Formation and Characterization of Titanium Modified Aluminide Coatings on IN738LC

Up to now, the aluminide coatings used to protect industrial components at high temperature and corrosive environments have been modified by Pt, Cr, Si and Ni. In this investigation, aluminide coatings were modified by titanium and the microstructural feature and formation mechanism were evaluated. The coatings were formed on a Ni-based superalloy(IN738LC) by a two stage process including titanizing at first and aluminizing thereafter. Pack cementation titanizing performed at temperatures 950℃ and 1050℃ in several mixtures of Ti, Al2O3 and NH4Cl. At the second stage,aluminum diffused into surface of the specimens by an industrial aluminizing process known as Elcoatl01(4 hrs at 1050℃C). The modified coatings were characterized by means of standard optical microscopy, scanning electron microscopy,energy dispersive spectroscopy and X-Ray diffraction methods. The results show that Ti in the coatings is mainly present in the form of TiNi and Al67CrsTi25. Titanium modified coatings grew with a mechanism similar to simple aluminizing; this includes inward diffusion of Al from the pack to the substrate and then outward diffusion of Ni from the substrate to the coating. The advantages and characteristics of this two-stage modified coating is discussed and the process parameters are proposed to obtain a coating of optimum microstructure.     

Structure of Al-modified silicide coatings on an Nb-based ultrahigh temperature alloy prepared by pack cementation techniques

In order to prepare Al-modified silicide coatings on an Nb-based ultrahigh temperature alloy, both a two-stage pack cementation technique and a co-deposition pack cementation technique were employed. The two-stage process included siliconizing a specimen at 1150 °C for 4 h followed by aluminizing it at 800-1000 °C for 4 h. The coating prepared by pack siliconization was composed of a thick (Nb,X)Si₂ (X represents Ti, Cr and Hf elements) outer layer and a thin (Nb,X)₅Si₃ transitional layer; after the siliconized specimens were aluminized at or above 860 °C, a (Nb,Ti)₃Si₅Al₂ phase developed at the surface of the coating, and furthermore, when aluminizing was carried out at 860 °C, a new (Nb,Ti)₂Al layer formed in the coating between the (Nb,X)₅Si₃ layer and the substrate, but when aluminizing was performed at 900-1000 °C, the new layer formed was (Nb,Ti)Al₃. The co-deposition process was carried out by co-depositing Si and Al on specimens at 1000-1150 °C for 8 h under different pack compositions, and it was found that the structure of co-deposition coatings was more evidently affected by co-deposition temperature than pack composition. An Al-modified silicide coating with an outer layer composed of (Nb,Ti)₃Si₅Al₂, (Nb,X)Si₂ and (Nb,Ti)Al₃ was obtained by co-depositing Si and Al at 1050 °C.     

用热扩散方法在Ti-6Al-4V合金表面获得铝化物和硅化物涂层

采用固体粉末包装热扩散方法,对Ti-6Al-4V合金分别进行表面渗铝和渗硅处理,以提高该合金的抗高温氧化性能。结果表明:Ti-6Al-4V合金表面形成的铝化物涂层的金相组织为单层结构,其上有少量贯穿裂纹存在;主要相结构是TiAl_3。而硅化物涂层的金相组织则为双层结构,外层较厚,呈柱状晶,由TiSi_2相组成;内层则较薄,由Ti_5Si_4相组成。表面渗铝和渗硅处理都可以大大提高Ti-6Al-4V合金的抗高温氧化性能。     

不锈钢表面振动冲击加速渗铝工艺研究

研究了利用喷丸加速制备涂层技术,对1Cr18Ni9Ti不锈钢分别进行600℃×4、6和8 h渗铝处理,研究了1Cr18Ni9Ti试样的单位面积增重、Al涂层厚度、主要元素沿涂层截面的分布;并将不同温度下获得的铝化物涂层与空白试样一起进行了高温氧化测试实验(900℃×100 h)。结果表明,在较低的温度600℃和较短的时间4 h,可以在1Cr18Ni9Ti钢基体上形成35μm厚的铝化物涂层;但抗氧化性能测试结果却表明,振动渗制处理6 h获得的铝化物涂层性能优于处理4 h和8 h的涂层。     

