Investigating bulk mechanical properties on a micro-scale: micro-tensile testing of ultrafine grained Ni–SiC composite to determine its fracture mechanism and strain rate sensitivity
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Date
2020-03-15
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Elsevier
Abstract
In this study, in-situ micro-tensile testing technique was used to investigate the mechanical properties of ultrafine grained Ni-3wt% SiC composite the size effect on the mechanical properties of the ultrafine grained Ni-3wt% SiC composite, and to further reveal the reasons for the low ductility of the bulk Ni-3wt%SiC composite. Dog-bone micro-tensile samples were manufactured using a Focused Ion Beam (FIB) milling machine to 15 μm length with a cross sectional area of 5 μm by 5 μm. The micro-tensile samples are pulled in tension at a quasi-static strain rate of 0.000087/s (LSR) and a relatively faster strain rate of 0.011/s (HSR). Analysis of experimental stress-strain plots for the LSR tests measured yield stress, ultimate tensile stress and modulus values that approach values previously reported for bulk/macro-level tensile tests. However, the elongation and fracture energy at the micro-level is approximately half that at the bulk scale. This discrepancy is attributed to the presence of unwanted carbon and silicon oxide impurities ∼1.5 μm in diameter which act as stress concentrators especially given their large size relative to the width of the tensile specimens. The composition of these impurities was validated by transmission electron microscopy, and they seem to be the most likely cause of low ductility of the Ni-3wt% SiC composite. In all, the study undertaken here was able to replicate mechanical properties observed at the macro scale as well as reproduce a strain rate effect. Furthermore, the failure mode of Ni-3wt% SiC composite was identified and analysed in detail. Crown Copyright © 2019 Published by Elsevier B.V
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Keywords
Fracture mechanics, Strain rate, Materials testing, Nickel alloys, Mechanical properties, Grain size
Citation
Xu, A., Yang, C., Thorogood, G., & Bhattacharyya, D. (2020). Investigating bulk mechanical properties on a micro-scale: micro-tensile testing of ultrafine grained Ni–SiC composite to determine its fracture mechanism and strain rate sensitivity. Journal of Alloys and Compounds, 817, 152774. doi:10.1016/j.jallcom.2019.152774