干摩擦条件下载荷和频率对Cu-15Ni-8Sn合金摩擦磨损性能影响研究

目的研究不同摩擦载荷及频率条件下Cu-15Ni-8Sn合金摩擦因数及磨损率的变化规律,探明机械参量变化对合金摩擦学性能的影响机制。方法采用熔炼法制备Cu-15Ni-8Sn合金,在干摩擦条件下对合金进行变载荷/变频率的销盘式往复摩擦实验,并对其摩擦因数、磨损率、磨损形貌及摩擦界面进行形貌及成分分析。结果随摩擦载荷的增大,2种载荷下Cu-15Ni-8Sn合金摩擦因数均呈现先增大后减小的趋势,整体在0.5~0.8之间;磨损体积随载荷的增加而增加;在2 Hz条件下合金的比磨损率随摩擦载荷的增大先降低后升高,在5 Hz条件下合金的比磨损率随摩擦载荷的增大先升高后降低;在高频高载条件下,磨损最为严重。磨痕及摩擦副表征结果显示,在干摩擦条件下,Cu-15Ni-8Sn合金主要以磨粒磨损和疲劳磨损为主;在摩擦过程中,合金基体及对偶同时发生磨损,剥落物以磨屑形式参与摩擦,因此在摩擦界面间发生元素转移。结论在干摩擦条件下,相较于摩擦频率,Cu-15Ni-8Sn合金受摩擦载荷的影响更大。合金磨屑以细小的颗粒状为主,但在低频率、高载荷条件下,会有大块片状磨屑。在干摩擦过程中,对磨副与合金之间会发生相互转移。随着载荷、频率的增加,摩擦层厚度也会变大,且摩擦过程中摩擦层内无剧烈氧化。

损失函数下逐步二型删失数据广义Pareto分布参数的Bayes估计

基于逐步二型删失数据,在几种不同的损失函数下,选择广义Pareto分布,讨论其形状参数的Bayes估计。当尺度参数给定时,为θ参数引入Gamma分布作为先验分布,得到了几种不同损失函数下参数θ的Bayes估计的数学表达式,通过数值模拟方法,比较了几种损失函数下所得到的Bayes估计的效果。结果表明:在Linex损失函数下,广义Pareto分布参数的Bayes估计效果最优。

双边定时截尾下线性指数分布的参数估计

为了研究双边定时截尾下线性指数分布的参数估计问题,分别采用极大似然法和贝叶斯方法对未知参数进行估计,并证明了极大似然估计是唯一存在的。利用MatlabR2022b进行了随机模拟,研究结果表明:在均方误差准则下,贝叶斯方法优于极大似然方法;在贝叶斯估计中,选取伽马先验分布并在平方损失函数下,未知参数的贝叶斯估计效果最优。

基于ARIMA模型的生产者价格指数预测

生产者价格指数(PPI)是衡量生产者支付的原材料、劳动力和其他生产成本的变化指标。对经济的稳定和企业的经营都有着重要的意义,可以帮助政府、央行和企业做出相应的决策和调整。文章选取2013年1月至2023年7月的PPI月度数据,建立了AMIMA(1,0,2)模型,并利用该模型对2023年1月至7月的PPI进行预测,随后,将预测结果与实际值进行了对比,结果显示,模型具有良好的预测效果,为未来6个月的PPI指数提供了可靠的预测,这一结果为制定经济政策提供了重要参考。

医学新生体育锻炼水平与学校适应的关系:运动友谊和锻炼投入的链式中介作用

目的探讨医学新生体育锻炼水平、运动友谊、锻炼投入、学校适应之间的关系,考察运动友谊和锻炼投入在体育锻炼与学校适应之间的中介作用。方法采用体育锻炼等级量表、中国大学生适应量表、青少年运动友谊质量量表和大学生体育锻炼投入自评量表对888名医学新生(男290人,女598人)进行团体心理测量。应用单因方差分析、链式中介作用检验和Bootstrap方法进行统计学分析。结果体育锻炼水平对医学新生学校适应、运动友谊、锻炼投入有显著影响。体育锻炼与学校适应(r=0.40,P<0.001)、运动友谊(r=0.19,P<0.001)、锻炼投入(r=0.47,P<0.001)呈显著正相关。运动友谊和锻炼投入在体育锻炼与学校适应之间起完全中介作用,且该中介作用包含3条路径:运动友谊的单独中介作用、锻炼投入的单独中介作用以及运动友谊和锻炼投入的链式中介作用,中介效应分别占总效应的45%、32%和13%。结论体育锻炼水平与医学新生的运动友谊和锻炼投入水平显著相关,体育锻炼通过运动友谊和锻炼投入的链式中介作用间接影响医学新生的学校适应情况。

