核燃料包壳锆合金表面铬涂层研究进展

锆合金凭借其较低的热中子吸收截面、优异的抗辐照性能以及良好的核燃料相容性等优点,被广泛应用于压水堆燃料包壳.福岛核事故后,表面铬涂层改性的锆合金成为耐事故包壳材料的重点研究方向之一,被认为是短期内最有可能投入商业应用的技术.综述了近年来核燃料包壳锆合金表面铬涂层的研究成果.介绍了铬涂层在事故条件下和正常工况条件下的性能优势,分析了其与锆合金基体在热性能上的匹配特性,重点对比了现有的铬涂层制备方法的优缺点,包括激光熔覆、喷涂、物理气相沉积等.其中激光熔覆和喷涂技术具有沉积速度较快、工艺条件相对简单的特点,但涂层厚度和粗糙度偏高,均匀性较差.物理气相沉积技术制得的涂层综合性能好,不足之处是涂层沉积速率较低,沉积过程需要高真空环境.兼顾高质量和低成本且适合商业化生产的包壳管表面铬涂层制备工艺仍有待于深入研究.归纳了铬涂层的高温氧化失效机制,提出在高温氧化过程中,涂层的分层、残余铬层的消耗以及锆元素沿铬晶界的扩散,是产生氧快速扩散通道并最终导致涂层失效的主要原因.最后指出了当前研究中存在的若干问题及其解决措施,为包壳锆合金表面铬涂层的进一步研究提供参考.     

核燃料包壳锆合金表面涂层研究进展

锆合金表面涂层是提高核燃料包壳事故容错能力的重要途径之一。本文综述了锆合金表面涂层的研究进展,包括涂层种类、制备工艺、微观组织以及抗水蒸气氧化性能、耐腐蚀性能等,介绍了锆合金表面涂层种类选择的依据,探讨了涂层的制备工艺、微观组织与性能之间的关系,分析了当前研究中存在的若干问题及未来涂层的发展方向,为进一步促进核燃料包壳锆合金表面涂层的研究提供了有价值的参考。     

Kinetics of high-temperature oxidation and embrittlement factors of zirconium alloys in tests simulating LOCA-type accidents in nuclear power plants

Tests of tube samples of fuel claddings of zirconium alloys of different chemical composition were performed with simulation of emergency situations at nuclear power plants with coolant loss including heating, high-temperature oxidation in steam, and cooling. Kinetics of high-temperature oxidation and structural phase changes under heating and cooling were studied, structure and analysis of fractures were studied quantitatively, and mechanic properties (residual ductility) of the samples after cooling were determined. The principal causes of alloy embrittlement were determined. Irrespective of the observed changes in the oxidation kinetics and microstructure character, the residual ductility of all the studied alloys was zero.     

锆合金包壳表面涂层的制备进展

锆因其极低的中子吸收截面、较高的熔点和优良的耐腐蚀性等特点,在核技术领域得到大量应用,主要作为核燃料的包壳材料。2011年日本福岛核事故后,事故容错燃料(ATF)的开发成为研究热点,尤其着重提高包壳材料的抗高温氧化性,而在锆合金表面制备涂层是提高该能力的重要途径之一。评述了锆合金包壳表面涂层的种类、性能、制备方法及各种方法的特点与发展。指出激光熔覆、等离子喷涂和冷喷涂都有沉积速率快、涂层厚的特点,但涂层过厚将降低核燃料的中子经济性。激光熔覆和等离子喷涂制得的涂层内应力大,存在较多气孔甚至微裂纹。冷喷涂涂层的应力和气孔得到改善,但喷涂法都存在粉尘及噪声污染等问题。重点分析了磁控溅射法(MS)和电弧离子镀(AIP)两种物理气相沉积技术在包壳涂层制备中的应用现状、存在的问题及未来发展方向。指出磁控溅射法因沉积速率可控、涂层的内应力小及涂层组分可调整等优势而应用最广。电弧离子镀因涂层致密、结合力强而最具发展潜力。这为进一步促进锆合金表面涂层的制备与研究提供了参考。     

