挤压和时效态Mg-Y-Cu合金的显微组织和力学性能

采用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)、维氏硬度计和万能试验机,研究了挤压和时效态Mg-6.8Y-2.5Cu(质量分数,％)合金的显微组织和力学性能.结果表明:挤压合金主要由α-Mg基体、沿挤压方向分布的片层状和块状18R类型的长周期堆垛有序相(18R-LPS...     

Ca和Al对Mg-Gd-Zn合金中的LPSO相及力学性能的影响

本文通过普通重力铸造方法熔炼制备了Mg_96.5Gd_2.5Zn₁、Mg₉₆Gd_2.5Zn₁Ca_0.5和Mg₉₅Gd_2.5Zn₁Ca_0.5Al₁三种合金,考察了合金元素Ca与Al对铸态Mg-Gd-Zn合金中LPSO相形成的影响及经固溶热处理和热挤压后微观组织的演变及力学性能变化, 分析了微观组织转变与力学行为之间的关系。     

压水堆燃料包壳锆合金中第二相腐蚀行为研究进展

锆合金是目前唯一大规模商用的压水堆燃料包壳材料,其耐水侧腐蚀性能是影响核反应堆安全性与经济性的重要因素。微量合金元素(Fe、Nb等)主要以第二相的形式弥散分布在锆合金基体中,但可对锆合金的腐蚀行为产生显著影响。本文比较了不同锆合金中第二相的差异,综述了锆合金中典型第二相的腐蚀行为及其影响因素。分别比较了二元及三元第二相中主要合金元素Fe和Nb的腐蚀过程,总结了不同水化学条件下第二相腐蚀产物的差异及其对锆合金基体腐蚀行为的影响,并指出当前针对第二相腐蚀行为研究中存在的不足。最后,对锆合金第二相腐蚀行为研究趋势进行了展望,先进微观表征手段可进一步完善含Fe、Nb元素第二相的腐蚀机理研究,将为提高我国新型锆合金包壳材料的耐腐蚀性能提供理论参考。     

不同尺寸Mg−Gd−Y−Zn−Ag镁合金零件冷却后的腐蚀行为

研究不同尺寸的Mg?6Gd?3Y?1Zn?0.3Ag(质量分数,％)镁合金零件冷却后的腐蚀行为.小型零件冷却较快,其显微组织由镁基体和粗大的长周期堆垛有序结构(LPSO)相组成.大型零件冷却较慢,其显微组织除镁基体和粗大的LPSO相外,晶粒内部有薄片状LPSO相析出.析氢测试结果表明,大型零件的腐蚀速度高于小型零件.交...     

新型铸造合金的组织及其腐蚀行为的AFM研究

对新设计新型铸造合金有用金相显微镜，Ｘ射线衍射，电子探针（ＥＭＰＡ）、扫描电镜（ＳＥＭ）及原子力显微镜（ＡＦＭ）研究了合金的组织及其腐蚀行为，试验结果表明，该合金经１１５０℃固溶处理后，具有良好的耐蚀性能。通过ＡＦＭ的观测，得到了新型铸造合金的超高分辨的三维腐蚀形貌图象，为该合金的开发应用奠定了技术基础。     

含Nb锆合金第二相及其与腐蚀行为关系研究进展

含Nb锆合金具有优异的耐腐蚀性能、良好的机械性能和加工变形能力,是目前锆合金研究的重点。本文综述了近年来含Nb锆合金的研究现状,包括化学成分、变形及热处理工艺对第二相粒子析出的影响,介绍了锆合金腐蚀理论的研究进展,讨论了研究中存在的若干问题,为含Nb锆合金组织控制和耐腐蚀性能改善提供参考。     

Zr-Sn-Nb合金的腐蚀行为研究

研究了我国开发的Zr-Sn-Nb合金（N18和N36）在360℃、18.6MPa含LiOH高温高压水，400℃和500℃、10.3MPa过热蒸汽中的腐蚀行为。结果表明，两种合金试样在500℃腐蚀500h未出现疖状腐蚀，而Zr-4合金在4h就出现疖状腐蚀；在400℃腐蚀245d后，N18试样的增重低于Zr-4，而N36怕增重高于Zr-4；在360℃含LiOH的高温高压水中腐蚀300d，两种合金试样的增重只有Zr-4的16％－25％。N18合金不仅在高温高压水中而且在过热蒸汽中都具有优良的抗腐蚀性能。在Zr-Sn系合金中加入适量的Nb，一部分固溶在α-Zr中可以抵抗C、N等杂质对腐蚀性能的有害影响，另一部分形成第二相均匀弥散分布在合金中可明显降低合金在高温水和过热蒸汽（500℃）中的氧化速率。氧化膜／金属界面处的氧化膜生长存在不均匀性，转折后氧化膜的不均匀生长更明显。     

