热处理对CoNiCrAlY(Re)合金氧化行为的影响

利用X射线衍射、扫描电镜和能谱分析研究了热处理前后的CoNiCrAlY(Re)合金在1000 ℃空气中的恒温氧化行为。结果表明：热处理有利于富铝相在合金中的均匀分布;热处理促进合金较快地进入稳定氧化阶段,且降低了合金的氧化速率;与不含Re的合金相比,含Re合金在初始氧化阶段具有较高的氧化增重及较快的亚稳态的θ-Al2O3向稳态的α-Al2O3相转变。     

铼对CoNiCrAlY涂层合金抗热腐蚀性能的影响

对一种掺3%～5%(质量分数,下同)铼(Re)的CoNiCrAlY燃气轮机用高温涂层合金在1000℃进行热腐蚀实验,利用X射线衍射、SEM和EDS分析其热腐蚀行为。结果表明,无论掺杂Re与否,涂层合金均产生内氧化现象;与不掺杂Re的合金相比,CoNiCrAlY合金中Re的加入能够减小贫Al区的厚度,稳定α-Cr(Re)相,有利于Cr2O3氧化膜的形成,进而阻挡了熔融的Na2SO4与基体的接触,防止熔盐对基体的热腐蚀。     

Influence of Pt on Oxidation Behavior of CoNiCrAlY Alloy

利用扫描电镜、维氏硬度计、X射线衍射和能谱分析研究了CoNiCrAlY合金及添加3%、5%Pt(质量分数)改进的CoNiCrAlY合金组织、硬度及恒温氧化行为。结果表明:Pt在合金中形成了一种β-(Ni,Pt)Al相,显著改变了合金的组织;Pt的添加使得合金的硬度有了略微的提高;Pt促进了亚稳态的θ-Al2O3向稳态α-Al2O3的相转变,降低合金的氧化速率,Pt还抑制了β-相的消耗及内氧化的产生,提高了合金的抗氧化性能。     

一种含铼单晶高温合金的恒温氧化行为

采用X射线衍射（XRD），扫描电镜（SEM）及能谱（EDAX）等手段，研究了含铼单晶高温合金DD32的高温氧化行为。结果表明，氧化初期增重迅速，由NiO的形成和生长控制，符合抛物线规律；随着氧化时间的延长，氧化增重变得十分缓慢，由α-Al2O3的形成和生长控制。在900，1000℃时的氧化膜由3层组成，最外层为（Ni，Co）O层，中间层由复杂化合物以及尖晶石化合物等组成，内层为靠近基体合金的连续的Al2O3层。氧化过程中，分布在中间层的富Re和W相起到“扩散障”的作用，降低基体合金中Al向外的扩散速率，在内层形成均匀连续的Al2O，氧化膜层，进而抑制氧化膜生长，导致氧化速率降低。     

On the Early Stage Isothermal Oxidation of APS CoNiCrAlY Coatings

The aim of this study is to analyze the evolution of microstructural and room temperature mechanical properties of air plasma sprayed (APS) CoNiCrAlY coatings before and after early stage high-temperature oxidation. To this purpose, selected samples were isothermally heat treated at 1110 °C for different durations. Phase analysis and oxide scale characterization were performed using x-ray diffraction. Morphological and microstructural features of as-sprayed and oxidized CoNiCrAlY coatings were analyzed by scanning electron microscopy and energy dispersive x-ray spectroscopy. After heat treatment, a duplex oxide scale, composed of an inner α-Al₂O₃ layer and an outer spinel-type oxide layer, was observed on coating top-surface. The nanoindentation technique was employed to study the evolution of the mechanical properties. An increase in Young’s modulus and hardness with increasing the aging time was observed, this effect was mainly addressed to the partial densification of coating microstructure.     