扫描速度对选区激光熔化高强Al-Mg-Sc-Zr合金组织与性能的影响

采用选区激光熔化(SLM)技术在不同扫描速度工艺条件下制备了高强Al-Mg-Sc-Zr合金,采用了光学显微镜(OM)、扫描电子显微镜(SEM)、室温拉伸实验、室温摩擦磨损实验等方法,研究了激光扫描速度对合金微观组织和力学性能的影响。结果表明:当激光功率不变,扫描速度在1250~1850 mm/s时,随着扫描速度从1250 mm/s升至1850 mm/s,合金致密度和力学性能均呈现先升高后降低的趋势。当扫描速度达到1850 mm/s时,由于能量密度低导致粉末无法充分熔化,层间润湿不充足,形成大量不规则孔隙,降低了材料力学性能。选区激光熔化成形合金在不同扫描速度下均可以完成冶金结合,且致密度均高于98.9%,当扫描速度为1450 mm/s时,合金成形性能达到最优,致密度为99.87%,其屈服强度、抗拉强度和断后延伸率分别为379 MPa、420 MPa和17.0%,摩擦磨损实验表明其磨损量和磨损速度均为最低,耐磨性能显著优于其他参数。

一种基于前向纠错码的图像DNA加密存储算法

近年来DNA(DeoxyriboNucleic Acid)存储发展迅速,实现数字图像DNA存储和安全传输成为有待解决的问题。因此该文提出了一种面向DNA存储的基于前向纠错码的图像加密算法。首先使用动态约瑟夫遍历算法对图像像素点进行行置换和列置换,以消除明文图像相邻像素之间的相关性。其次,使用图像分解方法将明文图像分解为8个子图,然后再重新组合,实现了对图像像素值的置换,从而进一步消除明文图像的纹理特征和破坏其统计学特征。再次,对图像进行全局扩散,使明文的微小变化以扩散的形式影响密文,以抵抗差分攻击。最后使用可纠错DNA编码表将图像加密编码为DNA序列,合成后进行存储。算法将明文图像加密成DNA序列并存储,这种存储方式与传统存储介质相比更为安全。同时,可纠错DNA码使得密文可以在DNA存储环境中可靠读取。该文使用3张常用图像包括lena_gray、peppers_gray、baboon_gray,测试算法的安全性以及在DNA存储环境下的鲁棒性。仿真结果表明,该方法可以有效抵御多种密码学攻击,并且在DNA存储环境下对碱基错误和序列缺失等问题表现出良好的鲁棒性。

智慧军营网上党校中智能化文本分类应用设计

针对智慧军营系统网上党校功能板块的分类学习和推送需求,分析其海量学习任务、新闻通知和组织管理等文档特性,提出了一种高效可行的智能化数据分析设计方案。首先,分析了网上党校各功能模块文本数据的相似性;其次,研究了系统十大建设板块中文本主题划分的聚类融合、文本知识特征抽取及递推关系构建3类关键技术;然后,提出了一种基于党政知识块摘要和深度学习模型的文档分类算法;最后,利用专家方阵、党建研究等板块的文档数据,验证了该算法的有效性,表明该设计方案可通过智能辅助系统为党政工作者提供决策支持,从而实现提高办事质量和效率的目标。

氢对金属有何作用

金属的制备和使用中易大量吸收氢元素从而导致氢脆,这是使金属构件脆化乃至断裂的原因之一。文章回顾了氢脆现象的机制和氢对金属的有害作用,并介绍了氢对金属的细化组织、净化熔体、增加塑性与促进非晶化等有益作用。合理利用氢元素可以制备更好性能和特殊性能的材料,并能改善加工性能,简化加工步骤。同时,可以利用氢气在特定金属膜中的溶解和析出,实现低纯度氢气的净化与提纯。

小儿高热惊厥急诊健康教育模式的探索

通过查阅文献和总结临床经验,本文整理出一种小儿惊厥急诊健康教育模式。院内以口头语言教育、视频教育、专人演示为主,主要侧重急救护理、对症护理及心理护理;院外则运用微信群、公众号平台进行文字、图片及视频教育,健康教育的内容分为急救护理、疾病相关知识、病情观察、心理护理和注意事项5个方面。