N含量对Cr-N涂层结构和抗高温水蒸汽氧化性能的影响

为提高锆( Zr)合金的抗高温水蒸气性能,采用磁控溅射技术,通过改变沉积过程中的 N₂ 流量,在 Zr 合金表面制备不同 Cr/ N 比的涂层,研究不同 N 含量对涂层结构和抗高温水蒸汽氧化性能的影响。 利用扫描电镜、 能谱仪、X 射线衍射仪对涂层氧化前后的表面与截面形貌、化学组成、相结构进行观察和分析,利用纳米压痕仪测量涂层的力学性能,通过高温水蒸汽氧化试验评估涂层的抗氧化性能。 结果表明,随 N 含量的增加,涂层的生长结构分别为“疏松柱状” 、“致密非柱状” 、“致密柱状” 。 其中,“ 致密非柱状” 结构的涂层具有最高的硬度,是“ 疏松柱状”涂层的 2 倍。 同时,该涂层在氧化过程中生成的 Cr₂O₃ 氧化层均匀致密,可以有效防护 Zr 合金基底 6 h 不被氧化。     

Die technischen Aspekte der Bildung von Oxidschichten und deren Verhütung

Industrial aspects of the formation of oxide layers and their prevention The corrosion losses acceptables in steam generators of nuclear power plants are about 2.25 mm in 30 years; this is why unalloyed or low alloy steels can be used only to a limited extent in hot carbon dioxide (during the first 2000 to 3000 hours the oxidation follows a parabolic law, afterwards breakaway is possible). Silicon killed steel are superior to rimmed steel. Low sulfur contents are favourable, while surface treatment with dichromate solution is generally deleterious because the dichromate formed is decomposed during oxidation and the resulting chromium enrichment facilitates oxygen diffusion and enhances oxidation. Tubing suspensions may produce tensile stresses in crevices, so that screws are even torn out. Likewise, fretting may occur under simultaneous oscillating loads. In the case of ZrCu alloys the oxidation is slower than that of pure zirconium, probably because the large atomic volume of copper makes oxygen diffusion more difficult.     

Diamond/WC bilayer formation mechanism by hot-filament CVD

A method for the growth of Diamond/WC bilayers in a single process is presented with interest for the production of well adhered electrical contacts to diamond surfaces. This process uses a common hot filament chemical vapor deposition (HFCVD) reactor, with W filaments as the source for the deposition of the metallic layer, and H₂ and CH₄ gasses as the reactive species for the diamond growth. The method begins by vaporizing the filaments in vacuum for a few minutes, followed by the chemical vapor deposition of diamond. The results have shown that by varying the filament vaporization time and temperature it is possible to deposit on the Si substrate tungsten containing coatings of different thicknesses. The process starts by vaporization of naturally oxidized filaments and deposition on the substrate. Afterward, the tungsten oxide carburises to W₂C and WC phases. The CVD growth of the diamond layers on these carbide layers is dependent on the CH₄/H₂ ratios, system pressure and substrate temperature. The seeding of the Si substrates with diamond powder before the CVD process, guarantees that diamond is nucleated inside the metallic carbide layer, anchoring the top nanocrystalline diamond layer.     

Cr涂层锆合金事故容错燃料包壳材料研究进展

自2011年日本福岛核事故后，事故容错燃料成为核电企业和相关科研机构的研究重点，旨在提升反应堆燃料系统的可靠性与安全性。锆合金包壳表面涂层技术是事故容错燃料研发的短期目标之一，其中，Cr涂层锆合金包壳为当前的主要技术路线。围绕涂层制备工艺、微观组织以及关键服役性能三方面，对Cr涂层锆合金的相关研究进展进行了综述。首先，对比介绍了锆合金表面金属Cr涂层制备工艺及其特点，涵盖了物理气相沉积、冷喷涂和3D激光熔覆等技术，同步介绍了国际核电巨头所采用的制备工艺及相关研发进展。其次，简单阐述了Cr涂层微观组织特征，重点阐述了正常运行工况下Cr涂层锆合金高温高压水腐蚀性能、高温高压水微动磨蚀性能、高温力学行为和辐照行为，以及事故工况下该材料体系高温内压爆破行为、高温蒸气氧化-淬火行为等，并同步针对其微观辐照机制、高温氧化/腐蚀机制等进行了归纳和深入分析。最后，对当前研究所存在的问题和未来发展方向进行了归纳分析。     

Mechanical and tribological properties of rhombohedral diamond-rich coatings grown on stainless steel by hot filament CVD

In this study, rhombohedral diamond-rich coatings were grown directly on stainless steel (SS) substrate and also on sputter deposited titanium nitride interlayer, by hot filament chemical vapour deposition technique. Grazing incidence X-ray diffraction measurement of the coatings confirmed the formation of polycrystalline rhombohedral phases of diamond. Field emission scanning electron microscopy revealed a jelly type morphology of the coatings. The coating deposited with titanium nitride interlayer showed improved resistance against scratch indentation, lower wear rate and had lower value of coefficient of friction in comparison to the coating deposited directly on SS.     

