Nb/NbCr_2合金表面硅化物涂层的高温抗氧化性能

用扩散渗法在Nb/NbCr2合金表面制备硅化物涂层,研究了基体合金和涂层在1250℃的氧化行为。结果表明:在Nb/NbCr2合金表面渗Si所得硅化物涂层由(Nb,Cr)Si2和(Cr,Nb)Si2两相组成,过渡层为(Nb,Cr)5Si3,涂层的生长动力学服从抛物线规律。基体合金在1250℃氧化形成的氧化膜为Nb2O5和CrNbO4交替分布的疏松组织,与基体有剥离现象。渗Si涂层在1250℃氧化形成的氧化膜较为致密完整,与残留涂层结合良好,为SiO2和CrNbO4混合氧化膜,改善了合金的高温抗氧化性能。     

TiAl合金表面Si-Al-Y共渗层的组织及高温抗氧化性能

通过在1050℃下Si-Al-Y扩散共渗0~4 h在TiAl合金表面制备了Al、Y改性的硅化物抗氧化渗层, 分析了共渗层的结构及相组成, 并对其组织形成机理及高温抗氧化性能进行了研究。结果表明: 1050℃共渗4 h所制备的共渗层具有多层结构, 由外向内依次为TiSi₂外层、(Ti,X)₅Si₄及(Ti,X)₅Si₃(X表示Nb, Cr)中间层、TiAl₂和γ-TiAl内层及富Al的过渡层, 其中Y元素主要富集于共渗层的外层和中间层。不同时间共渗的结果表明, Si-Al-Y共渗层的形成是一个在基体表面先沉积Al, 后沉积Si的有序过程。经1000℃高温氧化20 h后共渗层表面形成了由TiO₂外层及SiO₂·Al₂O₃次外层组成的致密氧化膜; Y的氧化物主要存在于氧化膜与残余共渗层的界面处, 能够有效地增强膜层的附着力。     

钼网表面MoSi2涂层的制备及其1500℃高温氧化性能

钼网被广泛用作高温催化剂载体,但关于其高温防护涂层的制备及失效机制却鲜有报道.用包埋渗硅方法在钼网表面制备了MoSi2高温抗氧化涂层,并在静态大气环境中开展了1500℃恒温氧化试验.利用X射线衍射仪(XRD)、扫描电镜(SEM)、能谱分析(EDS)等对氧化前后涂层的微观形貌和组织结构进行了表征.结果表明:1500℃氧化2h,MoSi2涂层中的Si元素会发生选择性氧化,在涂层表面形成一层连续的、具有“自愈合”功能的熔融态SiO2保护膜,阻挡氧向基体一侧的扩散,展现出了良好的高温抗氧化性能;高温条件下,涂层中的Si元素会和钼基体发生界面扩散反应生成抗氧化性能差的Mo5Si3,同时MoSi2不断地和氧发生反应生成Mo5Si3和SiO2,当涂层中的MoSi2完全转化为Mo5Si3,涂层将快速氧化失效.     

K4104镍基高温合金Al-Si涂层高温氧化过程中的元素扩散分析

采用无机盐料浆法在K4104镍基高温合金表面制备Al-Si涂层。依据GB/T13303-91《钢的抗氧化性能测定方法》标准,采用静态增重法对有涂层试样和无涂层试样进行了1000℃×200h抗高温氧化性能试验,并绘制了氧化动力学曲线。用带能谱扫描电镜对氧化膜的表面形貌和截面组织进行分析,研究有无涂层试样在高温氧化过程中的元素扩散。结果表明:Al-Si涂层和基体合金之间在高温氧化过程中的互扩散形成了厚度为120~140um的渗层。随着氧化时间的延长,外层铝含量逐渐降低,但仍能保持稳定的β-NiAl相。Si在扩散作用下形成内高外低的分布形式,形成的Cr3Si和富Si的M6C相有利于阻止涂层和基体元素之间的互扩散,降低化合物层的形成速度,体现了Al-Si涂层良好的抗高温氧化能力。     

TC4合金表面Y改性铝化物涂层的组织及高温氧化性能

为提高TC4合金的抗高温氧化性能。采用在900,940和980℃扩散渗2 h的方法在TC4合金表面制备了Y改性的铝化物渗层,并通过扫描电子显微镜、X射线衍射仪及能谱仪分析了渗层的结构及相组成,研究了渗层在1000℃时的抗氧化性能,讨论了其氧化机制。结果表明:不同温度所制备的渗层主要组成相均为Al_3Ti,此外在900℃制备渗层中含有少量的Al_(23)V_6,在940,980℃制备渗层中分别检测到了Al_2Ti_3及Al_2Ti相;渗剂中添加Y能够降低涂层的内应力,抑制渗层中裂纹的产生。940℃共渗2 h制备的Y改性Al化物渗层在1000℃氧化50 h后表面形成了致密的Al_2O_3氧化膜,显著的提高了TC4合金的抗高温氧化性能。     

