Failure Behavior of an Aluminide Coating on a Co-Base Superalloy during High-Temperature Oxidation in Air

A surface-morphology change has been observed for an aluminide coating on the Co-base superalloy DZ40M during oxidation at 1100°C in air. The oxide formed on the coating remained an even grayish-white color during the stable oxidation stage, whereas, dark-colored corrosion nodules were observed when oxidation of the coating accelerated. The number of nodules increased with time, along with growth of the nodules, eventually covering the entire surface which signified failure.     

High-Temperature Oxidation Behavior of the Co-Base Superalloy DZ40M in Air

The oxidation behavior of the Co-base superalloy DZ40M was studied in air at900–1100°C for times of up to 2000 hr. The results indicated thatthis alloy can grow a protective oxide scale at 900 and 1000°C duringisothermal oxidation, but not at 1100°C because of serious cracking andspalling of the oxide scales. Moreover, an internal-precipitate zone formedin the subsurface region of the alloy at all temperatures and times. Theprecipitates were rich in Cr in the vicinity of the alloy–scaleinterface and rich in Al deep in the alloy. The internal-precipitatemorphology changed from a granular to needlelike shape with increasingoxidation temperature.     

DZ40M钴基合金低压气相沉积铝化物涂层的高温氧化相变

研究了ＤＺ４０Ｍ钴基合金低压气相沉积简单铝化物和钛改性铝化物２种涂层的形成及其高温氧化时的相变退化过程。     

钴基超合金铝化物涂层的高温氧化寿命

通过分析钴基超合金外扩散型铝化物涂层的高温氧化及退化行为 ,并采用近似方法推算 ,得出了这类涂层氧化和退化与时间的关系。研究表明 ,涂层外侧退化主要由氧化反应驱动力所控制 ,涂层的外侧退化速率正比于其氧化速率 ;而涂层的氧化寿期近似正比于其主体层厚的平方。运用氧化退化与时间的关系式 ,进行简便的辅助实验 ,即可预测出这类涂层的高温氧化寿命。     

High-Temperature Oxidation of an Aluminized NiCr Alloy formed by a Magnetron-Sputtered Al Diffusion Coating

Aluminium diffusion coatings were obtained on Ni–20Cr substrate by sputtering an aluminium film, followed by a two stage diffusion treatment in an argon inert gas atmosphere (first stage at 600°C, second at 900 or 1100°C). Aluminides obtained at 900°C and 1100°C are close to those obtained by pack cementation process with high aluminium activity. These diffusion coatings are able to develop alumina scales during isothermal oxidation at high temperatures, whereas the untreated substrate had a chromia-forming behaviour. The weight gain recorded at 1100°C on coated sample is then smaller than the one of uncoated NiCr at 950°C. Presence of chromium was detected in the diffusion coating and Cr-rich precipitates were observed at the diffusion coating/substrate interface. After oxidation at 900°C and 1100°C, only α-Al₂O₃ was revealed by XRD. An intermediate scale with a “whiskered” morphology could however be observed after 48 hr oxidation at 900°C. After 100 hr of oxidation at 1100°C, the Ni_xAl_y diffusion phases were no longer detectable and the upper part of the oxide scale spalled away during cooling. Large cavities appeared at the initial location of the diffusion coating/substrate interface.     

定向凝固钴基合金DZ40M高温缺口疲劳性能及其断口研究

研究了定向凝固钴基高温合金ＤＺ４０Ｍ７００℃和９００℃缺口疲劳性能有疲劳断口。结果表明,ＤＺ４０Ｍ合金具有较高的抗高温缺口疲劳破坏能力,７００℃和９００℃缺口疲劳强度分别为２８５ＭＰａ和２０３ＭＰａ,且表现出低的疲劳缺口敏感性,７００℃和９００℃疲劳缺口敏感度仅为０．１４６和．１５３。在交变载茶作用下,７００℃缺口疲劳裂纹是以小平面方式,沿着｛１１１｝滑移面扩展,而９００℃缺口疲劳裂纹是在交变载荷     

