Precipitation Hardening of Mg-Zn and Mg-Zn-RE alloys

The age-hardening response of two cast Mg-Zn-RE alloys has been investigated and compared with that of a binary Mg-Zn alloy. The microstructures of the aged specimens were examined by analytical electron microscopy. Formation of a fine dispersion of rodlikeβ ₁ ^′ precipitates is the main cause for age hardening, while extensive precipitation of disc-shapedβ ₂ ^′ coincides with the onset of overaging. Rare earth additions retard the formation ofβ ₂ ^′ precipitates and thus postpone overaging. Four different orientation relationships betweenβ ₂ ^′ precipitates and matrix were found and explained in terms of the near-CSL model.     

The Solid Solution and Grain Boundary Hardening due to Mg in an Aluminum Alloy System at Room and Elevated Temperatures

Metallurgical and Materials Transactions A - The solid solution and grain boundary hardening due to Mg in Al-1.5wt pct Mn-0.5wt pct Cu system with 0.1 to 2.1 wt pct Mg has been studied at...     

Athermal Solid Solution Hardening in Tantalum

The influence of solute atoms on the athermal component of the flow stress, determined by means of dip-tests (incremental unloading), has been investigated at room temperature and slightly above in binary Ta-Re, Ta-Mo, Ta-W, Ta-Hf, Ta-Zr, and Ta-Nb alloys and in ternary Ta-W-Re, Ta-W-Mo, Ta-W-Hf, and Ta-W-Nb alloys. Binary athermal substitutional solid solution hardening in tantalum is linear up to high concentrations of solute and is dominated by the atomic size misfit parameter, in agreement with the authors’ recent model for binary athermal solid solution hardening in bcc metals at temperatures where the Peierls stress is still important. In this model, solid solution hardening is caused by interactions of solute atoms having a size misfit with polarity reversing kinks and constrictions in 〈111〉 screw dislocations. The observed solid solution hardening in the ternary alloys is well described by the authors’ phenomenological model for multicomponent solid solution hardening. L.A. GYPEN, formerly with the Departement Metaalkunde, Katholieke Universiteit Leuven, Belgium     

基于机器学习的Cu-Ni-Co-Si合金固溶处理晶粒尺寸预测

Cu-Ni-Co-Si合金在固溶处理后的晶粒尺寸会影响其服役性能。采用3种不同的机器学习方法——BP神经网络、随机森林、长短期记忆网络,分别建立了Cu-Ni-Co-Si合金固溶温度和固溶时间对固溶后晶粒尺寸影响的机器学习预测模型。对比分析3种不同机器学习模型的预测精度,发现BP神经网络模型预测精度最高,其平均相对误差为8.55%。随后采用遗传算法优化BP神经网络。结果表明,所建立的BPGA模型平均相对误差比BP神经网络模型降低了6.47个百分点,其平均相对误差为2.08%,能够有效地为Cu-Ni-Co-Si合金固溶处理工艺参数的选择提供指导。     

一烧固体燃料最佳粒度的研究

对一烧固体燃料的粒度、添加量作了具体的研究，并对生产中存在的问题进行了调查，提出了对一烧生产有指导意义的试验结果和意见。     

Solid Particle Erosion of Nanocrystalline Nickel Coatings: Influence of Grain Size and Adiabatic Shear Bands

The primary objective of the present study is to investigate the influence of nanocrystalline grain size on the solid particle erosion behavior of nickel. For the above purpose, 450-μm-thick nanocrystalline Ni coatings having the average grain sizes of 21, 42, 70, and 195 nm were obtained using pulsed electrodeposition (PED). All these samples along with bulk annealed Ni samples (43 μm grain size) were subjected to solid particle erosion using SiO₂ particles as an erodent at a constant impact velocity of 45 m/s and two impact angles (30 and 90 deg). Erosion results indicate that bulk Ni and PED Ni coatings of grain sizes 195 and 70 nm exhibit the same erosion rate, while PED Ni coatings of 42 and 21 nm grain size exhibit marginally higher erosion rates with a clear trend of increasing erosion rate with decreasing grain size. It was also observed that the higher erosion rates exhibited by 21- and 42-nm-grain size PED Ni samples were associated with the formation of adiabatic shear bands (ASBs) originating from the eroded surface and propagating into the eroded sample. The experimental observations have been understood on the basis of a transition from a localization model for erosion for coarse-grained Ni (> 70 nm) to an ASB-induced erosion model for grain sizes less than 70 nm.     