Sulfidation Behavior of Rhenium and Cobalt-Rhenium Alloys

The sulfidation behavior of Re and three Co-Realloys, 15, 30, and 45 w/o, was studied over thetemperature range 700-800^°C at sulfurpressures of 10^-4 and 10^-2 atm. The kinetics of sulfidation followed theparabolic rate law and the activation energies for allalloys were similar to that of pure cobalt. A positiverate dependency on sulfur pressure was observed and Pt markers were located at the metal-scaleinterface, both observations clearly suggesting thatoutward cation diffusion through a P-type sulfide scaleoccurred. Two dominant sulfides,Co₉S₈ and ReS₂, formed. Weight gainsdecreased for a given set of conditions with increasingrhenium content. An order of magnitude decrease in thesulfidation rate occurred as the rhenium content increased from 15 to 45 w/o. Preferentialsulfidation of cobalt initially occurred, causing arhenium-enriched zone to form in the substrate beneaththe cobalt-sulfide scale. Steep Re-concentrationgradients developed, the zone depth increasing withrhenium content. Significant sulfur diffusion into thesubstrate also occurred, with greater sulfur penetrationtaking place as the rhenium content increased. Sulfides formed at all temperatures were the same on thethree alloys, but the scales were denser on thehigher-rhenium alloys. The initial sulfide to form wasCo₃S₄, but, subsequently,Co₉S₈ became the dominant sulfide, forming beneaththe outer Co₃S₄ layer.ReS₂ formed at lower cobalt levels. Pure Rewas also studied, the sulfidation rate being about10⁴ times slower than that of cobalt. Thedecreasing rate of sulfidation with increasing Recontent is attributed primarily to slower cobaltdiffusion outward through the Reenriched substrate, aphenomenon similar to that observed by C. Wagner for theoxidation of Ni-Pt alloys.     

Microstructural Characteristics and Oxidation Behavior of Low-Pressure Cold-Sprayed CoNiCrAlY Coatings

CoNiCrAlY coatings were deposited by low-pressure cold spraying and subsequently heat-treated at 1050 °C for 4 h in a vacuum environment. The microstructural characteristics and oxidation behavior of CoNiCrAlY coatings were investigated. The as-sprayed coating exhibited low porosity and oxygen content. The high plastic deformation of the sprayed particles led to significant refinement of γ-matrix and dissolution of β-(Ni,Co)Al phase in the as-sprayed coating. After heat treatment, the single phase (γ) in the as-sprayed coating was converted into a γ/β microstructure, and a continuous single α-Al₂O₃ scale was formed on the coating surface. Vacuum heat treatment can postpone the formation of spinel oxides within 100 h. After being oxidized at 1050 °C for 400 h, the heat-treated coating exhibited better oxidation resistance than the as-sprayed coating. The reduced growth rate of the oxide scale and the suppression of the formation of spinel oxides can be attributed to the vacuum heat treatment, as well as the intrinsic microstructure of the cold-sprayed coating. Finally, the effects of the microstructural changes induced during the cold spraying process on the growth of the thermally grown oxide and the oxidation mechanisms of the CoNiCrAlY coatings were discussed.     

Al含量对二元Ti—Al合金高温氧化行为的影响

研究了Ａｌ含量为３３．３ａｔ％～５２ａｔ％Ａｌ的５种二元Ｔｉ－Ａｌ合金在８００℃和９００℃空气中的恒温氧化行为，用Ｘ射线衍射仪和扫描电子显微镜对其氧化产物，氧化物表面形貌和氧化层剖面结构进行了分析，研究发现：在该Ａｌ含量范围内，二元Ｔｉ－Ａｌ合金的氧化层均由具有典型形貌特征的一系列氧化薄层组成，而且在氧化层中均未形成连续致密分布的Ａｌ２Ｏ３；Ａｌ含量对氧化层中Ａｌ２Ｏ３的形态，分布以及恒温氧化反应     

铝及铝合金阳极氧化工艺问题

在铝和铝合金阳极氧化过程中常遇到一些问题 ,现选较为典型的与大家共同探讨。1　工件经阳极化并染色后表面有绑扎印痕问题按阳极化工艺要求 ,阳极化件的传导电流应用夹具 ,夹于工件的非装饰面的隐蔽部位 ,只有这样做才能达到安全、保险和避免产生绑扎印痕等质量问题 ,而上述质量问题显然是采取铝丝绑扎来代替夹具而引起的 ,其中的原因和影响有以下几个方面 :(1 )用作绑扎的铝丝都较细 ,由于截面积不足而影响电流的正常畅通引起发热并常因此而烧断 ,甚至工件掉入槽中 ,终止了阳极氧化过程的继续 ,从而带来一系列的麻烦 ;(2 )采用绑扎方法没…     

表面喷丸处理对NiCrAlYSi涂层恒温氧化行为的影响

采用真空电弧离子镀工艺制备了NiCrAlYSi涂层,研究了NiCrAlYSi涂层表面喷丸处理对其恒温氧化行为的影响.结果表明,喷丸处理工艺可降低涂层表面粗糙度,提高涂层表面致密性和平整性.在恒温氧化过程中,经过喷丸处理后的涂层能减少O原子向内扩散从而避免异常氧化区的出现,同时形成的热生长氧化(TGO)层厚度更加均匀,通...     

