Microstructural and mechanical properties assessment of transient liquid phase bonding of CoCuFeMnNi high entropy alloy

The transient liquid phase(TLP)bonding of CoCuFeMnNi high entropy alloy(HEA)was studied.The TLP bonding was performed using AWS BNi-2 interlayer at 1050℃ with the TLP bonding time of 20,60,180 and 240 min.The effect of bonding time on the joint microstructure was characterized by SEM and EDS.Microstructural results confirmed that complete isothermal solidification occurred approximately at 240 min of bonding time.For samples bonded at 20,60 and 180 min,athermal solidification zone was formed in the bonding area which included Cr-rich boride and Mn3Si intermetallic compound.For all samples,theγsolid solution was formed in the isothermal solidification zone of the bonding zone.To evaluate the effect of TLP bonding time on mechanical properties of joints,the shear strength and micro-hardness of joints were measured.The results indicated a decrement of micro-hardness in the bonding zone and an increment of micro-hardness in the adjacent zone of joints.The minimum and maximum values of shear strength were 100 and 180 MPa for joints with the bonding time of 20 and 240 min,respectively.

Bond Behavior between BFRP Bars and Hybrid Fiber Recycled Aggregate Concrete after High Temperature

The aim of this study is to improve the bond performance of basalt fiber reinforced polymer(BFRP)bars and recycled aggregate concrete(RAC)after being exposed to high temperatures.The bond behavior(failure modes,bond strength,bond stress-slip curves)between BFRP bars and hybrid fiber recycled aggregate concrete(HFRAC)after being exposed to temperatures ranging from 20℃up to 500℃was studied by using pull-out tests.The effect of high temperatures on mechanical properties of concrete(compressive strength,splitting tensile strength)and tensile strength of BFRP bars was also investigated.The bond strength decreased as the temperature increased and the drop of bond strength between RAC and BFRP bar was larger than that between HFRAC and BFRP bar.As the temperature rises,the key factor affecting the bond strength was gradually transformed from concrete strength to BFRP bar strength.The relationship between bond stress and slip in the dimensionless bond stress-slip ascending section was established,which was in good agreement with the experimental results.

B-C Bond in Diamond Single Crystal Synthesized with h-BN Additive at High Pressure and High Temperature

The synthesis of diamond single crystal in the Fe64Ni36-C system with h-BN additive is investigated at pressure 6.5 GPa and temperature range of 1300-1400℃. The color of the obtained diamond crystals translates from yellow to dark green with increasing the h-BN addition. Fourier-transform infrared （FTIR） results indicate that sp2 hybridization B-N-B and B-N structures generate when the additive content reaches a certain value in the system. The two peaks are located at 745 and 1425cm-1, respectively. Fhrthermore, the FTIR characteristic peak resulting from nitrogen pairs is noticed and it tends to vanish when the h-BN addition reaches 1.1 wt%. Furthermore, Raman peak of the synthesized diamond shifts down to a lower wavenumber with increasing the h-BN ~ddition content in the synthesis system.

A Study on the Bond Strength between High Performance Concrete and Reinforcing Bar

As a preliminary study for the erection of floating structures using high performance concrete, this paper examines the bond characteristics between concrete and the reinforcing bar. Since the floating structure is constructed in aquatic environment, corrosion of the reinforcing steel is likely to develop more prematurely than in onshore structure in case of concrete cracking. A solution to this corrosion problem could use FRP rebar instead of steel reinforcement. To that goal, an experimental study is conducted on the concrete-FRP bond strength to verify if such FRP rebar develops performance comparable to the conventional steel rebar. A series of tests are performed considering the bond length of ordinary steel rebar and G-FRP rebar as test variable with respect to the strength of concrete, and the results are presented.

Diffusion bonding behaviour of β-γTiAl alloys containing high niobium with Ti interlayer by spark plasma sintering

High niobium β-γ TiAl alloy(HNBG) was diffusion bonded using spark plasma sintering with pure Ti as interlayer. The joint microstructural evolution, growth kinetics and mechanical properties were investigated. The joint included three diffusion zones. The β/B2 phase formed in the Zone Ⅰ, α_(2)phase in the Zone Ⅱ, and β-Ti and α-Ti phases in the Zone Ⅲ. The thickness of β/B2 phase, the average grain size of α_(2)phase and the amount of β-Ti phase increased with the increase of bonding temperature or bonding time. The growth activation energies of β/B2 and α_(2)phases were 582 and 253 kJ/mol, respectively. The joint acquired at 1000 °C, 10 min and 10 MPa showed the maximum shear strength of 308 MPa. Fracture mainly occurred along the interfaces between Zone Ⅰ and HNBG alloy, and between Zone I and Zone Ⅱ. Fracture mechanism of the joint was characterized by brittleness rupture along the phase boundary.