铂含量对改性铝化物粘结层高温氧化和内应力的影响

研究镍基高温合金的热障涂层系统中不同铂含量的改性铝化物粘结层在1100℃空气中循环氧化和非连续氧化行为及生成的氧化铝层的内应力状态。发现在不同循环氧化条件下,铂铝粘结层表面都形成连续致密的α-Al2O3层,并且α-Al2O3具有相同的形态和相似的平均厚度。而在非连续氧化初期,Al2O3层热生长应力快速增大,在氧化至100h时内应力出现峰值。同时由于高含量铂促进Al元素的扩散从而改变了涂层力学性能,造成高含量铂涂层中表现较大的内应力,但铂含量不能影响Al2O3层中内应力曲线变化趋势。另外,低铂含量涂层γ′-Ni3Al多沿β-NiAl晶界生成,而高含量铂使涂层晶粒细化,导致γ′-Ni3Al相呈弥散分布生长,从而可以形成Al元素的"网"状快速扩散通道。     

Oxidation Behavior and Breakdown of an Aluminide Coating on DZ40M Alloy at High Temperatures

DZ40M alloy is a new Co-base superalloy, which is suitable for the blade material of gas turbines. In this paper, isothermal oxidation of an aluminide coating on this alloy was examined at 900–1100°C in air. It was observed that the weight gain at lower temperatures (900 and 1000°C) was greater than that at the higher temperature (1050°C), which was due to the formation of both -Al₂O₃ and -Al₂O₃ at 900 and 1000°C but only -Al₂O₃ at 1050 and 1100°C.     

高温合金Al-Si涂层抗高温氧化性能的研究

采用热扩散的方法 ,在K4 38高温合金表面制备了Al Si涂层。经 10 0 0℃× 5 0 0h高温氧化性能试验结果表明 ,K4 38镍基高温合金表面的涂层 ,在高温氧化过程中已转变成致密完整的α Al2 O3氧化层和富铝的 β NiAl和富镍的β NiAl化合物层 ,与基体金属的粘附性良好。Al Si涂层中Si元素的扩散和合理分布能有效的抑制β相的生长 ,延长涂层的退化速度 ,使涂层获得更佳的抗高温氧化性     

DZ40M钴基合金铝化物涂层的循环氧化

以新型定向凝固钴基高温合金ＤＺ４０Ｍ为基体,研究其低压化学气相沉积铝化物涂层的循环氧化行为,发现该涂层具有较高的抗循环氧化性能,涂层与基体结合良好。涂层退化主要是由外表面氧化膜的愈合消耗Ａｌ源所造成,沉积渗剂中加入Ｔｉ可加速涂层的退化。     

高温合金渗铝涂层抗高温氧化性能的研究

采用固体粉末包埋渗铝法，在K438高温合金表面制备渗铝涂层。对渗铝试样做了1000℃、500h高温氧化实验。实验结果表明：在氧化过程中，K438高温合金表面的涂层已转变成连续致密的α—Al2O3氧化膜、富Al的β-NiAl和富Ni的β—NiAl化合物层，氧化膜与基体合金粘附良好，在高温氧化过程中无明显剥落现象。随着氧化时间的增加，β相分解较慢，到500h时涂层仍具有良好的抗高温氧化性能。     

Hot Corrosion Behavior of a Cr-Modified Aluminide Coating on a Ni-Based Superalloy

A Cr-modified aluminide coating is prepared on a Ni-based superalloy using arc ion plating and subsequent pack cementation aluminizing.Hot corrosion behavior of the Cr-modified aluminide coating exposed to molten Na2SO4/K2SO4(3:1) or Na2SO4/NaCl(3:1) salts at 900 °C in static air are evaluated as well as the aluminide coating.The results indicate that compared with the aluminide coating,the anti-corrosion properties of the Cr-modified aluminide coating in the both salts are improved,which should be attributed to the beneficial effect of the Cr in the coating.The corrosion mechanism of the Cr-modified aluminide coating,especially the role of Cr in the mixture salt corrosion,is discussed.     

