TiAl合金与异种材料的摩擦焊接

TiAl合金与42CrMo直接摩擦焊接性较差,为此分别引入高温合金GH3039、K418、N80A和纯镍N6作为中间材料,对TiAl-GH3039/K418/N80A/N6-42CrMo异种材料的摩擦焊接工艺进行了研究。采用硬度计、扫描电镜和电子万能试验机对焊后接头区域的硬度、组织和焊合区成分变化以及接头力学性能进行了分析。研究表明,TiAl合金与异种材料焊后接头中形成了复杂的多层状金属间化合物;TiAl合金与GH3039、N80A的摩擦焊接性较好,与K418、N6的摩擦焊接性较差;根据不同材料线膨胀系数随温度的变化规律、与TiAl合金摩擦焊接后接头的性能及其与42CrMo的摩擦焊接性,最终选择GH3039作为中间材料。通过引入中间材料,摩擦焊制备了TiAl合金涡轮-42CrMo转轴的异种材料整体转子,使得TiAl合金在涡轮增压器领域的应用成为可能。     

富CoCr含量CoCrNiAlTi中熵合金的高温强韧化行为及微观机制

本工作研究了富CoCr含量的CoCrNi基中熵合金的高温力学性能及其变形机制。研究发现,经过热锻以及时效热处理,成分为Co_33.3Cr_30.6Ni_26.1Al₅Ti₅ (at%)中熵合金在600～800℃的温度范围内具有优异的瞬时拉伸性能。特别是,在700℃条件下出现反常屈服,屈服强度高达为944 MPa,拉伸塑性为16%,优于大多数镍基以及钴基高温合金。通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和三维原子探针(3D-APT)等手段,发现高体积分数的多主元γ′[(Ni,Co,Cr)₃(Al,Ti)]相的有序强化以及晶界处生成的多主元富(Co,Cr)面心立方相(fcc)结构相引起的晶界强化是该合金在高温条件下实现强韧化的主要因素。     

Effects of the configuration of a baffle–avalanche wall system on rock avalanches in Tibet Zhangmu: discrete element analysis

Rock avalanches with a high mobility and kinetic energy pose a potential geological risk to surrounding buildings. Baffles and avalanche walls are effective ways to protect these buildings. However, the primary focus of previous studies has been on baffles or avalanche walls alone, and there have been very few studies investigating the effectiveness of a combination of baffles and avalanche walls as a countermeasure against rock avalanches. In addition, previous studies on lab-scale tests and numerical analyses often did not take the actual topography effects into consideration. In this study we adopted a numerical simulation approach based on an actual project in the town of Zhangmu, Tibet, with the aim to investigate the effect of different configurations of a combined baffle–avalanche wall system on impeding the kinetic energy of rock avalanches. A series of numerical analyses with discrete element methods (DEM) were conducted. First, the effect of three different pile groups on the reduction of the effect of the rock avalanche was studied using the numerical modeling study. Secondly, the influence of the size of the retaining wall on the maximum impact force of the rock avalanche was studied. Finally, a DEM modeling study on the energy dissipation capacity of the baffle–avalanche wall system was conducted. The results demonstrate that an arrangement of different baffle–avalanche wall systems will produce different results in terms of dissipating the energy of rock avalanches: when the wall is long enough to block all rock masses, enhancing baffle density will decrease the maximum impact force exerted on the avalanche wall; however, if the wall is just long enough to protect the target region, reducing baffle density will decrease the maximum impact force exerted on the avalanche wall. The results of this study are significant in terms of providing guidelines for the design of baffle–avalanche wall systems for protection against rock avalanches.

     

基于修正关口-太田模型的归一化#br# 变形量开挖边坡失稳判据

由于普通土体本构模型不能反应土体初始应力状态及开挖应力路径,在进行有限元计算时得到的特征点位移也会与工程实际有偏差。选用可以对开挖前边坡土体的初始K0应力状态以及开挖应力路径进行合理描述的修正关口太田模型,对开挖边坡进行有限元计算。根据位移突变判据,采用单因素敏感性分析,对54例简单边坡进行有限元计算,得出与边坡位移量呈正、负关联的基本参量。利用灰色关联分析方法,首次同时考虑了土坡几何参数、物理参数、本构模型等基本参数,将边坡的变形量进行归一化处理,构建以变形量为基础的归一化失稳判据Fu及警戒位移值U′1,从而可以通过实时监控边坡位移及时给出滑坡体的安全性评价。     

浅埋矩形框架地铁车站结构抗震性能指标标定研究

针对目前地下结构抗震性能水准定义与性能指标标定研究的不足,文章参考地面建筑性能水准的划分方法,将地下结构的抗震性能水准划分为四个水平,并对每一水平条件下结构具备的功能性作了简略描述。在此基础上,选取18座不同断面类型的浅埋矩形框架地铁车站,建立土-结构三维整体分析有限元模型。采用倒三角分布荷载的地下结构Pushover分析方法进行分析,获得各个车站结构关键构件的完整能力曲线。通过几何作图法和概率统计方法建立以层间位移角为限值的矩形框架地铁车站结构横向抗震性能指标体系。该性能指标量化标准可在一定程度上指导地下结构抗震设计,并为进一步发展和完善现有地下结构抗震性能指标体系研究提供参考。     

Seam-tracking based on dynamic trajectory planning for a mobile welding robot

A new seam-tracking method based on dynamic trajectory planning for a mobile welding robot is proposed in order to improve the response lag of the mobile robot and the high frequency oscillation in seam-tracking. By using a front-placed laser-based vision sensor to dynamically extract the location of the weld seam in front of torch, the trend and direction of the weld line is roughly obtained. The robot system autonomously and dynamically performs trajectory planning based on the isometric approximation model. Arc sensor technology is applied to detect the offset during welding process in real time. The dynamic compensation of the weld path is done in combination with the control of the mobile robot and the executive body installed on it. Simulated and experimental results demonstrate that the method effectively increases the stability of welding speed and smoothness of the weld track, and hence the weld formation in curves and corners is improved.     