STUDIES ON PROCESS AND STABILITY OF BONDED Sm_2TM_(17)MAGNETS WITH HIGH COERCIVITY AND HIGH ENERGY PRODUCT

The process of the epoxy-bonded Sm_2TM_(17) magnets includes:(1)after melting,the ingots are treated by solid soluiion,and then aged and pulverized;(2)the obtained alloy powder is mixed with epoxy resin bind- er;(3)the mixture is pressed in a magnetic field;(4)the compacts are cured.When the SmCo_(4.9)Fe_(2.7)Cu_(0.54)Zr_(0.13) alloy is heat treated and pressed with optimum pressing parameters,the high quality bonded magnets with B_r=8250 G,_iH_c=13000 Oe,and(BH)_(max)=16MGOe can be obtained.The stability of the magnets is studied also.The irreversible loss of O.C.(open circuit)remanence B_r in the temperature range between 25 and 150℃,is less than 4%.The average temperature coefficient at temperatures between 25 and 70℃ is-0.03%/℃.The magnets obtained have heat resistance up to 130℃ even in long-term service, and have good corrosion resistance in acid,alkali and salt solutions.

Flexural Bond Behavior of Rebar in Ultra-High Performance Concrete Beams Considering Lap-Splice Length and Cover Depth

This study intends to find out the correlation between the cover depth and the bond characteristics of UHPC through pull-out tests of UHPC specimens with different cover depths and bond tests of rebar using flexural members. In this experimental study, specimens are fabricated with the lap-splice length as test variable in relation with the calculation of the lap-splice length for 180- MPa UHPC. Moreover, specimens are also fabricated with the cover depth as test variable to evaluate the effect of the cover depth on the UHPC flexural members. The load-displacement curves are analyzed for each of these test variables to compute the lap-splice length proposed in the K-UHPC structural design guideline and to evaluate the influence of the cover depth on the flexural members. As a result, the stability of the structural behavior can be significantly enhanced by increasing slightly the cover depth specification of the current UHPC Structure Design Guideline from the maximum value between 1.5 times of rebar diameter and 20 mm to the maximum value between 1.5 times of rebar diameter and 25 mm.

Development of a new instrument for measurement of high temperature mechanical properties of resin-bonded sand

The mechanical properties of resin-bonded sand mixtures at high temperatures significantly affect the quality of casting. However, the existing instruments for high-temperature performances testing mainly focus on inorganic binder-bonded sands no matter the test items or the atmospheric protection, while the instrumentss specially designed for resin-bonded sand are not yet available. A new instrument for testing the hightemperature performance of resin sand was designed including the confirmation of the testing parameters, loading, measurement and control systems, and the design of the frame shape and heating furnace. This instrument can test the compressive strength, heat tolerance time and restraining load of phenol-formaldehyde resin coated sand, self-hardened furan resin sand, and trimethylamine(TEA)-based resin bonded sand at high temperatures. The developed instrument has a high accuracy offering smaller than 0.3% deviation at a full scale in the measurement of the high temperature compressive strength and the restraining load over the range of 0-6.8 MPa and 0-2,000 N, respectively. The high temperature heat tolerance time range is 0-300 s and its measurement accuracy is ±1 s.

Ultrathin organic polymer with p-πconjugated structure for simultaneous photocatalytic disulfide bond generation and CO_(2)reduction

Combining photocatalytic organic reactions with CO_(2)reduction is an efficient solar energy utilization mode,but it is still limited by the organic species that can be matched and the low conversion.Herein,ultrathin organic polymer with p-πconjugated structure(TPP)was rationally designed and prepared,and showed a high yield of CO(15.2 mmol g^(-1))and conversion of SAS coupled products(100%),far exceeding the organic polymer with P=O structure.The enhanced photoredox activity of TPP is ascribed to the orbital interaction between the p-orbital on phosphorus and theπ-orbitals of aromatic,which can accelerate the photoinduced charge carrier separation and improve the CO_(2)adsorption capacity.TPP can also be used for the dehydrocoupling of various benzyl mercaptans to the corresponding SAS bond products.This work provides a new concept for the efficient synthesis of disulfide bonds combined with CO_(2)reduction in a photoreaction system.

