Mapping Residual-Stress Distributions in a Laser-Peened Vit-105 Bulk-Metallic Glass Using the Focused-Ion-Beam Micro-Sli
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Mapping Residual-Stress Distributions in a Laser-Peened Vit-105 Bulk-Metallic Glass Using the Focused-Ion-Beam Micro-Slitting Method B. Winiarski1, G. Wang2, X. Xie2, Y. Cao3, Y. Shin3, P. K. Liaw2 and P. J. Withers1 1
School of Materials, The University of Manchester, Grosvenor St., Manchester, M1 7HS, UK Dept. of Materials Sci. & Eng., The University of Tennessee, Knoxville, TN 37996, USA 3 School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, USA 2
ABSTRACT Measuring residual-stresses at the micron scale in glassy materials imposes experimental challenges, particularly when using diffraction, or other conventional laboratory methods, e.g., optical non-contact methods, grid methods, etc. In this short paper, a technique for mapping residual-stress profiles in amorphous materials with high spatial definition is used to measure residual-stresses in a laser-peened and fatigued bulk-metallic glass - Vit-105. The method involves local deposition of nano Pt dots patterns on the mapped region of the specimen and milling of a series of micro-slots of size 15 × 2 × 0.4 µm3 using the focused ion beam of a dual beam Field Emission Gun Scanning Electron Microscope / Focused Ion Gun (FEGSEM/FIB) instrument. The deformation fields in the vicinity of slots are reconstructed by the digital image correlation analyses (DICA) of FEGSEM images recorded during milling. The residual-stresses are inferred by fitting a reference displacement field obtained from finite-element analyses (FEA) with the recorded displacement field. In this way, residual-stress distributions have been characterized as a function of the distance from the laser-peened surface to a depth of 1,200 microns with a spatial resolution of 30 µm. The influence of fatigue loading on the compressive residual-stresses spatial distribution is studied and discussed. It was found that the fatigue loading significantly changes the compressive residual-stress spatial distribution in the laserpeened layer. INTRODUCTION Bulk Metallic Glasses (BMG) have recently been incorporated in high-performance applications at the macroscale [1, 2] and at the fine scale [3], as well as in two-phase (crystal/glass) microstructures [4]. BMGs have strengths approaching theoretical limits, very high hardness and elastic limits [5]. However their wider practical application is limited due to their quasi-brittle behavior [6]. The presence of residual-stresses in BMGs is of primary importance in tailoring their unusual ductility, fracture, fatigue properties and wear resistance. These benefits can only be achieved if the residual-stresses are precisely induced, controlled and measured. Surface treatment methods are an important means of modifying their behavior [5, 7]. Shot peening (SP) process improves the plasticity of BMG, where SP induced compressive residual-stresses (RS) reduced likelihood of surface cracking and induced a high population of shear band, thus more uniform deformation. Laser shock peening (LSP) process produces highpressure plasma shock waves in the w
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