Indentation Pileup Behavior of Ti-6Al-4V Alloy: Experiments and Nonlocal Crystal Plasticity Finite Element Simulations
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NANOINDENTATION is an effective technique to evaluate the elastic modulus, hardness, and plasticity mechanisms in material science.[1–5] Although the actual deformation process during nanoindentation is simple, the boundary conditions and kinematics involved are complex.[6] Accordingly, the structure formation below and around indents are complex too. Material around the contact area tends to deform upwards or downwards with respect to the indented surface plane, which results pileup or sink-in, respectively.[2] These characteristics are due to the crystallography and the orientation of the grain indented.[2,5,7,8] Several authors have tried to investigate the nanoindentation pileup or sink-in behavior of crystal materials, such as copper,[2,4] aluminum,[9] magnesium,[7] titanium,[5,8,10] and c-TiAl.[11] In most of these studies,[2,4,7,8,10,11] an efficient method by combining application of nanoindentation, electron backscatter diffraction (EBSD) orientation mapping, atomic force microscopy (AFM) topographic measurements, and crystal plasticity finite element (CPFE) modeling was used to analyze the pileup or sink-in behavior. As a typical a+b titanium alloy, Ti-6Al-4V has been widely used in aerospace industries, due to its low FENGBO HAN, BIN TANG, XU YAN, YIFEI PENG, HONGCHAO KOU, JINSHAN LI, and YONG FENG are with the State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, P.R. China. Contact e-mail: [email protected] YING DENG is with the Beijing Aeronautical Manufacturing Technology Research Institute, Beijing 100024, P.R. China. Manuscript submitted June 11, 2016. Article published online January 17, 2017 METALLURGICAL AND MATERIALS TRANSACTIONS A
density and attractive mechanical and corrosion-resistant properties.[12–14] The predominant constituent phase of this alloy, low-symmetry hexagonal-structured a phase, exhibits remarkable anisotropy of elasticity and plasticity. The critical resolved shear stresses (CRSS) of different kinds of slip systems of a phase vary a lot, leading to selective activation of only a few deformation systems for many boundary conditions.[10] Therefore, there will be a considerable heterogeneity of plastic flow during deformation at grain scale. One important deformation situation at such small scale is the aforementioned nanoindentation, during which the plastic flow of a phase is very complicated. Viswanathan et al.[3,15] made direct observation and analyses of dislocation substructures in a phase of Ti-6Al-4V alloy formed by nanoindentation with TEM on the focused ion beam (FIB) cutting thin-foil membranes. Han et al.[8] also studied the nanoindentation process of Ti-6Al-4V alloy by combining experiments and CPFE simulations using a local constitutive law. Although the pileup behavior of Ti-6Al-4V alloy was discussed briefly in these studies, a thorough understanding of the pileup behavior of this alloy is still lacking. In this work, we present a detailed micromechanical analysis of indentation pileup behavior of Ti-6Al-4V alloy.
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