Superplastic alloys generally exhibit a three-stage-sigmoidal variation of stress (f) with strain rate ($\dot{s}$), the stages being named region I, II and III according to the increasing order of stress or strain rate. In the recent years, two different types of papers have been published on the plastic deformation of Zn-22% Al eutectoid in region I differing in the strain-rate sensitivity m (= dℓn f/dℓn $\dot{s}$). In this paper, the data of the two groups have been analysed by applying Kim and Ree's theory of superplastic deformation. (1) We obtained the parametric values of $X_{gj}/\alpha_{gj}}$ and $\beta_{gj}$ (g: grain boundary, j = 1,2 indicating flow units) appearing in Kim and Ree's theory [Eq. (2a)]. (2) It was found that the value of $X_{g2}/\alpha_{g2}$ is small for the group data with small m, i.e.,$\alpha_{g2}$ which is proportional to the size of flow unit g2, is large whereas $\alpha_{g2}$ is small for the groups data with large m, i.e., the size of the flow unit g2 is small. In other words, the two types of behavior occur by the size difference in the flow units. (3) From the $\beta_{gj}$ value, which is proportional to the relaxation time of flow unit gj, the $\Delta H_{gj}^\neq$ for the flow process was calculated, and found that $\Delta H_{g2}^\neq$ is large for the group data with small m whereas it is small for the group data with large m. (4) The flow-unit growth was studied, but it was concluded that this effect is not so important for differentiating the two groups. (5) The difference in $\alpha_{g2}$ and in the growth rate of flow units is caused by minute impurities, crystal faults, etc., introduced in the sample preparation.
일반적으로 초소성 합금은 가해준 stress (I,II 그리고 III 범위)와 strain rate에 따라서 변형이 sigmoidal type를 나타낸다. 최근에, 작은 stress 범위(I)에서 Zn-22%Al eutectoid의 소성 변형에 2가지 서로 다른 경향의 논문이 발표됨으로써, 현재까지 논쟁이 계속되고 있다. 본 연구에서는 작은 stress 범위에서 서로 다른 경향 즉, strain rate sensitivity(m)의 현격한 차이를 보여주는 이들 실험 결과를 Ree-Eyring theory에 근거를 둔 Kim-Ree theory로 분석하여 매개 변수 값 $X_{gj}/\alpha_{gj}$ 와 $\beta_{gj}$[g:grain boundary, j=1,2 (flow unit)]을 구하여 비교 분석한 결과 $\alpha_{gj}$는 flow unit 크기에 비례하며, $\alpha_{gj}/X_{gj}$ 값이 클수록 m 값이 작았고, flow unit g2 값이 클수록 $\alpha_{g2}$ 값이 작았다. 따라서 이들 서로 다른 2가지 경향은 flow unit 크기에 의해서 야기된다.
완화 시간에 비례하는 $\beta_{gj}$ 값으로 부터 $\Delta H^{\neq}_{gj}$ 값을 얻었다. $\Delta H^{\neq}_{gj}$ 값이 클수록 m 값이 작았다. flow unit 성장은 2가지 서로 다른 경향을 구명 하는데 중요하지 못했으나 flow unit 성장 속도에 민감한 $\alpha_{g2}$ 값의 차이는 중요했다. $\alpha_{g2}$ 값의 차이는 샘플 제조에서 미세한 불순물, 결정 결함 등으로 야기된다.
