NbMoCr显微组织和耐腐蚀性的探讨

为了提高Inconel617合金(简称617合金)材料的表面性能,利用电子束熔覆技术在617合金表面制备了NbMoCr熔覆层. 对它的显微组织、硬度和耐腐蚀性能进行了研究,并与617合金进行了对比. 结果表明,NbMoCr熔覆层的组织更均匀,晶粒更细小,气孔等缺陷更少,且生成了微量M₂₃C₆,Cr₇C₃,Cr₄Si₄Al₁₃,CoCx等硬质相,提高了熔覆层的表面硬度及耐腐蚀性. 经检测,熔覆层硬度相比617合金硬度高出86 HV10. 电化学腐蚀测试表明,在1 mol/L H₂SO₄溶液中,617合金自腐蚀电流密度是NbMoCr熔覆层的5.16倍;在3.5 %的NaCl溶液中,617合金自腐蚀电流密度是NbMoCr熔覆层的4.6倍;在1 mol/L NaOH 溶液中,617合金自腐蚀电流密度是NbMoCr熔覆层的3.12倍.     

Corrosion Behavior of an Abradable Seal Coating System

A novel NiTi/BN composite abradable coating and two traditional Ni/C and Ni/BN coatings were manufactured with NiAl as the bond layer using thermal spray technology and their corrosion behaviors were investigated. In salt spray corrosion testing of the Ni/BN coating, defective sites of the metal matrix were corroded preferentially. Simulated occlusion experiments and electrochemical tests indicated that migration of ions resulted in pH decrease and Cl^? enrichment in defects, and a more aggressive electrolyte led to a decrease of the corrosion potential of the metal inside defects but an increase of the corrosion current density, representing an autocatalytic corrosion process. Moreover, galvanic corrosion between the top and bond coatings of the abradable system was studied via the electrochemical technique. The results showed that, for the NiTi/BN, Ni/BN, and Ni/graphite coatings with a NiAl bond coating, current flow was generated between the anode and cathode. The NiTi/BN coating acted as the cathode due to its passivation, while the Ni/BN and Ni/graphite coatings acted as the anode because of their lower corrosion potential compared with the NiAl coating. The anode suffered serious corrosion damage due to galvanic corrosion, while the cathode corroded only slightly.     

Effect of compositions on the microstructure and properties of plasma clad NiAl coating

NiAl intermetallic coating was in-situ synthesized by the plasma cladding process. The effect of atomic ratio of Ni to Al atoms 1 (coating 1), 2 (coating 2) and 3 (coating 3) on the microstructure and mechanical properties of plasma clad was studied by combining microstructural analysis and wear-resistant test. The obtained results indicated that the microstructure of the synthesized NiAl coating was compact and uniform in addition to few porosities and the NiAl coating well metallurgically bonded with the substrate. Coating 1 is mainly composed of NiAl and the solid solution γ-(Fe,Ni) phases. Coating 2 contains of NiAl, Ni₃Al and γ-(Fe,Ni). Coating 3 is mainly composed of Ni₃Al, γ-(Fe,Ni) and NiAl. Coating 3 has excellent wear-resistance property owing to high hardness and low friction coefficient. Ni3Al phase has great influence on wear-resistance property of coating 3. The main wear mechanism of coating 1 is multi-plastic deformation wear and adhesion wear. Grain abrasion is the main wear mechanism of coating 3. The main wear mechanism of coating 2 is grain abrasion and partly adhesive wear.