Low-temperature performance and high-rate discharge capability of AB_5-type non-stoichiometric hydrogen storage alloy

Low-temperature performance and high-rate discharge capability of AB5-type non-stoichiometric hydrogen storage are studied. X-ray diffraction(XRD),pressure-composition-temperature(PCT) curves and electrochemical impedance spectroscopy(EIS) are applied to characterize the electrochemical properties of ABx(x=4.8,4.9,5.0,5.1,5.2) alloys. The results show that the non-stoichiometric alloys exhibit better electrochemical properties compared with that of the AB5 alloy.

ISOCHRONOUS STRESS-STRAIN CURVES OF LOW ALLOY STEEL CROSS-WELD-SPECIMEN AT HIGH TEMPERATURE

In this work, a parametric approach is presented and utilized to determine the creep properties of weldments; then the model of creep strain for cross weld specimen is given. On the basis of the experimental results, attempt has been made to establish equations of the isochronous stress-strain for weld joint that can predict the function of loading and service time in use of the creep data of base metal and weld metal.

Thin Film Chip Resistors with High Resistance and Low Temperature Coefficient of Resistance

High resistance thin film chip resistors(0603 type) were studied,and the specifications are as follows:1 k? with tolerance about ±0.1% after laser trimming and temperature coefficient of resistance(TCR) less than ±15×10-6/℃.Cr-Si-Ta-Al films were prepared with Ar flow rate and sputtering power fixed at 20 standard-state cubic centimeter per minute(sccm) and 100 W,respectively.The experiment shows that the electrical properties of Cr-SiTa-Al deposition films can meet the specification requirements of 0603 ty...

High Performance ZrNbAl Alloy with Low Thermal Expansion Coefficient

Thermal expansion is a common phenomenon in both metals and alloys, which is important for metallic material applications in modern industry, especially in nuclear and aerospace industries. A lower thermal expansion coefficient may cause lower thermal stress and higher accuracy. A new Zr-based alloy is developed and presented.The XRD diffraction results demonstrate that only a close-packed hexagonal phase（α or α＇ phase） exists in the microstructure. The thermal expansion and mechanical properties are studied. According to the experimental results, the new Zr-based alloy presents a low thermal expansion coefficient and good mechanical properties.Also,its thermal expansion coefficient is stable through solution treatment.

Low temperature impact toughness of laser hybrid welded joint of high strength low alloy steel

High strength low alloy steel with 16 mm thickness was welded by using high power laser hybrid welding. Microstrueture was characterized by using optical microscopy, scanning electron microscopy （ SEM ） , transmission electron microscopy （TEM） and selected area electron diffraction （SAED）. Low temperature impact toughness was estimated by using Charpy V-notch impact samples selected from the upper part and the lower part at the same heterogeneous joint. Results show that the low temperature impact absorbed energies of weld metal are （202,180,165 J） of upper samples and （178,145,160 J） of lower samples, respectively. All of them increase compared to base metal. The embrittlement of HAZ does not occur. Weld metal primarily consists of refined carbide free bainite and a little granular bainite since laser hybrid welding owns the character of low heat input. Retained austenite constituent film ＂locates among the lath structure of bainitie ferrite. Refined bainitic ferrite lath and retained austenite constituent film provide better low temperature impact toughness compared to base metal.

Effect of high density pulse electric current on solidification structure of low temperature melt of A356 alloy

The effect of high density pulse electric current (HDPEC) on the solidification structure of the low temperature melt(LTM) of commercial A356 alloy was investigated. In the experiments, the HDPEC was discharged in the LTM (953?K, 903?K and 873?K). By the control experiments, the results showed that the solidification structure of the LTM of A356 alloy is refined apparently when the HDPEC is discharged in low temperature melt. However, the holding time of melt treated has an adverse effect on the solidification structure. The longer the holding time of the melt treated with HDPEC, the coarser the microstructure. With the same discharge voltage, the lower the temperature of LTM, the more obscure the refinement of solidification structure. Finally, the mechanism of microstructure refining by HDPEC was analyzed.