Effect of Low-Levels of Strontium on the Oxidation Behavior of Selected Molten Aluminum–Magnesium Alloys

The effects of small additions of strontium on the oxidation behavior of aluminum–magnesium alloy melts were investigated by thermogravimetry at 750 °C for times up to 48 h. Oxidized samples were examined by FEGSEM, and phases formed within the oxide layer and in the alloy were identified by EDS, WDS and low-angle X-ray diffraction techniques. In the absence of Sr, the Al–Mg samples gained substantial amounts of weight by formation of spinel (MgAl₂O₄) at the oxide–metal interface. Samples containing Sr had significantly lower weight gains. A very significant decrease (98%) of total weight gain was observed for small Sr additions in the low Mg-bearing Al–Mg alloys. This change in oxidation behavior was linked to the presence of Sr enrichment of the liquid beneath the initial MgO layer suppressing the formation of spinel crystals.     

铝合金微弧氧化的研究进展

综述了微弧氧化技术的发展历程、成膜机理,论述了铝合金微弧氧化的特点。基于铝合金微弧氧化工艺研究现状,详细阐述了氧化时间、占空比、电压、电流密度、电解液浓度、基体粗糙度、纳米颗粒添加剂以及复合工艺等对铝合金微弧氧化膜层的组织与性能的影响。如电流密度会影响涂层的生长机理,使膜层的表面结构和内部缺陷产生较大的差异;采用不同的电解液所得到的膜层的厚度和粗糙度有明显的区别;在不同的电压参数下膜层的均匀性及膜层中微孔的尺寸大不相同;制备微弧氧化复合涂层以及采用纳米增强颗粒可使膜层的结构和性能有大幅提升。通过改变以上影响因素对铝合金微弧氧化膜层组织和结构加以调控,从而实现了对膜层性能的优化,如膜层的硬度、耐磨性、耐腐蚀性、抗疲劳性能的提高。最后对铝合金微弧氧化的发展方向提出了展望。     

The Effect of Heat Treatment on the Oxidation Behavior of HVOF and VPS CoNiCrAlY Coatings

Free-standing VPS and HVOF CoNiCrAlY coatings were produced. The as-sprayed HVOF coating retained the γ/β microstructure of the feedstock powder, and the VPS coating consisted of a single (γ) phase. A 3-h, 1100 °C heat treatment in vacuum converted the single-phase VPS coating to a two-phase γ/β microstructure and coarsened the γ/β microstructure of the HVOF coating. Oxidation of free-standing as-sprayed and heat-treated coatings of each type was carried out in air at 1100 °C for a duration of 100 h. Parabolic rate constant(s), K _p, were determined for free-standing, as-sprayed VPS and HVOF coatings as well as for free-standing coatings that were heat treated prior to oxidation. The observed increase in K _p following heat treatment is attributed to a sintering effect eliminating porosity from the coating during heat treatment. The lower K _p values determined for both HVOF coatings compared to the VPS coatings is attributed to the presence of oxides in the HVOF coatings, which act as the barrier to diffusion. Oxidation of the as-sprayed coatings produced a dual-layer oxide consisting of an inner α-Al₂O₃ layer and outer spinel layer. Oxidation of the heat-treated samples resulted in a single-layer oxide, α-Al₂O₃. The formation of a thin α-Al₂O₃ layer during heat treatment appeared to prevent nucleation and growth of spinel oxides during subsequent oxidation.     