TC4合金表面Y改性铝化物涂层的组织及高温氧化性能北大核心CSCD

为提高TC4合金的抗高温氧化性能。采用在900,940和980℃扩散渗2 h的方法在TC4合金表面制备了Y改性的铝化物渗层,并通过扫描电子显微镜、X射线衍射仪及能谱仪分析了渗层的结构及相组成,研究了渗层在1000℃时的抗氧化性能,讨论了其氧化机制。结果表明:不同温度所制备的渗层主要组成相均为Al3Ti,此外在900℃制备渗层中含有少量的Al23V6,在940,980℃制备渗层中分别检测到了Al2Ti3及Al2Ti相;渗剂中添加Y能够降低涂层的内应力,抑制渗层中裂纹的产生。940℃共渗2 h制备的Y改性Al化物渗层在1000℃氧化50 h后表面形成了致密的Al2O3氧化膜,显著的提高了TC4合金的抗高温氧化性能。     

0Cr18Ni10Ti不锈钢热浸镀铝及高温扩散后的高温氧化行为

为提高0Cr18Ni10Ti不锈钢的抗高温氧化能力,采用熔剂法在0Cr18Ni10Ti不锈钢表面制备热浸镀铝层,并经950℃、2 h高温扩散。采用SEM、EDS对热浸镀铝高温扩散试样及不锈钢试样900℃氧化不同时间的表面、截面进行了形貌观察及成分分析。结果表明:镀铝高温扩散试样的氧化动力学曲线较平缓且氧化增重较小;0Cr18Ni10Ti不锈钢经900℃、100 h氧化后表面主要由Fe2O3组成,氧沿晶界向内扩散产生内氧化;镀铝高温扩散试样900℃氧化期间,表面主要由Al2O3氧化膜组成,有效地阻止了合金元素与氧的互扩散,Ni元素在Fe Al层与Al固溶层富集阻碍了Fe Al合金层Al向基体扩散,使镀铝高温扩散试样Fe Al合金层经900℃、100 h氧化后Al元素贫化量较少。镀铝高温扩散试样900℃、100 h下的抗氧化性能优于0Cr18Ni10Ti不锈钢。     

温度对TiAl合金表面Si-Al-Y共渗层组织结构的影响

通过在1000,1050,1100℃和1150℃下Si-Al-Y扩散共渗4h的方法,在TiAl合金表面制备了Y改性Si-Al共渗层,采用SEM,EDS和XRD分析了共渗温度对共渗层组织及相组成的影响。结果表明:不同温度所制备的Si-Al-Y共渗层均具有多层复合结构,共渗层的内层都是由TiAl2和γ-TiAl相组成,互扩散区为富Al的TiAl相,随温度的升高,共渗层外层和中间层的组成相都发生改变。经1000℃/4h共渗的最外层主要为TiAl3相;温度为1050℃时,由外向内依次为TiSi2外层,(Ti,X)5Si4及(Ti,X)5Si3(X表示元素Nb和Cr)中间层;1100℃和1150℃/4h条件下共渗层具有相似的结构,在1100℃/4h条件下其外层由(Ti,X)5Si4,(Ti,X)5Si3相组成;在1150℃/4h条件下其外层由(Ti,X)5Si3相组成。在四种温度条件下,1050℃/4h下制备的共渗层较厚,组织致密,适合用于Si-Al-Y共渗层的制备。     

奥氏体不锈钢等离子渗锆合金层的抗高温氧化性研究

研究了0Cr18Ni9Ti不锈钢及其分别经过双辉等离子渗Zr、渗Zr+渗C、渗Zr+预氧化、渗Zr+渗C+预氧化不同工艺阶段处理后的试样在静态空气中的抗高温氧化性。在1150℃静态空气中氧化20h后,经过渗Zr+渗C+预氧化、渗Zr+预氧化、渗Zr+渗C、渗Zr处理的氧化增重分别只有未处理基材的0.04、0.07、0.09、0.12,表明抗氧化性能较未处理的基材都有很大程度的提高,其中经过渗Zr+渗C+预氧化处理后,效果最佳,其次依次是经过渗Zr+预氧化、渗Zr+渗C、渗Zr处理的试样;高温氧化后,不锈钢基材表面氧化严重,氧化层多次剥落,截面上出现了非常宽的裂缝;渗Zr、渗Zr+渗C、渗Zr+预氧化处理、渗Zr+渗C+预氧化处理的试样高温氧化后,表面致密度及截面形貌依次渐好,说明经以上各阶段处理后,材料的抗高温氧化性依次有所提高。特别是经渗Zr+渗C+低温预氧化处理的试样在高温氧化后,截面无孔洞与裂纹,其结构非常致密,表面平整,基体与改性层有一条明显的界面且结合比较牢固。     