Effects of Dissimilar Alumina Particulates on Microstructure and Properties of Cold-Sprayed Alumina/A380 Composite Coatings

In this study,alumina/A380 composite coatings were fabricated by cold spray.The influence of alumina particulates' morphology(spherical and irregular) and content on the deposition behavior of the coatings(including surface roughness,surface residual stress,cross-sectional microstructure and microhardness) was investigated.Results revealed that the spherical alumina mainly shows micro-tamping effect during deposition,which result in remarkable low surface roughness and porosity of the coatings.In addition,very low deposition efficiency and good interfacial bonding between the coating and the substrate were achieved.For irregular alumina particles,the embedding of ceramic particulates in the coating was dominant during deposition process,resulting in high retention in the final deposit.However,it showed limited influence on porosity,surface roughness and interfacial bonding of the deposit.The coatings containing irregular alumina particulates exhibited much higher microhardness than those containing spherical alumina due to the higher load-bearing capacity of deposited alumina.     

K2ZrF6含量对ZrH1.8表面微弧氧化阻氢膜层的影响

采用微弧氧化技术在ZrH_1.8表面制备阻氢膜层,研究在Na₅P₃O₁₀-NaOH-Na₂EDTA电解液体系中K₂ZrF₆含量对膜层组织结构和阻氢性能的影响。借助场发射扫描电子显微镜(FESEM)和X射线衍射仪(XRD)分析膜层的微观结构和物相组成。采用涂层测厚仪对膜层的厚度进行测量,通过真空脱氢实验表征膜层的阻氢性能。相比未加入K₂ZrF₆时,电解液中添加适量K₂ZrF₆有助于改善膜层的表面质量,减少膜层中微孔和裂纹等缺陷的出现。XRD分析表明,不同K₂ZrF₆浓度时ZrH_1.8表面微弧氧化制备的膜层均主要由m-ZrO₂,t-ZrO₂和少量c-ZrO₂相组成。膜层厚度和氢渗透降低因子(PRF)随K₂ZrF₆浓度的增加均呈先增大后减小趋势,当K₂ZrF₆为4g·L^-1时,膜层的厚度最大为68.7μm,PRF最大为13.1,且膜层中大尺寸缺陷较少,添加K₂ZrF₆制备的陶瓷膜的阻氢性能均得到提高。K₂ZrF₆添加剂的加入可以使ZrH_1.8表面微弧氧化膜层的厚度增大,致密性增强,进而阻氢性能提高,膜层表面质量也得到改善。     

大数据监测平台下的长江流域典型城市房间空调器温度设置分析

房间空调器是中国长江流域地区改善室内热环境的重要措施,然而,在以往的房间空调器的行为研究中,只能通过现场实测、问卷调查等方式获取其使用行为,由于数据获取方式本身所存在的局限性,无法对空调的使用行为进行可靠且深入的挖掘,尤其是对于空调的设置温度。为了研究长江流域地区房间空调器的设置温度行为,包括设置温度的分布、设置温度调节习惯、设置温度与一天中不同时间段的关系、设置温度与室外温度的关系,依托于大数据平台下的房间空调器监测数据,针对长江流域地区的3个典型城市（重庆、武汉、上海）的房间空调器的设置温度习惯,对重庆地区575台房间空调器、武汉地区430台房间空调器、上海地区540台空调器的夏季上万次运行数据、冬季上千次运行数据进行了基本的统计与相关分析,结果表明：空调器的设置温度及其调节习惯在不同城市之间存在一定差异性,夏季用户在一次空调使用过程中存在对较低设置温度（低于26℃）的短时需求情景,同时,设置温度与1 d中的不同时刻以及室外温度也有明显关联。     

连铸结晶器保护渣渣膜传热特性研究进展

传统保护渣主要以CaO和SiO₂为基料,辅以适量助熔剂如CaF2等构成;而无氟保护渣则是选用B₂O₃、TiO₂等合适的助熔剂来替代CaF₂达到绿色环保的目的。从保护渣的碱度、化学成分和结晶性能三方面,分别综述了传统含氟渣系CaO-SiO₂-CaF₂和新型无氟渣系CaO-SiO₂-B₂O₃、CaO-SiO_2-TiO₂渣膜传热的影响规律,总结了近十年来冶金工作者对含氟和无氟保护渣渣膜传热的研究成果,得出无氟保护渣结晶矿相中硅硼酸钙和钙钛矿与传统保护渣中枪晶石具有相似的结晶行为,B₂O₃和TiO₂的含量在4%~8%和3%~11%可有效控制传热,从而减少铸坯纵裂纹的发生。并提出了开发新型高效无氟保护渣的进一步研究方向,即无氟渣中氟化物替代物的迁移赋存规律对渣膜传热性能的影响机理。