The Oxidation Behavior of TBC with Cold Spray CoNiCrAlY Bond Coat

Cold gas dynamic spray (CGDS) has been considered a potential technique to produce the metallic bond coat for TBC applications, because of its fast deposition rate and low deposition temperature. This article presents the influence of spray processes for bond coat, including air plasma spray, high velocity oxy-fuel, and in particular CGDS, on the oxidation performance of TBCs with a Co-32Ni-21Cr-8Al-0.5Y (wt.%) bond coat and an air plasma sprayed topcoat. Oxidation behavior of the TBCs was evaluated by examining the coating microstructural evolution, TGO growth behavior, and crack propagation during thermal exposure at 1050 °C. The relationship between the TGO growth and crack propagation will be discussed.     

工艺方法对Cu—Si和Fe-Si合金高温氧化行为的影响

采用电弧熔炼(CA)和机械合金化(MA)方法制备了不同显微组织的二元Fe-Si和Cu-Si合金,并研究了它们在不同温度下纯O2中的高温氧化行为.动力学分析表明,制备工艺对两种合金高温氧化行为的影响结果截然不同,机械合金化方法提高了Cu-Si合金的抗高温氧化性能但降低了Fe-Si合金的抗高温氧化性能.X射线衍射、扫描电镜和能谱分析表明,两种方法制备的Fe-1Si合金氧化生成了Fe2O3→Fe3O4 FeO→FeO→ FeO SiO2结构的氧化膜;而Cu-1.3Si合金氧化后生成了CuO→Cu2O→Cu2O SiO2→内氧化区结构的氧化膜;虽然两种合金氧化后均生成了富SiO2的混合氧化区,但未形成连续的SiO2保护膜.探讨了晶粒尺寸对合金高温氧化行为的影响机理.     

铁基高温金恒温氧化行为研究

采用OM,XRD及SEM/EDX研究了铁基高温合金GH 1140的高温静态空气氧化行为,得到了该合金的氧化动力学曲线、氧化膜形貌及其相组成,评价了合金的抗氧化性能并分析了其氧化机理.结果表明:铁基高温合金GH1140在750～900℃时氧化动力学遵循抛物线规律,无氧化膜剥落;在950℃氧化时氧化动力学近似遵从直线规律,且有少量氧化膜剥落;合金氧化过程中有内氧化现象发生,生成的氧化膜以Cr2O3为主;该合金可满足850℃以下高温使用要求.     

铝及其合金的微弧氧化技术

综述了近年来利用微弧氧化技术对铝及其合金进行表面处理的研究进展;着重分析归纳了电流密度、电压、频率等电参量以及不同基体材料对铝合金微弧氧化膜的生长、成分、结构和性能等方面的影响;分类评价了铝合金微弧氧化处理中常用的电解液体系;简要描述了铝合金微弧氧化的动力学特点和膜层的生长机理;指出电参量的控制以及电解液成分和浓度的调整是将来铝合金微弧氧化技术的研究重点.     

Influence of Reactive Element Oxide Coatings on the High Temperature Oxidation Behavior of Alumina-Forming Alloys

Reactive-element-oxide coatings were processed by a metal-organic chemical-vapor-deposition technique on the surface of a model FeCrAl alloy. The high-temperature performances of Nd₂O₃-, Y₂O₃-coated and uncoated alloys were tested in air under atmospheric pressure at 1050, 1100 and 1200° C. The coated samples did not exhibit the expected reactive-element effects since the oxidation rates were not decreased, and the oxide-scale adherence was only slightly improved. The study of the oxide-scale morphology revealed very convoluted oxide scales, except for alumina scales formed on uncoated materials at 1100 and 1200° C. Two-stage oxidation experiments showed that the reaction proceeded by a mixed anionic–cationic diffusion process; consequently, the growth of alumina within the existing alumina layer results in convoluted scales. It is proposed that the weak incorporation of the reactive elements within the thermally growing alumina scales was responsible for the limited reactive element effects, when reactive-elements were applied as oxide coatings on alumina-forming steels.     

纯镁的高温氧化特性研究

通过差热分析法和氧化动力学曲线测定法对纯镁的高温氧化特性作了详细研究,结果表明,纯镁在低温下氧化缓慢,更不会发生燃烧,只有当温度上升至873 K以上近熔点温度范围时,与氧的反应才会剧烈起来,因此建议阻燃镁合金的开发应将重点放在近熔点温度范围内表面保护膜的生成热力学、动力学及其组织结构上,这对阻燃镁合金的进一步发展具有指导意义.     

Thermal Oxidation Behavior of TiNi Alloys

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