A comparative study of CrN, ZrN, NbN and TaN layers as cobalt diffusion barriers for CVD diamond deposition on WC-Co tools

Chromium, zirconium, niobium and tantalum nitrides layers have been sputtered onto WC-12 wt.% Co substrates as diffusion barriers and buffer layers for improving performances of diamond surface coating. X-ray diffraction shows under specific reactive sputtering conditions, only MN (M = Cr, Zr, Nb, Ta) type phase exits. Their electric resistivity has been measured on samples deposited onto silica under the same conditions and related to those published.Surface and transverse scanning electron microscopy shows a dense columnar morphology.Thermo chemical computing proves the stability of those nitrides against Co, hydrogen and methane up to 1150 K (877 °C). A computed diagram of nitrogen partial pressure is given for their carburization with methane showing the highest stability for ZrN and TaN. Diamond deposition for 5 h up to 1153 K (880 °C) highlights a different behaviour for each of those materials. Auger Electron Spectroscopy (AES) profiles show a massive diffusion of cobalt through the decomposed CrN layer, a transformation of TaN and NbN into carbide without diffusion of cobalt while ZrN is outstandingly well preserved.     

Natural and synthetic polycrystalline diamond, with emphasis on ballas ‘Ballas’ — Radially grown, polycrystalline diamonds?

The successful synthesis of diamond by chemical vapor deposition (CVD) at low pressures has generated renewed interest in polycrystalline diamond. It is now possible to deposit on relatively large surfaces a metal-free ‘polycrystalline diamond ceramic’, which is nearly equivalent in optical, thermal and mechanical properties to single crystal diamond. Some microstructures found in CVD diamond are clearly related to those seen in natural ballas and the possibility of making an even better ‘polycrystalline CVD diamond’ and exploiting its capabilities is considered here.     

锆合金在HCl和H2SO4溶液中的耐蚀性能研究

采用化学浸泡、电化学测试和物理检测技术,研究了HCl和H2SO4溶液中锆合金的腐蚀行为.结果表明,锆合金在还原性的HCl和低浓度H2SO4溶液中,具有优异的耐蚀性,而在高浓度的氧化性H2SO4溶液中腐蚀速率显著增大.物理检测结果显示,腐蚀的锆合金表面均匀地覆盖着弥散分布的微小颗粒状ZrO2.还原性的HCl和低浓度H2SO4溶液中ZrO2膜保持了原有的致密性,增强了锆合金的耐蚀性能.而高浓度H2SO4溶液中,在其强氧化作用下,锆合金基体/膜界面处不断生成ZrO2.当膜增加到一定厚度时,氧化膜的晶格参数与金属的晶格参数不一致,产生内应力,降低了氧化膜的附着力,直至氧化膜破裂,露出新鲜的锆合金表面.继之,新鲜的锆合金再次被氧化,以此循环往复,导致锆合金在浓H2SO4溶液中腐蚀加剧.     

Investigation of the Tribological Properties of Diamond Films

A chemical vapor deposition (CVD) system has been used to produce polycrystalline and nanocrystalline diamond (NCD) films. For biomedical and electronic engineering applications, it is highly desirable to deposit smooth films with decreased crystal size. In general, diamond coatings with a crystal size of 10-100 nm range are known as NCD. There are several ways in which NCD may be deposited including growth from fullerene precursors with argon dilution. Several workers have proposed various mechanisms for the growth process using inert gas dilution to conventional hot filament (HF) or microwave chemical vapor deposition (MWCVD) systems, or NCD growth through the deployment of CO₂/CO or O₂-rich gas environments. However, the use of inert gas dilution, with carbon containing species is the least complex approach to growing nanocrystalline, and more recently, ultrananocrystaline diamond (UNCD). Mechanical properties of UNCD have been determined by nanoindentation, and their nanotribological properties have been measured by nano-scratch and nano-impact testing. The relative importance of toughness (∼E/H ratio) and elastic strain-to-break (∼H/E ratio) of these systems on their behavior in nano-scratch and nano-impact tests is considered, and strategies for optimizing the deposition conditions for enhanced durability under different contact conditions are suggested in this short communication.     