Fe代替V制备低成本钛合金:相体积分数的计算

钛合金因其优异的综合性能,如比强度高、耐热性强、耐腐蚀性能优异、低温性能好等特点,而被应用在航天、航空、航海等诸多领域,然而钛合金的高成本严重制约了其大规模的使用。本文以综合性能最好、使用最广泛的Ti-6Al-4V合金为基础,在使用廉价合金元素代替昂贵合金元素的思路下,设计了几组V、Fe元素含量不同的Ti-Al-V-Fe合金。借助稳定系数Kβ,分析钛合金中β相的稳定程度和β稳定元素的作用,通过理论推导的方法建立了合金淬火态和退火态的β元素临界晶胞系数的计算模型,并在此基础上确立了α相与β相的体积分数的计算方法,从而实现了对Ti-Al-V-Fe合金中相体积分数的理论计算。本文以Ti-6Al-3V-1Fe合金为例,首先对合金内α相与β相的体积分数分别做了理论计算,继而利用真空非自耗电弧熔炼炉制备了Ti-6Al-3V-1Fe合金的铸锭,取样并进行热处理,最终利用X射线衍射法测定了Ti-6Al-3V-1Fe合金淬火态和退火态α相与β相的实际体积分数。对比发现,实验测定的结果与理论计算的结果较为吻合,说明建立的模型用于预测α相与β相两相的体积分数是切实可行的。

镁基储氢合金吸放氢机理及组织与性能调控

随着能源危机和环境问题的日益加剧,迫切需要寻求一种高效的可再生能源,而氢能被认为是最具前景的能量载体之一。氢燃料电池是氢能利用的最主要形式,其中车载储氢需要更轻便、紧凑和经济的体系来取代高压气体储氢装置。作为最具潜力的固体储氢体系之一,镁基储氢材料具有诸多优点,但阻碍其实际应用的瓶颈问题同样难以克服。文章通过介绍镁基储氢材料的吸放氢机理,阐述了热力学和动力学性能对其实际应用的制约及成因,归纳了当前的研究方法和进展,包括主要的组织调控和材料改性方法,并对镁基储氢的发展前景进行了展望。

Ti90及其优化合金的组织与力学性能研究

Ti90合金是我国自主研发的一种新型近α型钛合金,具有高比强度、高韧性、耐蚀和加工性能好等优点。本课题组前期对Ti90合金进行了成分优化,得到一种名义成分为Ti-5. 5Al-4. 0Zr-1. 0Sn-0. 3Mo-1. 0Nb的优化合金。利用X射线衍射仪、金相显微镜、电子探针显微分析仪、电子万能试验机和电化学工作站等检测仪器,对Ti90及其优化合金的组织与力学性能进行对比分析。结果表明,优化合金组织为带有网篮特征的魏氏组织,原始β晶界和α集束清晰可见,有少量残留β相分布于α片层之间。与Ti90合金相比,优化合金的压缩屈服强度与断裂韧性得到了显著的提高,极限应变量有所增加,电化学腐蚀性能较好。

Lamellar orientation control in directionally solidified TiAl intermetallics

TiAl-based alloys are potentially used as high-temperature structural materials with a high specific strength in the range of^900°C.However,the mechanical properties of TiAl-based alloys are extremely anisotropic with respect to the lamellar orientation of the microstructures.A balance combination of room-temperature ductility and strength can be achieved when the lamellar orientation are aligned parallel to the tensile stress direction.Lamellar orientation control of TiAl-based alloys by directional solidification technique has been widely studied in recent years.Two different directional solidification processes can be used to modify the lamellar orientation.One is a seeding technique and the other is adjusting the solidification path.This paper reviews the principles of the two methods and their progress.The influence of alloy composition and solidification parameters on lamellar orientation control is also discussed.

Study on traveling magnetic field casting of sheet components

The distribution of a magnetic field over an inductor used for sheet castings has been investigated experimentally.With an increase in height from the surface, the magnetic field density decreases according to the exponential law.In the transverse direction, the magnetic field density is approximately uniform except near the edges.The magnetic field density is direct proportional to the number of turns multiplied by the current in amperes.Ferro-magnetic material in the upper mould can enhance the magnetic field density.Under the electromagnetic force, the mould-filling process of sheet casings has been studied by physical simulation method.The difference in filling capability between gravity casting and travelling magnetic field casting has been studied.The electromagnetic force can enhance the filling process, but it also brings a problem.With an increase in the magnetic field density, the surface quality of the aluminum alloy sheet castings becomes poor.The reason is discussed.

