沉积硫酸盐对Fe-20Cr合金800℃氧化行为的影响

采用动力学测量、SEM、X-射线等手段研究了沉积硫酸盐对Fe-20Cr合金800℃氧化行为的影响.结果表明,沉积盐引起Fe-20Cr合金加速氧化.     

纳米 NiCrBSi-TiB2 涂层在硫酸熔盐中的热腐蚀行为研究

目的研究纳米NiCrBSi-TiB2涂层在800℃下的Na2SO4-30%(质量分数)K2SO4熔盐中的热腐蚀行为。方法采用超音速火焰技术在中碳钢表面喷涂纳米NiCrBSi-TiB2涂层,以饱和Na2SO4-30%K2SO4溶液为腐蚀介质,研究该涂层在800℃时的热腐蚀行为。结果微米涂层晶粒粗大,Si的扩散系数低,易出现贫Si富Cr层,形成的Cr2O3膜在碱性熔盐中具有较低的溶解度,对涂层具有良好的保护作用。结论微米涂层在Na2SO4-30%K2SO4熔盐中具有更优的抗热腐蚀性能。     

Comparison of inward and outward grown Pt modified aluminide diffusion coatings on a Ni based single crystal superalloy

Two commercial Pt modified aluminide coatings (RT22 and MDC150L) on the same single crystal Ni-based superalloy (CMSX-4) were studied by: scanning electron microscopy; transmission electron microscopy; energy dispersive X-ray spectrometry; and gravimetry. The RT22 coating is an inward grown coating (high activity), while MDC150L is produced by outward growth (low activity). Samples were oxidised in still laboratory air at 1050 °C for various times up to 2000 h. It was found that the outward grown coating produced a slower growing oxide that was more spallation resistant. Several possible reasons for this were identified including: coating purity; coating surface topography; and ductile to brittle transition temperature. The microstructural differences between the two coatings in the as-coated condition were investigated and the development of their microstructure during heat treatment was described. A model for coating growth during heat treatment was proposed.     

High-Temperature Corrosion Resistance of Al–Re and Re Coatings

The oxidation behavior in air at 1473 K, and sulfidation behavior in a H2S–H2 gas mixture with a sulfur partial pressure of 10^–2 Pa at 973 K of Al–Re coated CMSX-4 were studied. Investigation on the sulfidation behavior of the Re-coated CMSX-4 was carried out in a H2S–H2 gas mixture with a sulfur partial pressure of 10^–2 Pa at 973 K. The experimental results show that a Re-rich alloy layer was formed between an -Al₂O₃ layer and the inner concentration zone of Ta and Ti for the CMSX-4 single crystal alloy with an Al–Re coating after oxidation. The Re-rich alloy layer containing Cr, W, Ni, Co, and Mo effectively inhibited the outward diffusion of alloying elements and the inward diffusion of Al. The Al/Re-coated CMSX-4 single crystal alloy had excellent sulfidation resistance; the Re-rich alloy layer, containing W, Ti, Ta, and Mo, which formed during the sulfidation process and located between the alumina scale and the CMSX-4 base alloy, plays a role in inhibiting the outward diffusion of alloying elements. The sulfidation resistance of CMSX-4 single-crystal alloy is greatly improved by a Re coating on the CMSX-4 alloy surface; this is attributed to a Re–Cr–W alloy layer that retarded the outward diffusion of cations and the oxide layer containing Ta, Ti, and Al, which inhibited the inward penetration of sulfur.     

