Surface Roughening and Microscopic Inhomogeneity of Polycrystalline Iron during Cyclic Plastic Deformation.

Abstract

Changes in surface roughness and the relation between the roughening and microscopic inhomogeneity of polycrystalline iron during cyclic plastic deformation were experimentally investigated. Cyclic four-point bending tests were performed under the alternating strain and the pulsating strain conditions, and the three-dimensional shape of the roughened surface were measured by a stylus instrument. The characteristics of respective grains, that is, the crystallographic orientation and the hardening ratio were also investigated, and the relationship between those characteristics and the deformation behavior of each grain was discussed. It is found that the surface roughness changes with the absolute value of the applied strain on the free surface at the early stage of cyclic bending, because the roughening on the surface grows with straining, and then decreases with reversal of the strain. The roughness is cumulated during cyclic deformation, and the cumulative ratio under the alternating strain condition is larger than that under the pulsating strain condition. The hardness numbers of respective grains become large after cyclic bending, and their deviations also increase. It is also found that some grains having larger Schmid factor tend to locate on the slope of the surface roughening. Such grains are considered to deform preferencially during cyclic deformation, and locate on the slope of the roughened surface.