Structure-dependence of intergranular corrosion in high purity nickel

Electrochemical studies were conducted in 2 N H₂SO₄ at 303 K in order to assess the applicability of the CSL/DSC model of interface structure to intergranular corrosion susceptibility at grain boundaries in high purity (99.999%) polycrystalline nickel. Susceptibility to the initiation of localized corrosion at grain boundaries was manifested through characteristic overpotentials for passive film breakdown. These characteristic overpotentials were found to (1) decrease with increasing bulk sulphur concentration (0.3–50 ppm), and (2) be strongly dependent on interface structure (CSL/DSC). Boundaries close (Δθ) to low ΣCSL relationships were observed to be most resistant to the initiation of localized corrosion. A limiting structural field was determined, not extending beyond Σ25, and restricted to an angular deviation limit defined by a relation of the type: Δθ = 15° Σ^−5/6. Results were determined to be consistent with a mechanism whereby susceptibility to intergranular corrosion is dictated by the (1) geometry, and (2) chemistry (i.e. solute concentration) of intrinsic grain boundary dislocations.     

Modification of cast aluminum-matrix composite materials by refractory nanoparticles

The effect of SiO₂ and Al₂O₃ oxide ceramic nanoparticles on the solidification of model samples based on a commercial D16 alloy is studied. The composite samples are fabricated by reaction casting when titanium, nickel, and ceramic powders are mixed with an aluminum melt. The grain size in a matrix, the size and shape of Al₃Ti intermetallic inclusions, and the interphase distances in eutectics are determined with optical and scanning electron microscopes. A certain modifying effect of oxide ceramic nanoparticles on the structure of model CMs during their in situ formation is detected, and the inoculation effect of SiO₂ added to a melt on the reaction products is most pronounced.     

Mechanical properties and wear behaviour of PM aluminium composite reinforced with (Fe3Al) particles

Abstract

Mechanical properties and wear behaviour of an aluminium matrix composite reinforced with Fe₃Al intermetallics have been studied. A 2014 alloy manufactured through mechanical alloying was used as the matrix. Three different Fe₃Al intermetallics have been used as reinforcement, also manufactured through mechanical alloying. The difference between them was the different mechanical alloying times (5 and 20 h were used) and the possibility of carrying out a heat treatment at 1000°C (on the 20 h milled intermetallic) before admixing to the aluminium matrix. The processing of these composite materials included mixing and cold compacting (conventional powder metallurgy) followed by hot extrusion (without caning and degassing). The effect of a T6 heat treatment was also evaluated. The influence of intermetallic additions on the mechanical properties (hardness and tensile strength) and wear behaviour (pin on disk test) was established. All intermetallics showed a good link with the matrix, and high reactivity with it during the heat treatment, as the microstructural study supports.     

多壁碳纳米管和氧化铝复合增强铝基复合材料阻尼特性的研究

采用粉末冶金的方法制备了四种不同增强体组分的铝基复合材料,这四种复合材料分别为:10%A l2O3/A l复合材料、1%MWCNT+9%A l2O3/A l复合材料、5%MWCNT+5%A l2O3/A l复合材料、10%MWCNT/A l复合材料.用动态机械热分析仪研究了上述四种复合材料的阻尼特性.     

TiC颗粒增强钛基复合材料的摩擦磨损性能

采用Ti粉末分别与碳化物Mo2C和VC粉末混合,通过冷等静压、真空高温烧结原位生成6种不同成分的TiC颗粒增强钦基复合材料,用UMT-3型摩擦试验机研究合金元素Mo和V以及Mo2C、VC添加量对钛基复合材料干磨擦性能的影响.测定不同样品的洛氏硬度和基体的显微硬度,用金相显微镜(OM)、X射线衍射仪(XRD)观察和分析样...     