铝化物高温防护涂层的现状

介绍了高温防护涂层的主要类型、制备方法及其失效方式，重点突出了铝化物涂层在高温防护领域的重要性和高温涂层、高温氧化问题研究的重要性，从而点出了应该进一步深人地研究铝化物涂层高温氧化规律的重要意义。     

钛合金表面微弧氧化膜及抗氧化性能的研究

利用微弧氧化技术，通过增加涂层致密性的方法及选择合适的放电电压，在钛合金表面制备出致密的、与基体结合优良的微弧氧化膜。微弧氧化膜分为3层：过渡层、致密层和疏松层。XRD分析表明，微弧氧化膜主要由Al2TiO5和Al2SiO5组成。在700℃循环氧化100h后，经微弧氧化处理的钛合金的氧化增重量为2．08mg／cm^2，低于未经微弧氧化处理的钛合金的增重量（20mg／cm^2），因而微弧氧化能有效地提高钛合金的抗高温氧化性能。     

高温空气氧化作用下低铝含量FeCrAl涂层的组织演变（英文）

通过磁控溅射技术在Zr-4合金基体上沉积了厚度约为18μm的FeCrAl涂层,以提高Zr合金的高温抗氧化性能。通过空气氧化实验研究了低Al含量的FeCrAl涂层抗氧化性能。为了评估涂层界面演变和元素迁移之间的关系,采用了场发射扫描电子显微镜、能谱仪和掠入射X射线衍射仪进行了深入分析。结果表明,尽管FeCrAl涂层在1000℃空气氧化后会出现分层剥落,但该涂层仍然有效地保护了Zr-4合金基体不被氧化。FeCrAl涂层性能下降的主要原因是高温下Al元素严重向外扩散以及Fe、Cr元素向内扩散,最终导致涂层内部分层和剥落。此外,还讨论了FeCrAl涂层在800、900和1000℃时的空气氧化行为。     

Substrate Effect on the High-Temperature Oxidation Behavior of a Pt-Modified Aluminide Coating. Part I: Influence of the Initial Chemical Composition of the Coating Surface

The effect of substrate composition on the oxidation behavior of the industrial NiPtAl coating RT22 ^TM was investigated by studying the isothermal and cyclic-oxidation behavior of this coating deposited on three different Ni-base superalloys (CMSX-4 ^TM , SCB ^TM and IN792 ^TM ). Isothermal tests were performed at 900, 1050 and 1150°C for 100 h. Cyclic oxidation was studied at 900°C with a holding time of 300 h for up to 52 cycles (i.e, 15,600 h at 900°C). Thermogravimetric analysis (TGA), X-ray diffraction (XRD), microstructural and analytical investigations using scanning-electron microscopy (SEM) and transmission-electron microscopy (TEM), both equipped with energy-dispersive X-ray spectroscopy (EDS) were performed to characterize the oxidation behavior of the systems studied. An effect of the superalloy substrate was observed and related to the initial chemical composition of the coating surface which depends on the superalloy and the associated heat treatments. The effect of the substrate’s alloying elements is discussed. Particularly the influence of Ti and Ta that formed rutile-type oxides inducing oxide-scale cracking and spallation. The excellent resistance to cyclic oxidation of the coating systems studied at 900°C was also demonstrated from very long duration tests of 15,600 h.     

镍基高温合金上Co改性铝化物涂层的组织结构与耐蚀性能

为研究Co改性铝化物涂层在室温环境中的耐蚀性,利用包埋法渗Co和气相沉积渗Al(两步法)制备出两种不同Co含量的Co改性铝化物涂层,采用XRD、SEM、EDS分析涂层的组织结构。结果表明:850℃和1 000℃渗Co涂层外层和内层均为γ-(Ni,Co)相,内层有氮化物/碳化物相析出。Co改性铝化物涂层与简单NiAl涂层结构一致,外层为β-(Co,Ni)Al相,内层为互扩散区含有大量的富Cr(W)相。简单NiAl涂层的自腐蚀电流为0.04μA/cm2,约为Co改性铝化物涂层的十分之一。这说明在涂层中添加Co降低涂层的耐蚀性,一方面因为Co的腐蚀电位(-0.28V)低于Ni的腐蚀电位(-0.25V),另一方面因为渗Co过程中产生的夹杂物与涂层电位不一致,容易成为微阴极区,加速涂层的腐蚀。     