The Influence of Oxidizing Medium on Structure,Mechanical Properties,and Breakage Pattern of Oxide Films of Zr—1% Nb Alloy under Conditions Simulating Oxidizing Media of WWER and PWR Reactors

This article investigates into the structure, phase composition, mechanical properties, and breakage pattern of oxide films formed on the surface of Zr—1% Nb alloy after corrosion tests in autoclave in water, steam, and water with lithium. Oxidation in water with lithium promotes formation of oxide films with a thickness of more than 100 μm, and, after oxidation in water or steam, the thickness is 5–15 μm. Upon oxidation in water, oxide films are generated with laminar structure: in the substrate, the grains are extended with the thickness of ~80 nm, near film surface the grains are equiaxial with the diameter of ~30 nm. After holding of the specimens in steam the oxide films are comprised mainly extended grains with the thickness of ~95 nm with a minor amount of equiaxial grains, 10%, with a diameter of ~30 nm, after oxidation in water with lithium the mixture of equiaxial and weakly extended nanograins is observed in the film structure. Upon loading of specimens with the structure of equiaxial and weakly extended grains the oxide films are broken due to generation of transversal cracks propagating to basic metal. The oxide films with laminar structure oxidized in water are broken due to exfoliation along the interface between the layers of extended and equiaxial grains. Breakage of films with the structure of equiaxial and weakly extended grains starts at the stage of elastic deformation at a stress of 300 MPa. The highest breakage stresses of 1150 MPa are characteristic for alloy specimens oxidized in steam. Breakage of films with laminar structure after oxidation in water occurs at average stresses of 798 MPa. The cohesive/adhesive strengths of films oxidized in water and steam are nearly the same. In thick alloys, oxide films oxidized in water with lithium, substrate does not open even at loading of 100 N. According to data of Raman spectroscopy, oxide film is mainly comprised of monoclinic phase of zirconium oxide; however, after oxidation in steam at the metal—film interface, a barrier layer of tetragonal phase of zirconium dioxide has been detected that prevents accelerated oxidation.     

Enhancement of Service Life of Steam Generating Tubes in Oil-Fired Boiler for Power Generation Employing Plasma Spray Technology

The effects of Ni-50 mass% Cr alloy coating, that is plasma-sprayed onto the fire-side of steam generating tubes in a heavy oil-fired boiler, on the high temperature corrosion resistance were examined. One of the severe environments in the industrial manufacturing facilities, where thermal sprayed coatings are employed, is the high temperature corrosion such as the oxidation, sulfidation, and low melting fuel ash corrosion in the fire-side of boiler tubes. In the fossil fuel-fired steam generating boiler facilities, the degradation or failure of steam generating tubes that were derived from the contaminants in a lower grade fuel have often occurred. The situation of degradation of the water evaporator and superheater tubes and corrosion-preventing effects of plasma sprayed coating are described. The enhanced effects of plasma sprayed Ni-50 mass% Cr alloy coating for the suppression of hot corrosion failure of the steam generating tubes of boiler are summarized.     

Comparative investigation of smooth polycrystalline diamond films on dental burs by chemical vapor deposition

Depositions of hot filament chemical vapor-deposited diamond on cobalt-cemented tungsten carbide (WC-Co) rotary cutting dental burs are presented. Conventional dental tools made of sintered polycrystalline diamond have a number of problems associated with the heterogeneity of the crystallite, decreased cutting efficiency, and short life. A preferential (111) faceted diamond was obtained after 15 h of deposition at a growth rate of 1.1 μm/h. Diamond-coated WC-Co dental burs and conventional sintered burs are mainly used in turning, milling, and drilling operations for machining metal ceramic hard alloys such as CoCr, composite teeth, and aluminum alloy in the dental laboratory. The influence of structure, the mechanical characteristics of both diamond grains and hard alloys on the wear behavior, as well as the regimen of grinding on diamond wear are considered. Erosion wear properties are also investigated under air-sand erosion testing. After machining with excessive cutting performance, calculations can be made on flank and crater wear areas. Diamond-coated WC-Co dental burs offered significantly better erosion and wear resistance compared with uncoated WC-Co tools and sintered burs. This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in St. Paul, MN.     

