铂改性铝化物涂层的热生长层内应力研究

研究了镍基高温合金热障涂层系统中铂改性铝化物粘结层在空气中非连续高温氧化生成的Al2O3层内应力状态及相应的粘结层微观结构。利用Raman光激发荧光谱技术,发现铂铝粘结层在900℃氧化初期生成了θ-和α-Al2O3,而在1100℃氧化时,表面则形成连续致密的α-Al2O3层。通过α-Al2O3的光激发荧光谱偏移量,计算得到了热障涂层中热生长层的内压应力略高于3.0GPa。铂改性铝化物涂层表面Al2O3"背脊"处的内应力相对较低,同时由于没有陶瓷层的压制,生成的Al2O3起伏较大,并发生局部的Al2O3脱落。随氧化时间延长,由于Al元素沿晶界扩散较快,导致更多的γ′-Ni3Al在粘结层晶界处形成,粘结层中基本相β-NiAl向γ′-Ni3Al转变,改变了粘结层本身的热膨胀系数,引起热生长层中内应力变化。     

Oxide Dispersion Strengthened Bond Coats with Higher Alumina Content: Oxidation Resistance and Influence on Thermal Barrier Coating Lifetime

Oxidation of Metals - The oxidation resistance of the bond coat in thermal barrier coating systems has significant influence on thermal cycling performance of the protective coating. In this study,...     

铂铝涂层高温氧化的影响因素研究

研究比较沉积热障涂层和无热障涂层的镍基高温合金铂改性铝化物涂层在900,1000和1100℃空气中高温氧化生成的氧化铝层表面形态和断面结构。发现低铂含量涂层氧化初期热生长层(TGO)表面有放射状裂纹形成和长大,造成氧化铝的局部脱落,并在TGO与铂铝涂层界面形成空洞。涂层900℃循环氧化300h后TGO内部均形成空洞。而在1100℃氧化时,TBC陶瓷层的存在改变了两种铂铝涂层TGO的内应力变化趋势,升高温度使TGO厚度迅速增大,涂层寿命迅速下降。     

High-Temperature Oxidation Behavior of NiCrA1Y Bond Coats and Stellite-6 Plasma-Sprayed Coatings

Ni–22Cr–10A1–1Y and Stellite-6 coatings were deposited on boiler-tube steels, namely ASTM-SA210-Grade A1, ASTM-SA213-T-11 and ASTM-SA213-T-22, by a shrouded plasma-spray process. The NiCrA1Y alloy powder was also sprayed as a bond coat before applying a Stellite-6 coating. The cyclic-oxidation behavior of the NiCrA1Y bond coats and Stellite-6 coating were evaluated at 900 °C. Visual observations and gravimetric data were measured at the end of each cycle. Finally, the scale was analyzed using X-ray Diffraction, Scanning-Electron Microscope, Energy-Dispersive X-Ray Studies and Electron-Probe Micro-Analyzer techniques. The coatings were found to be effective in increasing resistance to oxidation at the test temperature of 900 °C. The protection is higher in the case of the Stellite-6 coating. The protection is lesser for both coating types when T22 steel was the substrate and higher in the case of GrA1 steel. The deleterious behavior of Mo present in the T22 steel is perhaps responsible for conferring lesser protection.     

High Temperature Oxidation Behavior of High Speed Steel for Roll in Water Vapor

The oxidation behavior of high speed steel (HSS) was researched by high temperature thermo balance at 500 to 800℃ in water vapor. The morphology was observed by scanning electron microscope, the microstructure of oxide scale was analyzed by energy dispersive spectrometer and X-ray diffraction spectrum. The results indicate that the mass gain of HSS increases with oxidation temperature rising, the effect of oxidation temperature on the morphology is obvious, water vapor temperature only affects mass gain and affects hardly morphology of oxide scale at the same oxidation temperature. The relevant oxidation mechanisms are also discussed.     