Zr-1.0Fe-0.2Cu合金在400 ℃/10.3 MPa过热蒸汽中的腐蚀行为

以高纯锆为母材制备Zr-1.0Fe-0.2Cu合金,并在400 ℃/10.3 MPa过热蒸汽中进行腐蚀实验。用SEM和TEM对合金基体及其腐蚀后生成氧化膜的显微组织进行研究。结果表明：Zr-1.0Fe-0.2Cu合金中只存在底心正交的Zr₃Fe第二相,Cu元素易偏聚在Zr₃Fe相内,使其不易以Zr₂Cu相的形式析出,Cu元素的添加能够细化合金中Zr₃Fe第二相。Zr-1.0Fe-0.2Cu合金在 400 ℃/10.3 MPa过热蒸汽中腐蚀100 d后,耐腐蚀性能优于Zr-1.0Fe以及Zr-4重熔合金,表明添加少量的Cu元素有利于改善合金的耐腐蚀性能。在腐蚀氧化过程中,含Cu的Zr₃Fe相会滞后于合金基体α-Zr相氧化而进入氧化膜。随着氧化进程的加深,第二相中的Zr元素氧化后会以t-ZrO₂的形式存在,Fe元素则氧化成m-Fe₃O₄。伴随着第二相的氧化进程,合金元素Cu和Fe会在氧化膜中扩散流失,不再呈现聚集状态。     

含Bi易切削变形Zn-Al合金的腐蚀行为

对自行研制的4种不同Bi含量易切削Zn-Al合金在3.5%的NaCl溶液中进行浸泡腐蚀试验,并与潮湿和干燥空气中的试样作对比。采用X射线衍射、场发射扫描电镜、能谱分析以及电化学测试等手段研究了合金在不同介质中的腐蚀行为。结果表明,合金的腐蚀主要表现为点蚀。随着Bi含量的增加,平均腐蚀速率加快。合金中的富铝α相是易腐蚀相,Zn-Al合金的腐蚀过程是以η相作为阴极,Al组元作为阳极而溶解的电化学腐蚀过程。     

Microstructure and mechanical properties of Mg-Gd-Dy-Zn alloy with long period stacking ordered structure or stacking faults

The Mg-6.5Gd-2.5Dy-1.8Zn (wt.%) alloy with high strength and ductility was prepared by conventional casting method. At room temperature, the as-cast alloy with 14H long period stacking ordered (LPSO) structure exhibits an ultimate tensile strength of 276 MPa and elongation to failure of 10.8%, while they are 392 MPa and 6.1% for the peak-aged alloy with basal plane stacking faults (SF). The results indicate that the kinking of LPSO structure is beneficial for both work hardening and plasticity, and 14H LPSO structure contributes more to the improvement of ductility while SF is more effective in increasing strength.     

Microstructure and mechanical properties of a compound reinforced Mg95Y2.5Zn2.5 alloy with long period stacking ordered phase and W phase

The microstructure evolution of Mg100-2xYxZnx(x=2, 2.5, 3, 3.5) alloys was investigated. Results show that the Mg100-2xYxZnx alloys are composed of α-Mg, long period stacking ordered(LPSO) phase and eutectic structure phase(W phase), and the Mg95Y2.5Zn2.5 alloy has the best comprehensive mechanical properties. Subsequently, the microstructure evolution of the optimized alloy Mg95Y2.5Zn2.5 during solidification and heat treatment processes was analyzed and discussed by means of OM, SEM, TEM, XRD and DTA. After heat treatment, the lamellar phase 14H-LPSO precipitated in α-Mg and W phase transforms into particle phase(MgYZn2). Due to the compound reinforcement effect of the particle phase and LPSO phase(18R+14H), the mechanical properties of the alloy are enhanced. The tensile strength and elongation of the Mg95Y2.5Zn2.5 alloy is improved by 9.1% and 31.3% to 215 MPa and 10.5%, respectively, after solid-solution treatment.     

Investigation of two-phase Mg-Gd-Ni alloys with highly stable long period stacking ordered phases

The effects of the Ni addition on the microstructures of Mg-2Gd-xNi (at.%, x = 0, 0.25, 0.5 and 1) alloys were systematically investigated. A series of two-phase Mg-Gd-Ni alloys consisting of long period stacking ordered (LPSO) phase and α-Mg were obtained. The LPSO phase presented block-like shape and was distributed between α-Mg dendrite arms. Its volume fraction was found to be proportional to the Ni content, ranging from 0 to ∼40% with the Ni content increasing from 0 to 1 at.%. After a heat treatment at 500 °C for 100 h, the LPSO phase experienced a structure transformation from 18R to 14H but was hardly dissolved into the α-Mg matrix, which evidenced a high thermal stability. The mechanism for the effects of the Ni addition on the formation of the LPSO phase was discussed.     

Effect of Li on formation of long period stacking ordered phases and mechanical properties of Mg-Gd-Zn alloy

Alloys with composition of Mg_(96-x)Gd_3Zn_1Li_x(at.%)(x=0, 2, 4, and 6) were prepared by conventional casting. The microstructures of these alloys under as-cast and solid-solution conditions have been observed, and the mechanical properties were investigated. The results showed that Li is an effective element to refine the grains and break the eutectic networks in as-cast MgGd_3Zn_1 alloy. During solid solution treatment, these broken eutectic networks are spheroidized and highly dispersed. In addition, plentiful lamellar long period stacking ordered(LPSO) phases are precipitated in an α-Mg matrix when the Li addition is not more than 4%. Solid-solution treated Mg_(92)Gd_3Zn_1Li_4 alloy exhibits an optimal ultimate tensile strength(UTS) of 226 MPa and elongation of 5.8%. The strength of MgGd_3Zn_1 alloy is improved significantly, meanwhile, the toughness is apparently increased.     