As-cast structure refinement of Ti-46Al alloy by hafnium and boron additions

The influence of Hf and B on the solidification structure of cast Ti-46Al alloys was investigated. The results show that the coupling effect of Hf and B changes the solidification structure morphology and strongly refines the grain size. When the Hf＋B contents were increased from 0 ＋ 0.0 to 3 ＋ 0.2, 5 ＋ 0.6 and 7 ＋ 1.0 （in at. %）, the solidification structure morphology changed from coarse columnar dendrite to fine columnar dendrite, then to equiaxed dendrite, and further to fine near granular grain whilst the average grain size decreased to 20 μm. It is concluded that the columnar dendrite refinement is due to the effect of Hf and B on the decrease of AI diffusion coefficient in the melt. The fine near granular grain formation is attributed to the combined constitutional supercooling formed by AI and B segregation that is strengthened by Hf and B additions at the solid/liquid interface during solidification, and the TiB2 precipitates acting as heterogeneous nuclei.

Influence of silicide on fracture behavior of a fully lamellar Ti-46Al-0.5W-0.5Si alloy

The fracture behavior of fully lamellar binary γ-TiAI alloys is extremely anisotropic with respect to the lamellar orientation. For the fully lamellar Ti-46Al-0.5W-0.5Si alloy, the existence of silicide clusters plays a critical role on the fracture behavior. In the present study, tensile test and three point bending test were performed at room temperature with the loading axis parallel and perpendicular to the lamellar orientation, respectively. To investigate the influence of silicide clusters on the initiation and propagation of cracks, the fracture surface and the cracks adjacent to the fracture zone of the specimens have been analyzed. Results show that the fracture process is related to the morphology and distribution of the silicide clusters. Crack preferentially initiates at and propagates along the interface of silicide and a2/7 lamellar with the loading axis perpendicular to the length direction of silicide. While the silicide can prevent the propagation of cracks from running across with the crack growth direction perpendicular to the length direction of silicide.

Influence of columnar grain boundary on fracture behavior of as-cast fully lamellar Ti-46Al-0.5W-0.5Si alloy

The fracture behavior of fully lamellar γ-TiAl alloys depends on the angle between the lamellar orientation and loading axis,but the role of the presentation of grain boundary cannot be ignored.To investigate the influence of the grain boundary on the initiation and propagation of cracks,the tensile test of the alloy was conducted at room temperature with loading axis parallel and perpendicular to the lamellar orientation,respectively.The cracks adjacent to the fracture zone of the tensile specimens have been investigated to analyze the fracture behavior.Results show that the grain boundary has dual influences on the fracture behavior.When the loading axis is parallel to the lamellar orientation,cracks are preferentially initiated at and propagate along the grain boundaries.When the loading axis is perpendicular to the lamellar orientation,the grain boundaries can prevent the propagation of cracks from running across.Additionally,serrated-shape grain boundaries have a better inhibiting effect on the propagation of cracks than planar boundaries.

Efect of growth rate on characteristic lengths of microstructure in directionally solidiied Ti-46Al-2Cr-2Nb-0.2B alloy

The microstructure of TiAI based alloys is sensitive to growth rates. In this paper, Bridgman directional solidification of Ti-46Al-2Cr-2Nb-0.2B （at.%） alloy was carried out at a constant temperature gradient （G） to investigate the effects of various growth rates （v） on characteristic lengths （primary dendritic arm spacing, secondary dendritic arm spacing and lamellar spacing） of the microstructure. Results show that under the experimental conditions of G = 18 K-mm-1 and v = 15 IJm.s-1 to 70 iJm.s-1, the primary phase of directionally solidified Ti-46AI-2Cr-2Nb-0.2B alloy is a phase, the values of primary dendritic arm spacing （2,）, secondary dendritic arm spacing （λ2） and lamellar spacing （λta） decrease with the increase in growth rate. The results were compared with theoretical models and similar experimental results of TiAI based alloys. The Bouchard-Kirkaldy model agrees well with the relationship between primary dendritic arm spacing and growth rate obtained in the experiment; the relationship between them can be expressed by ,; = 758.6v-039. The relationship between the secondary dendritic arm spacing and the growth rate can be expressed by 2 = 113.9v-045, while the relationship between the lamellar spacing and growth rate can be expressed by ,; = 22.88v-v94.

Effect of power parameter and induction coil on magnetic field in cold crucible during continuous melting and directional solidification

Bottomless electromagnetic cold crucible is a new apparatus for continuous melting and directional solidification;however,improving its power efficiency and optimizing the configuration are important for experiment and production.In this study,a 3-D finite element (FE) method based on experimental verification was applied to calculate the magnetic flux density (Bz).The effects of the power parameters and the induction coil on the magnetic field distribution in the cold crucible were investigated.The results show that higher current intensity and lower frequency are beneficial to the increase of Bz at both the segment midpoint and the slit location.The induction coil with racetrack section can induce greater Bz,and a larger gap between the induction coil and the shield ring increases Bz.The mechanism for this effect is also discussed.