발간논문

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Vol.36, No.4, 486 ~ 494, 1998
Title
Effect of Grain Size and Volume Fraction of Constituent Phases on Superplastic Deformation Behavior of Pb-Sn Alloy
하태권 , 신광섭 , 장영원 Tae Kwon Ha , Kwang Sup Shin , Young Won Chang
Abstract
In this study, the internal variable theory of structural superplasticity has been applied to Pb-Sn alloys. The basic concept of the theory is that superplastic deformation of crystalline materials consists mainly of interface sliding and a dislocation glide process accommodating incompatibilities caused by the former process. A special attention has been focused on the effects of grain size and the volume fraction of constituent phases on deformation characteristics of the typical microduplex superplastic material, generally known to reveal a pronounced phase boundary sliding. For this purpose, a series of load relaxation tests has been conducted to obtain the flow curves at room temperature. A new quantitative method to determine the optimum strain rate for superplastic forming process has also been suggested. The phase boundary sliding in the two phase alloy was characterized as a viscous flow process with the power index value of M_g=0.5 which is much less than the previously reported value of M_g=1.0 for grain boundary sliding. The optimum strain rate was found to shift into a faster region as the grain size decreased.
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