In Situ Diagnostics of Damage Accumulation in Ni-Based Superalloys Using High-Temperature Computed Tomography
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In Situ Diagnostics of Damage Accumulation in Ni-Based Superalloys Using High-Temperature Computed Tomography K. KAGEYAMA, F. ADZIMAN, E. ALABORT, T. SUI, A.M. KORSUNSKY, and R.C. REED The design, operation, and performance of a laboratory-scale X-ray computed tomography arrangement that is capable of elevated-temperature deformation studies of superalloys to 800 °C and possibly beyond are reported. The system is optimized for acquisition of three-dimensional (3D) backprojection images recorded sequentially during tensile deformation at strain rates between 104 and 102 s1, captured in situ. It is used to characterize the evolution of damage—for example, void formation and microcracking—in Nimonic 80A and Inconel 718 superalloys, which are studied as exemplar polycrystalline alloys with lesser and greater ductility, respectively. the results indicate that such damage can be resolved to within 30 to 50 lm. Collection of temporally and spatially resolved data for the damage evolution during deformation is proven. Hence, the processes leading to creep fracture initiation and final rupture can be quantified in a novel way. https://doi.org/10.1007/s11661-018-4737-6 Ó The Author(s) 2018
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INTRODUCTION
NICKEL-BASED superalloys are ubiquitous in development of high-temperature systems for use in jet propulsion and power generation more broadly. The overarching reason for this is their superior properties—both mechanical and chemical—at operating conditions which can approach 800 °C or beyond. There are significant technical, commercial, and legislative pressures requiring enhancement of their high-temperature performance. Improvements in fuel economy and thus CO2 emissions are a significant driver for this. Due to the nature of these applications, great emphasis is placed on characterization of the behavior of superalloys under tensile, fatigue, as well as creep loading conditions. Traditionally, such testing has emphasized measurements of force and displacement to deduce the stress and strain fields; this can be regarded as a form of macroscopic characterization. Microscopic analysis is
K. KAGEYAMA and E. ALABORT are with the Department of Materials, University of Oxford, Parks Road, Oxford, OX13PH, UK. Contact e-mail: [email protected] F. ADZIMAN and A.M. KORSUNSKY are with the Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX13PJ, UK, T. SUI is with the Department of Mechanical Engineering Sciences, University of Surrey, Guildford, Surrey, GU27XH, UK. R.C. REED is with the Department of Materials, University of Oxford and also with the Department of Engineering Science, University of Oxford. Manuscript submitted March 8, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
usually carried out post mortem on, for example, failed[1–5] or interrupted test pieces[6–11] and most commonly at ambient temperature. However, a significant difficulty with this approach is that one can never be totally sure that damage deduced post mortem is truly representative of that driving deformation
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