The Effect of NiAl Coatings on Oxidation Behavior of AISI 403 Stainless Steel

STAINLESS STEEL TYPE AISI403possess a highdegree of resistance to atmospheric corrosion becauseof its ability to form a dense adherent oxide film,whichprotects the material from further attack[1].Thiscomposition was developed to meet the requirementsfor some gas turbine components.The alloy is notparticularly recommended for use in hot corrosion andoxidation environments.Therefore,a protective coatinglayer is essential for such applications as hot sectioncomponents in gas turbine[2].A…     

电弧离子镀制备 TiSiN 纳米复合涂层

目的在SiH4气氛下制备Si掺杂的TiSiN纳米复合涂层,为SiH4用于工业化TiSiN涂层生产提供依据。方法采用电弧离子镀技术,在SiH4气氛下,于单晶硅和硬质合金衬底上制备Si掺杂的TiSiN纳米复合涂层,研究SiH4流量对TiSiN涂层化学组分、微观结构、硬度和耐磨性能的影响。结果 SiH4流量对TiSiN纳米复合涂层的微观结构、硬度及摩擦系数的影响明显。随着SiH4流量的增加,TiSiN涂层由柱状晶生长的晶体结构逐渐转变为纳米晶镶嵌于非晶基体的复合结构。Si在涂层中以Si3N4非晶相存在,随着涂层中Si含量逐渐增加,TiN晶粒尺寸逐渐减小,Si3N4起到细化晶粒的作用。在42 m L/min的SiH4流量下,涂层硬度高达4100HV0.025。在对磨材料为硬质合金的条件下,TiSiN涂层摩擦系数小于0.6。结论 SiH4气氛下可以制备出Ti N纳米晶镶嵌于Si3N4非晶相结构的TiSiN纳米复合涂层,涂层的显微硬度较高。SiH4可以作为Si源用于TiSiN纳米复合涂层的工业化生产。     

Corrosion Behavior of Fe–Al Coatings Fabricated by Pack Aluminizing Method

In this study,the two kinds of Fe–Al coatings were fabricated by pack aluminizing on low-carbon steel at different temperatures.The corrosion behavior of the Fe–Al coatings in artificial seawater was investigated by the electrochemical and weight loss techniques.Results show that the thickness of coating layer increases with increasing aluminizing temperature.The coatings exhibit high micro-hardness and good metallurgical bonding with the substrate.In comparison with the steel substrate,the corrosion current density Icorrof the Fe–Al coatings is always lower than that of substrate,about 1/38 or 1/33 after 2 h immersion,and 1/3 or 1/6 for 720 h immersion.As can be seen from the weight loss curve,the Fe–Al coatings show less loss than that of the substrate within 30-day immersion.The corrosion products formed on the surface of the coatings include oxides of Al,Mg,Fe and Ca,and pitting defect has also been found.The Fe–Al coating with higher content of Fe_2Al_5 has better corrosion resistance.     

简单/改性铝化物涂层的研究现状

航空发动机各部件高温结构材料在苛刻环境下服役时,会遭受严重的高温氧化和热腐蚀.在合金表面施加铝化物涂层后,高温下表面能够生成一层致密且生长缓慢的Al2O3氧化膜,从而隔绝腐蚀介质,以防止合金被快速氧化腐蚀.概述了铝化物涂层的优点,包括制备简单、成本低廉.重点综述了以Ni、Fe、Ti/TiAl为合金基体的铝化物涂层微观结构.涂层的微观结构主要由渗铝工艺、基材成分及后处理工艺等因素决定,渗铝工艺包括渗剂成分、渗铝温度和渗铝时间.在高温下渗铝,Al的活度较低,涂层主要以基体元素向外扩散形成外扩散型涂层为主;在低温下渗铝,Al的活度较高,涂层主要以Al向内扩散形成内扩散型涂层为主.还归纳了不同渗铝涂层在干燥空气和水蒸气环境中的高温氧化行为,阐述了水蒸气对铝化物涂层高温氧化行为的影响,比较了Ni-Al系和Fe-Al系涂层的抗高温氧化性能.同时介绍了Cr-Al、Si-Al和Pt-Al 3种改性铝化物涂层的研究进展,包括制备方法、微观结构及抗高温氧化和腐蚀性能.最后,展望并总结了高温防护涂层的发展趋势.     

