Enhanced Oxygen Diffusion Along Internal Oxide–Metal Matrix Interfaces in Ni–Al Alloys During Internal Oxidation

A study of the internal oxidation of dilute Ni–Al alloys in an NiO/Ni Rhines pack was performed at 800, 1000, and 1100°C. Considerable deviations from the classical internal oxidation model have been observed. The rate of internal oxidation depends not only on the concentration of the alloying element but also on its nature, which contributes to determining the size, shape, orientation and distribution of the internal oxide precipitates. For instance, the precipitates in the Ni–Al alloys are continuous rods, arranged in a cone-shaped configuration that extends from the surface to the internal oxide front. The observed depths of internal oxidation for the various concentrations of aluminum are discussed and related to the morphologies of the internal oxide precipitates. The apparent N^(s) _oD_o values determined from internal oxide penetrations increase with increasing solute content in the alloy. It is postulated that diffusivity of oxygen is enhanced along the internal oxide–metal matrix interface compared with that in the metal matrix.     

Oxygen Transport during the High Temperature Oxidation of Pure Nickel

The high temperature oxidation of nickel has been investigated in air under atmospheric pressure in the temperature range 600–900°C. The oxidation kinetic curves deviate from the parabolic law for temperatures over 800°C. The observation of scale morphologies and the use of two stage oxidation experiments under ¹⁶O₂/¹⁸O₂ atmospheres showed that oxygen transport through the NiO scale had to be taken into consideration during the oxidation process. Despite the main outward diffusion of Ni species through the oxide scale, the inward oxygen diffusion at lower temperatures (<800°C) or the oxygen transport, probably as molecular species, via pores or micro-cracks were found to play a major role in the formation of duplex oxide scales, made of small equiaxed oxide grains at the metal/oxide interface overgrown by larger columnar grains at the gas/oxide interface. Oxygen diffusion coefficients into thermally grown NiO scales were determined and compared to the values of Ni diffusion coefficients from the literature.     

Zirconia Layer Formed by High Temperature Oxidation of Pure Zirconium: Stress Generated at the Zirconium/Zirconia Interface

Oxidation of pure zirconium metal at high temperature (500 and 600 °C) under air at normal atmospheric pressure was investigated using the Raman Spectroscopy technique. Analysis of the absolute intensities as well as the positions of the Raman bands for the tetragonal and the monoclinic zirconia phases was performed. Evolution of the thermal stress has been presented and discussed in comparison to the Raman mode shift recorded in situ during cooling. Ex-situ analyses of cross-sections confirm the presence of tetragonal phase preferentially located close to the metal/oxide interface and show the existence of a relaxed and highly disordered tetragonal phase preferentially located in the outer part of the scale. Using a micro tension––compression machine, it is shown that compression loads lead to a significant intensity change of the Raman peaks for the tetragonal zirconia. The effect of tension load appears less clear which demonstrates that the relation between Raman peak shift and stress is not as simple as generally considered.     

Internal Oxidation of Ternary Alloys Forming a High Oxygen Conductive Oxide

Five ternary alloys consisting of a noble base metal (Ni, Co, Fe, Cu) and two reactive metals (Zr + Y, Ce + Gd) being able to form a high oxygen ion conductive oxide were internally oxidized under low oxygen partial pressures. All alloys developed either a continuous yttria-stabilized zirconia phase or a continuous gadolinia-doped ceria phase behind the front of internal oxidation. A Ni–Ce–Gd alloy showed extraordinarily high internal oxidation rates of up to 120 µm²/s at 900 °C. High internal oxidation rates in these ternary alloys were not limited to low concentrations of the reactive metals. The type of the internal oxide phase was found to be more important for the internal oxidation kinetics than the noble base metal.     

Oxidation of Silver by Atomic Oxygen

Oxidation of Metals - Interaction of silver with atomic oxygen has been studied at low incident-flux conditions (1015–1017 atoms?cm?2s??1, corresponding to a pressure of...     

In Situ Measurement of Stresses and Phase Compositions of the Zirconia Scale During Oxidation of Zirconium by Raman Spectroscopy

Raman spectroscopy was used to determine the stress and phase compositions of the zirconia scale in situ during the oxidation of zirconium at 600–900 °C in ambient air. The results show that the compressive stresses in the zirconia scale vary with the oxidation temperature and the oxidation time. The tetragonal (t) phase forms at the metal/oxide interface and the t to monoclinic phase transformation occurs far away from the interface during the oxide scale growth. The compressive growth stress at the oxidation temperature is favourable to the formation of t phase.     

