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Title: Investigation of fatigue crack initiation from a non-metallic inclusion via high energy x-ray diffraction microscopy

Crack initiation at inclusions is a dominant, unavoidable and life-limiting failure mechanism of important structural materials. Fatigue progresses in a complex manner to find the ‘weakest link’ in the microstructure, leading to crack nucleation. In this study, fully 3-D characterization methods using high-energy synchrotron x-rays are combined with in-situ mechanical testing to study the crack initiation mechanism in a Ni-based superalloy specimen. The specimen was produced via powder metallurgy and seeded with a non-metallic inclusion. Two x-ray techniques were employed: absorption contrast computed micro-tomography (μ-CT) to determine the morphology of the inclusion and its location in the gauge section of the specimen; and far-field high-energy diffraction microscopy (FF-HEDM) to resolve the centroids, average orientations, and lattice strains of the individual grains comprising the microstructure surrounding the inclusion. Sequential μ-CT and FF-HEDM scans were carried out at both peak and zero applied stress following schedules of cyclic deformation. The µ-CT data showed the onset and location of crack initiation, and the FF-HEDM data provided temporal and spatial evolution of the intergranular strains. Strain partitioning and the associated stress heterogeneities that develop are shown to stabilize within a few loading cycles. Elasto-viscoplastic fast Fourier transform simulations were utilized to supplement interpretation ofmore » the experimental stress distributions and compared with the experimental stress distributions. In conclusion, appropriate conditions for crack nucleation in the form of stress gradients were demonstrated and created by virtue of the inclusion, specifically the residual stress state and local bonding state at the inclusion-matrix interface.« less
Authors:
 [1] ; ORCiD logo [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [4] ;  [5] ;  [2] ;  [6]
  1. Purdue Univ., West Lafayette, IN (United States)
  2. Air Force Research Lab., Wright-Patterson AFB, OH (United States)
  3. Air Force Research Lab., Wright-Patterson AFB, OH (United States); Nutonian Inc., Somerville, MA (United States)
  4. Argonne National Lab. (ANL), Argonne, IL (United States)
  5. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  6. Rolls-Royce plc, Derby (United Kingdom)
Publication Date:
Grant/Contract Number:
AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 137; Journal Issue: C; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); Air Force Research Laboratory (AFRL), Air Force Office of Scientific Research (AFOSR); Rolls Royce Plc; Air Force Research Laboratory (AFRL), Materials and Manufacturing Directorate
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; HEDM; Fatigue crack initiation; Non-metallic inclusions; Polycrystalline deformation; Microstructure; Synchrotron radiation; X-ray diffraction
OSTI Identifier:
1392597