Viscous Flow of Copper at High Temperatures

Changes in length of copper foils of varying thickness and grain size were measured under such conditions of low stress and high temperature that it is believed that creep was predominately the result of interboundary diffusion of the type recently discussed by Conyers Herring. The surface tension of copper was calculated and results confirmed previous work within the limits of experimental error. Under the assumption of viscous flow, viscosities were calculated as a function of temperature and grain size. Predictions of the Nabarro-Herring theory of surface grain boundary flow were borne out fully and the Herring theory of diffusional viscosity is strongly supported.     

高温、短时Pd/Ti之间相互扩散行为的研究

为了研究高温下短时间Pd/Ti间的互扩散行为,在Ti表面利用磁控溅射技术沉积了Pd膜层,然后分别对Pd/Ti试样进行500℃/5 h,550℃/5 h,600℃/5 h和700℃/5 h高温处理,用XRD、SEM和EDS研究合金层的相组成、微观组织和元素分布。研究发现:当Pd/Ti试样经500℃/5 h处理后,Pd/Ti之间有极轻微的互扩散发生。当温度升高到550℃时,Pd/Ti间产生了连续的扩散层,随着温度升高,膜层之间的互扩散加剧。并且,当温度升高到700℃时,Pd/Ti之间形成了相图中除Ti3Pd5相和Ti3Pd相以外的其余各化合物相。还分析了Pd/Ti界面扩散反应动力学。结果表明,扩散层厚度的增加经历了一个由界面反应动力学控制到扩散控制的过渡。     

TA15钛合金高温摩擦磨损性能研究

目的 为探究TA15钛合金高温耐磨性能的潜力,研究了TA15钛合金在室温~800 ℃下的摩擦磨损性能。方法 利用Rtec摩擦磨损试验机(Rtec,San Jose,USA)进行TA15钛合金的摩擦磨损性能测试,通过激光共聚焦显微镜、JSM-7800F扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)等手段,分析了TA15钛合金在不同温度下的磨痕形貌、成分变化以及磨损机理。结果 在不同试验温度下,微观组织没有出现明显变化,主要为等轴α相和β相;不同温度下的摩擦因数波动不大,从室温的0.279下降到600 ℃的0.224,而在800 ℃时,表面严重氧化导致摩擦因数增大到0.309;在室温~400 ℃时,试样表面磨痕不断变窄变浅,犁沟和磨屑不断减少,而到400 ℃以上时磨痕逐渐变宽,比磨损率也大幅增大,且在600 ℃时的磨损量最大;在600 ℃时,以氧化磨损为主,并伴随着磨粒磨损和黏着磨损,且表面磨痕形貌和宽度比较均匀;在800 ℃时磨损表面以黏着磨损和氧化磨损为主,并伴随着高温焊接的发生。结论 TA15合金表面的O元素含量随温度的升高而逐渐升高,并且氧化反应主要发生在β相内。随着试验温度的升高,TA15钛合金磨损表面的氧化磨损现象也更加明显。     

Ti-6Al-3Nb-2Zr-1Mo钛合金在低温高应变速率下的变形行为

在变形温度为193~298 K、应变速率为2000~3000 s^-1的范围内,对Ti6321钛合金进行动态压缩试验,研究温度和应变速率对材料力学性能和变形行为的影响。采用光学显微镜（OM）、透射电子显微镜（TEM）和电子背散射衍射（EBSD）表征和分析了合金的微观结构演变。结果表明,随着温度的降低和应变速率的增加,Ti6321钛合金的动态屈服强度和平均流动应力均增大,而断裂应变明显降低。采用Johnson-Cook本构方程预测了Ti6321钛合金在低温高应变速率下的力学行为,拟合结果与实验结果吻合较好。微观结构分析表明,随着变形温度的降低,｛112｝和｛101｝2种孪晶的含量明显增加,即变形机制逐渐由孪晶的辅助作用转变为孪晶占主导地位。     

低温钛合金的研究进展

因具有优异的低温综合性能,钛合金作为重要的低温工程材料而逐渐受到广泛重视。本文概述了当前国际低温钛合金的应用现状,从α钛合金、α/β两相钛合金及β钛合金方面,综述了钛合金低温变形机制的最新研究进展,并总结了这3类不同相成分的钛合金的低温变形机制。从温度、合金成分、形变因素和显微组织方面,归纳总结了不同因素对钛合金低温塑性变形机制的影响。另外,还探讨了低温钛合金的发展趋势,以期为新型综合性能更好的低温钛合金的设计和研发提供参考。     