Formation of aluminide coatings on Fe-based alloys by chemical vapor deposition

Aluminide and Al-containing coatings were synthesized on commercial ferritic (P91) and austenitic (304L) alloys via a laboratory chemical vapor deposition (CVD) procedure for rigorous control over coating composition, purity and microstructure. The effect of the CVD aluminizing parameters such as temperature, Al activity, and post-aluminizing anneal on coating growth was investigated. Two procedures involving different Al activities were employed with and without including Cr–Al pellets in the CVD reactor to produce coatings with suitable thickness and composition for coating performance evaluation. The phase constitution of the as-synthesized coatings was assessed with the aid of a combination of X-ray diffraction, electron probe microanalysis, and existing phase diagrams. The mechanisms of formation of these CVD coatings on the Fe-based alloys are discussed, and compared with nickel aluminide coatings on Ni-base superalloys. In addition, Cr–Al pellets were replaced with Fe–Al metals in some aluminizing process runs and similar coatings were achieved.     

Y对Nb基体表面包埋渗铝涂层微观组织和生长机制的影响

通过向包埋渗铝剂中添加Y₂O₃粉末在纯Nb基体表面制备了Y改性的渗铝涂层,研究了Y对涂层微观组织和生长机制的影响。结果表明,Y对涂层的相组成和NbAl₃相的晶粒形态均无明显影响。随包埋剂中Y₂O₃添加量的增加,涂层表面的Y含量升高。Y改性后,涂层的生长机制由受Al原子的沿晶扩散控制转变为受Al原子的晶内扩散控制,降低了涂层的生长速率,并使NbAl₃相的柱状晶区形成了<010>//ND和<110>//ND的2种丝织构。     

Effect of Al Content on Microstructure and Cyclic Oxidation Performance of Pt-Aluminide Coatings

The effect of Al content, i.e., the amount of Al picked up during aluminizing, on the microstructure and cyclic oxidation properties of Pt-aluminide coatings has been investigated. The cast Ni-base superalloy CM-247 was used as the substrate material and a single-step, high-activity pack aluminizing process was used to produce the Pt-aluminide coatings. The Al content of these coatings was varied by using packs with different compositions of the Al source. Pt-aluminide coatings having three different Al contents, namely 6.5, 16, and 21 mg cm^-2, were evaluated for their cyclic oxidation resistance at 1200°C in air. It was found that the Pt-aluminide coatings, irrespective of their Al contents, evolve in the same manner during aluminizing and result in a three-layer structure with an outer PtAl₂+NiAl two-phase layer, an intermediate NiAl layer, and the inner interdiffusion layer. The stability of this three-layer coating structure over long periods of aluminizing, however, is dependent on the availability of Al from the pack during this period. Below a certain threshold Al availability, the two-phase outer layer transforms to a single-phase NiAl structure causing the coating to change from its three-layer structure to a two-layer one. Cyclic oxidation results indicate that, while a minimum Al content in Pt-aluminide coatings is essential for deriving the best oxidation performance, increasing the Al content beyond a certain level does not significantly enhance oxidation behavior. The effect of Al content on aspects, such as coating degradation and nature of coating–surface damage during cyclic oxidation, is also discussed.     

钼表面包埋渗法制备(Ti, Mo)Si2/MoSi2 涂层及其在1200 ℃周期性氧化环境下的氧化行为

利用连续沉积的包埋渗法,在钼表面制备了(Ti,Mo)Si₂/MoSi₂复合涂层。利用X射线衍射、扫描电子显微镜、能谱仪和热力学计算对涂层进行了表征与反应机理分析。结果表明,共沉积法无法实现Ti的有效沉积。先渗Ti、再渗Si的两步沉积工艺能有效制备Ti改性硅化物涂层。涂层分为3层,最外层为(Ti,Mo)Si₂三元化合物层,次外层为MoSi₂层,次外层与基体间为Mo₅Si₃过渡层。渗硅温度对涂层结构无明显影响。Ti改性硅化物涂层的生长速率略低于单一渗硅涂层的生长速率。(Ti,Mo)Si₂/MoSi₂复合涂层的形成由Ti、Si内扩散控制。Ti元素集中在涂层表层,Si元素通过(Ti,Mo)Si₂化合物层与基体作用形成MoSi₂层和Mo₅Si₃过渡层。渗Ti过程中,埋渗料间反应会引入游离态铝氟化物AlF₃。在随后的渗硅过程中,游离态Al以Al₃Mo的形式在(Ti,Mo)Si₂层中靠近MoSi₂层的上界面处析出。在1200 ℃周期性氧化过程中,(Ti,Mo)Si₂/MoSi₂复合涂层持续循环氧化180 h后未出现明显失重。(Ti,Mo)Si₂层氧化形成的SiO₂与TiO₂致密复合氧化层能填充涂层表面裂纹,持续阻碍氧扩散,因此其在周期性氧化环境下的抗氧化性能显著优于单一渗硅涂层。     