钼网表面MoSi_2涂层的制备及其1500℃高温抗氧化性能

钼网被广泛用作高温催化剂载体,但关于其高温防护涂层的制备及失效机制却鲜有报道。用包埋渗硅方法在钼网表面制备了MoSi_2高温抗氧化涂层,并在静态大气环境中开展了1 500℃恒温氧化试验。利用X射线衍射仪(XRD)、扫描电镜(SEM)、能谱分析(EDS)等对氧化前后涂层的微观形貌和组织结构进行了表征。结果表明:1 500℃氧化2 h,MoSi_2涂层中的Si元素会发生选择性氧化,在涂层表面形成一层连续的、具有"自愈合"功能的熔融态SiO_2保护膜,阻挡氧向基体一侧的扩散,展现出了良好的高温抗氧化性能;高温条件下,涂层中的Si元素会和钼基体发生界面扩散反应生成抗氧化性能差的Mo_5Si_3,同时MoSi_2不断地和氧发生反应生成Mo_5Si_3和SiO_2,当涂层中的MoSi_2完全转化为Mo_5Si_3,涂层将快速氧化失效。     

Nickel aluminide coating produced on γ-TiAl alloy by high activity aluminising process

Abstract

Ni aluminide diffusion coatings on the surface of γ-TiAl alloy were produced by electroplating a Ni layer followed by a single step high activity aluminising carried out in Ar+H₂ atmosphere with a mixture of Al, NH₄Cl and Al₂O₃ powders at 1000°C for 5 h. The effect of initial thickness for Ni layer on microstructure of produced Ni aluminide coating was highlighted. The thickness of initial Ni layer was changed to 4–20 μm. In the case of the Ni layer with thickness of 4 μm, only a little amount of NiAl phase was formed in a TiAl₃ matrix. However, the microstructure of coating, in the case of the Ni layer with thickness of 8 μm, consisted of an outer layer of two phases (NiAl+TiAl₃), an intermediate layer of TiAl₃ and an interdiffusion layer. For thicker initial Ni layers (16 and 20 μm), beside the latter coating microstructure, a continuous surface layer of NiAl phase was observed. Isothermal oxidation tests on these aluminide coatings reveal that the oxidation resistance of the aluminide coatings increases with increase in initial thickness of Ni layer.     

Oxidation Behaviour of Sputtered Ni-3Cr-20Al Alloy

1. IntroductionNi-base superalloys are the important materialsused at high temperature and greatly rely on the presence of Cr and/or Al to form a protective scale ofCrook or Allot. Therefore, the investigation of oxidation of the simple Ni-Cr-Al ternary alloys is beneficial to the understanding of oxidation patterns of complex Ni-base superalloys. Some works have been conducted on the Ni-Cr-Al alloys with normal grain sizeand the results indicated that different oxides couldbe formed accor…     

溅射Ni11Co26Cr6Al0.5Y涂层对镍基合金在1000 ℃氧化行为的影响

通过对有/无Ni11Co26Cr6Al0.5Y涂层镍基合金在1000℃进行氧化动力学曲线测定,及组织结构观察,研究了Ni11Co26Cr6Al0.5Y涂层对镍基合金高温氧化行为的影响。结果表明:高温氧化期间,合金发生外氧化和内氧化,外氧化层由NiO、NiCrO_4、CoWO_4构成,中间氧化物由TiO_2、Al_2O_3、NiWO_4构成,中间层氧化物层抑制了基体中Al元素向外扩散,形成平直连续的Al_2O_3内氧化物层;合金氧化动力学曲线呈现起伏波动的特征。镍基合金经溅射Ni11Co26Cr6Al0.5Y涂层,可有效改善合金的抗氧化性能;涂层的氧化动力学曲线仅在氧化初期有轻微增重而后趋于平稳,遵循抛物线规律,其形成的Al_2O_3氧化膜未发生明显剥落,仅在涂层内及近涂层/基体界面区域存在少量Al_2O_3内氧化物。     

