Effects of Pt on the short-term oxidation behavior of γ-Ni+γ′-Ni3Al alloys

Abstract

The aim of this study was to elucidate the beneficial role played by platinum addition in promoting the formation of a protective Al₂O₃ scale on γ′-Ni₃Al+γ-Ni alloys during oxidation at high temperatures. To do this, the early-stage oxidation behavior of γ′-Ni₃Al-based alloys of composition (in at.%) Ni–22Al and Ni–22Al with 10, 20, and 30 Pt was investigated in terms of oxidation kinetics, scale evolution and resulting composition profiles during heating to 1150°C in air. Platinum addition did not appear to affect the nature of the native oxide layer present on the γ′-based alloys at room-temperature; however, it was found that the presence of increasing Pt content aided in promoting the establishment of a continuous Al₂O₃ scale during heating above about 600°C. This beneficial effect can be primarily ascribed to the fact that Pt is non-reactive and its addition decreases the chemical activity of aluminum in γ′. Related to the latter, Pt partitions almost solely to the Ni sites in the ordered L1₂ crystal structure of γ′, which has the effect of amplifying the increase in the Al:Ni atom fraction on a given crystallographic plane containing both Al and Ni. Such an effective Al enrichment at the γ′ surface kinetically favors the formation of Al₂O₃ relative to NiO. A further contributing factor is that the Pt-containing γ′-based alloys showed subsurface Pt enrichment during the very early stages of oxidation. This enrichment reduces Ni availability and can increase the Al supply to the evolving scale, thus kinetically favoring Al₂O₃ formation.     

Ni60-Ni包MoS_2-Ni包C复合自润滑涂层的结合强度及摩擦学性能

镍基合金涂层材料具有良好的耐磨性和耐蚀性.在其中加入适量复合固体润滑剂可有效改善合金的摩擦学性能,并保持一定的结合强度.以Ni60为基体粉末,Ni包MOS2和Ni包C(石墨)为复合自润滑粉末,以均匀设计方法设计喷涂粉末配比,采用超音速火焰喷涂技术制备涂层,测试了涂层的抗拉结合强度、摩擦系数和磨损失重,并对涂层的结合强度、摩擦系数和磨损失重进行了回归分析.结果显示:回归方程均具有较好的拟合性;Ni包MoS2与Ni包C具有协同效应,对Ni60涂层的性能具有显著的影响;当Ni包MoS2为33%(质量分数)、Ni包C为13%(质量分数)时,复合涂层的结合强度大于30 MPa,摩擦系数和磨损失重最小,表明涂层具有较好的结合性能及最佳的摩擦学性能.     

Ca-La2O3-Ni体系的热力学研究

计算了用Ca还原La2O3生成纯金属La(3Ca La2O3=2La 3CaO),La与Ni反应生成LaNi5合金（La 5Ni=LaNi5)的标准吉布斯自由能和吉布斯自由能变化,以及反应平衡时的钙分压,在1223,1273,1323,1373K温度下制得了LaNi5合金,XRD鉴定了反应产物的物相,热力学计算说明在La-NI系化合物中生成物只能是L aNi5。     

Microstructural development in cast alloys based on the β-NiAl–β′-Ni2AlTi–γ′-Ni3Al–α-Cr system

An investigation of microstructural development in three arc-cast Ni–Al–Cr–Ti multiphase alloys derived from the B2 type -NiAl phase is presented. Detailed microstructural characterization of Ni–25 at % Al–20 at % Cr–15 at % Ti, Ni–26 at % Al–21 at % Cr–11 at % Ti and Ni–25 at % Al–24 at % Cr–15 at % Ti materials by transmission electron microscopy (TEM), is described. Microstructural development is examined in both the as-cast condition and after 140 h homogenization treatments at both 850 and 1100 °C. The formation of a eutectic between an L21-type phase (Heusler phase, with a nominal composition of Ni2AlTi) and elemental -Cr is examined. The precipitation of within () and vice versa, in both the inter- and intradendritic regions, is considered. The formation of L12-type (nominally Ni3Al) precipitates within the and -phases is discussed, as is the transformation of to two-phase / during ageing. © 1998 Chapman & Hall     