La-（Ca-Ba-Sr）-Mn-O锰氧化物高低温输运特性

用固相反应烧结法制备了多晶体材料La2/3Ca1／3MnO3(LCMO)，La2／3(Ca0.5Ba0.5)1/3MnO3(LCBMO)、La2，3Ba1/3MnO3(LBMO)，La2／3(Sr0.5Ba0.5)1/3MnO3(LSBMO)和La2/3Sr1／3MnO3(LSMO)，测量了它们在77K～800K的电阻和磁电阻特性。实验发现，通过一定的工艺技术制备出的CMR材料有强烈的相界效应，在低温下有大的磁电阻，且在Tc附近存在明显的从金属态向半导体态的转变：用自旋极化电子隧道效应和靠近居里点逾渗模型较好地解释了电阻和磁电阻行为：用非绝热小极化子跃迁模型对高温的电阻特性进行拟合处理，得到了激活能；同时发现退火处理对样品的电阻率有重要的影响。     

一种可在低温高应变速率下超塑成形的钛合金研究及其 …

研制出一种以 Ti2 Co相弥散强化 α- Ti基体的钛合金 Ti- 8Co- 5 Al。实验表明 ,在变形温度为 72 5℃ ,应变速率为 1× 10 - 3s- 1 的条件下可获得断裂延伸率 70 8%。从实测应变速率敏感性指数为 0 .47,并结合试样断口处纵向剖面显微组织的扫描电镜观察 ,表明在Ti- 8Co- 5 Al合金中发生了α- Ti晶界及α- Ti/ Ti2 Co相界的滑移为主要变形机制的变形过程。采用 Ti- 8Co- 5 Al合金在 730℃和 1× 10 - 3s- 1 应变速率条件下成功地等温锻造出飞机零件 ,比 Ti- 6 Al- 4V合金低约 2 10℃     

Fatigue Damage Mechanism of AL6XN Austenitic Stainless Steel at High Temperatures

By the combination of transmission electron microscope, neutron diffraction and small-angle neutron scattering methods, mechanical fatigue behavior of AL6XN austenitic stainless steel was investigated in the temperature range of 400–600 °C. At 400 °C, in addition to the occurrence of dynamic strain aging, the formation of short-range order was evidenced from the forbidden electron diffraction spot of 1/3 {422} in face-centered cubic(fcc) structure viewed down [111] zone axis, which facilitate the planar slip mode of dislocation and result in the work hardening during the fatigue deformation. The fatigue damage is mainly dominated by the accumulation of planar slip band and the interaction among various slip systems. With increasing temperature, precipitates of chi phase, Laves phase and sigma phase were formed during the fatigue tests at 500 and 600 °C. An increase in precipitation content at 600 °C has also been confirmed by both scanning electron microscope and small-angle neutron scattering analysis. The dislocation pileup originating from the uncoordinated deformation between precipitate and austenitic matrix is an important fatigue damage leading to crack. The continuous cycle softening behavior was also observed on the fatigue curve at 600 °C, which is considered to be caused by dynamic recovery.     

冲击加载条件下化学气相沉积高纯钨的塑性变形机制

采用较低温度下的化学气相沉积技术制备了高纯钨，利用分离式HOPKINSON压杆装置对制备的高纯钨和商用粉末烧结纯钨进行应变率为1000／s～2000／s的冲击加载，对冲击后的样品进行了变形机制对比分析。结果表明：在冲击载荷作用下粉末烧结纯钨变形机制以滑移和品界滑动为主，析化学气相沉积纯钨则是孪生变形起到很大的作用：临近孪生间的交互作用会产生2种类型的穿晶断裂，这是化学气相沉积纯钨致脆的原因：在低于10^3／s应变率量级化学气相沉积纯钨不会发生绝热剪切，难以与钨合金一样通过绝热翦切变形提高其塑性变形能力。     

Ti基合金熔体停止流动机理研究

采用Ti-6Al—4V合金熔体浇注螺旋形流动性试样。通过对螺旋形试样的宏观组织观察,研究了Ti基合金熔体的停止流动机理,并建立了Ti基合金熔体的停止流动模型。结果表明,Ti基合金的停止流动机理复杂,不能仅仅归结为传统的端部堵塞机理,更主要的原因是根部柱状晶生长丰富,形成穿晶组织导致颈缩,阻止液态流体通过,从而导致合金熔体停止流动。     

TA32新型钛合金高温流变行为及本构模型研究

为了研究TA32钛合金的高温流变行为,建立该材料本构模型,对TA32钛合金进行了温度范围为650～850℃,应变速率为10-1～10-4s-1条件下的高温拉伸试验。结果表明,TA32型钛合金较高的温度依然能保持较好的综合性能,在650～750℃区间内应变速率为10-1～10-3s-1条件下,变形呈现出明显的加工硬化和再结晶现象,当温度升至800℃及以上时其塑性延伸率显著提高而强度下降,同时出现了稳态流动应力。随后,基于统计学和正则化原理,提出一种修正本构模型参数的方法,并建立了TA32新型钛合金的Arrhenius-type型应力流变本构模型。通过对比验证实验结果可知,相对于传统的最小二乘法得到的模型,该修正方法得到的模型能有效地提高模型的精度。     

