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.     

高速电弧喷涂FeMnCrAl/Cr3 C2涂层热腐蚀行为

用高速电弧喷涂技术和自行研发的FeMnCrAl/Cr3C2粉芯丝材,在20钢样品表面制备了FeMnCrAl/Cr3C2涂层,采用光学显微镜、场发射扫描电镜、能谱分析和X射线衍射等方法,对FeMnCrAl/Cr3C2涂层的显微组织和热腐蚀行为进行了研究,并与20钢做了对比试验研究.结果表明:FeMnCrAl/Cr3C2涂层主要由固溶相的凝片叠加组成,中间夹杂着氧化物相、未熔颗粒相和孔隙;FeMnCrAl/Cr3C2涂层抗热腐蚀性能明显优于20钢基体,热腐蚀增重约为20钢的1/3-1/4,涂层抗腐蚀性能提高的原因主要是:涂层热腐蚀后表面生成具有保护性的、致密的含Al、Cr氧化物和Cr与Fe的复合氧化物,阻碍了涂层进一步腐蚀.     

高速电弧喷涂FeMnCrAl/Cr_3C_2涂层的抗高温冲蚀磨损性能

采用高速电弧喷涂技术在20(AISI 1020)钢基体表面制备FeMnCrAl/Cr3C2涂层,通过光学显微镜(OM)、场发射扫描电镜(FE-SEM)等方法,对FeMnCrAl/Cr3C2涂层显微组织、抗高温冲蚀磨损性能和冲蚀磨损机理进行研究。结果表明:在全部冲击角范围内,FeMnCrAl/Cr3C2涂层表现出优于20钢的抗高温冲蚀磨损性能;FeMnCrAl/Cr3C2涂层的冲蚀磨损机理如下:在低冲击角下,破坏模式以犁耕和切削作用为主;在高冲击角下,破坏模式以挤压疲劳开裂和脱落作用为主;在中间冲击角范围,破坏模式表现为挤压和切削;在全部冲击角下,破坏模式都伴随着新鲜表面在二次冲击下的脆性开裂脱落和过度塑性变形导致疲劳脱落的复合失效形式。     

高速电弧喷涂FeNiCrAl/Cr_3C_2涂层的高温氧化性能和氧化机理

选用两种不同外皮的Fe Ni Cr Al/Cr3C2金属陶瓷粉芯丝材,采用高速电弧喷涂技术在45钢基体上制备涂层.采用增重法研究Fe Ni Cr Al/Cr3C2涂层在750℃时的氧化动力学曲线,利用金相显微镜、扫描电镜、X射线衍射仪研究涂层的显微组织结构和氧化产物,分析涂层在750℃时的抗高温氧化性能和氧化机理.结果表明,Fe NiCr Al/Cr3C2涂层的氧化动力学曲线呈抛物线型,涂层的增重明显低于20G钢,并且以304不锈钢为外皮的涂层的抗高温氧化性能明显优于以430不锈钢为外皮的涂层;涂层氧化后表面生成致密的氧化膜,阻塞氧的扩散通道,抑制氧化,起到保护作用.     

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.     

The role of microstructure in the mechanism of high velocity erosion of Cr3C2-NiCr thermal spray coatings: Part 1 — As-sprayed coatings

Carbide based thermal spray coatings are routinely applied to mitigate erosion under industrial conditions. However, the mechanism of erosion response under aggressive high velocity impact conditions remains unclear. In this work Cr₃C₂-25%NiCr thermal spray coatings were eroded at an impact velocity of 150 m/s by 20-25 µm alumina grit. Coatings were deposited by High Velocity Air Fuel (HVAF) and High Velocity Oxygen Fuel (HVOF) thermal spray techniques to generate a range of coating quality spanning that applied industrially. In Part 1 of this two-part series, the mechanism of erosion as a function of coating composition and microstructure variation is discussed. The HVOF coating underwent significant in-flight dissolution of the carbide phase. The erosion response of the supersaturated NiCr matrix was characterised by brittle cracking and fracture. The HVAF coating retained a high carbide content with minimal phase dissolution. However, the rapid solidification of the matrix material made the coating prone to brittle interphase cracking during impact. On a larger scale, splat based erosion mechanisms played a significant role, especially in the HVOF coating. The mechanisms of impact response of these coatings were dependent upon the depth of erodent penetration and could not, therefore, be extrapolated from erosion testing at lower velocities.     