Effects of Cr–Si Diffusion Barrier Layer on the Oxidation Resistance of NiCrAlY Coating System with Aluminized Top Layer

A multilayer coating, which consisted of a Cr–Si co-deposited layer as the diffusion barrier, a plasma sprayed NiCrAlY middle layer, and an aluminized top layer, was developed. During the aluminizing treatment, Cr in the NiCrAlY layer was released as the γ/γ′ structure of this layer transformed to the β phase. The released Cr was inhibited by the inner Cr–Si layer to diffuse into the substrate, and a Cr layer eventually formed over the Cr–Si layer. The Cr layer impeded the inward diffusion of Al due to the low solubility of Al in the Cr layer so that more Al atoms remain in the coating and contributed to the oxidation resistance of the coating. The multilayer coating exhibited better oxidation and spallation resistance than coatings without a Cr–Si layer, at least at 1050 °C for up to 1000 h.     

TC4钛合金表面B-Al复合渗层的组织和性能

采用固体粉末包埋渗两步法,在TC4钛合金表面先1050 ℃渗硼 4~6 h再950~1050 ℃渗铝 4 h制备出B-Al复合耐磨渗层。利用X射线衍射仪(XRD)、扫描电镜(SEM)、波谱仪(WDS)和能谱仪(EDS)、显微硬度仪和摩擦磨损试验机对复合渗层的物相组成、显微组织、微区成分、表面硬度和摩擦因数进行测试和分析。结果表明:B-Al复合渗层厚为37~115 μm,主要由TiB₂相和TiAl₃相组成,外层是弥散分布TiB₂的TiAl₃层,向内依次形成厚度较小的TiAl₂、TiAl及Ti₃Al等Ti-Al金属间化合物层。B-Al复合渗层表面硬度为1041.7~1429.4 HV0.1,约为TC4钛合金硬度的3.03~4.16倍;经1050 ℃×6 h渗B后1050 ℃×4 h渗Al,其摩擦因数约为0.3,较TC4钛合金基体下降约25%。     

阴极等离子体电解沉积技术研究进展

阴极等离子体电解沉积(CPED)技术是一种新型材料表面改性技术,在腐蚀防护、高温抗氧化和催化等诸多领域具有潜在应用前景。首先简要介绍了CPED技术的发展历程,包括推进该技术发展的一些重要事件。概述了CPED放电机理的相关研究,包括在其不同发展阶段提出的单一气膜层击穿理论和气-固双电介质层理论模型。在此基础上对CPED工艺及涂层制备的改性调控方法进行了系统性的总结,包括通用性的气膜层改性和特异性的涂层调控改性,并提出了其中的问题和不足。重点综述了近年来CPED技术沉积涂层的研究进展,包括CPED技术制备金属涂层、合金涂层、合金基复合涂层、陶瓷涂层、改性陶瓷涂层和碳材料等方面的研究,着重总结了CPED制备金属和合金基涂层及改性陶瓷涂层的结构与性能。最后,针对CPED技术的研究前景、发展方向和待解决问题进行了展望,包括其潜在的应用领域、工艺与机制研究、可制备涂层体系以及环境友好性的不足和相应的改进研究方向。CPED技术应用潜力巨大,仍需开展更加系统、深入和全面的研究工作,以进一步拓展其可制备涂层体系和应用领域。     

Factors affecting the microstructure of platinum-modified aluminide coatings during a vapor phase aluminizing process

Platinum (Pt)-modified aluminide coatings were developed by electroplating a thin layer of Pt followed by an industrial vapor phase aluminizing process. The goal of this work was to systematically investigate the effect of critical coating process parameters (such as the electroplated Pt thicknesses, Al contents in Cr-Al nuggets, diffusion heat treatments) and substrates on the final Pt-modified aluminide coatings. Surface morphology and cross-section microstructure of the developed coatings were inspected and compared by using Optical Microscope, Scanning Electron Microscope (SEM) equipped with energy dispersive spectroscopy (EDS). Experimental results showed that the Al and/or Pt increase shall favor the formation of ξ-PtAl₂ phase; transformation of ξ-PtAl₂ into β-(Ni,Pt)Al phase can be obtained via a heat treatment process; Cr, Co elements in the studied Ni-base superalloy substrates did not show significant influence on coating outer layer microstructure; while substrate elements affect the microstructure of the coating interdiffusion layer.     

