Characterization of the mechanical properties and failure modes of hard coatings deposited by RF magnetron sputtering

Chromium oxide coatings with thicknesses of several micrometers were deposited by RF magnetron sputtering at various oxygen flow rates and sputter powers on carbon steel and high speed steel (HSS) substrates, respectively. The compositions and structures of the coatings were characterized by EDS, XRD, and XPS. The mechanical properties of the coatings, in terms of hardness and reduced elastic modulus, were determined by nanoindentation technique. UMT was used to carry out scratch test to study the coating failure mode. Correlations between the mechanical properties of the coating and substrates and the coating failure mode are discussed, which reveal that the coating with a low thickness and high hardness underwent plastic deformation during the scratch process, while the thicker coating with a lower hardness failed in chipping or spallation. The substrate plays a more important role than the coating itself in determining the coating failure mode.     

开放环境下激光内送粉熔覆TC4钛合金的氧化行为

目的研究开放环境下激光熔覆TC4钛合金的氧化行为。方法采用激光内送粉熔覆技术制备了不同氩气流量下的TC4钛合金熔覆涂层,通过SEM、EDS和XRD分析了不同氩气流量下涂层氧化层的表面和横截面微观形貌、微观组织、元素分布和物相组成,通过维氏硬度计分析涂层的显微硬度。结果随着氩气流量的减小,涂层表面颜色逐渐变深,由银白色依次变成黄色、蓝色、深灰色。XRD分析表明,颜色的变化与有色氧化物有关,黄色氧化层主要为黄色TiO,蓝色氧化层主要为蓝色Ti2O3,深灰色氧化层主要为白色TiO2,呈现深灰色与厚的氧化层结构有关。无氩气保护下的涂层表面粗糙,氧化层为厚而疏松多孔结构,与涂层存在缝隙;有氩气保护且随着氩气流量的增加,涂层表面变得光滑,氧化层厚度逐渐减小,致密性好,且与涂层结合良好。随着氩气流量的增加,组织由板条状转变成针状,这主要与冷却速率有关。当涂层颜色为蓝色时,涂层硬度变高,说明氧扩散深度大且氧含量多。结论在不同的氩气流量下,熔覆涂层表面形成多种不同氧化色。蓝色可作为可接受和不可接受氧化程度的临界颜色。     

激光熔覆FeCoCrxNiB高熵合金涂层的组织结构与耐磨性

为探究Cr元素对高熵合金涂层组织结构和性能的影响,在45钢基体上用激光熔覆方法制备了FeCoCrxNiB高熵合金涂层,采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、显微硬度和耐磨测试等方法研究了Cr含量对FeCoCrxNiB激光熔覆高熵合金涂层组织结构、硬度和耐磨性能的影响。结果表明:熔覆态高熵合金的组织均由先共晶M2B相和共晶组织(面心立方结构相(FCC)+M2B相)组成。随着Cr含量的增加,共晶组织含量增多,M2B相减少,先共晶硼化物形态呈现不规则颗粒状到树枝状再到条块状的变化,共晶组织形貌由蜂窝状向片层状转变。涂层平均硬度随着Cr含量增加逐渐降低,FeCoCr0.5NiB涂层平均硬度最高为860HV0.2。涂层的耐磨性能与硬度呈正相关关系,即FeCoCr0.5NiB涂层耐磨性最高,FeCoCr3NiB涂层耐磨性最低。     

高铬铸钢激光熔覆NiAl涂层高温冲蚀性能

在高铬铸钢表面采用激光熔覆技术制备NiAl金属间化合物涂层,以提高电站锅炉高铬铸钢燃烧器喷嘴耐高温冲蚀性能．采用电子探针及高温冲蚀设备研究其组织及高温冲蚀性能．结果表明,高铬铸钢激光熔覆NiAI涂层成形良好,与基体呈冶金结合,涂层由NiAl金属间化合物和y。（FeNi）固溶体组成．熔覆层硬度达到450HV0．2以上,且过渡较为平缓．激光熔覆NiAl涂层的耐高温冲蚀磨损性能较高铬铸钢基体明显提高,冲蚀磨损机制为脆性剥落．     