高速电弧喷涂FeMnCrAl/Ni包覆WC涂层组织与性能

采用无需常规敏化活化的预处理常温超声波化学镀方法制备Ni包覆WC复合粉体,以其作为增强相的粉芯丝材通过高速电弧喷涂技术制备FeMnCrAl/Ni包覆WC涂层。采用光学显微分析（OM）、场发射扫描电镜分析（FE-SEM）、能谱分析（EDS）以及涂层性能测试方法,研究Ni包覆WC复合粉体对涂层组织结构及性能的影响。结果表明：Ni包覆WC复合粉体能改善涂层中各相之间的结合状态,减少涂层中氧化物和孔隙率,提高涂层与基体的结合强度和涂层的内聚强度,改善了涂层抗冲蚀磨损性能。     

The role of microstructure in the mechanism of high velocity erosion of Cr3C2-NiCr thermal spray coatings: Part 2 — Heat treated coatings

In Part 1 of this two part series the variation in erosion mechanisms as a function of as-sprayed coating microstructure was presented. The oxidation resistance of Cr₃C₂-NiCr coatings means that they are used in high temperature applications where WC-Co based systems are no longer suitable. High temperature exposure has been shown to generate microstructural development in these coatings, leading to variations in coating hardness. In this work the effect of such coating development on the high velocity erosion response is investigated. The HVAF and HVOF coatings of Part 1 were heat treated for up to 30 days at 900 °C to generate a range of coating microstructures up to steady state. Erosion was performed under the same conditions as in Part 1. Heat treatment increased the ductility of the NiCr phase, enabling ductile erosion deformation to occur. Intersplat sintering reduced the significance of splat based erosion mechanisms and forced mass loss to become dictated by the phase microstructure. Such developments improved the quantified erosion resistance of both coating systems relative to the as-sprayed conditions. The coating microhardness was shown to be a poor indicator of erosion response across the range of coating microstructures investigated.     

超声冲击处理提高超音速等离子喷涂Cr3C2-NiCr涂层性能

Cr₃C₂-NiCr涂层是中高温下理想的耐磨、抗氧化、耐蚀涂层,常用于高温下的燃气冲蚀磨损、磨粒磨损、微动磨损、硬表面磨损等场合.文中采用超音速等离子喷涂的方法在CuCrZr合金表面制备Cr₃C₂-NiCr涂层,并采用超声冲击的方法对涂层进行后处理.结果表明,经超声冲击处理后,涂层孔隙率由2.34%降低至1.83%;涂层的平均显微硬度由8.9 GPa提高至9.6 GPa,且硬度分布更均匀;在650℃下进行热震试验,涂层的热震寿命显著提高,热震裂纹的扩展路径也发生了变化.     

Microstructure and properties of Cr3C2-modified nickel-based alloy coating deposited by plasma transferred arc process

The nickel-based alloy with 30 wt.% chromic carbide (Cr₃C₂) particles has been deposited on Q235-carbon steel (including 0.12 wt.% C) using plasma transferred arc (PTA) welding machine. The microstructure and properties of the deposited coatings were investigated using optical microscope, scanning electron microscope (SEM) equiped with X-ray energy spectrometer (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), microhardness testes, and sliding wear test. It was found that the γ(Ni, Fe), M₇(C,B)₃, Ni₄B₃, and (Cr,Fe)₂B phases existed in the Cr₃C₂-free nickel-based alloy coating obtained by PTA process. The typical hypoeutectic structure and composition segregation in the solid solution could be found clearly. The addition of 30 wt.% Cr₃C₂ particles led to the existing of Cr₃C₂ phase and the microstructure changing from hypoeutectic structure into hypereutectic structure. The composition segregation in the solid solution could not be found clearly. The average microhardness of the Cr₃C₂-free nickel-based alloy coating increased by 450-500 HV after the addition of 30 wt.% Cr₃C₂ particles. The partial dissolution of Cr₃C₂ particles led to the enrichment of carbon and chromium in the melten pool, and hence caused the formation of more chromium-rich carbides after the solidification process. The undissolved Cr₃C₂ particles and the increasing of chromium-rich carbides was beneficial to enhance the hardness and wear resistance of the Cr₃C₂-modified nickel-based alloy coating deposited by PTA process.     

Microstructure and adhesion of Cr3C2-NiCr vacuum plasma sprayed coatings

Vacuum plasma spraying (VPS) was used to spray a Cr₃C₂-NiCr coating of ∼ 150, 300 and 450 μm in thickness onto a plain carbon steel substrate, employing a commercially available Cr20Ni9.5C powder. The splat microstructures observed in the coating were found to consist of a NiCr matrix with a predominant Cr₃C₂ phase, besides Cr₇C₃ and Cr₂O₃. The adhesion of the coating to the substrate was evaluated by means of interfacial indentation techniques. It has been found that the interfacial toughness value changes from 7.6 to 10.1 MPa m^1/2 when the thickness increases from 150 to 450 μm. Also, it has been found that the parameter Kca_o, determined by linear regression from the Kca versus 1 / e² curve by means of the interfacial indentation model advanced by Chicot et al., has a value of ∼ 9.8 MPa m^1/2.     

