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Vol.35, No.2, 191 ~ 201, 1997

Title

Research Paper - Mechanical Behavior : An Internal Variable Approach to the Superplastic Deforation Behavior of a Pb - Sn Eutectic Alloy

하태권Tae Kwon Ha, 신홍철Hong Chul Shin, 장영원Young Won Chang

Abstract

The main objective of this study is to apply the internal variable theory of structural superplasticity proposed recently to the room temperature superplastic deformation of a two phase Pb-Sn eutectic alloy. A series of load relaxation and tensile tests were conducted on Pb-62 wt.% Sn eutectic and its constituent single phase alloys at room temperature and the results were analyzed based on the theory proposed. The flow curve of superplastic Pb-Sn eutectic alloy obtained from load relaxation test was shown to consist of the contributions from garin or phase boundary sliding (GBS/PBS) and the accommodating plastic deformation of grain matrix. The boundary sliding behavior of Pb-Sn eutectic alloy could be described as a viscous flow process characterized by the power index value of M_g = 0.5. This value is much less than that of quasi-single phase Al alloys, such as 7475 Al and 8090 Al-Li alloys. Strain rate range within which boundary sliding is predominant deformation mechanism was obtained as roughly 7×10^(-7) /s≤ε≤10^(-4)/s in superplastic Pb-Sn eutectic alloy used in this study. By carefully examining deformed surfaces of tensile test specimens of eutectic and its constituent single phase alloys, following results were also obtained. The existence of Pb rich phase is indispensable to the superplastic deformation of the Pb-Sn eutectic alloy and the onset of α/β interphase boundary sliding is responsible for the smaller value of the parameter M_g.

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