Mechanism of Increase in Strength of Sodium Silicate-bonded Sand by Silica Sand Surface Modified in High Temperature.

With the aid of XRD, SEM and EDS etc., there is absorbed film on sand grain surface, high temperature modify makes the film sintered firmly on sand grain surface. Thus it changes physical and chemical characteristics of the film and sand grain surface, improves the wetting properties greatly, makes the fracture features of bonding bridge change from the adhesive to the cohesive and raises the strength of sodium silicate-bonded sand.

Bond Elut PBA固相萃取柱净化-高效液相色谱-串联质谱法同时测定鸡肉中金刚烷胺和利巴韦林的残留量

取鸡肉样品约2.0 g,加入100μg·L^(-1)金刚烷胺-d6和利巴韦林-13C5的混合内标溶液100μL和体积比为7∶3的20 g·L^(-1)三氯乙酸溶液-乙腈的混合溶液15 mL,涡旋30 s,振荡15 min,离心5 min,上层有机相转移至50 mL离心管中。重复上述操作一次,合并上层有机相,过普通滤纸,滤液用约100μL氨水调节酸度至pH 8.5,过活化好的Bond Elut PBA固相萃取柱。固相萃取柱先以体积比1∶9的乙腈-0.25 mol·L^(-1)乙酸铵混合溶液3 mL和含5%(体积分数)氨水的甲醇溶液3 mL淋洗,然后以含2%(体积分数)甲酸的甲醇溶液4 mL洗脱。收集洗脱液,氮吹至干,残渣用体积比1∶9乙腈-水混合溶液1 mL复溶后,过0.22μm滤膜。滤液进入高效液相色谱-串联质谱仪,在Eclipse XDB-C8色谱柱上用不同体积比的含5 mmol·L^(-1)乙酸铵的1%(体积分数)甲酸溶液-甲醇-水的混合溶液梯度洗脱分离其中的金刚烷胺和利巴韦林,在多反应监测模式和电喷雾离子源正离子模式下检测,以内标法定量。结果显示:金刚烷胺和利巴韦林在Eclipse XDB-C8色谱柱上的保留较强,分别在4.30,9.13 min出峰;标准曲线的线性范围均为2~40μg·L^(-1),检出限(3S/N)分别为0.2,0.3μg·kg-1;对空白鸡肉样品进行3个浓度水平的加标回收试验,回收率分别为70.5~84.4%和98.5%~99.6%,测定值的相对标准偏差(n=6)均小于5.0%。

高强钢管超高性能混凝土界面黏结滑移性能试验

目的为了研究高强钢管超高性能混凝土的黏结滑移性能,方法考虑径厚比、长径比和钢纤维掺量3个参数的影响,设计并制作15根构件进行试验研究,通过推出试验,得到轴向荷载与加载端位移的荷载-位移曲线,以及高强钢管与超高性能混凝土之间的黏结强度,根据试验结果,对影响黏结强度的参数进行定性定量分析。结果结果表明:随着高强钢管长径比和径厚比的增加,黏结强度减小;随着钢纤维掺量增加,试件黏结强度先增加后减小,即当钢纤维掺量从1%增加到2%时,黏结强度增加,但当钢纤维掺量从2%增加到3%时,黏结强度反而降低;试件荷载-滑移曲线表现为两种形式,一是有明显的峰值点,峰值点后曲线急速下降(部分出现尾部上升的现象),二是曲线无明显峰值点,拐点后曲线持续缓慢增长。高强钢管超高性能混凝土的黏结破坏分为黏结阶段、滑动阶段和抗摩擦阶段。结论以长径比、径厚比、含钢率和套箍系数为参数,结合试验数据并对其进行回归分析,得到适用于高强钢管超高性能混凝土黏结强度的计算模型,并将计算结果与试验结果进行对比,计算值与试验值吻合较好,可为实际工程提供一定参考。

