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STABILITIY OF MARTENSITE IN Cu-Zn-Al SHAPE MEMORY ALLOY AFTER DIRECT OR STEPPED QUENCHING

LU Xiaoye Central south University of Technology , Changsha , China Lecturer , Dept.of Materials Science and Engineering , Central South University of Technology , Changsha 410083 , China

金属学报(英文版)

The stability of thermoelastic martensite in a Cu-14.84 wt-%Zn-7.75 wt-%Al shape mem- ory alloy with M_s=106°C after direct quenching or stepped quenching has been investigated by using TEM,X-ray diffroctometer and double electric bridge instrument.The martensite aged for about 3 h at room temperature after either direct quenching or stepped quenching (150°C,2 rain)is the M18R structure.The martensite just directly quenched is not so stable, both its certain diffraction peaks and specific electric resistivity,change with aging at room temperature;whereas it is stable after stepped quenching(150°C.2 min),and its diffraction peaks and specific electric resistivity change no more with aging at room temperature.The above mentioned results seem to be explained by the martensite reordering.

关键词: Cu-Zn-Al alloy , null , null , null

EFFECT OF Zr ON PHASE TRANSFORMATION IN Cu-Zn-Al SHAPE MEMORY ALLOYS

XIAO Jichuang FANG Jianneng South China University of Technology , Guangzhou , China XIAO Jichuang Associate Professor , Dept.of Mechanical Engineering No.2 , South China University of Technology , Guangzhou 510641 , China

金属学报(英文版)

An investigation was made of the influence of Zr additive on the high temperature phase trans- formations,martensitic forward/reverse transformations,and shape memory effect of Cu-Zn-Al base alloys by means of differential scanning calorimetry(DSC),X-ray diffraction and TEM.It was found that an addition of 0.35 wt-% Zn could effectively inhibit the precipitation of α and γ phases and hence promote the order-martensitic transformations β_2→DO_3→18RM,thus resulting in a minimum activation energy of the martensitic trans- formation and narrow temperature ranges(M_s-M_f)and(A_s-A_f);the alloy so obtained pos- sessed smooth and mobile martensite intervariant interfaces,therefore showing the best shape memory effect.

关键词: Cu-Zn-Al alloy , null , null , null

ON THE STABILIZATION OF THERMOELASTIC MARTENSITE IN A Cu-Zn-Al ALLOY

WANG Mingpu , LIU Jinwen Central South University of Technology , Changsha , China Lecturer , Dept.of Materials Science and Engineering , Central South University of Technology , Changsha 410083 , China

金属学报(英文版)

The stabilization of thermoelastic martensite in a rapidly solidified Cu-Zn-A1 alloy is be- lieved to be the process of disordering in atomic configuration during which the structure of martensite gradually transforms into N9R(b/a=1/3~(1/2))from M18R.This is dependent upon the intrinsic decomposition tendency of the martensite.

关键词: Cu-Zn-Al alloy , null , null , null

EFFECT OF MARTENSITE ORDERING ON SME IN A Cu-Zn-Al ALLOY

QI Xuan JIANG Bohong XU Zuyao(T.Y.HSU) Shanghai Jiaotong University , Shanghai.China Qi Xuan , Dept.Marter.Sci.and Eng. , Shanghai Jiaotong University , Shanghai , China

金属学报(英文版)

The correlation between the shape memory effect(SME)and the ordering degree in martensite formed through various heat-treatment processes,e.g.ice water quenching, step-quenching and aging etc.,has been studied in a Cu-26Zn-4Al alloy.The martensite or- dering degree is estimated by △d,the spacing difference of some pairs of diffracting planes with indices satisfying a relation of(h_1~2-h_2~2)/3=(k_2~2-k_1~2)/n(n=1 for 9R martensite,n=4 for 18R martensite).M 18R martensite is obtained from step-quenching,in which the value of △d increases with the holding duration of step-quenching,and the shape recovery rate η increases synchronouslly.9R martensite is obtained from direct water-quenching,the value of △d is quite large and SME is also good at just quenching state.But both △d and η decrease continuously with aging time at room temperature.This stabilization phe- nomenon of martensite is explained by the observation of TEM lattice fringe image,and it may be attributed to the clustering of quenched-in supersaturated vacancies at (001)_M close-packed plane in martensite and decreasing the ordering degree.A reduction in △d and η occuring in the specimens on step-quenching or aging at higher temperature, which may be related to the precipitation of the α-phase and the enrichment of solute atoms, decreases the ordering degree.