ZrO2-Ni等离子喷涂涂层的残余应力

对不同镍含量的ＺｒＯ２－Ｎｉ等离子喷涂层应用Ｘ射线应力分析技术测试涂层表面应力,用曲率测试应力分析方法测定涂层平均应力,两者有较好的相关性,均表明涂层的残余应力为较小张应力。据测试的曲率半径估算了二层、三层、和六层阶梯涂层各层的平均残余应力和涂层喷涂的平均温度,结果表明多层过渡结构以残余应力作用甚微,所估算的喷涂温度与实际操作条件基本相符。     

浸渍α-Ni(OH)2稳定性的研究

通过X射线衍射 (XRD)分析证实含B添加剂的镍电极活性物质晶型结构为α型 ,差热 热重 (DTA TG)分析则表明α Ni(OH) 2 层间有结构水或化学吸附水存在。探讨了添加剂B分别与Na2 S、Ca(NO3) 2 共沉积的镍电极性能。通过XRD及 50多次大电流充放电循环表明 ,该电极仍具有α型结构 ,且大电流放电容量的衰减受到一定程度抑制。     

碳纤维-Ni/尼龙66复合材料的制备与性能表征

为制备低电阻率的尼龙66基复合材料,以碳纤维和镍粉(Ni)填充尼龙66制备碳纤维-Ni/尼龙66高导电复合材料。研究填料表面改性和含量对碳纤维-Ni/尼龙66复合材料导电性能和力学性能的影响。结果表明:KH550改性碳纤维和Ni有助于降低碳纤维-Ni/尼龙66复合材料的电阻率。碳纤维-Ni/尼龙66复合材料的电阻率随着碳纤维和Ni含量的增加而减小,且碳纤维和Ni填充尼龙66的导电逾渗阈值均为20wt%,此时制备的碳纤维-Ni/尼龙66复合材料的电阻率为455Ω·cm,熔融温度为202.2℃。碳纤维-Ni/尼龙66复合材料的弯曲强度和拉伸强度随着碳纤维或Ni含量的增加而先增大后减小。当Ni含量为20wt%时,碳纤维-Ni/尼龙66复合材料的弯曲强度和拉伸强度在碳纤维含量分别为20wt%和10wt%时达到最大值,分别为98MPa和70 MPa;当碳纤维含量为20wt%时,碳纤维-Ni/尼龙66复合材料的弯曲强度和拉伸强度则在Ni含量为30wt%和20wt%时达到最大值,分别为120 MPa和67 MPa。     

α-Ni(OH)2/SiO2核壳以及α-Ni(OH)2空心微球的制备及表征

采用以正硅酸乙酯(TEOS)水解为基础的硅溶胶种子生长法制备了粒径约为270nm的近单分散二氧化硅球型颗粒.采用一种新的溶液生长法,以氢氟酸作为溶液中镍离子配位剂,加入氨水调节溶液pH值的同时作为镍离子补充配位剂,60℃水浴条件下在已制得SiO2微球表面均匀包覆α-Ni(OH)₂得到Ni(OH)₂/SiO₂核壳结构,Ni(OH)₂壳层厚度约为35nm.结合多步包覆法提高Ni(OH)₂壳层厚度,三次包覆后壳层厚度达到约100nm,四次包覆后约为140nm.采用20wt％的强碱NaOH溶液对三次包覆后的Ni(OH)₂/SiO₂核壳结构进行处理,得到了壳层厚度约为95nm的α-Ni(OH)₂空心微球.空心微球具有较大的比表面积为141.06m²/g.     

