Point defect behavior and its relation to the material properties in B2-type Intermetallic compounds.

点缺陷在任何温度和成分下都以稳定状态存在于金属和合金中，并强烈影响其材料性能。利用粉末X射线和中子衍射方法测定了B2型有序结构金属间化合物中的点缺陷结构，并通过热力学处理探讨了B2型有序结构金属间化合物中缺陷的形成机理. B2型FeAl合金中的点缺陷表现出一定的混杂状态，其中通常出现四种点缺陷，类似于我们的研究小组已经报道的B2 NiAl和CoAl合金。此外，在点缺陷行为中发现了两个奇怪的特征，即随着温度的升高，第一，在Fe和Al位置上产生热空位（随机空位分布，RVD），第二，反位原子倾向于恢复到它们自己的位置（反位原子恢复，ASAR）。这些 ...更多信息 基于Bragg-Williams方法，对B2型合金中点缺陷的形成过程进行了热力学处理.在构造缺陷模型时，假定：（1）基态的结构缺陷是反位原子，（2）由于温度升高而引起的缺陷行为可以描述为混合态，其中RVD反应和ASAR以及RVD过程之后的其他反应同时发生。NiAl和FeAl合金的数值结果很好地再现了它们观察到的趋势，例如，在两种体系中，Ni（Fe）空位的优先形成和反位Al原子的产生，在FeAl中，出现了类似RVD和ASAR的行为，得到了B2 AuCd合金中空位浓度与成分的关系。在Cd含量高于49.5%时，合金的抗氧化能力迅速增强，在Cd含量为51.5%时，合金抗氧化能力达到1%左右，这与B2 FeAl合金的抗氧化能力相当。因此，点缺陷的行为可以预期是一个类似的混合在FeAl。B2 AuCd合金在低温下转变为马氏体相。在马氏体状态下时效时出现的“马氏体时效效应”被认为与点缺陷行为有关。本文测量了缓冷和水淬Au-49.8Cd合金马氏体时效后的晶格常数、基波和超晶格反射积分强度的变化。结果表明，没有检测到的变化，表明空位迁移，也在老化过程中的长程有序不发生。这表明在这种合金中的马氏体时效效应的长程有序的独立性。少

Point defects which exist as a stable state in metals and alloys in any temperatures and compositions are well established to strongly affect their material properties. Aim of the present research is to determine the point defect structure in the intermetallic compounds with B2-type ordered structure by means of powder X-ray and neutron diffraction measurements and also to discuss the defect formation mechanism in these B2-type intermetallics by thermodynamic treatment.Point defects determined for B2 FeAl alloys showed a certain hybrid state in which four kinds of point defect generally appears, similarly as has already been reported for B2 NiAl and CoAl alloys by our research group. Further, two curious features were found in point defect behavior, that is with increasing in temperature, first, thermal vacancies are created on both Fe and Al sites (random vacancy distribution, RVD) and second, antisite atoms tend to recover into their own sites (antisite atom recovering, ASAR). These … More situations can never be interpreted within a framework of the defect model previously proposed.Thermodynamic treatment on the point defect formation in B2-type alloys was developed based on the Bragg-Williams method. In constructing the defect model, it was assumed : (1) constitutional defect in the ground state is the antisite atom and (2) defect behavior due to the temperature increase can be described as a hybrid state where the RVD reaction and the ASAR and other reactions succeeding the RVD process simultaneously occur. Numerical results for NiAl and FeAl alloys reproduced well their observed trends, e.g., the preferable formation of Ni (Fe) vacancies and a certain creation of the antisite Al atoms in both systems, and in the FeAl, the RVD and ASAR like behaviors.Vacancy concentration in B2 AuCd alloys was obtained as a function of composition. It showed a rapid increase above 49.5%Cd and reached to about 1% at 51.5%Cd, which is comparable with the results in B2 FeAl alloys. So, the point defect behavior can be expected to be a similar hybrid one as in the FeAl. B2 AuCd alloys transform to the martensite phase when decreasing in temperature. The 'martensite ageing effect' appearing in ageing in the martensitic state is believed to related to the point defect behavior. Changes in the lattice constant and the integrated intensities of fundamental and superlattice reflections due to martensite ageing were measured for slow-cooled and water-quenched Au-49.8Cd alloy. The results showed no detectable change, indicating that vacancy migration and also long-range ordering during ageing do not occur. This suggests an independence of the long-range order on the martensite ageing effect in this alloy. Less