【作者】 何欢；

【导师】 董闯； Thierry CZERWIEC； Henri MICHEL；

【作者基本信息】 大连理工大学 ， 材料学， 2004， 博士

【摘要】 镍基超合金Inconel 690具有优良的抗腐蚀性能和热稳定性，在航空、航海及核工业上具有广阔的应用前景，目前已应用于压水反应堆的蒸汽发生器上。在高的机械载荷作用下这种材料也会发生磨损破坏。等离子体渗氮已经成功用于提高各种合金的摩擦学性能。奥氏体不锈钢经低温等离子体渗氮处理可以生成一种叫做γN相的氮过饱和固溶相。γN相层不仅具有比基体高得多的硬度，而且表现出良好的抗腐蚀性能。在本文中我们对Inconel 690的等离子体渗氮处理进行了系统研究，一方面是基于工程应用的需要，另一方面是为了加深对γN相的了解。等离子体渗氮处理利用脉冲直流等离子体在N₂-H₂混和气中进行。作为比较，我们对AISI 316L奥氏体不锈钢也进行了相同的处理，此外还以Inconel 690为靶材利用磁控溅射在Ar-N₂混和气中合成了γ_N相薄膜。为了全面了解这种材料的渗氮行为，采用不同技术对渗氮样品的显微结构、摩擦学特性和电化学性能等进行了表征。我们揭示了在这种材料中渗氮层厚度与晶粒取向的依赖关系并对其做出了解释。本文主要研究结果如下： 在低于475℃温度下处理的Inconel 690样品其渗氮层不均匀，并且与晶粒取向密切相关。在425℃这种晶粒取向对渗氮层厚度的影响尤为明显。利用电子背散射（EBSD）技术测量了不同晶粒的取向，发现渗氮层厚度与θ<100>境氏咝怨叵担?100>巧闵し较蛴刖Я?100>虻淖钚〖薪恰５?100>∠虻木ЯＶ芯哂凶畲罄┥⑸疃取＝⒘艘桓鍪öＰ投陨鲜鱿窒蠼辛私馐停河捎诿嫘牧⒎浇鹗糁械阅Ａ砍矢飨蛞煨裕虼松讨胁煌蛏系挠αΑ⒂Ρ洳煌佣斐闪死┥⒓せ钅茉诓煌蛏系牟钜欤钪毡硐治诰哂胁煌∠虻木ЯＤ诘睦┥⑺俾什煌ＤＤ饧扑憬峁胧笛楣鄄旖峁鞠喾? 在低于400℃温度下处理的Inconel 690样品其渗氮层也具有双层结构：最外层为固溶氮量比较高（最高可达30 at．％）的f．c．c．γN1相层，次外层则为固溶氮量比较低（<10 at．％）的f．c．c．γN2相层。当渗氮温度高于400℃，或在400℃进行超过4小时渗氮处理，γN相将发生分解，分解产物为f．c．c．氮化铬析出相和贫N和Cr的γ-FeNi奥氏体相。 对Inconel 690渗氮样品的电化学测试表明，在350℃经2h渗氮处理的样品在0.5 mol／LH₂SO₄水溶液中具有比原始样品更好的抗腐蚀性能。摩擦学测试表明渗氮样品不仅摩擦系数大大降低了，而且表面硬度也获得了显著提高。 采用相同的脉冲等离子体工艺，在低于440℃温度下处理的奥氏体不锈钢样品其渗氮层由两个具有明显分界面的亚层构成:最表层为固溶氮量比较高的知l相层，次表层则为固溶氮量比较低并富积了少量碳元素的翔2相层。研究表明渗氮处理之前在Ar--HZ等离子体中的离子轰击预处理是产生这种双层结构的必要条件。 以Inconel 690为靶材，在不同Ar--NZ混和气中利用磁控溅射制备了均匀的翔相薄膜，其饱和氮浓度和等离子体渗氮样品的基本相同。在真空中对一个知相薄膜样品进行加热处理并做了原位XRD观察，结果表明YN相的分解温度大约在400oC。更多还原

【Abstract】 Inconel 690, a nickel-based alloy with high chromium contents, is an important engineering material to substitute austenitic stainless steels and is widely used in aerospace, marine and nuclear industries. Despite its excellent corrosion resistance and high-temperature performances, this material suffers from wear damages under high mechanical loads. Plasma assisted nitriding (PAN) has been proved successful in improving the tribological properties without deteriorating the corrosion resistance of a varieties of alloys. In the case of austenitic stainless steels, PAN treatments produce a highly nitrogen-enriched YN layer that is responsible for the improved performances. In this paper, we investigate PAN of Inconel 690, both for engineering purposes and for enriching the knowledge on YN in alloys other than common austenite stainless steels. The PAN technique employed is pulsed d.c. plasma type in N2-H2 gas mixtures. As comparisons, we also carry out PAN of AISI 316L austenitic stainless steels as well as reactive magnetron sputtering coating of the YN layer on Inconel 690. We have characterized the microstructure, wear and corrosion resistances of the nitrided samples by a variety of techniques so as to have a comprehensive understanding on the nitriding behaviors of this material. In particular we have revealed and explained the nitriding thickness dependence on grain orientations. The main results are the following:The nitrided Inconel 690 samples show inhomogeneous nitrided layers at nitriding temperatures below 500℃, and the layer thickness is grain-orientation dependent, especially at temperatures around 425℃. The thickness is approximately a linear function of 9<100> which denotes the minimum angle between the nitriding direction and the <100>directions of the nitrided grains as measured by Electron Backscatter Diffraction (EBSD). The deepest penetration of nitrogen is associated with the <100>oriented grains. A model is established to explain this phenomenon: the anisotropic elastic modulus of this f.c.c. alloy results in the anisotropic strain and stress and hence in the anisotropic activation energy of the N diffusion.Similar to stainless steels, a nitriding processing of Inconel 690 at temperatures below 400 results in a two-layer structure: a top f.c.c. YN1 layer with relative high solid solution nitrogen (up to 30 at.%), and an f.c.c. YN2 sublayer with relative low solid solution nitrogen (<10 at.%). Nitriding at temperatures above 400℃ or at 400℃ for long durations (>4h) leads to the decomposition of the YN phase into the f.c.c. chromium nitride and austenite depleted in nitrogen and chromium.Electrochemical tests on the nitrided Inconel 690 samples show that the YN phase obtained by the 2h nitriding treatment at 350℃ exhibits a better corrosion resistance than theoriginal Inconel 690 substrate in a 0.5 mol/L H2SO4 aqua solution. Tribological tests reveal that the friction coefficients of the nitrided samples are greatly reduced, and the surface hardness is remarkably improved at the same time.Using the same pulsed d.c. plasma method, PAN of austenitic stainless steels at temperatures below 440癈 produces two distinct yN layers with well-defined interface: a top layer with a high solid solution nitrogen content, and a yN2 sublayer with a relative low solid solution nitrogen content and a small amount of enriched carbon. We prove that an in-situ ion bombardment cleaning in an Ar-H 2plasma before the nitriding is the necessary condition to produce such a dual structure in the nitrided layer.Reactive magnetron sputtering (RMS) of Inconel 690 in Ar-N2 gas mixtures is conducted to produce homogeneous coatings with well-defined composition of metastable f.c.c. N nitrogen solid solution. The saturated nitrogen content, as well as the lattice parameters of the rN phase prepared by RMS are nearly the same as those of the rN phase obtained in PAN. Real-time XRD observations on a YN coating heated in vacuum from room temperature to 525癈 reveal that the decomposition of the YN phase occurs nea更多还原