钼及钼合金表面高温防护涂层的研究进展

系统总结了国内外关于钼及钼合金表面高温防护涂层的最新研究成果，分析了钼在不同温度区间的氧化特征，并基于涂层组织结构稳定性、涂层缺陷、涂层与基体界面结合强度、界面物理和化学相容性、氧扩散等多方面，概述了钼及钼合金表面高温防护涂层的性能要求。归纳了现阶段应用于钼及钼合金表面的高温防护涂层体系，主要包括单一硅化物涂层、改性的硅化物涂层、硅化物基梯度复合涂层、铝化物涂层、耐热合金涂层和氧化物涂层，重点讨论了涂层的成分和结构对其抗高温氧化性能的影响。同时，对比介绍了钼及钼合金表面高温防护涂层常用的制备方法，主要包括料浆烧结法、包埋渗法、等离子喷涂法、熔盐法、化学气相沉积法、磁控溅射法等。最后，对钼及钼合金表面高温防护涂层现阶段存在的问题及未来发展方向进行了展望。     

A study on composite coatings of yttrium ion-plating and pack aluminizing for high-temperature applications

Yttrium (Y) was incorporated by an ion-plating method either before or after pack aluminizing to maximize the corrosion resistance of IN 713C. Various combinations of pack aluminizing and yttrium-ion plating were examined with respect to coating sequence, aluminum activity, and corrosive environment. Of all the various coating combinations examined, the best corrosion resistance was obtained from H/A + Y (high-activity aluminizing + Y-ion plating) type composite coatings. Uniformity of the Y deposition was greatly dependent upon the surface condition of the aluminide-coating layer. The high-activity aluminide coating gave better uniformity of Y deposition than did the low-activity-aluminide coating.Improvement of corrosion resistance by the Y-modified-aluminide composite coatings of H/A + Y type occur because the presence of Y between the Al₂O₃ columns improves Al₂O₃ scale adherence and substantially prevents depletion of Al in the aluminide-coating layer.     

Preparation of aluminide coatings at relatively low temperatures

1 Introduction Protective coatings by pack aluminizing are frequently applied to metals to protect them from high temperature oxidation and hot corrosion attack [1, 2]. Pack aluminizing consists of heating the parts to be coated in a closed or vented pac…     

The effects of ultrasonic nanocrystal surface modification (UNSM) on pack aluminizing for the fabrication of Pt-modified aluminide coatings at low temperatures

An 8–9 μm thick Pt layer was coated on a superalloy and transformed to a Ni–Pt alloy layer by the interdiffusion of Ni and Pt at 1050 °C for 3 h. The surface of the Ni–Pt alloy layer was pack aluminized to form a Pt-modified aluminide coating. Ultrasonic nanocrystal surface modification (UNSM) was applied to the alloy layer prior to pack aluminizing. The effects of UNSM on Pt-modified aluminide coatings fabricated at 750, 850, 950, and 1050 °C were studied. The treated Ni–Pt alloy layers had finer grain sizes than the untreated specimens. In addition, UNSM made the grain size of the Ni–Pt alloy finer and reduced the surface roughness. During pack aluminizing, the Pt-modified aluminide coatings fabricated following UNSM uptook more Al and were thicker than the untreated Pt-modified aluminide coatings at the various temperatures (750, 850, 950, and 1050 °C). The untreated Pt-modified aluminide coatings with pack aluminizing performed at 750 and 850 °C were composed of only a two-phase (NiAl + PtAl₂) layer, due to insufficient diffusion of Pt at the lower temperatures. However, two-phase and one-phase (NiAl) layers were obtained in the treated Pt-modified aluminide coatings which were pack-aluminized at 750, 850, 950, and 1050 °C, due to the diffusion of Pt through the greater amount of grain boundaries and increased volume generated by UNSM before the pack aluminizing. Additionally, the treated coatings had smoother surfaces even after the pack aluminizing. During cyclic oxidation at 1150 °C for 1000 h, the treated Pt-modified aluminide coatings aluminized at relatively low temperatures (750 and 850 °C) showed better cyclic oxidation resistance than the untreated Pt-modified aluminide coating aluminized at 1050 °C.