常温和低温下铝的阳极氧化研究

对常温和低温下铝的阳极氧化效果进行了比较,解释了所获得的氧化膜在厚度和硬度上不同的现象.试验以硫酸为电解液,分别在25℃和(3±1)℃下对铝进行阳极氧化.结果发现3℃下获得的氧化膜的硬度约是25℃下获得的1.5倍,而且膜的厚度也有所增加.扫描电镜发现这两个温度下得到的氧化膜形貌大不相同.25℃下所得氧化膜的孔呈百合花状,口大而底窄,孔径达到2μm.而3℃下所得氧化膜呈立体网络结构,有如桦树叶的堆积,空隙在200nm左右.可见,前者有利于染色,后者有利于提高硬度.     

Flow Stress-Strain Rate Behavior of Ti-3Al-2.5V Alloy at Low Temperatures in the Superplastic Range

Flow stress-strain rate behavior of Ti-3Al-2.5V, an α + β titanium alloy was studied at 750 and 800 °C by using the method of crosshead speed cycling. The alloy was found to exhibit superplasticity at these temperatures on the basis of complete flow stress, strain rate and strain rate sensitivity data. Strain-induced softening was observed in the alloy to a small extent at 750 °C and was thought to be related to the grain refinement occurring in both α- and β-phases during the initial stages of deformation. However, at 800 °C the effect was seen only under increasing strain-rate conditions. Flow stress versus strain rate curves generally exhibited only region II which corresponded to low- and intermediate-strain rates and region III corresponding to high-strain rates.     

高熵合金高温抗氧化性的研究进展

高熵合金在高温下具有优异的力学性能,但在高温下抗氧化性能的不足制约了其实际工业应用.概述了高熵合金的氧化机理,包括氧化动力学规律、氧化行为以及合金元素氧化顺序规律等,归纳了高熵合金在高温下存在的问题.在此基础上,重点综述了近年来高熵合金高温抗氧化性的研究进展.其中,通过添加可生成保护性氧化物的元素可以提高高熵合金氧化层...     

Scientific-Technical Conference on Structural Strength at Low Temperatures

Metal Science and Heat Treatment -     

高温低能高电流密度离子注入材料的摩擦学应用

高温低能高电流密度离子注入技术,已表明可以显著改善各种材料的摩擦学性能。本文综述了此领域中一些研究结果,并在奥氏体不锈钢和工具钢材料上对该技术与离子氮化和在相同条件下高能离子注入技术作了比较。显微结构分析及摩擦学性能评价表明,三种技术可以产生差不多相同的显微结构,但低能离子注入层由于具有较高的氮浓度和较深的扩散层而显示了较高的耐磨性。本文提出了一个物理模型来表示这种现象的机理。高电流密度是形成较深氮化层的主要原因,而离子能量具有次要作用,只要它能克服表面障碍,去除原有的氧化层,防止表面氧化,井在表面上建立起较高的氮浓度就可促进随后的快速扩散。对该技术的应用与限制也进行了论述。     

Oxidation of Inconel 718 in Air at High Temperatures

Experiments were conducted with Inconel 718 at high temperatures to evaluate the rate of oxidation of the material over as wide a temperature range as possible, as well as to determine the high-temperature failure limit of the material. Samples of Inconel 718 were inserted into preheated furnaces at temperatures ranging from 973 to 1620 K and oxidized in air for varying periods of time. After being oxidized in air at a constant temperature for the prescribed time and then being allowed to cool, the samples were reweighed to determine their mass gain due to the uptake of oxygen. From these mass-gain measurements, it was possible to identify three regimes of oxidation for Inconel 718: a low-temperature regime in which the samples behaved as if passivated after an initial period of transient oxidation, an intermediate-temperature regime in which the rate of oxidation was limited by diffusion and exhibited a constant parabolic rate dependence, and a high-temperature regime in which material deformation and damage accompanied an accelerated oxidation rate above the parabolic regime.     

Rhenium Oxidation by Steam at High Temperatures

The kinetics of rhenium oxidation were studied under flowing steam+argon mixtures, at atmospheric total pressure and steam partial pressure in the range 24–74 kPa, and at temperatures from 1600°C up to 2200°C. No regime change was observed in the temperature dependence of the oxidation rate, which shows that the same chemical regime extends up to the highest temperature investigated. Moreover, at high temperature, the results showed a dependence of the oxidation rate on the gas velocity and the steam partial pressure, in good agreement with a gas-phase mass-transfer correlation for laminar flow, revealing that, for the conditions used, mass-transport processes in the gas phase also act as a limiting factor. It was assumed that the mass-transport limiting factor is the steam diffusion through a volatile oxides gaseous layer above the rhenium surface. A comparison of these results with rhenium oxidation rates reported for air leads us to propose the dissociative adsorption of the H₂O molecule as the limiting chemical stage of the oxidation process.