Microstructure and Mechanical Properties of ZrO_2-Ni Functionally Gradient Material

The fabrication. microstructure and mechanical properties of ZrO2-Ni functionally gradient materials (FGM ) have been studied. FGM as well as non-FG M of ZrO2-Ni system was developed by powder metallurgical process. X-ray diffractometer (XRD ). electron probe microanalyzer (EPMA), scanning electron microscope (SEM ) and optical microscope were employed to investigate the crystalline phases. chemical composition and microstructure Experimental results demonstrate that the composition and microstructure of ZrO2-Ni FGM have the expected gradient distribution. There are no distinct interfaces in the FGM due to the gradient change of components. that is, the constituents are continuous in microstructure everywhere. Moreover, Vickers hardness and flexural strength were measured for the common composites as a function of composition. It is made clear that the mechanical properties of the FGM vary corresponding to the constitutional changes as well     

Cast and aged β-NiAl-β′-Ni2AlTi-γ′-Ni3Al-α-Cr alloys: a microstructural and mechanical properties investigation

Microstructural development and stability in cast Ni-30 at% Al-21 at% Cr-4 at% Ti, Ni-28 at% Al-18 at% Cr-6 at% Ti and Ni-26 at% Al-19 at% Cr-8 at% Ti alloys are examined in this paper. The paper considers the extent to which microstructural control and stability is improved in these alloys, when compared with earlier work by the authors on similar materials with lower aluminum (25 or 26 at%) and higher titanium (11 to 15 at%) contents. The paper discusses detailed transmission electron microscopy investigations of both as-cast and aged (140 h at 850 and 1100°C) samples. Attention is focussed on the transformation of L2₁ type (nominally Ni₂AlTi) dendrites. In particular, the influence of the formation of intradendritic L1₂ type (nominally Ni₃(Al,Ti)) on the stability of the -phase is examined. Morphological changes and phase transformations within a --Cr eutectic are discussed. Various modes of second-phase precipitation are considered. The microstructures of selected samples are correlated with mechanical properties determined by tensile testing and fractography.     

(TiC-TiB2)-Ni复合陶瓷的高温摩擦磨损性能

为了进一步优化复合陶瓷的制备工艺,以采用高温自蔓延合成法(SHS)制备的(Ti C-Ti B2)-30%Ni复合陶瓷材料作为研究对象,研究其在不同温度、载荷和摩擦速度下的摩擦系数和磨损率。采用光电分析天平对磨损前后试样进行称重,采用扫描电子显微镜(SEM)对磨损形貌进行观察。结果表明:在磨损温度、摩擦载荷和速度较低时,摩擦系数较高,此时的磨损机制主要为磨粒磨损;随着温度、载荷和速度的升高,磨损表面生成氧化膜,此时磨损机制变化为氧化磨损,摩擦系数降低;磨损率随温度的升高呈现降低的趋势,但随着载荷和速度的增加,磨损率也随之增大。     

β-Ni(OH)2纳米粉末制备方法的改进

研究了纳米级β-Ni(OH)2粉末的制备方法，使纳米粉末的产率提高了近5倍，达到了85％，并保持纳米粉末的尺寸在50－80nm。制备的β-Ni(OH)2纳米粉末可以提高镍电极容量的10％－12％。     

二次干燥法制备高密度α-Ni(OH)2

采用二次干燥的化学共沉淀法制备出了高密度α-Ni(OH)2,研究了烘干温度、陈化时间对其晶体结构和振实密度的影响,XRD图谱结果表明,采用该法所制备的一系列Ni(OH)2均为α型结构,其中在120℃烘干,陈化24h的条件下制备的α-Ni(OH)2晶体结构较为完整,并且在该条件下制备出了密度达到1.70g/cm3的α-Ni(OH)2.     

One-step synthesis of spherical α-Ni(OH)(2) nanoarchitectures

We report the synthesis of sphere-like α-Ni(OH)(2) nanoarchitecture by self-assembly with the aid of hexamethylenetetramine (HMT). The α-Ni(OH)(2) nanoarchitectures, with a diameter of several micrometres, are composed of many nanoflakelets about 10?nm in thickness. The influences of the reaction temperature, time, reagent, nickel salt and pH?value on the morphology and structure of the α-Ni(OH)(2) were studied, the chemical and thermal stability are discussed, and the formation mechanism is proposed. The α-Ni(OH)(2) nanoarchitectures display a good electrochemical capacity.     

