Mechanism of atomic diffusion in nickel-based intermetallic compounds of L1_2-type

本文通过对Ni_3Al、Ni_3Ga和Ni_3Ge的热力学性质，特别是本征点缺陷浓度的测定，研究了Ni_3Al、Ni_3Ga和Ni_3Ge的原子扩散机制，并由Ni_3（Al，Fe）系列合金的相变温度计算了Ni_3Al的有序-无序相变温度。通过电阻率的原位测量确定了Ni_3Al的相变温度，外推到零Fe含量时，得到Ni_3Al的相变温度为1721 ± 34K。该值与用蒙特-卡罗模拟的结果分析热力学活度数据得到的1680 - 1740 K值吻合得很好。我们提出了一个原子扩散模型，其中Ni和Al原子在晶体中的迁移主要是通过Ni原子在亚晶格中的空位机制（α亚晶格空位机制）进行的; ...更多信息 el能合理地解释Ni和Al在Ni_3Al中的扩散系数。在基于热力学性质的对相互作用模型的讨论中，原子之间的有效相互作用能的值是最关键的。用固体电解质电动势法测定了Ni_3Ga和Ni_3Ge的热力学活度。对Ni_3Ga，由活度随组分的变化确定了有效相互作用能为0.101 ± 0.002eV。点缺陷的浓度和化学扩散的热力学因子已估计与援助的热力学模型，并在其基础上的扩散机制已被检查。该化合物的示踪扩散和化学扩散数据也可用α亚晶格空位机制来解释。为了解决这个问题，需要了解Ni-Ge-O三元相图的细节，但目前还没有。这是留给未来的任务。因此，没有得到该化合物中有效相互作用能的可靠值。然而，如果假设相互作用能高达1.5eV，则该化合物中的扩散行为可以用α亚晶格空位机制来理解。因此，α亚晶格空位机制是这类材料中最合理的扩散机制。少

The mechanism of atomic diffusion in Ni_3Al, Ni_3Ga and Ni_3Ge has been studied by examining the thermodynamic properties of these materials, most importantly the concentrations of intrinsic point defects, using various experimental techniques.The hypothetical order-disorder transformation temperature of Ni_3Al has been evaluated from the transformation temperatures of a series of alloys Ni_3 (Al, Fe). The transformation temperatures have been determined by in situ measurements of electrical resistivity, and extrapolation to zero Fe content gives 1721 ± 34 K as the transformation temperature of Ni_3Al. This value is in good agreement with the value 1680-1740 K deduced from an analysis of thermodynamic activity data using the results of Monte-Carlo simulation. We proposed earlier an atomistic model of diffusion, where both Ni and Al atoms are assumed to migrate in the crystal primarily by the vacancy mechanism in the sublattice for Ni atoms (the α sublattice vacancy mechanism) ; the mod … More el can reasonably explain the diffusivities of Ni and Al in Ni_3Al. In that discussion, which is based on a pair interaction model of thermodynamic properties, the value of the effective interaction energy between atoms is most critical. The transformation temperature is physically equivalent to the effective interaction energy, and thus the value obtained in this investigation substantiates the discussion made earlier.The thermodynamic activity of components has been measured for Ni_3Ga and Ni_3Ge by solidelectrolyte electromotive-force method. For Ni_3Ga, the effective interaction energy has been determined to be 0.101 ± 0.002 eV from the variation of the activity with composition. The concentrations of point defects and the thermodynamic factor for chemical diffusion have been estimated with the aid of a thermodynamic model, and on their basis the mechanism of diffusion has been examined. The data of tracer diffusion and chemical diffusion for this compound can also be accounted for by the α sublattice vacancy mechanism.The method of activity measurements employed has turned out inappropriate for Ni_3Ge. To resolve the problem, knowledge of the details of the Ni-Ge-O ternary phase diagram is required but is not available at the moment. This is the task left to the future. Thus, no reliable value of the effective interaction energy in this compound has been obtained. Nevertheless, it has been shown that the diffusion behavior in this compound can be understood in terms of the α sublattice vacancy mechanism, if the interaction energy is assumed to be as high as 1.5eV.The α sublattice vacancy mechanism is thus a most plausible mechanism of diffusion for this class of materials. Less