On the Pile-Up and Sink-in Behavior of Indented Nickel Considering Dislocation Structures
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RESEARCH PAPER
On the Pile-Up and Sink-in Behavior of Indented Nickel Considering Dislocation Structures F.Y. Huang 1 & J.C. Kuo 1 Received: 11 June 2019 / Accepted: 15 June 2020 # Society for Experimental Mechanics 2020
Abstract Background: Surface topography of pile-up and sink-in is an issue of strain-hardening behavior around pyramidal and spherical indentations. The relationship between the surface profile and the activated dislocations is not clearly understood. Objective: This study combined electron channeling contrast imaging (ECCI), electron backscatter diffraction-based (EBSD) techniques and 3D laser microscopy to visualize the stress field and understand the influence of activated dislocations on the surface topography around an indent. Methods: The dislocation structures were identified using ECCI and geometrically necessary dislocation (GND) analysis. The stresses and GND densities were calculated to characterize the plastic deformation in terms of activated dislocations. The 3D laser microscopy was applied to reveal the surface topography. Results: The activated slip systems were identified as screw-type on 11 1 ½110, 11 1 ½101, 111 ½011, ð111Þ 110 and ð111Þ 101 slip systems, and edge-type on 11 1 ½101, 111 101 and 1 11 101 slip systems by combining ECCI and GND techniques. Furthermore, the surface morphology reveals a combination of pile-up and sink-in patterns around the indent, as observed by 3D laser microscopy. According to GND analysis, pile-up is generated from the 11 1 1 10 , ð111Þ 110 , 11 1 ½101 and 1 11 ½101 slip systems, and sink-in is caused by the 111 01 1 , 11 1 101 , and 111 101 . Conclusions: The surface profile reveals a combination of pile-up and sink-in patterns resulting in the activated dislocations, where the deformation around the indent is dominated by screw-type dislocations. Keywords ECCI . EBSD . Indentation . GND . Dislocation
Introduction Indentation methods have been widely used in the determination of hardness, which is a measure of the resistance to plastic deformation. A large hydrostatic component of stress occurs around the indent, but this phenomenon does not contribute to plastic deformation. Generally, the mean contact pressure of the indenter is approximately three times as large as the uniaxial flow stress of materials. Therefore, indentation can be applied not only to observe the local strain field and evaluate the properties of materials, such as elastic modulus and hardness, but also to investigate the deformation mechanism of a single crystal [1, 2]. During indentation into single-crystalline * J.C. Kuo [email protected] 1
Department of Materials Science and Engineering, National Cheng-Kung University, No.1, University Road, Tainan 701, Taiwan, Republic Of China
materials, the deformation behaviors of sink-in and pile-up lead to variations in the projection area of the residual impressions and, hence, to uncertain values of hardness [3]. Since this effect is gener
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