The wear characteristics of Ni-P-SiC composite coatings

The wear resistance of an electroless co-deposited Ni-8.73% P-SiC coating has been studied and the effects of microstructure and properties of the coating on wear have also been researched by comparing it with Ni-8.9% P, Ni-4.5% P-SiC and electroplated chromium coatings. It has been found that the high wear resistance of the Ni-8.73% P-SiC coating results from the SiC particle reducing the matrix grain size, increasing the coating hardness and resisting microcuts; and the Ni-P alloy matrix with high phosphorus content is hard and supports the SiC properly. The Ni-8.73% P-SiC coating is more wear resistance than the electroplated chromium coating as the latter surface is highly cracked and its high hardness will decrease quickly at high temperature.     

高铬铸铁芯焊条堆焊层组织分析

基于焊芯过渡合金元素的技术思路,研制了高铬合金铸铁同质堆焊焊条．分析了不同药皮堆焊焊条的堆焊层组织及性能,定量表征了合金元素的过渡系数．结果表明,通过焊芯过渡合金元素的高铬合金铸铁堆焊焊条可获得组织和性能均匀的堆焊层．合金过渡系数高于85％．碱性药皮堆焊焊条堆焊层为亚共晶成分高铬合金铸铁,组织由奥氏体γ＋马氏体M＋碳化物Cr7C3组成．堆焊层硬度为44．5～56．5HRC．碱性石墨化型药皮堆焊焊条堆焊层组织由初生碳化物Cr7C3＋马氏体M＋碳化物Fe7C3＋少量石墨G组成,堆焊层硬度可达59～67HRC．     

Propylene flow,microstructure and performance of WC–12Co coatings using a gas-fuel HVOF spray process

Five WC–12Co coatings were deposited by a high velocity oxy-fuel (HVOF) system using constant oxygen flow and varying propylene flow. The phase composition, microstructure, as well as abrasive and sliding wear performance of the as-sprayed coatings were investigated. The degree of tungsten carbide (WC) decarburization in the as-sprayed coatings increases while the coating porosity decreases with the increase of the propylene flow. The coating hardness, fracture toughness, resistance to abrasive and sliding wear increases with the increase of the propylene flow, reaches maximum and then decreases. At the low flow of the propylene, relatively loose coating microstructure is formed, which leads to fracturing and pulling off the WC particles during abrasive and sliding wear process. Herewith, at the high flow of the propylene, the high degree of the WC decarburization and high brittleness of the coating leads to micro-cutting during abrasive wear as well as to cracking and delamination of the coating in the sliding wear process.     

Mechanical and tribological evaluation of PVD WC/C coatings

Five different WC/C coatings deposited by physical vapour deposition (PVD) on high speed-steel (HSS) have been evaluated with respect to their mechanical and tribological properties. For all coatings a chromium layer was deposited first to enhance coating adhesion. The carbide phase (WC) and the carbon (C) phase were deposited simultaneously by direct-current magnetron sputtering of a WC target and plasma-assisted chemical vapour deposition using hydrocarbon gas, respectively. The influence of the chromium interface layer thickness, the amount of WC phase and the flow of hydrocarbon gas on the mechanical and tribological properties of the coatings have been investigated. The coatings have been characterised with respect to their chemical composition (glow discharge optical emission spectroscopy), hardness (Vickers microhardness), morphology (scanning electron microscopy, SEM), roughness (profilometry), residual stress (beam bending), critical load (scratch testing) and abrasive wear resistance (the “dimple grinder test”). Furthermore, a ball-on-plate test was employed to obtain information about the frictional properties and sliding wear resistance of the coatings. The wear mechanisms and wear debris were analysed by SEM, Auger electron spectroscopy and electron spectroscopy for chemical analysis. All WC/C coatings displayed a thickness between 2 and 4 μm and a surface roughness in the range of 10 to 70 nm. The hardness varied between 1500 and 1800 HV. The coating residual stress was found to range from −2.5 to −0.5 GPa. The scratch test revealed a relatively high critical normal load, i.e., a relatively good adhesion of the WC/C coatings to the HSS. The abrasive wear resistance was found to be very high, in fact equally as high as that of PVD TiN. In the sliding wear test it could be seen that the coating containing the lowest amount of carbide phase (WC), i.e., the highest amount of carbon phase (C), and which had the highest compressive residual stress yielded the lowest friction and wear rate against steel. In addition, this coating was also found to yield the lowest wear rate of the counter material. In summary, a WC/C coating with overall good mechanical and tribological properties was obtained provided a relatively thin chromium layer was deposited first and if a relatively high acetylene gas flow was utilised during deposition of the WC/C layer.     