Comparative study of Cr3C2-NiCr coatings obtained by HVOF and hard chromium coatings

In the present work the corrosion resistance of micro-cracked hard chromium and Cr₃C₂-NiCr (HVOF) coatings applied on a steel substrate have been compared using open-circuit potential (E_OC) measurements, electrochemical impedance spectroscopy (EIS) and polarization curves. The coatings surfaces and cross-section were characterized before and after corrosion tests using optical microscopy (OM) and scanning electron microscopy (SEM). After 18 h of immersion, the open-circuit potential values were around −0.50 and −0.25 V/(Ag∣AgCl∣KCl_sat) for hard chromium and Cr₃C₂-NiCr, respectively. The surface analysis done after 12 h of immersion showed iron on the hard chromium surface inside/near surface cracks, while iron was not detected on the Cr₃C₂-NiCr surface even after 18 h. For longer immersion time hard chromium was more degraded than thermal sprayed coating. For hard chromium coating a total resistance values between 50 and 80 kΩ cm² were measured and two well-defined time constants were observed, without significant change with the immersion time. For Cr₃C₂-NiCr coating the total impedance diminished from around 750 to 25 kΩ cm² as the immersion time increased from 17 up to 132 h and two overlapped time constants were also observed. Polarization curves recorded after 18 h of immersion showed a lower current and higher corrosion potential for Cr₃C₂-NiCr coating than other samples studied.     

AC-HVAF制备Cr_3C_2-25CoNiCrAlY和Cr_3C_2-25NiCr涂层的高温氧化及摩擦磨损行为

为提高热作模具的高温氧化和高温耐磨性能,采用活性燃烧高速燃气喷涂(AC-HVAF)技术于H13钢基体上分别制备了Cr_3C_2-25CoNiCrAlY和Cr_3C_2-25Ni Cr涂层,并对比研究两种涂层的高温氧化和摩擦磨损行为,利用SEM、EDS和XRD分析其组织形貌与结构。结果表明:在800℃循环氧化100 h后,Cr_3C_2-25CoNiCrAlY涂层比Cr_3C_2-25Ni Cr涂层表面生成的氧化保护膜更致密,并生成大量高温稳定性好的尖晶石相,前者的氧化增重(0.80 mg/cm2)略小于后者(0.87 mg/cm2),说明Cr_3C_2-25CoNiCrAlY涂层的抗高温氧化能力略优;在700℃下,Cr_3C_2-25CoNiCrAlY涂层也具有更低的摩擦因数和磨损率,这归因于γ-matrix相(Co-Ni-Cr固溶体)具有很好的高温强度和热疲劳性能,对碳化物硬质相起到更强的联结支撑作用,提高了涂层的抗剥落能力。     

复合热源喷涂NiCr-Cr3C2涂层及其性能分析

采用激光与等离子复合热源喷涂技术,在38CrMoA1基体上制备NiCr-Cr3C2涂层,对涂层的结合强度、显微硬度、微观组织结构以及抗高温滑动摩擦磨损性能等进行了测试分析.结果表明,与传统的等离子喷涂层相比,复合热源喷涂时,NiCr-Cr2C2粉末受热熔融更充分,流动性好,铺展均匀.涂层实现了冶金结合,具有更高的结合强...     

Cr3C2-NiCr and WC-Ni thermal spray coatings as alternatives to hard chromium for erosion-corrosion resistance

Cr₃C₂-NiCr and WC-Ni coatings are widely used for wear applications at high and room temperature, respectively. Due to the high corrosion resistance of NiCr binder, Cr₃C₂-NiCr coatings are also used in corrosive environments. The application of WC-Ni coatings in corrosive media is not recommended due to the poor corrosion resistance of the (pure Ni) metallic matrix. It is well known that the addition of Cr to the metallic binder improves the corrosion properties. Erosion-corrosion performance of thermal spray coatings is widely influenced by ceramic phase composition, the size of ceramic particles and also the composition of the metallic binder. In the present work, two types of HVOF thermal spray coatings (Cr₃C₂-NiCr and WC-Ni) obtained with different spray conditions were studied and compared with conventional micro-cracked hard chromium coatings. Both as-sprayed and polished samples were tested under two erosion-corrosion conditions with different erosivity. Tungsten carbide coatings showed better performance under the most erosive condition, while chromium carbide coatings were superior under less erosive conditions. Some of the tungsten carbide coatings and hard chromium showed similar erosion-corrosion behaviour under more and less erosive conditions. The erosion-corrosion and electrochemical results showed that surface polishing improved the erosion-corrosion properties of the thermally sprayed coatings. The corrosion behaviour of the different coatings has been compared using Electrochemical Impedance Spectroscopy (EIS) and polarization curves. Total material loss due to erosion-corrosion was determined by weight loss measurements. An estimation of the corrosion contribution to the total weight loss was also given.     