The Effect of Crystallographic Orientation on the Oxidation Behavior of a Single-Crystal Nickel-Base Superalloy

The oxidation kinetics of DD100 nickel-base single-crystal alloy, with (221) and (100) surface orientations were tested in this study by thermogravimetry. A pronounced anisotropy in both the cyclic and isothermal oxidation resistance of DD100 alloy was observed. The (221) crystallographic surface of DD100 had a slower oxidation rate than the (100) surface when isothermally exposed to stationary air at 950°C, whereas the opposite results were obtained at 1050°C. When cyclically oxidized at 1100°C, the weight loss of samples with (221) surfaces was significantly greater than that of (100) surfaces, so that the cyclic-oxidation anisotropy was more remarkable at 1100°C than at 950°C. The different spatial alignment of the / interface is thought to be responsible for the anisotropic oxidation behavior of the nickel-base single crystal alloy.     

包埋法制备NiAl涂层NiCrW基高温合金的抗氧化性能

以CaCl₂为活化剂,采用包埋法在NiCrW基高温合金表面制备了NiAl涂层。采用X射线衍射、扫描电子显微镜和能谱仪对涂层表面和横截面进行了分析。结果表明,CaCl₂可以替代NH₄Cl,是一种有效的活化剂。在950 ℃下,通过4 h的包埋渗铝,制备出几乎为单相、厚度为30 μm的NiAl涂层,涂层与基体之间为富铬中间层。当包埋渗剂填充率小于100%时,NiAl层表面生成针状θ-Al₂O₃。在1000 ℃恒温空气氧化试验中,NiAl涂层开始时被高速氧化,然后逐渐变为缓慢氧化,完成了亚稳态针状θ-Al₂O₃向稳态不规则颗粒状α-Al₂O₃的转变,最终稳定的α-Al₂O₃为基体提供了良好的抗氧化保护。     

Substrate Effect on the High Temperature Oxidation Behavior of a Pt-modified Aluminide Coating. Part II: Long-term Cyclic-oxidation Tests at 1,050 °C

This second part of a two-part study is devoted to the effect of the substrate on the long-term, cyclic-oxidation behavior at 1,050 °C of RT22 industrial coating deposited on three Ni-base superalloys (CMSX-4, SCB, and IN792). Cyclic-oxidation tests at 1,050 °C were performed for up to 58 cycles of 300 h (i.e., 17,400 h of heating at 1,050 °C). For such test conditions, interdiffusion between the coating and its substrate plays a larger role in the damage process of the system than during isothermal tests at 900, 1,050, and 1,150 °C for 100 h and cyclic-oxidation tests at 900 °C which were reported in part I [N. Vialas and D. Monceau, Oxidation of Metals 66, 155 (2006)]. The results reported in the present paper show that interdiffusion has an important effect on long-term, cyclic-oxidation resistance, so that clear differences can be observed between different superalloys protected with the same aluminide coating. Net-mass-change (NMC) curves show the better cyclic-oxidation behavior of the RT22/IN792 system whereas uncoated CMSX-4 has the best cyclic-oxidation resistance among the three superalloys studied. The importance of the interactions between the superalloy substrate and its coating is then demonstrated. The effect of the substrate on cyclic-oxidation behavior is related to the extent of oxide scale spalling and to the evolution of microstructural features of the coatings tested. SEM examinations of coating surfaces and cross sections show that spalling on RT22/CMSX-4 and RT22/SCB was favored by the presence of deep voids localized at the coating/oxide interface. Some of these voids can act as nucleation sites for scale spallation. The formation of such interfacial voids was always observed when the β to γ′ transformation leads to the formation of a two-phase β/γ′ layer in contact with the alumina scale. On the contrary, no voids were observed in RT22/IN792, since this β to γ′ transformation occurs gradually by an inward transformation of β leading to the formation of a continuous layer of γ′ phase, parallel to the metal/scale interface.