Ti-Si-N纳米复相薄膜及Si含量对脉冲直流PCVD镀膜质量的影响

用工业型脉冲直流等离子体增强化学气相沉积(PCVD)设备，在高速钢(W18Cr4V)表面沉积Ti-Si-N三元薄膜，研究了不同N2流量对薄膜组织及性能的影响，结果表明：随N2流量增大，膜层沉积速率及膜层中Si含量减少，薄膜组织趋于致密，膜层颗粒尺寸明显减小，划痕法临界载荷和显微硬度显著增加，硬度最高可达50GPa以上。研究发现，对应N2流量，薄膜相组成发生变化，依次存在有TiN／a-Si3N4／Si，TiN／a—Si3N4／TiSi2／Si，TiN／a—Si3N4／TiSi2三种相组成形式，分析认为，低N2或高Si效果不佳的原因在于直流PCVD是以工件为阴极，膜层中过多的Si3N4和Si将严重劣化阴极的电导性，致使膜层疏松，说明脉冲直流PCVD与射频PCVD存在很大的区别。     

Optimization of Arc-Sprayed Ni-Cr-Ti Coatings for High Temperature Corrosion Applications

High Cr content Ni-Cr-Ti arc-spray coatings have proven successful in resisting the high temperature sulfidizing conditions found in black liquor recovery boilers in the pulp and paper industry. The corrosion resistance of the coatings is dependent upon the coating composition, to form chromium sulfides and oxides to seal the coating, and on the coating microstructure. Selection of the arc-spray parameters influences the size, temperature and velocity of the molten droplets generated during spraying, which in turn dictates the coating composition and formation of the critical coating microstructural features—splat size, porosity and oxide content. Hence it is critical to optimize the arc-spray parameters in order to maximize the corrosion resistance of the coating. In this work the effect of key spray parameters (current, voltage, spray distance and gas atomizing pressure) on the coating splat thickness, porosity content, oxide content, microhardness, thickness, and surface profile were investigated using a full factorial design of experiment. Based on these results a set of oxidized, porous and optimized coatings were prepared and characterized in detail for follow-up corrosion testing.     

氮含量对直流磁控溅射(TiAlTaCrZr)N涂层力学及钛合金切削性能影响研究

解决传统刀具耐磨涂层导热性差的问题。本文采用直流磁控溅射方法,在不同氮气流量下制备了(TiAlTaCrZr)N涂层,研究了不同氮含量对涂层微结构和硬度、结合力、导热等性能的影响。随着氮气流量的增加,涂层中N含量增加,涂层微观结构会由纳米晶向柱状晶转变。涂层的硬度从TiAlTaCrZr 涂层的11.0 GPa增加到5 SCCM氮流量时(TiAlTaCrZr)N 涂层的20.6 GPa。涂层在氮气流量为5 SCCM时膜基结合力可达到130 N以上,之后随着氮含量增加逐渐降低。(TiAlTaCrZr)N涂层的导热性均优于TiAlN涂层的导热性,但随着氮含量增加导热性降低。(TiAlTaCrZr)N涂层的高导热性、高结合力、高硬度等特性使其在钛合金高速切削时切削距离比TiAlN涂层提高175%,这为钛合金加工提供了一种新型耐磨涂层。     

