A computational study of how surfaces affect slip family activity

TL;DR

This study uses crystal plasticity simulations to explore how surfaces influence slip activity in polycrystalline metals, revealing depth-dependent effects that vary with slip family type and number of slip systems.

Contribution

It provides new insights into surface effects on slip activity, highlighting the role of slip family kinematics and number of slip systems in different crystal structures.

Findings

Surface effects on slip activity extend up to two grains deep.

Slip activity decreases near the surface for easy slip families with fewer than six slip systems.

Harder slip families show increased activity with depth.

Abstract

Plastic deformation behavior is most conveniently assessed by characterization on a surface, but whether such observations are representative of bulk properties is uncertain. Motivated by reported inconsistencies in slip resistance probed at different depths, we investigated (i) whether the average slip family activity is affected by the presence of a surface and (ii) how the kinematic nature of available slip families influences a potential surface effect. The slip family activity as a function of distance from the surface was extracted from full-field crystal plasticity simulations of random polycrystalline hexagonal close-packed (HCP) and body-centered cubic (BCC) metals as examples of mixed in contrast to universally-high numbers of slip systems per family. Under certain conditions, a deviation from bulk slip activity is observed up to about two grains from the surface. For the easiest (least slip-resistant) family, a surface effect of decreasing activity with depth emerges if the number of slip systems falls below about six. For harder families, slip activity always increases with depth. These phenomena are explained on the basis of varying constraints with depth in connection with the kinematic properties of slip families in the material.