Preparation of nanometer δ- and β-bismuth trioxide by vacuum vapor-phase oxidation

1 Introduction Bismuth trioxide is an important function material. It exits in four polymorphs[1-4], i.e. the monoclinic α-phase, the tetragonal β-phase, the body-centered cubic(bcc) γ-phase and the face-centered cubic(fcc) δ-phase. Below 730 ℃, bism     

Al2O3/Cu复合材料的内氧化制备及性能研究

采用高能球磨制备出亚稳态的Cu-1%Al（质量分数）合金粉,再将Cu2O粉与其一起进行高能球磨,然后将复合粉末压坯在N2保护炉中同时进行氧化和烧结,制备出Al2O3/Cu复合材料。分析了分别采用湿法球磨和干法球磨时的合金化效果,讨论了模压压力对材料性能的影响。结果表明,对于Cu-Al混合粉来说,采用湿法球磨容易产生分层,采用干法球磨具有良好的合金化效果;在本试验条件下,750MPa为最佳的模压压力,但烧结后材料的电导率还是偏低,因此有必要进行后续的处理来进一步提高材料的性能。     

Changes of an Outer β-NiAl and Inner α-Cr Coating on Ni–40 at% Cr Alloy during Oxidation at 1373K in Air

Formation mechanisms of a coating with a duplex layer, outer β-NiAl(Cr) and inner α-Cr(Ni) layer structure on a Ni–40.2 at% Cr alloy were proposed and change in the coating structure was investigated during high temperature oxidation. The Ni–40.2 at% Cr alloy was electro-plated with about 12μm Ni followed by a high Al activity pack cementation at 1073K to form a coated layer with an outer δ-Ni₂Al₃ and an inner layer containing Al more than 70at% which grew with an inward diffusion of Al. The coated Ni–40.2at% Cr alloy was oxidized at 1373K in air for up to 2592ks. It was found that at the initial stage of oxidation the as-coated layer structure changed to a two-layer, outer β-NiAl(Cr) and inner α-Cr(Ni), structure. Al contents in the α-Cr(Ni) layer was less than 0.3at%. With long term oxidation an intermediate γ-Ni(Cr, Al) layer formed between the outer and inner layers, whereas the inner α-Cr(Ni) layer became thinner and then disappeared after the 2592ks oxidation at 1373K. Coating processes and changes in the coating structure during high temperature oxidation were discussed based on diffusion and composition paths plotted on a Ni–Cr–Al phase diagram     

Cu-Al预合金粉末中Al内氧化工艺的分析

对高能球磨制备的Cu-Al预合金粉末中Al内氧化的工艺进行了研究．结果表明,温度是决定临界氧分压Po2的关键因素,随着温度的升高,临界氧分压增加．适当提高温度可以减小环境氧分压的控制难度．高能球磨制粉对Al内氧化的热力学条件影响不显著,但对动力学条件影响显著．当Al的质量分数大于0．5％时,对于不同的Al含量的Cu-Al预合金粉末应有不同的加热工艺．当工艺参数适宜时,采用Cu-Al预合金粉末可以制备出组织均匀的Al2O3／Cu复合材料,其中Al2O3颗粒粒径2—5μm,颗粒间距5—10μm．     

超音速火焰喷涂NiCoCrAlY/Al2O3-10%B4C涂层的制备及抗氧化性能研究

目的 提高金属/陶瓷体系高温固体润滑耐磨涂层的抗氧化性能。方法 采用离心喷雾造粒、高压氢还原镀镍和固相合金化技术,制备包覆型NiCoCrAlY/Al₂O₃-10%B₄C复合粉体,并采用超音速火焰喷涂技术在镍基高温合金上沉积复合涂层材料,通过SEM和XRD研究粉体和涂层的显微结构和物相组成,通过马弗炉研究涂层在高温下的氧化性能。结果 Al₂O₃-B4C颗粒表面均匀包覆着一层厚度为2～3μm的NiCoCrAlY合金。超音速火焰喷涂NiCoCrAlY/Al₂O₃-10%B₄C复合涂层结构致密,孔隙率仅为0.45%±0.05%,涂层与基体结合良好。涂层和粉体的主晶相均为Ni的固溶体、α-Al₂O₃相和B4C相,涂层衍射峰强度比粉体有所降低。在850℃氧化96 h后,涂层表面生成了一层连续的灰色物质,其厚度为1～3μm,经EDX分析,其主要元素组成为O、Ni、Al和Cr,说明主要...     