Microstructure refinement and second phase particle regulation of Mo-Y_(2)O_(3) alloys by minor TiC additive

The oxide dispersion strengthened Mo alloys(ODS-Mo)prepared by traditional ball milling and subsequent sintering technique generally possess comparatively coarse Mo grains and large oxide particles at Mo grain boundaries(GBs),which obviously suppress the corresponding strengthening effect of oxide addition.In this work,the Y_(2)O_(3) and TiC particles were simultaneously doped into Mo alloys using ball-milling and subsequent low temperature sintering.Accompanied by TiC addition,the Mo-Y_(2)O_(3) grains are sharply refined from 3.12 to 1.36μm.In particular,Y_(2)O_(3) and TiC can form smaller Y-Ti-O-C quaternary phase particles(~230 nm)at Mo GBs compared to single Y_(2)O_(3) particles(~420 nm),so as to these new formed Y-Ti-O-C particles can more effectively pin and hinder GBs movement.In addition to Y-Ti-O-C particles at GBs,Y_(2)O_(3),TiOx,and TiCx nanoparticles(<100 nm)also exist within Mo grains,which is significantly different from traditional ODS-Mo.The appearance of TiOx phase indicates that some active Ti within TiC can adsorb oxygen impurities of Mo matrix to form a new strengthening phase,thus strengthening and purifying Mo matrix.Furthermore,the pure Mo,Mo-Y_(2)O_(3),and Mo-Y_(2)O_(3)-TiC alloys have similar relative densities(97.4%-98.0%).More importantly,the Mo-Y_(2)O_(3)-TiC alloys exhibit higher hardness(HV0.2(425±25))compared to Mo-Y_(2)O_(3) alloys(HV0.2(370±25)).This work could provide a relevant strategy for the preparation of ultrafine Mo alloys by facile ball-milling.

BEHAVIOR OF OXYGEN IN DG^(TM) INVAR-Cu ALLOYS AND ITS EFFECTS ON MECHANICAL AND PHYSICAL PROPERTIES

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Lattice distortion and magnetic property of high entropy alloys at low temperatures

Deformation mechanisms and magnetic properties of medium and high entropy alloys(MEA/HEAs)closely relate to lattice distortion and are strongly temperature-dependent,in particular,at low temperature ranges.However,little attention has been paid to the evolution of lattice distortion with temperature decreasing and its effects on deformation behavior and magnetic state transition.In this work,we carry out in situ synchrotron radiation based X-ray powder diffraction(SR-XRD)experiments from 293 to 123 K aiming for determining lattice distortion evolutions of Cr Co Ni MEA,Cr Fe Co Ni and Cr Mn Fe Co Ni HEAs.Magnetic measurements at corresponding low temperatures and cryogenic ranges are further conducted.The in situ SR-XRD results demonstrate a general reduction of lattice distortion magnitude with temperature decreasing,which shows a similar tendency with that of reported stacking fault energy(SFE)values.It is thus suggested that lattice distortion reduction possibly makes a critical contribution to deformation mechanism transition.The magnetic measurement results show a clear ferromagnetic transition of Cr Fe Co Ni HEA when temperature is below 173 K.While,no obvious magnetic state transition is observed for Cr Co Ni MEA and Cr Mn Fe Co Ni HEA.The present findings on lattice distortion evolutions will pave the way for designing targeted HEAs with particular properties.

Effect of Solid Solution Treatment on Microstructure of Fe-Ni Based High Strength Low Thermal Expansion Alloy

The influence of solid solution treatments on the dissolution of carbides precipitates,the grain size,and the hardness of high strength low expansion alloy were investigated through XRD analysis,microstructure observations,and theoretical computation.It was seen that most primary Mo2C type carbide band dissolved in a temperature range of 1 100-1 150 ℃.When the temperature was over 1 200 ℃,the grain size increased remarkably,which led to the reduction of hardness.

Fabrication of nano-crystalline W-Ni-Fe pre-alloyed powders by mechanical alloying technique

Nano-crystalline pre-alloyed powders of W-Ni-Fe were fabricated by high energy ball milling mechanical alloying (MA) technique. The change of appearances and the crystallite sizes of powders before and after high energy ball milling were investigated by XRD, TOPAS P software, SEM and EDS. The results show that the nano-crystalline pre-alloyed powders can be fabricated by 5 h high energy ball milling. During the MA process, the diffusion of W, Ni and Fe happens in the process of repeated welding and fracturing. As a result, nano-crystalline supersaturated solid solutions are formed. The crystallite sizes won't be refined after 10 h ball milling. The crystallite sizes of different compositions are almost the same under the same MA condition. Due to the toughening mechanism of rare earth element, the powders of 90W-4Ni-2Fe-3.8Mo-0.2RE alloy are seriously agglomerated after ball milling compared with the other alloys. It can be concluded that the optimal sintering temperature of 90W-4Ni-2Fe-3.8Mo-0.2RE pre-alloyed powders after 15 h mechanical alloying is 1 300-1 350 ℃.