电子封装超声互连研究新进展

超声振动摩擦和局部高温高压可实现同材或异材的低温、快速、可靠的互连,超声技术在电子封装中显示出无与伦比的技术优势。综述了超声引线键合、块体母材直接超声键合、母材/焊料/母材三体超声固相键合等超声固相键合技术,超声钎焊、超声瞬态液相扩散焊等超声液相键合技术,超声纳米烧结、混合(复合)焊料超声互连等超声固液混合键合技术。无论是高频低功率的高速超声键合,还是中频高功率超声常速键合,超声的作用规律和效果相似,其互连质量和互连机理与接触材料及其状态有着最为密切的关系;考虑由于超声互连过程快、时间短、互连界面窄、接头不透明,可以采用焊接实时高速摄像技术和同步辐射X射线成像技术相结合,实时观察液态焊料润湿流动、焊料颗粒运动轨迹、母材的剥离过程及界面形成规律;考虑由于微焊点尺寸放大,可以借助温度传感器和压力传感器进行超声的温度效应和瞬态压强实时测量;基于双超/多超声诸多影响因素,多超声的数值模拟分析将成为微焊点超声互连机理研究的有效手段。

氯盐环境下UHPC-NC界面黏结性能试验研究

氯盐环境作为一种较为常见的化学侵蚀环境,研究其对超高性能混凝土(ultra-high performance concrete,UHPC)和普通混凝土(normal concrete,NC)界面耐久性能的影响对于UHPC加固混凝土结构和UHPC-NC组合结构的工程应用均具有重大的现实意义.基于此,通过在常规环境以及氯盐环境下的推出试验,获得了干湿循环次数(0次、25次、50次)、氯盐浸泡天数(0 d、50 d、100 d)及界面处理方式(钢丝刷刷毛、高压水射流冲毛、表面缓凝处理)对UHPC-NC界面黏结强度、界面黏结刚度及界面黏结滑移曲线的影响.结果表明:在100 d试验周期内,干湿循环及氯盐浸泡作用造成的界面黏结强度损失率不超过20%;氯盐环境作用时长的增加会导致界面黏结刚度的降低;随着界面粗糙度的增加,UHPC-NC试件的界面黏结强度以及界面黏结刚度均会增加;界面粗糙度的提高有助于界面抗氯盐侵蚀能力的提升.受到界面处理方法的影响,UHPC-NC试件经历干湿循环及氯盐浸泡后,荷载滑移曲线呈现2种不同的形式,分别对应光滑界面(钢丝刷刷毛界面)和其他界面(高压水射流冲毛界面和缓凝剂处理界面).各组试件的黏结滑移曲线在荷载到达峰值前趋于一致;荷载到达峰值后,前者存在荷载骤降段及持荷段,后者则随着滑移量的增加荷载不断降低.根据UHPC-NC黏结滑移曲线特征,提出了黏结滑移建议模型.

科创债券是否存在发行溢价?——来自中国债券市场的实证研究

本文基于2021—2023年我国债券市场发行的科创债券数据,使用科创债券与普通债券匹配的方法构造研究样本,并构建计量模型考察了科创债券的发行溢价效应。实证分析结果显示,科创债券一级市场发行存在显著的溢价效应,科创债券发行利率较普通债券高27个基点。同时,目前科创债券发行主体主要为高评级企业,而主体资质较弱的科技型中小企业获得债券融资的机会较少。积极引导各类市场投资主体参与科创债券业务,有效降低科创债券发行溢价。此外,要加快中国版高收益债券市场建设,打通科技型中小企业债券融资渠道。

HRB635级高强钢筋与C70高强混凝土黏结锚固性能试验研究

目的 研究HRB635级高强钢筋与C70高强混凝土之间黏结锚固性能,为工程应用提供参考。方法 设计制作了5组45个直锚试件进行拉拔试验,分析了锚固长度、配箍率、混凝土保护层厚度等因素对锚固性能的影响。结果 试件极限承载力随配箍率和锚固长度的增加而增加,但当箍筋率ρsv大于1.26%,锚固长度la大于15d后,配箍率和锚固长度的增加不再对试件极限承载力产生明显的影响;对于未配置箍筋的试件,当试件保护层厚度从2d增加到3d时,试件极限承载力随着保护层厚度的增加而增加,但当保护层厚度大于3d后,保护层厚度的增加对试件极限承载力基本没有影响。结论 在进行HRB635级高强钢筋和C70高强混凝土试件设计时,锚固长度可按《混凝土结构设计规范》(GB 50010-2010)中相关公式进行计算,且具有足够的安全储备。