Grain Size Effects in Hydrogen-Assisted Cracking

There is conflicting evidence in the literature with respect to the effect of grain size on hydrogen embrittlement. Differences may arise because of the degree of segregation in different grain size materials, because of different structures obtained in the effort to produce varying grain sizes, or because of the grain-size dependency of diffusion and growth processes. An extremely dirty heat of 4340 steel with 0.07 S and 0.015 P was investigated so that any tramp element segregation or hydrogen recombination poison effects would be present. Measurements were obtained on cathodically-charged samples with average grain sizes of 20, 50, 90 and 140 μm. In general, tramp element effects were not controlling. For those cases where the grain diameter was significantly larger than the plastic zone, increased grain size improved resistance. This was reflected by a slight increase in threshold stress intensity and an inverse grain-size squared dependence of crack velocity. Although the data are consistent with a pressure tensor hydrogen-assisted migration model, they could also be interpreted in terms of high austenitizing temperatures promoting retained austenite. Formerly Graduate Student, Department of Chemical Engineering and Materials Science, University of Minnesota. The present paper is based on a portion of the thesis submitted by J. F. Lessar in partial fulfillment of the requirement for the M.S. degree at the University of Minnesota.     

Grain Size Effects in Hydrogen-Assisted Cracking

There is conflicting evidence in the literature with respect to the effect of grain size on hydrogen embrittlement. Differences may arise because of the degree of segregation in different grain size materials, because of different structures obtained in the effort to produce varying grain sizes, or because of the grain-size dependency of diffusion and growth processes. An extremely dirty heat of 4340 steel with 0.07 S and 0.015 P was investigated so that any tramp element segregation or hydrogen recombination poison effects would be present. Measurements were obtained on cathodically-charged samples with average grain sizes of 20, 50, 90 and 140 μm. In general, tramp element effects were not controlling. For those cases where the grain diameter was significantly larger than the plastic zone, increased grain size improved resistance. This was reflected by a slight increase in threshold stress intensity and an inverse grain-size squared dependence of crack velocity. Although the data are consistent with a pressure tensor hydrogen-assisted migration model, they could also be interpreted in terms of high austenitizing temperatures promoting retained austenite.     

回火对超细贝氏体晶粒取向和尺寸的影响

用50kg真空感应炉冶炼的钢锭,经1150℃开轧,两阶段控制轧制,830℃终轧成12mm钢板,驰豫27s,720℃进水快冷(冷却速率30～35℃/s)后,超低碳贝氏体钢(成分%:0.023C、1.63Mn、0.52Cu、0.25Mo、0.055(Nb+Ti)、0.0011B)具有板条贝氏体+少量粒状贝氏体和不规则铁素体的复合组织,贝氏体束团尺寸为3～5μm,块状和不规则铁素体尺寸为1～2.5μm。650℃和700℃回火对贝氏体晶粒取向无显著影响。     

6061棒材晶粒度大、粗晶环严重工艺研究

阐述了6061合金生产时粗晶环产生的机理,结合正交实验及多年的生产实践经验,提出了解决6061合金棒材晶粒粗大的措施.     

6063铝型材组织晶粒度控制的研究

本文讨论了影响6063铝型材组织晶粒度的因素及如何减小晶粒的的措施方法.     

晶粒度自动分析软件

根据国家标准ＧＢ６３９４－８６，利用ＫＳ４００型图像仪，编制了晶粒度自动分析软件。经测试，该软件具有准确度高，机动灵活，省时省力的特点。     

Experimental Determination of Mg Activities in Fe-Mg Solutions

The thermodynamics of magnesium in liquid iron was determined at 1823 K (1550 °C). For this purpose, liquid iron was equilibrated with Ag-Mg alloys in a semienclosed molybdenum vessel. From the partition of magnesium between iron and silver, the activity coefficient of Mg and the self-interaction parameter e_\textMg^\textMg \varepsilon_{\text{Mg}}^{\text{Mg}} were determined.     

Determination of Activity Coefficients in Solid Solutions

Abstract

A method of determining activity coefficients in metallic solid solutions has been developed. This method, based on the measurement of solidification partition coefficients, has been tested for the tin-bismuth system, and used for a thermodynamic study of the Pb - 16.3% Sn alloy.

Résumé

Nous avons élaboré une méthode de détermination de coefficients d'activité d' éléments en solution solide. La méthode, basée sur la mesure de coefficients de partage en solidification, a été éprouvée par comparaison des résultats obtenus aux données publiées du système étain-bismuth, puis utilisée pour une étude de l'alliage Pb - 16.3% Sn.     

Secondary Hardening, Austenite Grain Coarsening and Surface Decarburization Phenomenon in Nb-Bearing Spring Steel

 The secondary hardening, the austenite grain coarsening and the surface decarburization phenomenon of Nb-bearing spring steel were investigated, and the effects of niobium on tempered microstructure was studied using scanning electron microscope. The results show that the micro-addition of niobium increases the tempering resistance and produces secondary hardening. The effect of niobium on the size and distribution of cementite particles is one of the primary reasons to increase the hardness after tempering. The grain-coarsening temperature of the spring steel is raised 150 ℃ due to Nb-addition. Furthermore, both the secondary hardening and the austenite grain coarsening phenomenon congruously demonstrate niobium begins observably dissolving above 1100 ℃ in the spring steel. Besides, niobium microalloying is an effective and economy means to decrease the decarburization sensitivity of the spring steels.     

用激光粒度分析仪测定二氧化锆粒度

介绍以六偏磷酸钠作为分散剂，采用激光粒度分析仪测量二氧化锆粒度的一种新方法。该方法的测量范围为0．05～300μm。