孔挤压强化对GH4169孔结构高温疲劳裂纹扩展行为影响研究

为探究孔挤压强化对镍基高温合金GH4169孔结构疲劳裂纹扩展行为的影响规律,针对孔挤压强化后螺栓孔特征模拟件开展残余应力松弛及疲劳裂纹扩展试验。结果表明,经热松弛稳定后,孔边依旧可以保持至少400 MPa的残余压应力水平,且孔壁表面残余应力松弛幅度高于内部;孔挤压强化后疲劳裂纹扩展速率降低一个数量级,随着相对挤压量增加,疲劳裂纹扩展速率降低幅度增大,疲劳裂纹扩展寿命增幅为4~22倍。结合有限元仿真及断口分析,孔挤压强化对疲劳裂纹扩展的影响机制可归结为松弛至稳定后的残余压应力抵消部分外载应力,导致有效应力强度因子范围减小,使得疲劳裂纹扩展速率降低。基于该机制,利用残余应力修正的Walker模型对疲劳裂纹扩展寿命进行预测,误差在1.8倍分散带以内。

TMCP工艺下Q390钢板厚度、温度场与组织演变的关系

采用TMCP工艺制备三种不同厚度的Q390热轧钢板,基于冷却温度场有限元分析揭示了厚度对组织演变和硬度的影响规律。结果表明:在相同冷却条件下,40 mm厚热轧钢板厚度方向组织存在明显差异,即边部以贝氏体为主,而心部为铁素体和珠光体,对应显微硬度差值约40 HV;13、20 mm厚热轧钢板厚度方向组织较为均匀,以贝氏体为主,显微硬度分布也相对均匀。温度场有限元分析表明厚板(40 mm)试样的心部组织铁素体+珠光体主要形成于空冷阶段;而对于其他厚度钢板,在水冷阶段,心部和边部获得较为一致的终冷温度和冷速,且均在贝氏体相变温度区间。

低熔点合金高低温循环浸渍杨木的性能及机理研究

利用气-液相变自驱动原理,选用Sn-Bi-Pb低熔点合金(LMPA),通过木材含水率的调控及采用高低温交替循环浸渍法,在不破坏木材本身结构的条件下制备了金属化杨木,探讨了低熔点合金在木材中的渗透机理,并分析了金属化杨木的增重率、吸水率、顺纹抗压强度及导热性能。结果表明:提高木材的含水率并在高低温循环条件下浸渍有助于LMPA渗透到木材导管中,当杨木的含水率为60%时,其增重率高达52.47%;浸泡144 h后的吸水率比对照样减小了78.4%,顺纹抗压强度提高了33.75%,导热系数是对照样的2.6倍,在地暖地板领域显示出较好的应用前景。

锆合金表面高温抗氧化涂层的研究进展

锆合金因其热中子吸收截面小、热膨胀系数低,以及与UO2良好的相容性而成为当前核反应堆中主要的构件材料。然而,在高温蒸汽氧化环境中,锆合金会快速氧化失效,并产生大量氢气,从而引发氢爆炸。为了提高核反应堆的安全性,对锆合金表面进行强化形成高温抗氧化防护涂层,是解决这一难题的有效途径。本文介绍了锆合金表面高温氧化行为,重点综述了高温抗氧化涂层(包括金属涂层、陶瓷涂层以及复合涂层)的氧化行为和失效机理,对比分析了不同锆合金表面涂层高温氧化性能。另外,还对锆合金表面高温抗氧化涂层的多元素成分设计、制备方法和梯度结构设计的发展方向进行了展望。

