Characterization of surface deformation around vickers indents in monocrystalline materials
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6/30/04
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Characterization of Surface Deformation around Vickers Indents in Monocrystalline Materials P. PERALTA, R. LEDOUX, R. DICKERSON, M. HAKIK, and P. DICKERSON The deformation surrounding Vickers indents on copper and MoSi2 monocrystals has been characterized for two orientations of the indenter diagonals using optical, electron, and scanning probe microscopy. The surface topography around the indents was characterized using atomic force microscopy (AFM), whereas orientation imaging microscopy (OIM) was used to map the local crystallographic orientation of the surface surrounding one indent on copper and measure lattice rotations due to plastic strain. The results indicate that sink-in and pile-up behavior depend on in-plane crystallographic orientations rather than the orientation of the indenter. Regions with multiple slip show larger lattice rotations and sink-in, whereas regions with lower slip density have smaller lattice rotations and show pile-ups. Strains outside one indent were obtained from OIM data using kinematical relations for single-crystal plasticity. A von Mises strain of 29 pct next to the middle of indent edge on the surface of the sample was deduced from the analysis. This agrees well with the characteristic strain reported for Vickers indents.
I. INTRODUCTION
INDENTATION tests can provide valuable information from probing small volumes, which provides an easy method to evaluate mechanical properties of metallic thin films and advanced intermetallic materials.[1–10] The examination of the imprint left by a hard indenter and measurements of load and penetration have led to methods to measure elastic properties, yield strength, and even hardening behavior.[1–5,7–11] Sharp indenters also lead to geometrically similar indentation states that result in a characteristic strain around them.[7] These characteristics make sharp indenters quite useful in estimating mechanical properties. Most models for indentation behavior used to estimate mechanical properties assume isotropic material behavior; however, a small indent in a polycrystalline material is likely to be in a single grain, where the behavior can be highly anisotropic. Indentation has also been used extensively to study mechanical properties of single crystals,[6,9–25] mostly because conventional testing methods are difficult to implement. Single crystals display hardness anisotropy in terms of both the crystallography of the indentation plane and the diagonal orientation in pyramidal indenters.[13–15,21,22] This anisotropy is compounded by variations on the surface deformation as a function of the diagonal orientation with respect to the crystallographic axes of the sample. Both sinkin and pile-up, which are indicative of high and low strain hardening rates, respectively,[7,26] have been observed around Vickers indents on a given plane for two orientations of the indent diagonals.[15] This implies that the true contact
P. PERALTA, Assistant Professor, and R. LEDOUX and M. HAKIK, Graduate Students, are with the Departm
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