关键词: Cu-Zn-Al alloy , null , null , null , null

多晶Cu-Zn-Al合金变形过程中马氏体的精细结构变化

朱敏 , 李国斌 , 杨大智

金属学报

本文利用透射电子显微镜研究了多晶Cu-Zn-Al形状记忆合金在马氏体状态的变形过程中,其精细结构的变化。结果表明:在变形的初期阶段,变形通过变体的再取向实现,但再取向常有不完全性,而且再取向后,原先变体间的界面依然存在。变形量较大时,马氏体中出现大量的孪晶,孪晶面为(001)。在局部区域出现位错。这时马氏体失去热弹性,记忆效应被破坏。

关键词: 形状记忆合金 , shape memory alloy , Cu-Zn-Al alloy

热弹性马氏体的长大

邓永瑞 , G.S.ANSELL

金属学报

本文用金相显微镜观察Cu-Zn-Al合金中热弹性马氏体的长大过程,结果发现,马氏体片无论在径向或厚度方向,均为热弹性地(即可逆地)长大。这与Cohen等的观点不同。本文提出了一个模型,并通过计算来解释上述现象。

关键词: 热弹性 , martensite , Cu-Zn-Al alloy

淬火在Cu-Zn-Al合金马氏体中引入的一种新缺陷

朱敏 , 杨大智

金属学报

本文报道了Cu-Zn-Al合金中18R马氏体里存在的一类新的面缺陷。实验结果的统计表明,在由高温直接淬入冰水中的样品里,马氏体中常出现非基面上的层错。衍衬分析证明,这种层错常位于(125)_M面上。通过对晶体结构和处理条件分析,提出了这种层错出现的机制,并给出了层错的结构模型。

关键词: 马氏体 , Cu-Zn-Al alloy , Crystal defects

Cu-Zn-Al形状记忆合金直接淬火和分级淬火后马氏体稳定性的研究

鲁小叶

金属学报

用透射电镜,X射线衍射仪和电阻法研究了Cu-14.84wt-%Zn-7.75wt-%Al形状记忆合金在直接淬火和分级淬火后马氏体的稳定性。试验结果表明,直接淬火和分级淬火(150℃,2min)后于室温时效约3h的马氏体均为M18R结构,但刚直接淬火后马氏体并不稳定,其某些衍射峰位置和电阻率均随室温时效而变化;而分级淬火(150℃,2min)后马氏体是稳定的,其所有衍射峰位置和电阻率几乎不随室温时效而变化。上述结果可用“马氏体再有序化机制”解释。

关键词: Cu-Zn-Al合金 , shape memory alloy , martensite , stabilization

Cu-Zn-Al合金中马氏体的有序化对形状记忆效应的影响

漆璇 , 江伯鸿 , 徐祖耀

金属学报

研究了Cu-Zn-Al合金分别经水淬、分级淬火和淬火加时效处理后,马氏体的有序化程度及其和形状记忆效应(SME)之间的关系.有序化程度用一些特定马氏体线对的面间距差值△d来表征,线对指数应满足下式:(h_1~2-h_2~2)/3=(k_2~2-k_1~2)/n(对9R马氏体n=1,对18R马氏体N=4).分级淬火得到M18R马氏体,其△d值随分级等温时间而增大,与形状恢复能力η的提高一致.水淬得到M9R马氏体,刚淬火状态有相当大的△d和良好的SME,但室温停留使△d和η均下降,TEM点阵条纹象证实这是淬火过饱和空位在(001)_M基面聚集、降低有序程度的结果.淬火后高温时效(180℃)或过高的分级温度都会使△d和η下降,这与α相析出以及可能发生的溶质原子偏聚有关,都会降低有序程度.

关键词: Cu-Zn-Al合金 , martensite , ordering , shape memory effect

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