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Study of Point Defects in B2-type Ordered Alloys by Means of Positron Annihilation

正电子湮灭研究B2型有序合金点缺陷

基本信息

批准号：
61550480
负责人：
SHIRAI Yasuharu
金额：
$ 1.28万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

项目摘要

Recently, intermetallic compounds or ordered alloys, are being used in verious fields as new functional materials such as shape memory alloys, hydrogen-containing metals, semiconducting materials and so on. Also, they are used in high-strength, light-weight, heat-resistant materials. In such materials, the lattice defect usually reduces their efficacy, it is desired to fully understand and control the concentration and the state of distribution of the defects.In this present study, the composition/temperature-dependence of point defects such as vacancies and antistructure atoms (ASA) in ordered alloys were investigated by means of the positron lifetime measurement. The results are summarized as follows:CuZn (B2-structure):The concentration of vacancies in thermal equilibrium is fairly high, and the saturation of the mean lifetime occures below the order-disorder transition temperature,Tc (740)K). At temperatures near Tc, the mean lifetime increases by about 5 ps, owing to the decrease in the degree of order. The temperature dependence of the mean lifetime can be delineated by using the defect concentrations estimated from our method which gives the equilibrium concentration of defects.AuCd (B2):Au-47.5%Cd alloy shows martensitic transformation at around 300K. Both the formation and the migration energy of vacancies are higher in martensite phase than in parent-phase. Consequently, the vacancy concentration increases aburptly on the reverse transformation from martensite to parent phase. On martensitic transformation, the high concentration of vacancies in parent-phase are retained in martensite-phase. These excess vacancies are responsible for the aging phenomena appearing in martensite phase.Cu_3Au (L1_2):The positron mean lifetime increases about 2 ps owing to the increase in the lattice parameter and also the change of atom arrangement. The formation energy of a vacancy in high-temperature disorderedstate is found to be 1.42<plus-minus>0.09 eV.

近年来，金属间化合物或有序合金作为新型功能材料，如形状记忆合金、含氢金属、半导体材料等，被广泛应用于各个领域。此外，它们还用于高强度、轻质、耐热材料。在此类材料中，晶格缺陷通常会降低其功效，因此需要充分了解和控制缺陷的浓度和分布状态。在本研究中，通过正电子寿命测量研究了有序合金中空位和反结构原子（ASA）等点缺陷的成分/温度依赖性。结果总结如下： CuZn（B2结构）：热平衡时的空位浓度相当高，平均寿命在有序-无序转变温度Tc（740）K以下出现饱和。在接近 Tc 的温度下，由于有序度降低，平均寿命增加约 5 ps。平均寿命的温度依赖性可以通过使用我们的方法估计的缺陷浓度来描述，该方法给出了缺陷的平衡浓度。AuCd (B2):Au-47.5%Cd 合金在 300K 左右表现出马氏体转变。马氏体相中空位的形成和迁移能均高于母相。因此，在从马氏体向母相的逆转变过程中，空位浓度突然增加。在马氏体相变中，母相中高浓度的空位保留在马氏体相中。这些多余的空位是马氏体相出现老化现象的原因。Cu_3Au (L1_2):由于晶格参数的增加和原子排列的变化，正电子平均寿命增加了约2 ps。发现高温无序状态下空位的形成能为1.42±0.09eV。