BFRP筋与超高性能纤维混凝土黏结性能试验研究

为探究玄武岩纤维增强复合材料(BFRP)筋与超高性能纤维混凝土(UHPFRC)之间的黏结性能,通过中心拉拔试验,对BFRP-UHPFRC试件破坏模式、黏结-滑移曲线进行分析,且探讨了筋材直径、单一纤维及钢-PVA混杂纤维对黏结强度的影响。结果表明,试件破坏模式包括BFRP筋拔出破坏与拉断破坏。BFRP筋直径的增大将导致黏结强度降低。随着单一纤维掺量增加,黏结强度呈先增大后减小的趋势。而相较于单一纤维,钢-PVA混杂纤维显著提高了试件的黏结强度,当掺入1%钢纤维和0.5%PVA纤维时,黏结强度最高(25.35 MPa)。此外,通过灰狼算法优化的支持向量回归模型实现对黏结强度的预测,预测值与实际值拟合较好。

可恢复功能装配式高强再生混凝土剪力墙抗震性能试验研究

为推动高强再生混凝土构件应用于可恢复功能建筑结构,提出一种边缘构件配置弱粘结超高强纵筋的装配式高强再生混凝土剪力墙。对4个剪跨比为2.2的装配式高强再生混凝土剪力墙进行低周反复荷载试验,分析了边缘配置弱粘结超高强纵筋、墙体有无钢纤维的装配式高强再生混凝土剪力墙的损伤破坏形态、滞回性能、刚度退化、残余变形、裂缝宽度等抗震与可恢复性能指标。结果表明:在大变形条件下,边缘配置弱粘结超高强纵筋的装配式高强再生混凝土剪力墙水平承载力持续增大,混凝土损伤程度较轻,抗侧刚度退化缓慢,残余变形与裂缝宽度较小。基于试验结果,建议了可恢复功能装配式高强再生混凝土剪力墙在1%位移角下的抗震承载力计算方法,其计算结果与试验结果符合较好。

高温后钢管高强混凝土柱的黏结性能

为了研究高温后钢管高强混凝土柱的黏结性能,通过有限元软件ABAQUS建立模型,并与已有试验结果进行验证,吻合良好。研究表明:钢管高强混凝土柱的黏结应力随着温度的升高呈现出先增加后减小的趋势;黏结应力随着混凝土强度的增大而增大,随着径厚比的增大而减小;长径比在2.74~7.72的范围内,随着长径比的增加,黏结力逐渐增加;黏结界面破坏的速度随温度的增加而减缓;随着温度的增加耗能因子呈现先增大后减小的趋势。

高温后钢-PVA混杂纤维高性能混凝土与变形钢筋黏结性能试验

为研究高温后钢-聚乙烯醇(polyvinyl alcohols,PVA)混杂纤维高性能混凝土(hybrid fiber high performance concrete,HFHPC)与变形钢筋的黏结性能退化规律,以200、400、600、800℃为目标温度,选取钢纤维体积率、PVA纤维体积率、矿粉掺量为正交试验因素设计并制作25组HFHPC试件,完成了单调荷载下的中心拉拔试验。结果表明:高温后各组HFHPC试件黏结破坏形态均表现为钢筋拔出破坏;试验温度范围内,对HFHPC试件黏结强度的影响程度均为:钢纤维体积率最大、矿粉掺量次之、PVA纤维体积率最小;随着温度的升高,HFHPC试件黏结强度逐渐下降,且在相同温度条件下,HFHPC试件黏结强度和峰值滑移相比于未掺纤维的混凝土试件均有所提升,其中,200℃时HFHPC试件的黏结强度提升最为显著,分别提升了33.69%、35.76%、37.54%和46.03%;混杂纤维能显著提高高温后高性能混凝土与钢筋的峰值界面能,明显改善黏结延性和耗能能力;提出的考虑温度作用后的混杂纤维混凝土与钢筋黏结-滑移模型与试验实测结果吻合较好,可为火灾后混杂纤维高性能混凝土结构损伤评估及加固方案提供参考。