TC4钛合金恒定高温和高低温环境下疲劳性能研究

目的 研究TC4钛合金在恒定高温和高低温环境(25~390℃)的疲劳性能。方法 分别开展恒定高温和高低温环境的疲劳试验及断口分析,研究材料在2种环境下的疲劳性能差异及温度效应机理。结果 当温度从25℃升高至390℃时,TC4钛合金恒定温度的疲劳性能在短寿命段(N<106循环)逐渐降低,疲劳性能在长寿命段(N>106循环)呈非线性的变化趋势,先降低、后升高。通过断口分析发现,氧化现象随着温度升高和试验时间变长越来越明显。同一应力水平下,高低温环境疲劳试验的疲劳寿命介于最高温度和最低温度疲劳试验的疲劳寿命之间。结论 当温度处于25~390℃时,温度和氧化现象同时影响着TC4钛合金的疲劳性能。温度升高使材料的疲劳性能下降,高温环境生成的保护性氧化膜提高了材料的疲劳性能。钛合金的高低温疲劳寿命可以用等效恒定温度的疲劳曲线来预测,并有较好的预测精度。

双相高熵合金研究综述

双相高熵合金融合了两种单相高熵合金的优点,能够实现出色的强度和韧性的结合,即使在高温、低温等极端环境下也表现出良好的应用潜力。双相高熵合金的设计通常是基于具有优良韧性的单一FCC相合金,通过调整合金成分和引入第二相结构来提高性能,这在实现合金强度和延展性的平衡方面具有明显的优势,这预示着它们具有更广泛的应用潜力。通过对合金的成分进行精心设计,我们能够更有效地制备出综合性能卓越的双相高熵合金。在确保合金的强度与延展性达到平衡的过程中,它们展现出了明显的优越性,这也意味着它们拥有更为广大的应用前景。遵循高熵合金相形成的标准,通过对合金成分的精心设计,我们能够更有效地制备出综合性能卓越的双相高熵合金。

Correlation of Microstructure Feature with Impact Fracture Behavior in a TMCP Processed High Strength Low Alloy Construction Steel

The present article aims at elucidating the effect of thermo-mechanical controlled processing(TMCP), especially the finish cooling temperature, on microstructure and mechanical properties of high strength low alloy steels for developing superior low temperature toughness construction steel. The microstructural features were characterized by scanning electron microscope equipped with electron backscatter diffraction, and the mechanical behaviors in terms of tensile properties and impact toughness were analyzed in correlation with microstructural evolution. The results showed that the lower finish cooling temperature could lead to a considerable increase in impact toughness for this steel. A mixed microstructure was obtained by TMCP at lower finish cooling temperature, which contained much fine lath-like bainite with dot-shaped M/A constituent and less granular bainite and bainite ferrite. In this case, this steel possesses yield and ultimate tensile strengths of ~ 885 MPa and 1089 MPa, respectively, and a total elongation of ~ 15.3%, while it has a lower yield ratio of ~ 0.81. The superior impact toughness of ~ 89 J at-20 °C was obtained, and this was resulted from the multi-phase microstructure including grain refinement, preferred grain boundaries misorientation, fine lath-like bainite with dot-shaped M/A constituent.

低温下TiZrHf系高熵合金的动态压缩力学特性与点火行为

针对高熵合金在低温条件下力学特性以及点火行为研究不足的现状,以含微量元素Cu、Al或Ni的TiZrHf系多主元高熵合金(HEA)为研究对象,结合SHPB试验系统与高速摄像系统,开展不同温度下高熵合金的动态压缩实验及点火特性实验,获得了弹性模量、应力峰值、硬化模量以及应变率与温度、元素种类的关联规律,并明确了元素种类对火焰面积、点火延迟时间、点火对应时刻以及剧烈反应持续时间的影响规律。结果表明,低温条件下3种HEA的应力-应变曲线均经历弹性、强化以及卸载阶段;在相近载荷条件下(~20 m/s,-40℃),含Cu和Ni的2类试件均发生了点火现象,而含Al试件只有细微点火,试件的点火延迟时间均为25μs,含Cu试件的剧烈反应持续时间与点火持续时间均大于含Ni试件。

低合金高强钢的疲劳断裂行为研究

为研究低合金高强钢的断裂机理,以260LAD、340LAD、420LAD材料为例,在高温、低温、酸性腐蚀条件下用万能试验机测试其应力比为0.3、1.0时的疲劳性能。结果表明:高温、低温都会导致试样的应力幅值降低,但在0、600℃下,试样的抗疲劳性能较好;酸性腐蚀溶液对试样影响较大,易疲劳断裂;在pH值为7时,试样的应力幅值较高,抗疲劳性能较好,不会发生严重断裂;其中420LAD的抗疲劳性能最高。