Preparation and wear performance of NiCr/Cr3C2-NiCr/hBN plasma sprayed composite coating

NiCr clad hexagonal BN powder (NiCr/hBN) was added to NiCr/Cr₃C₂ feedstock to improve the tribological properties of chromium carbide nichrome coating. The microstructure, flowability and apparent density of the composite powder, as well as the structure and mechanical properties of the plasma sprayed coating were characterized. The friction and wear behavior of the NiCr/Cr₃C₂-NiCr/hBN coating from ambient temperature up to 800 °C was evaluated on a ball-on-disk wear tester and compared with that of NiCr/Cr₃C₂ coating and NiCr/Cr₃C₂-NiCr/BaF₂·CaF₂ coating. The results show that NiCr cladding can reduce the decarburization of Cr₃C₂ and oxidation of hBN during the thermal spray. The main wear mechanisms of the NiCr/Cr₃C₂-NiCr/hBN composite coating are ploughing and adhesive wear. Layered hexagonal BN particle reduce the direct contact and severe adhesion between friction pairs, thus decreasing the friction coefficient. The NiCr/Cr₃C₂-NiCr/hBN composite coating shows a promising application in the high temperature environment with the request of both wear resistance and friction reduction.     

激光熔覆Ni3Al/Cr3C2复合材料耐磨性能研究

采用激光熔覆技术在304不锈钢基板上制备了Ni_3Al合金和Ni_3Al/Cr_3C_2(25%,质量分数)复合材料耐磨涂层,分析了Ni_3Al合金和Ni_3Al/Cr_3C_2熔覆层的显微组织、硬度和耐磨性能。结果表明,Ni_3Al/Cr_3C_2熔覆层显微组织由基体γ'-Ni_3Al相和原位自生M_7C_3(M=Cr,Fe)型碳化物组成,且细小M_7C_3弥散分布于γ'-Ni_3Al基体。与Ni_3Al合金熔覆层相比较,Ni_3Al/Cr_3C_2熔覆层显微硬度提高了约4000 MPa。650℃时,Ni_3Al/Cr_3C_2熔覆层磨损量仅为对比材料蠕墨铸铁的28%左右,表明Ni_3Al/Cr_3C_2复合材料熔覆层具有良好的耐磨性能。     

高速电弧喷涂FeCrAl/Ni95Al复合涂层的性能

利用电弧喷涂技术在45钢基体表面制备了FeCrAl/Ni95 Al复合涂层,先喷涂Ni95Al打底层增强涂层的结合强度,FeCrAl涂层作为工作层.利用扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪、拉伸试验机、显微硬度计和CETR微动摩擦磨损试验机研究了涂层的显微组织、力学性能及摩擦磨损性能.结果表明,复合涂层组织均匀致密,主要由Fe3Al金属间化合物、(Fe,Cr)固溶在涂层基体中.涂层结合强度为43 MPa,硬度值为530 HVO.1,涂层磨损失效形式为剥落和氧化磨损.     

高速电弧喷涂Fe-TiB2/Al2O3复合涂层的组织及性能

采用低碳钢包覆0～70%TiB2/Al2O3硬质相的粉芯丝材和高速电弧喷涂(HVAS)原位合成MMC涂层,分析和测试了涂层的组织、相组成及耐磨粒磨损性能.结果表明:涂层的性能由其组织和相组成决定,HVAS的非平衡制造过程在涂层中形成多种相:在Fe基固溶体上存在TiB2、Al2O3、FexB及少量的金属间化合物AlFe3和NiAl;随着TiB2及Al2O3在涂层中体积分数的增加,涂层的耐磨粒磨损性能明显提高,磨损质量损失随陶瓷相体积分数的增加呈线性减少;添加合金元素Ni和Al可降低孔隙率,增加涂层耐磨性.使用HVAS方法制备了含TiB2的高性能耐磨复合陶瓷涂层.     

Effect of Cr7C3 on the mechanical, thermal, and electrical properties of Cr2AlC

In this work, phase pure Cr₂AlC and impure Cr₂AlC with Cr₇C₃ have been fabricated to investigate the mechanical, thermal, and electrical properties. The thermal expansion coefficient is determined as 1.25 × 10⁻⁵ K⁻¹ in the temperature range of 25-1200 °C. The thermal conductivity of the Cr₂AlC is 15.73 W/m K when it is measured at 200 °C. With increasing temperature from 25 °C to 900 °C, the electrical conductivity of Cr₂AlC decreases from 1.8 × 10⁶ Ω⁻¹ m⁻¹ to 5.6 × 10⁵ Ω⁻¹ m⁻¹. For the impure phase of Cr₇C₃, it has a strengthening and embrittlement effect on the bulk Cr₂AlC. And the Cr₂AlC with Cr₇C₃ would result in a lower high-temperature thermal expansion coefficient, thermal conductivity, specific heat capacity and electrical conductivity.