A complex structure in the (β+γ0) region of the Cu–Al alloys

The identification, characterization and stability range of the phases present in a series of Cu–Al alloys, with Al content from 11.0 to 15.0 wt.%, were studied by Differential Thermal Analysis (DTA), Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED), Auger Electron Spectroscopy (AES), Energy Dispersive X-Ray Spectroscopy (EDX) and X-Ray Diffraction (XRD). In some alloys and in a temperature range from 790°C to 850°C the presence of black spots exhibiting regular shapes and an homogeneous distribution was noticed through metallographic microscopy. Data from TEM and AES indicate that these spots are made of two monocrystalline phases having different Al contents and a crystallographic orientation relationship.     

Effect of Water Vapor on the Oxidation Behavior of Fe–1.5Si in Air at 1073 and 1273 K

The oxidation behavior of Fe–1.5Si was investigated at 1073 and 1273 K in air, air–H₂O, Ar–H₂O, O₂–H₂O, and O₂ atmospheres. The extent of corrosion in atmospheres containing H₂O increased rapidly after an incubation period of slow oxidation, the incubation period becoming shorter in the order, O₂–H₂O, air–H₂O, and Ar–H₂O. With increasing H₂O contents in air–H₂O, the incubation time decreased. During the incubation period, oxidation was slow, because of the formation of an inner Si-rich oxide layer and a Pt marker was located between the external Fe₂O₃ (Fe₃O₄ included) and an inner Si-rich oxide layer. During the rapid oxidation, the inner FeO+Fe₂SiO₄ layer thickened and a Pt maker was at the interface between an external Fe-oxide and an inner FeO+Fe₂SiO₄ layer. Observations of scale cross sections indicated that voids made channels along the boundaries of columnar FeO crystals, suggesting transport of water molecules. The Si-rich oxide layer changed into an FeO+Fe₂SiO₄ mixture due to penetration of water molecules. A combined process of perforating dissociation and transport of water molecules is suggested to be the cause of the rapid growth of the inner FeO+Fe₂SiO₄ layer.     

Ce改性ZSM-5分子筛载Pd催化剂的CeO2-Pd协同作用研究

采用XRF、XRD、SEM和CH4-TPR表征手段,研究了Ce改性ZSM-5分子筛载Pd催化剂在CO、CH4氧化过程中的CeO2-Pd协同作用。结果表明,经Ce改性后ZSM-5分子筛的载Pd量提高;Pd/Ce-ZSM-5催化剂对 CH4的起始吸附温度降低;Pd/Ce-ZSM-5催化剂中 Ce 主要以 CeO2形态存在。Pd是CO的催化氧化活性物种,CeO2-Pd协同作用可促进CO的氧化。Pd和PdO均是CH4的催化氧化活性物种,CeO2的供氧-储氧特性有助于Pd→PdO的转化,CeO2与Pd的相互作用使Pd/Ce-ZSM-5催化剂具有高的CO和CH4催化氧化活性。     

TEM Study of the Internal Oxidation of an Fe–Mn–Al–C Alloy After Hot Corrosion

The internal oxides formed in Fe–31.1Mn–9.07Al–0.89C at 750–850°C in air with 2 mg/cm² NaCl deposits initially were investigated by means of transmission electron microscopy (TEM). The results showed that the volatile species generated by hot corrosion accelerated internal oxidation in the internal voids. The alloys suffered severe subscale attack at 750 and 800°C because a protective alumina scale was not formed. The morphology of attacked subscale can be divided into three layers. The interconnecting voids in the outer subscale are finer and denser than those in the inner subscale. The products inside the voids of the outer subscale are metal oxides, while the oxides inside the voids of the inner subscale are filled with fine Fe₃O₄ particles. However, due to the formation of an aluminum-rich oxide scale at 850°C, only a small amount of internal oxidation was generated in the subscale, which provided the best corrosion resistance in this study.