Physicochemical laws of the interaction of nickel aluminides with alloying elements: II. Interaction of nickel aluminides with alloying elements and/or interstitial phases

The Ni-Al-X (X is an interstitial element or phase) phase diagrams are analyzed to reveal systems that can be used as the basis for designing promising alloys and natural composites based on nickel aluminides reinforced by interstitial phases (natural composites I). The most thermally stable materials are shown to be heterophase alloys and composite materials (CMs) located in the eutectic-type (including degenerate eutectic) pseudobinary sections of ternary or multicomponent phase diagrams. They exhibit insignificant (or zero) dissolution of interstitial phases at operating temperatures and the absence of an intense interaction between CM components (natural composites II). Natural composites I based on the NiAl-or Ni₃Al-interstitial phase alloys produced upon cooling from a melt can be reinforced by the refractory thermally stable rigid interstitial phases, namely, borides and carbides, that are present in pseudobinary sections in equilibrium with these nickel aluminides, since the elements forming these phases dissolve completely in matrix melts and the mutual solubility of these phases in the solid state is low. Such borides are TiB₂ and HfB₂ in equilibrium with β-NiAl, and such carbides are, e.g., TiC and HfC in equilibrium with β-NiAl and La₂C₃, NbC, and TaC in equilibrium with γ′-Ni₃Al. Natural composites II should be produced using solid-phase methods (NiAl with AlN, Y₂O₃, Al₂O₃) or a combination of methods, where a refractory interstitial phase of the Al₂O₃ or Y₂O₃ type is solid and the intermetallic NiAl or Ni₃Al matrix is liquid. NiAl-TiB₂ (HfB₂), NiAl-Al₂O₃ (Y₂O₃), and Ni₃Al-La₂C₃ (NbC, TaC) composites are considered as examples.     

Shock-induced chemical reactions and synthesis of nickel aluminides

Chemical reactions in Ni and Al powder mixtures, initiated by the passage of shock waves, are used for the synthesis of nickel aluminides. Mechanistic investigations reveal that the extent of these shock-induced chemical reactions and the type (stoichiometry) of shock-synthesized compound formed depend on shock-loading conditions and the initial powder particle morphology. More intense shock conditions and irregular powder morphology assist in attaining an intimately (mechanically) mixed and activated closed-packed mass, thereby favoring bulk chemical reactions and resulting in the synthesis of compounds. While the Ni₃Al compound is the preferred reaction product at lower shock conditions, more intense shock conditions favor the formation of the equiatomic B2-phase NiAl compound (having highest melting temperature and highest heat of reaction in contrast to other nickel aluminides), in spite of the starting powders mixed in a volumetric ratio corresponding to the Ni₃Al compound. This paper is based on a presentation made in the symposium “Reaction Synthesis of Materials” presented during the TMS Annual Meeting, New Orleans, LA, February 17–21, 1991, under the auspices of the TMS Powder Metallurgy Committee.     

沉淀硬化不锈钢耐蚀抗磨性能的研究

用失重法测定了沉淀硬化不锈钢17-4PH在硫酸、石英砂固液两相介质中的腐蚀磨损速率,研究了介质浓度、冲刷速度和冲刷时间对17-4PH耐蚀抗磨性能的影响规律.试验结果表明,介质浓度越高、冲刷速度越大,17-4PH腐蚀磨损失重越大;而随着冲刷时间间隔的延长,腐蚀磨损失重越小.     

颗粒增强高铬铸铁基复合材料界面及摩擦学特性

以机械破碎的废弃钨钴钛类硬质合金为增强颗粒,采用负压铸渗工艺制备颗粒增强高铬铸铁基复合材料,通过金相显微镜和X射线衍射仪分析材料的显微结构和物相组成,利用销-盘式两体磨料磨损试验机研究该复合材料的耐磨性能,并将其与工程中常用的热处理态Cr20高铬铸铁材料进行对比.结果表明:由于在铸渗过程中增强颗粒的部分熔解以及W、C、Ti、Co、Fe、Cr等元素的互扩散,在界面处形成了含Fe、W、Co等元素的多种化合物,确保界面的冶金结合;该复合材料的耐磨性比热处理态Cr20高铬铸铁材料有显著提高,且当加载载荷从0.4 kg增大到2 kg时,复合材料的耐磨性表现得更为突出,相对耐磨性是热处理态高铬铸铁的3.5倍以上.     