Properties of Zirconia Material as Oxygen Sensor

The properties and applications of ZrO_2-Y_2O_3 material used as oxygen sensor were studied.Oxygensensors are studied by X-ray diffraction technique,microstructure determination and thermal shock resistancetest,and are tested on the spot.Oxygen sensors made from the sintered dense ZrO_2 stabilized by Y_2O_3 can beused to measure the oxygen concentration in molten steel at 1600℃.The data obtained are stable and reliable,and the thermal shock resistance is high.The oxygen concentration is measured at(1～150)×10~(-4)% with re-sponse time of 2～3s.     

First Stages of Oxidation of Pt-Modified Nickel Aluminide Bond Coat Systems at Low Oxygen Partial Pressure

The θ-Al₂O₃?→?α-Al₂O₃ phase transformation was investigated in thermally grown oxide formed on β-(Ni,Pt)Al bond coats during isothermal exposures at 900–1,200?°C in an argon atmosphere stream with the O₂ partial pressure of 1?×?10^?5?atm. Local curve fitting was used to evaluate the evolution of the parabolic rate constant, k _p , using a general kinetic model (t?=?A?+?BΔm?+?CΔm ²), during the first 5?h of oxidation. All net mass–gain curves exhibited deviations from the classic parabolic model, Δm?=?k _p t ^?; a steady state regime was established only after 4?h of exposures, except for the sample oxidized at 1,100?°C.     

Fast Internal Oxidation of Ni–Zr–Y Alloys at Low Oxygen Pressure

Oxidation tests of Ni alloys with additions of Zr and Y were carried out at 1000° C under low oxygen partial pressure. Oxidation kinetics as well as particle morphologies and structures were investigated by scanning-electron microscopy, energy-dispersive X-ray analysis and X-ray diffraction. Internal oxidation was observed under all circumstances. The kinetics of the internal oxidation was determined. A binary Ni–Zr alloy shows in situ internal oxidation according to theory. Yttrium was found to have a strong influence on the oxidation kinetics. Even minor Y contents considerably accelerate internal oxidation. Fast internal oxidation of ternary Ni–Zr–Y alloys can not be explained by standard internal oxidation theory.     

ZrO2基氧传感器电极用Pt浆的研制

通过选用合适的Pt粉,相应的溶剂、防沉剂和分散剂等有机载体和少量的无机粘结剂,研制出一种ZrO2基氧传感器电极用Pt浆,测试了烧成电极后的附着力、方阻及组装成汽车氧传感器后的电势跃迁等性能.结果表明:研制的Pt浆在YSZ电解质上附着性优良、方阻小、车载怠速时高电势跃迁大于800 mV,响应时间小于170 ms,能够满足制备汽车氧传感器电极的使用要求.     

内氧化法制备Al2O3/Cu复合材料的再结晶

利用内氧化法制备了Al2O3/Cu复合材料,研究了该材料在不同冷拔变形量和Al2O3含量下,其硬度值随退火温度变化的规律,并进行了显微组织结构分析。结果表明:采用内氧化法制备的Al2O3/Cu复合材料,在铜基体中弥散分布着纳米级的Al2O3颗粒;经900℃×1h退火后,其硬度可保持室温的87%以上;其再结晶温度高达1000℃;变形量和Al2O3含量增加均使硬度提高,但对软化和再结晶温度影响不大。     

低氧分压预处理对镍基合金028耐蚀性的影响

对镍基合金Alloy028在900℃进行低氧分压预处理10h,金相观察和硬度测试结果表明,预处理后析出物减少,组织得到细化,硬度明显提高。SEM、EDS及XRD分析比较试样表面微观形貌与结构特征表明,预处理后钝化膜形成元素Cr在表面发生富集,且部分形成由Cr2O3和NiCr2O4组成的氧化膜。极化曲线测试表明,预处理后合金的自腐蚀电位从-0.37V正移至-0.25V(SCE),腐蚀电流密度比空白试样显著降低。电化学阻抗测试表明,预处理试样的电荷转移电阻比空白试样提高一个数量级,膜电阻提高2倍多。     

Observation of TaB x O y Along the Ta Diffusion Path Through a Boron and Oxygen Containing Tri-layer Structure

Diffusion and migration of elements are commonly observed in the fabrication of multilayer thin-film devices, including those of STT-RAM. The CoFeB/MgO/CoFeB tri-layer thin-film stack has been widely used in the design of STT-RAM devices as the functional magnetic-tunnel-junction (MTJ) structure. Such issues faced in the fabrication of these devices have been extensively researched from the stand point of engineering the materials property and structure to achieve the best MTJ performance. In this work, we conducted a detailed examination of the chemical-state change of the Ta and B in a CoFeB/MgO/CoFeB/Ta film stack by using x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry. We showed that the chemical-state change of Ta and B is a result of the Ta diffusion phenomena through the CoFeB/MgO/CoFeB tri-layer structure. In particular, we report the evidences of the formation of TaB _x O _y compound at some considerable depth away from the Ta layer. Also of value to XPS spectroscopy, the Ta binding energy for such TaB _x O _y compound is reported for the first time.     

