亞鉛多結晶の熱サイクルによる塑性變形

Abstract

When certain non-cubic metals and alloys are subjected to cyclic thermal treatment, plastic deformation results from the anisotropy of thermal expansion inherent in these metals and alloys. In this paper, the plastic deformation of zinc polycrystals caused by thermal cycles is described. The specimens cycled at higher temperature ranges show, in addition to the usual deformation by slip, kinking and micro-kink bands in some grains and also grain boundary sliding and migration. Slip bands, and kinking and boundary migration were already detected by a hot-stage microscope at about 50°, and about 100° respectively. No abnormal slip has been detected in all the specimens cycled thermally. The surface rumpling of the specimens results mainly from kinking and cell structures are formed readily in some grains as a result of kinking. The specimens cycled at lower temperature ranges show slip bands, micro-kink bands, micro-ridges, twins, accommodation kinks and cleavage cracks. Slip bands and micro-kink bands were already detected after one cycle between 15° and -30°. The formation of micro-kink bands becomes more pronounced in all grains as the minimum temperature of the cycle is lowered. Micro-kinklng may be the principal mechanism of plastic deformation at low temperatures. Twins and cleavage cracks were detected in some grains after one cycle between 15° and -100° and between 15° and -190°, respectively. Some grains showed signs of cleavage cracking after only one cycle even over the range 15° and -150°.