High Temperature Oxidation Behavior of TP304H Steel Coated with CeO2 in Water Vapor

The oxidation behavior of TP304H steel with electrodeposited CeO₂ in water vapor was investigated at 650 °C under isothermal conditions. The oxide scales were studied with glancing incident XRD, SEM and EDX. The results showed that the oxidation rate of the steel was effectively reduced, especially at the initial stage, and the adherence of the scale was improved by the CeO₂ coating. A Ce-rich oxide band was located between the inner and outer layers. Differing from reports in the literature, it was inferred from the current analysis that CeFeO₃ and CeO₂ were contained in the Ce-rich oxide band.     

铝在高温水蒸气中表面氧化膜的性能

采用X射线衍射法(XRD)和扫描电镜(SEM)研究了纯铝在高温水蒸气中表面氧化膜的相组成及形貌特征.结果表明,本次实验条件下,在高温水蒸气中铝表面生成的是由一水软铝石AlO(OH)相组成的氧化膜,延长氧化时间氧化膜的相组成不发生改变,氧化膜表面的微观形态由微米数量级大小的颗粒构成,在一定临界值内,随着氧化时间延长,氧化膜厚度增加.     

铬含量对镍基合金涂层高温氧化行为的影响机理

采用增重法对铬质量分数分别为30%和40%～45%的两种镍基合金涂层在500℃、650℃和800℃下的高温氧化行为进行了研究.并使用配有能谱分析仪的扫描电镜以及X射线衍射仪等检测设备对涂层氧化产物的形貌、成分和相组成进行了分析.发现铬含量对镍基合金涂层的抗高温氧化性能和氧化机理有着重要的影响.铬含量为40%～45%的涂层,其表面生成了连续的Cr2O3保护膜,具有相对较低的氧化速度.     

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。     

Al对高温合金高温抗氧化性能的影响

通过加入Al改善高温合金氧化膜的稳定性,并辅以微量强化元素Nb与合理的热处理工艺来提高高温合金抗氧化性。在真空感应熔炼炉中熔炼合金,利用扫描电镜、X射线衍射仪研究了Al元素对高温抗氧化性能的影响。结果表明:Al的加入提高了钢的抗氧化性,但含5%Al试样的氧化膜表面出现大量裂纹;合金氧化膜主要是由Cr2O3和具有尖晶石结构的FeCr2O4、Fe3O4以及少量Al3Fe5O12组成。     

晶粒尺寸对耐热钢在高温水蒸汽中的氧化行为的影响

从氧化动力学、氧化膜相组成及微观结构方面,研究了晶粒尺寸对18Cr-8Ni耐热钢在700 ℃下的高温水蒸汽中氧化行为的影响。结果表明：晶粒细化提高了耐热钢的抗水蒸汽氧化性能,降低了其氧化增重,推迟了失稳氧化的发生;晶粒细化改变了耐热钢氧化膜的微观结构,减小了“弹坑”区的尺寸且促进了“弹坑”区与合金界面上富Cr氧化物层的形成;晶粒细化对耐热钢抗水蒸汽氧化性能的改善主要归因于其对氧化物的形核和Cr向氧化膜/合金界面扩散的促进作用。     

Pd-Ni-Al涂层的高温长期氧化行为

利用TGA,XRD,SEM／EDS等方法,研究了Pd改性铝化物涂层在900—1100℃的长期高温氧化行为．结果表明,在900-1100℃下,与简单铝化物涂层相比,β-(Ni,Pd)Al涂层具有较好的抗高温氧化性能．添加改性元素Pd加速了涂层表面的θ-Al2O3向α—Al2O3转变,有利于形成致密的保护膜;另外,Pd还促进了合金基体中Ti元素向涂层的表面以及氧化膜中扩散．     

The Influence of Al Content on the High Temperature Oxidation Properties of State-of-the-Art Cast Ni-base Alloys