内氧化法制备Al2O3/Cu点焊电极的装机试验

采用内氧化法制备了0．6Al2O3／Cu复合材料，以该复合材料棒材为原料制备了点焊电极，并进行了装机试验和微观组织结构分析。研究结果表明：采用内氧化法制备的0．6Al2O3／Cu复合材料在铜基体中弥散分布着纳米级细小Al2O3颗粒。由于Al2O3颗粒硬度高，热稳定性和化学稳定性好，使该复合材料制备的点焊电极抗塑性变形能力强、抗坑蚀能力优良、再结晶温度高，并具有优越的抗粘接能力，使用寿命是铬锆铜电极的3倍多。     

Grain Boundary Diffusion of Nickel into Copper

A high resolution autoradiographic study of the diffusion of a nickel isotope (Ni⁶³) into copper in the temperature range of 650° to 925°C, with particular emphasis on grain boundary diffusion, has been made. The extent of grain boundary diffusion is a function of the grain boundary angle and the diffusion temperature. The ratios of the grain boundary diffusion coefficient to the lattice diffusion coefficient ranges from 10⁴ to 10⁵. The activation energy for grain boundary diffusion decreases with increasing grain boundary angle.     

内氧化法制备Cr_2O_3弥散强化铜基复合材料的研究

综述了弥散强化铜基复合材料研究进展及各种制备方法,对内氧化法制备Cr2O3弥散强化铜基复合材料进行了详细的阐述,并对今后的研制方向做了展望。     

内氧化法制备Al2O3／Cu复合材料的再结晶行为

以Cu2O为氧化剂，采用Cu-Al合金粉末内氧化及后续的粉末冶金法制备了Al2O3／Cu复合材料。并将不同Al2O3含量的试样进行不同变形量的冷拔处理，在氮气保护下进行高温退火处理(700℃～1050℃，1h)。研究了硬度随退火温度的变化规律，观察了显微组织。结果表明：在铜基体中弥散分布着纳米级的Al2O3颗粒：经900℃，1h退火后Al2O3／Cu复合材料的硬度可保持室温的87％以上；其再结晶温度高达1000℃；变形量和Al2O3含量增加均使硬度提高，但对软化和再结晶温度影响不大。     

内氧化法制备Al2O3/Cu复合材料的研究现状

综述了内氧化法制备Al2O3／Cu复合材料的研究现状，总结了内氧化法制备Al2O3／Cu复合材料的必备条件，对内氧化动力学和热力学进行了详细的阐述，并以Cu2O为氧源，采用内氧化法制备了Al2O3／Cu复合材料，验证了其优越的室温和高温性能；对以复合材料棒材为原料制备的点焊电极进行装机试验，结果表明其寿命为传统Cu-Cr—Zr电极的3～5倍；最后着重分析了内氧化法制备Al2O3／Cu复合材料发展过程中亟待解决的问题。     

钛合金／镍箔／不锈钢脉冲加压扩散连接界面结构及接合强度

采用纯镍箔作中间过渡层，在脉冲加压扩散连接工艺下，对TA17钛合金与0Cr18Ni9Ti不锈钢进行了连接试验，并测定了接头的拉伸强度。结果表明：采用镍箔作中间过渡金属的脉冲加压扩散连接，实现了钛合金与不锈钢的高效良好连接，接头抗拉强度达到了334MPa。采用金相显微镜和扫描电镜，对拉伸断口形貌进行了观察和分析；利用能谱仪（EDS）测定了拉伸断口各区域内的微区成分；并对拉伸断口进行了剥层试验。结果表明：拉伸断裂发生在Ni-Fe和Ni—Ti之间，Ni-Fe和Ni—Ti区均承载拉伸力，中间层Ni的存在成功地阻止了Fe与Ti之间的互扩散。     

Solid-State Phase Transformation in Diffusion Couples of U-Mo/Nb

采用包覆热轧法制备了U-Mo/Nb固相复合扩散偶。在790 ℃下对U-Mo/Nb固相复合扩散偶进行了扩散热处理。采用扫描电镜（SEM）观测了扩散偶的扩散层,采用能谱法测定了扩散层中不同固溶体相的组成。结果表明,30 h热处理后扩散偶Nb金属基体一侧得到的3种形式U-Nb固溶体,分析认为扩散层中最终固溶体相组成与U晶型转变及其合金化因素有关。