Deformation Microstructure Under Nanoindentations in Cu Using 3D X-Ray Structural Microscopy
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Deformation Microstructure Under Nanoindentations in Cu Using 3D X-Ray Structural Microscopy Wenge Yang1, B.C. Larson1, G.M. Pharr1,2, C.P. Lepienski3, G.E. Ice1, J.D. Budai1, J.Z. Tischler1, and Wenjun Liu1 1 Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 2 University of Tennessee, Knoxville, Tennessee 37996 3 University of Sao Paulo, Sao Paulo, Brazil ABSTRACT We have used a recently developed x-ray structural microscopy technique to make nondestructive, submicron-resolution measurements of the deformation microstructure below a 100mN maximum load Berkovich nanoindent in single crystal Cu. Direct observations of plastic deformation under the indent were obtained using a ~0.5 µm polychromatic microbeam and diffracted beam depth profiling to make micron-resolution spatially-resolved x-ray Laue diffraction measurements. The local lattice rotations underneath the nanoindent were found to be heterogeneous in nature as revealed by geometrically necessary dislocation (GND) densities determined for positions along lines beneath a flat indent face and under the sharp Berkovich indent blade edges. Measurements of the local rotation-axes and misorientation-angles along these lines are discussed in terms of crystallographic slip systems. INTRODUCTION Fundamental aspects of materials properties and evolution are being investigated in increasing detail both experimentally and computationally [1-3]; accordingly, the importance of detailed microstructural information on the plastic deformation of materials on mesoscopic length scales (tenths to hundreds of microns) is increasing as well [4]. As mechanical devices decrease in size, a large effort has been directed toward understanding local microstructural distributions and evolution. This is especially true with respect to dislocation structures, where it is important to understand the fundamental processes and micro-mechanisms associated with plastic deformation. In most circumstances, plastic deformation is controlled by dislocation motion and self-arrangement [3,4]. Nanoindentation experiments have long been a very useful method for materials characterization as an overall experimental tool for evaluating basic properties of materials from small samples [5,6]. Nanoindentatation is known to produce a range of plastic deformation structures under indent tips on mesoscopic length scales and analyses often result in size- and depth-dependent hardness effects [7-9]. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and finite element methods (FEM) have been used to investigate the hardness, indentation loading curves, phase transitions, and dislocation structure [7,10,11]. However, these experimental tools provide detailed microstructure information only from surface layers, thin sections, or thin film structures. Until recently, nondestructive 3D microstructural probes with the submicron, intra-granular spatial resolution required to investigate the heterogeneous deformation induced below nanoindents have not been available. High brilliance
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