The aim of the study was to investigate the impact of the Al and Cr content on the oxidation behaviour of the commercial spun cast Ni-base alloy Centralloy^® 60 HT R, an Al₂O₃ former. State-of-the-art Ni-base alloys intended for service temperatures above 1,000 °C rely on secondary carbide or γ′ formation in order to obtain sufficient creep strength and formation of either Cr₂O₃ or Al₂O₃ for corrosion protection. Decreased Cr and increased Al contents promote γ′-formation. The oxidation resistance suffers with decreased Cr and the ductility and thermal shock resistance becomes catastrophic with increased Al. 60 HT R has Cr and Al contents that result in a good compromise between oxidation and creep resistance. Samples from a cast of 60 HT R with modified Al content have been exposed in artificial air for up to 500 h at 1,200 °C. The Cr₂O₃ former G4879 has been co-exposed as a reference. The exposed samples were evaluated using gravimetry, optical microscopy and SEM/EDX. The results showed that too much Al, 10 % (even though the oxidation properties were passable but worse than the for 60 HT R), destabilizes the austenitic matrix, resulting in a non-controllable multiphase structure.     

High Temperature Oxidation Behaviour of High Al Content Ferritic and Austenitic Stainless Steels With and Without Rare-Earth Element Addition

The oxidation behaviour of austenitic and ferritic alloys containing 4% Al and rare-earth element addition of (La?+?Ce) has been investigated, and comparisons made to an austenitic alloy with no such addition. The alloys were all found to exhibit good oxidation resistance; although, such resistance was highest when the alloy contained rare-earth elements. The addition led to a reduction in the amount of scale spalling. The scales formed after 10 and 100?h at 1,000?°C were examined using transmission electron microscopy and found to have bi-layered microstructures. The dislocation density and an amount of distortion in the scale were found to differ, depending on the absence or presence of (La?+?Ce) in the metal. It was observed that the outer-to-inner layer thickness ratio changed with time and the rare-earth element addition promoted growth of the inner layer relative to the outer layer. Analysis of the scale compositions demonstrated an apparent synergistic relationship between the effects of the rare-earth element addition and the degree to which iron is incorporated within the scales. The results are discussed in relation to the relative oxidation performance of the austenitic and ferritic alloys.     

Enhanced Characteristics of HVOF-sprayed MCrAlY Bond Coats for TBC Applications

This study is focused on the variation of the microstructures of different CoNiCrAlY bond coats sprayed by the high-velocity oxy-fuel (HVOF) process for thermal barrier coating (TBC) applications. Three different size fractions of the CoNiCrAlY bond coat powder have been considered for this investigation: AMDRY 9951 (5-37 μm), AMDRY 9954 (11-62 μm), and AMDRY 995C (45-75 μm). The influence of HVOF process parameters and process conditions have been studied in detail to achieve quality bond coats in terms of low porosity level, low oxygen content, and high surface roughness. The results have been promising and have shown that dense bond coats with low porosity can be achieved by HVOF spraying through the appropriate selection of powder size and process parameters. Importantly, HVOF bond coats appear to be competitive to VPS bond coats in terms of its oxygen content and high surface roughness.     

Pt─Al涂层的高温氧化行为

在Ｍ３８Ｇ高温合金上镀铂，然后进行粉末包装渗铝，最后形成Ｐｔ－Ａｌ涂层。经１０００℃、１５００ｈ氧化后，发现涂层中加铂．明显改善氧化膜的粘附性和影响铝的扩散。并讨论铂在氧化中的作用机理。     

W、B、Y微合金化高铌TiAl基合金高温抗氧化性研究

使用元素W、B、Y对Ti-45Al-8Nb合金进行了微合金化,研究了微合金化后高铌TiAl基合金在900℃静止空气中的断续氧化行为。结果表明,与Ti-45Al-8Nb合金相比,经过0.2B与0.1Y联合微合金化后合金的氧化增重小,氧化膜与基体的粘附性强,抗氧化性明显改善;经过0.2W与0.1Y微合金化后合金氧化增重明显,氧化膜容易脱落,合金抗氧化性下降;经过0.2B、0.2W、0.1Y联合微合金化后合金抗氧化性没有明显变化。对氧化膜进行的扫描电镜(SEM)、能谱分析(EDS)及X射线衍射(XRD)分析表明,联合添加B、Y促进了合金中的连续致密的Al2O3条带的形成,W、Y联合微合金化的合金中靠近基体处未形成连续的Al2O3条带,并且混合层中形成了较厚的低铌含量的TiO2层。W、B、Y联合微合金促进了混合层中富Al2O3层的形成。