不同电解液体系中锆合金微弧氧化陶瓷层组织结构和耐磨性能

采用磷酸盐和硅酸盐体系的电解液分别对锆-4合金进行微弧氧化,对比分析不同体系的电解液中所制备陶瓷层的组织形貌、相结构及耐磨性能。结果表明:在磷酸盐体系电解液中形成的陶瓷层,其致密层厚度约占总膜层的2/3,高于硅酸盐体系的相应值;陶瓷层表面呈典型火山状,比硅酸盐体系的陶瓷层粗糙,但孔洞数量少,内部组织也比硅酸盐体系的陶瓷层致密;两体系电解液中形成的陶瓷层的组成相均主要为t-ZrO2和m-ZrO2,但磷酸盐体系下陶瓷层中m-ZrO2相的质量分数明显要高,而硅酸盐体系中陶瓷层的外侧可能形成硅酸锆。锆合金经微弧氧化处理后,耐磨性能大幅提高,磷酸盐体系中陶瓷层的耐磨性能在总体上优于硅酸盐体系中的陶瓷层。     

直流等离子体-热丝化学气相沉积金刚石薄膜的研究

通过在传统热丝化学气相沉积装置中引入直流等离子体,设计了直流等离子体-热丝化学气相沉积金刚石薄膜的设备,设备中既包括相互独立的灯丝电压和施加的偏压。通过调节偏压可以控制所形成的等离子体的偏流。在这一改进的系统中研究了金刚石薄膜形核和生长过程,利用扫描电子显微镜（SEM）、X射线衍射（XRD）分析了金刚石的样品,结果表明,施加偏压不仅能大大促进金刚石的形核密度（10^10cm^-2）、提高金刚石薄膜的生长速率,金刚石薄膜的取向也随机取向变为（111）定向生长。     

锆合金包壳Cr涂层界面元素扩散行为研究进展

随着核反应堆向高燃耗和更长服役寿命方向发展,对包壳材料的安全可靠性提出了更高的要求。锆合金表面Cr涂层由于其优异的抗高温氧化性能、耐腐蚀性能以及与基体良好的兼容性,被认为是最有前景的耐事故涂层包壳材料。综述了近年来涂层Cr与基体Zr界面元素扩散行为的研究成果,重点介绍了Cr涂层不同状态下的界面结构及演变规律,包括沉积、退火、辐照、氧化等状态。总结了Cr的扩散、分布和金属间化合物Zr-Cr-(Fe)层的生长动力学模型,归纳了界面扩散对涂层结构及性能的不利影响。扩散阻挡层是一种抑制涂层与基体互扩散的有效结构,介绍了阻挡层设计制备原则以及现有的和潜在的金属或陶瓷阻挡层材料,分析了2类典型阻挡层的优缺点。金属阻挡层能抑制Cr的扩散并延迟Cr-Zr共晶反应,但需要考虑中子经济性;虽然陶瓷阻挡层阻隔元素扩散的性能优异,但由于其与锆合金力学性能和热膨胀系数的差异明显,易产生微裂纹,需要考虑其抗裂性。最后提出了采用实验与分子动力学等相结合的多尺度研究方法开展界面研究,同时指出了目前研究工作中亟待解决的关键问题,这为后续的锆合金表面耐事故涂层研究与开发提供了重要参考。     

Preparation,characterization and electrochemical properties of boron-doped diamond films on Nb substrates

A series of boron-doped polycrystalline diamond films were prepared by hot filament (HF) chemical vapor deposition on Nb substrates. The effects of B/C ratio of reaction gas on film morphology, growth rate, chemical bonding states, phase composition and electrochemical properties of each deposited sample were studied by scanning electron microscopy, Raman spectra, X-ray diffraction, microhardness indentation, and electrochemical analysis. Results show that the average grain size of diamond and the growth rate decrease with increasing the B/C ratio. The diamond films exhibit excellent adhesion under Vickers microhardness testing (9.8 N load). The sample with 2% B/C ratio has a wider potential window and a lower background current as well as a faster redox reaction rate in H₂SO₄solution and KFe(CN)₆ redox system compared with other doping level electrodes.