Mg97Y2Zn1合金中18R型长周期有序相的微观结构（英文）

通过第一性原理计算研究Mg97Y2Zn1合金中18R型长周期有序相(LPSO)的微观结构,从理论上确定Zn和Y原子在LPSO相中的排列。结果表明:添加原子首先分布在18R型LPSO相两端的层错层,然后向内部的层错层延伸。计算结果与实验现象非常吻合。同时,也揭示了18R与其他LPSO相之间的微观结构关系;结合能和形成焓表明了18R型LPSO相的稳定性与Y和Zn原子含量之间的关系。计算得到的电子结构揭示了18R型LPSO相微观结构和稳定性潜在的机理。     

Effect of long-period stacking ordered phase on mechanical properties of Mg97Zn1Y2 extruded alloy

The mechanical properties of Mg97Zn1Y2 extruded alloy, composed of Mg matrix phase and a long-period stacking ordered phase, the so-called LPSO phase, with a volume fraction of approximately 24%, were investigated using compression tests at room temperature. The microstructure was varied to a large degree by various heat treatments at high temperatures above 400 °C, and the relationship between the microstructure and mechanical properties was clarified. The plastic behavior of the Mg/LPSO two-phase alloy was compared with that of Mg99.2Zn0.2Y0.6 alloy, composed almost Mg-solid-solution phase, and the strengthening mechanisms at work in the Mg97Zn1Y2 extruded alloy are discussed. The existence of the LPSO phase strongly enhanced the refinement of Mg matrix grains during extrusion, which led to a large increase in yield stress through the Hall–Petch relationship. In addition, the LPSO phases, which were aligned along the direction of extrusion in the Mg97Zn1Y2 extruded alloy, acted as hardening phases, being roughly coordinated with the short-fiber reinforcement mechanism.     

Formation of 14H long period stacking ordered structure and profuse stacking faults in Mg–Zn–Gd alloys during isothermal aging at high temperature

This paper proposes a time–temperature-transformation diagram of an Mg–Zn–Gd alloy. An Mg₉₇Zn₁Gd₂ (at.%) alloy shows different precipitation sequences at low, medium and high temperatures. Low-temperature aging at <523 K brings about coherent β′-phase precipitation to a -Mg solid solution, resulting in increase in strength of the alloys. However, aging at medium and high temperatures >623 K led to strengthening of the Mg–Zn–Gd alloy, owing to the formation of profuse stacking faults and 14H long period stacking ordered structure from the supersaturated -Mg matrix, respectively.     

The structure of long period stacking/order Mg-Zn-RE phases with extended non-stoichiometry ranges

We propose structural models of the unique long period stacking/order (LPSO) phases formed in Mg-Zn-RE alloys, based on Z-contrast scanning transmission electron microscopy observations and first principles calculations. The LPSO structures are long period stacking derivatives of the hcp Mg structure, and the Zn/RE distributions are restricted at the four close-packed atomic layers forming local fcc stacking (i.e. a local ABCA stacking). Chemical order is well developed for the LPSO phases formed in Mg₉₇Zn₁Er₂ (14H type) and Mg₈₅Zn₆Y₉ (18R type) alloys with pronounced superlattice reflections, and the relevant Zn/RE distributions clearly emerge in the Z-contrast atomic images. Initial ternary ordered models were constructed by placing all the atoms at the ideal honeycomb sites, leading to plausible space groups of P6₃/mcm for the 14H type and C2/m, P3₁12 or P3₂12 for the 18R type. The characteristic ordered features are well represented by local Zn₆RE₈ clusters, which are embedded in the fcc stacking layers in accordance with the L1₂ type short-range order. Energy favored structural relaxations of the initial model cause significant displacement of the Zn/RE positions, implying that strong Zn-RE interactions may play a critical role in phase stability. The LPSO phases seem to tolerate a considerable degree of disorder at the Zn and RE sites with statistical co-occupations by Mg, extending the non-stoichiometric phase region bounded along the Zn/RE equiatomic line from ∼Mg_94.0Zn_2.0Y_4.0 to ∼Mg_83.3Zn_8.3Y_8.3.     

Creep behaviour of long range ordered Cu50Zn alloy

Creep behaviour of long range ordered β′-brass was investigated with the aim of obtaining more information exploitable in an explanation of the physical basis of creep taking place in the ordered structure of metallic materials. In addition to conventional analysis of creep based on an analysis of the applied stress and temperature dependence of the steady-state creep, extensive constant structure experiments in the steady-state creep were performed and analysed. Comprehensive investigations yielded a new view, primarily in the internal stress and mechanisms acting in the creep of the investigated alloy.