HVOF Combustion spraying of inconel powder

A major trend in the thermal spray industry has been to increase the gas jet velocity to obtain better coating attributes. One emerging technology now used in industry is the high-velocity oxygen fuel process (HVOF). High-velocity spray guns combine oxygen and a fuel gas to generate heat and extremely high particle velocities. In this study, Inconel 718 powder was deposited on steel substrates. The primary coating function was electrical resistivity for a heater application. Experiments were conducted using a Taguchi L8 statistical fractional/factorial design parametric study. The Taguchi experiment evaluated the effect of six HVOF processing variables on the measured responses. The parameters were oxygen flow, fuel flow, air envelope gas flow, powder feed rate, spray distance, and nozzle configuration. The coatings were characterized by hardness tests, surface profilometry, optical metallography, and image analysis. This article investigates coating hardness, porosity, surface roughness, deposition efficiency, and microstructure with respect to the influence of the processing parameters. Analytical studies were conducted to investigate gas, particle, and coating dynamics for two of the HVOF thermal spray experiments.     

电沉积非晶态铬镀层的组织与性能

用电沉积方法制备了非晶态铬镀层，用X射线衍射仪分析了镀层的相结构，对镀层的组织与性能以及热处理对镀层组织与性能的影响进行了研究。结果表明，非晶态铬镀层的硬度值约为969HV0．025，热处理后由于Cr7C3相的析出使硬度最高可升至1345HV0．025，非晶态铬镀层表现出良好的耐磨性和耐蚀性能，明显优于普通晶态铬镀层。热处理后，镀层与基体的结合力也有明显提高。     

身管内膛复合镀铬层的组织退化特征

研究了某型号身管后膛射击后复合镀铬层(由顶层的高收缩性铬和底层的低收缩性铬组成)的组织及显微硬度退化特征.结果显示:经3000发射击后,复合镀铬层沿着涂层厚度方向呈现梯度性再结晶,其组织由射击前的柱状晶粒团簇逐渐转变成等轴晶粒团簇,这导致镀铬层的硬度梯度分布;高收缩性铬层的表层晶粒成长最大,其相应的硬度由初始的960HV左右急剧下降到330HV左右.另外,高收缩性铬层许多短小的镶嵌微裂纹消失,而且一些穿透镀铬层的主裂纹形成并扩展到基体.根据服役条件下镀铬层的组织及性能退化特征,调整优化镀铬层的组织或许能有效地延长身管内膛镀铬层的寿命.     

淬火工艺对Cr26高铬耐磨铸铁组织与硬度的影响

利用光学显微镜、洛氏硬度计等研究了不同淬火工艺对Cr26高铬耐磨铸铁组织与硬度的影响。结果表明:铸态Cr26高铬铸铁组织主要由初生奥氏体和碳化物组成。经980~1060 ℃不同温度淬火、空冷后,高铬铸铁组织中有大量二次碳化物析出。随着淬火温度的升高,析出的二次碳化物先增加后减少,试样硬度先升高后降低。1020 ℃淬火试样硬度达到峰值,为65.7 HRC。1020 ℃淬火高铬铸铁,经空淬、油淬和水淬不同方式冷却,随着冷却速度的增大,高铬铸铁组织中碳化物颗粒、碳化物比例逐渐增大,硬度逐渐增大,其中水淬高铬铸铁试样硬度最大,达到68.2 HRC。     

Processing optimization,surface properties and wear behavior of HVOF spraying WC–CrC–Ni coating

In this work, the optimal coating process (OCP) designed by Taguchi program for high velocity oxy-fuel (HVOF) thermal spraying WC–CrC–Ni powder on Inconel 718 substrate (IN 718) is obtained by optimizing hardness (38 FMR oxygen flow rate, 53 FMR hydrogen flow rate, 25 g/min powder feed rate and 7 in. spray distance). Oxygen flow rate affects hardness mostly. The surface properties such as microstructure, crystalline phase, hardness, and porosity of WC–CrC–Ni coating have been investigated. The phase of coating has been changed during the OCP spraying because a portion of carbides, such as WC, Cr₇C₃, Ni₃C decomposes to W₂C, Cr, Ni and free carbon. Hardness (1150 ± 50 Hv) and porosity (1.2 ± 0.2%) of the OCP coating have been improved by optimization. The friction and wear behaviors of the WC–CrC–Ni coating, electrolytic hard chrome (EHC) plating and IN 718 have been studied comparatively. The lubrication due to free carbon and metal oxide debris results in a decrease of friction coefficients of the WC–CrC–Ni, compared to EHC and IN 718 at both 25 and 450 °C. It is concluded that HVOF WC–CrC–Ni coating performs more excellent anti-wear than others at both temperatures.     