纳米TiO_2-Ni基镀层的电刷镀沉积行为研究

为了使纳米颗粒均匀地悬浮在镀液中从而获得纳米颗粒均匀分布的复合镀层,研究了不同表面活性剂对纳米TiO2在镀液中的分散行为的影响,采用电刷镀方法制备纳米TiO2-Ni基复合镀层,并运用SEM、EDS和XRD研究了纳米TiO2-Ni基镀层的表面形貌和成分特点。结果表明,阳离子型表面活性剂十六烷基三甲基氯化铵(CTAB)对纳米TiO2颗粒的分散效果最好,沉降时间超过40min;CTAB分散的纳米TiO2-Ni基镀层显微硬度比不加表面活性剂的提高50%左右,镀层结合性较好,孔隙率显著降低;CTAB分散的纳米TiO2-Ni基镀层均匀细致、晶粒细小,纳米TiO2被生长着的镍晶粒夹持嵌埋,分布于镍基间隙中,镀层由纳米TiO2颗粒和镍基组成。纳米粉末与镍共沉积符合迁移、吸附、嵌埋的过程。     

纳米Ti02-Ni基电刷镀参数的优化及镀层性能

为了得到性能优异的纳米Ti02-Ni基复合电刷镀层,通过正交试验研究了镀镍液中纳米TiO2颗粒含量、刷镀电压等因素对纳米Ti02-Ni基镀层性能的影响。通过锉削试验、骤冷骤热试验、划痕试验定性表征了纳米Ti02-Ni基镀层与钢基体的结合性能,并运用扫描电镜（SEM）和能谱仪（EDS）分析了纳米Ti02-Ni基镀层的表面...     

纳米级β-Ni(OH)2的制备和放电性能

本文采用均相沉淀法和无水乙醇溶剂法制备出了纳米级β-Ni（OH）₂运用XRD、TG、DTA、TEM及ICP测试对制备的样品作了分析研究．制备过程中表面活性剂、转型条件及后处理温度的选择对样品性质影响很大,对纳米β-Ni（OH）₂进行了充放电实验研究．     

ZrO2-Ni功能梯度材料的热冲击与热疲劳行为

通过抗热震参数分析和热循环试验研究了ZrO2-Ni功能梯度材料（FGM）的热冲击与热疲劳行为及其影响因素。结果表明,ZrO2-Ni FGM热热震参数呈梯度分布,ZrO2侧抗热冲击断裂能力强而富Ni区热疲劳抗力高。其热震破坏符合热疲劳损伤机理,裂纹的准静态扩展为其控制因素。热疲劳裂纹在梯度层内以微孔聚集、连接方式萌生和扩展,而在梯度层间无横向贯穿裂纹,克服了传统陶瓷／金属结合体的界面热应力剥离问题。     

锰掺杂α-Ni(OH)2的合成及其电化学性能

以硫酸镍和硫酸锰为原料、聚乙二醇为结构导向剂,采用化学共沉淀的方法制备了纳米片状的锰掺杂氢氧化镍.用X射线衍射(XRD)、场发射扫描电镜(SEM)对样品的结构和形貌进行了表征;用傅里叶变换红外光谱(FT-IR)和热重分析(TG)手段对样品的成分进行了测定;用循环伏安、恒电流充放电等测试方法对其电化学性能进行研究.研究结果表明,采用该方法制备的样品,其电化学性能随锰含量的增加而变化;锰含量为30%时性能最佳,其比容量可达330mAh/g,有望成为Ni/MH电池的正极材料.     

真空烧结炉漏气率对TiB_2-Ni金属陶瓷性能的影响

研究了真空烧结炉的不同漏气率对ＴｉＢ２Ｎｉ金属陶瓷的机械性能的影响。结果表明：低漏气率真空烧结炉烧出的ＴｉＢ２Ｎｉ试样性能比高漏气率炉烧出的试样性能优异得多。