冷喷涂制备TiAl_3-Al复合层及其抗高温氧化性能

为了提高γ-TiAl合金的抗高温氧化性能,采用冷喷涂技术在γ-TiAl合金基体上喷涂纯Al层后进行热扩散处理,制备了厚约250μm的TiAl3-Al复合涂层,研究了该涂层在950℃下的长时间高温氧化行为,用X射线衍射仪(XRD)分析了复合涂层的相组成,用场发射电子显微镜研究了其形貌,用电子探针分析了其成分。结果表明:冷喷涂纯Al层致密,存在少量微裂纹和微气孔;TiAl3-Al复合涂层和基体之间生成了TiAl3相,TiAl3与Al的界面有空洞;γ-TiAl合金高温氧化70 h即失重,氧化产物为TiO2和Al2O3的混合物;TiAl3-Al复合涂层进入稳态氧化阶段后,增重缓慢,遵循近抛物线规律,高温氧化1 000 h后涂层仍完好,氧化产物主要为Al2O3相,还有微量的TiO2及钛氮化合物;TiAl3-Al复合涂层提高了γ-TiAl合金的抗高温氧化性能。     

Thermal stability of a platinum aluminide coating on nickel-based superalloys

An investigation was carried out to determine the thermal stability of a platinum aluminide coating on the directionally solidified alloy MAR M 002 and its single-crystal version alloy, SRR 99, at 800, 1000 and 1100°C. The morphology, structure and microchemical composition of the coating were characterized using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. In the as-deposited condition, the coating was found to consist of two layers. Most of the platinum was concentrated in the outer coating layer which consisted of a fine dispersion of PtAl₂ in a matrix of β-(Ni, Pt)Al containing other elements in solid solution, such as cobalt and chromium. The inner coating layer was relatively free of platinum and consisted essentially of β-NiAl. Exposure at 800°C was found to have no significant effect on the structure and composition of the coating on each alloy. At temperatures ?1000°C, however, PtAl₂ became thermodynamically unstable and significant interdiffusion occurred between the coating and alloy substrate. After exposure at 1000°C, the components of the outer coating layer were NiAl and Ni₃Al. However, after exposure at 1100°C, the outer coating layer consisted only of Ni₃Al. Also, after exposure at both temperatures, the composition of the outer coating layer approached that of the inner layer due to interdiffusion. Although the coating on both alloys exhibited similar structural stability at all temperatures investigated, the coating on alloy MAR M 002 was found to develop a more protective scale. This behaviour was correlated with differences in alloy substrate composition particularly rare-earth elements such as hafnium.     

High temperature oxidation of Ni–W coatings electroplated on steel

The high-temperature oxidation of Ni–16 at.% W coating electroplated on the steel substrate was studied at 700 and 800 °C in air. Before oxidation, the coating consisted of supersaturated, nanocrystalline Ni grains. During oxidation, oxygen diffused inward, Ni and the substrate elements such as Fe and Cr diffused outward. The outer NiO layer was not pure but had some dissolved ions of W⁶⁺ and Fe³⁺. Some Fe³⁺ ions were dissolved in the inner (NiO+NiWO₄) mixed layer, below which (W, Fe)-supersaturated, unoxidized Ni grains existed. Below these grains, tiny Ni–W–Fe precipitates, which were formed by the outward diffusion of Fe from the substrate, were surrounded by unoxidized (Fe-enriched, Cr-containing) Ni grains. Detailed oxidation mechanism of Ni–16 at.% W coating is proposed.     

合金元素在MCrAIY涂层中的行为

采用电弧离子镀在新型γ′-Ni     

Oxidation resistance of diffusion coatings formed by pack-codeposition of Al and Si on γ-TiAl

Oxidation resistance of the aluminide and silicide diffusion coatings pack-deposited on -TiAl were studied in air over the temperature range of 800 and 850°C for up to 4596 h. The oxidation kinetics of the coatings was monitored by intermittent weight gain measurement at room temperature. The XRD and SEM/EDS techniques were used to identify the oxide scales formed during the oxidation process and to assess the thermal stability of the coatings at the oxidising temperatures. It was revealed that the TiAl₃ coating underwent preferential Al oxidation to form the Al₂O₃ scale in the early oxidation stage, which resulted in Al depletion and formation of TiAl₂ in the subsurface of the coating. The Al depletion could not be sufficiently compensated by Al diffusion from the inner layer of the coating and eventually, in the late oxidation stage, led to the Ti oxidation and formation of the TiO₂ phase in the scale. The preferential Si oxidation was the main oxidation mechanism for the coatings with an outer silicide layer and an inner TiAl₃ layer with the formation of SiO₂ as the stable oxide scale. The thermal stability of the coatings over the temperature range up to 850°C was discussed in relation to the high-temperature stability of diffusion couples of different coating layers.