等离子渗镀CrON复合涂层结构与抗铝液熔蚀性能

采用等离子渗氮/电弧离子镀复合方法在H13模具钢表面制备出CrON涂层,研究氧流量对CrON复合涂层结构及抗铝液熔蚀性能的影响。结果表明,随着氧流量的增加,所制备的涂层主要物相由氮化物向氧化物转变,在氧流量较低时主要呈现面心立方CrN结构,而在氧流量为200 mL/min时制备的涂层形成典型的Cr₂O₃晶体相特征。掺入适量的氧,CrN涂层柱状晶生长受到抑制,涂层结构更加致密。涂层表面缺陷和粗糙度随着氧含量的增加而增大。CrON复合涂层在铝液中的失效形式是局部点蚀。由于形成致密的结构和良好的热稳定性,在氧流量为50 mL/min时制备的涂层具有优异的抗铝液熔蚀能力,而氧流量较高时表面生成致密的Cr₂O₃抗氧化层也有利于提高抗铝液熔蚀性能。     

固-液复合铸造锤头的组织与性能

研究高铬铸铁-碳钢固-液复合铸造锤头的组织及硬度分布特征。结果表明,固-液复合铸造高铬铸铁锤头部分具有较高的硬度,远离复合面高铬铸铁硬度增加,碳钢硬度降低。远离复合面高铬铸铁组织为M7C3型碳化物+回火马氏体+残余奥氏体,固-液复合铸造高铬铸铁组织中碳化物有定向分布的趋势,有利于提高锤头的耐磨性;远离复合面碳钢部分的组织为珠光体和较多的铁素体,复合面附近碳钢组织珠光体数量明显增加,铁素体数量明显减小,高铬铸铁中的碳通过复合界面向碳钢进行扩散。     

Corrosion and tribological behaviors of chromium oxide coatings prepared by the glow-discharge plasma technique

In order to improve the corrosion and tribological properties of steel, chromium oxide coatings were prepared by a new combined process, namely, chromizing and plasma oxidizing treatments using double glow plasma technology under various oxygen flow rates. The composition and microstructure of the coatings were analyzed respectively by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results indicated that the oxygen flow rates had a great effect on the surface structure of the prepared Cr₂O₃ coatings, and dense and smooth Cr₂O₃ coatings were prepared at the oxygen flow rate of 10 sccm. The Cr₂O₃ coatings exhibited the better corrosion resistance which was in good agreement with the results obtained by the microstructure studied. Further mechanical properties test showed that the Cr₂O₃ coatings with high hardness and elastic modulus adhered well to the steel substrates and displayed excellent wear resistance and low coefficient of friction under dry sliding wear test conditions. The wear mechanism was mostly dominated by the “soft abrasion”.     

高速电弧喷涂FeCrBSiMo涂层抗高温氧化性能

采用高速电弧喷涂工艺在20钢基体上制备铁基FeCrBSiMo涂层,孔隙率为3.64%,显微维氏硬度为9 002.5 MPa,结合强度达52 MPa;采用扫描电镜、能谱分析仪和X射线衍射仪对涂层的显微组织和抗高温氧化性能进行了研究,并与锅炉管道常用20钢的相关性能进行了比较.结果表明,FeCrBSiMo涂层组织结构致密,在450~750℃下氧化80 h后其氧化增重均明显低于锅炉管道用20钢增重,其中750℃时的氧化增重仅是20钢的1/25.高温氧化时,涂层表面生成连续致密的铁,铬氧化物膜,能阻碍O元素从涂层表面扩散渗入涂层内部,防止涂层的进一步氧化,具有很好的保护性.