The effects of cold working on sensitization and intergranular corrosion behavior of AISI 304 stainless steel

The effects of prior cold rolling of up to an 80 pct reduction in thickness on the sensitization-desensitization behavior of Type AISI 304 stainless steel and its susceptibility to intergranular corrosion have been studied by electrochemical potentiokinetic reactivation (EPR) and Strauss-test methods. The results indicate that the prior deformation accelerated the sensitization as compared to the undeformed stainless steel. The deformed Type 304 stainless steel experienced desensitization at higher temperatures and times, and it was found to be enhanced by increased cold deformation. This could be attributed to the increased long-range chromium diffusion, possibly brought on by increasing pipe diffusion and vacancies. The role of the deformation-induced martensite (DIM) and texture, introduced by uniaxial cold rolling, on the sensitization-desensitization kinetics has also been discussed. This study could not reveal any systematic relationship between texture and the degree of sensitization (DOS) obtained. The effect of DIM on DOS seems to be pronounced at 500 °C when the steel retained significant amounts of DIM; however, the retained DIM is insignificant at higher sensitization times and temperatures.     

Service properties of aluminum-matrix precipitation-hardened composite materials and the prospects of their use on the modern structural material market

The methods of production, the structure, and the service properties of aluminum-matrix composite materials (CMs) hardened by high-strength high-module particles are discussed. Owing to high wear resistance, a low specific weight, and a low cost, such CMs are promising for application in many fields of machine building. The need for commercial development of these new functional reinforced CMs with hardening fillers of various natures and fraction compositions (including nanoparticles) as high-temperature and wear-resistant materials instead of traditional materials is grounded.     

含Cr管线钢的力学性能和耐蚀性能

基于国内油气工业管线应用需要,采用控轧控冷工艺,研制了强韧性匹配优良的2%Cr低合金管线钢,并测试了其组织和力学性能.以针状铁素体和多边形铁素体为主的含2%Cr管线钢具有良好的强韧性组合.采用高温高压冷凝釜模拟湿气管线中的CO₂顶部腐蚀环境试验方法,研究含2%Cr低合金管线钢的抗CO₂顶部腐蚀性能.相较于传统管线钢,添加2%Cr后,其CO₂腐蚀产物膜是一层连续、致密的富Cr胶泥状非晶态产物膜,从而提高了其抗CO₂顶部腐蚀性能.     

Deformation behavior of continuous-fiber metal-matrix composite materials

The deformation behavior of continuous-fiber, metal-matrix composites was studied in terms ofin situ deformation behavior of the matrix and the fibers. X-ray diffraction techniques were employed to monitor the stress-strain behavior of the composite components (matrix and fibers) as a function of total composite stress-strain behavior. This experimental technique provided a unique approach to the study of metal-matrix composites since the deformation response of the components could be measuredin situ while the composite was under load. Furthermore, the influence of residual stress, component mechanical properties, and stress interactions between the matrix and the fibers could be incorporated into the analysis of composite deformation behavior. The study was conducted on composites of 2024 aluminum reinforced with tungsten fibers, and composites of 2024 aluminum reinforced with boron fibers. Composites were tested on a specially-designed, tensile device which served as a diffractometer specimen holder such that diffraction experiments could be performed while the specimen was incrementally deformed in uniaxial tension. Experimental results indicated that, except for the residual stress effects, the composites exhibited rule-of-mixture s behavior in the stage I, II, and in deformation regions. Measurements obtained perpendicular to the fiber and tensile axis during the tensile tests indicated that negligible stresses were developed as a result of Poisson’s ratio differences between the matrix and the fibers. Composite yield behavior was significantly influenced by residual stresses present in the individual components. Residual stresses parallel to the fiber axis could be included in the rule-of-mixtures analysis by considering the amount of prestrain which was present in each component. Formerly, Graduate Student, Department of Metallurgical Engineering, Drexel University, Philadelphia, Pa. This paper is based on a thesis submitted by H. P. CHESKIS to the Graduate Faculty in Materials Engineering at Drexel University in partial fulfillment of the requirements of the degree of Doctor of Philosophy.