Deformation-induced microstructural evolution of fiber-matrix interface in pyrolytic carbon-carbon composites. (1st January 2023)

• Record Type: Journal Article
• Authors: Mohammed, Ahmed Sameer Khan; Rateick, Richard; Sehitoglu, Huseyin
• Is Part Of: Acta materialia. Volume 242(2023)
• Publication Date: 2023-01-01
• Subjects: Carbon -- Composites -- Graphitization -- Pyrocarbon -- Interface -- Nanoindentation -- Electron microscopy; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2022.118498
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Mechanical properties of Carbon-Carbon (C/C) composites critically depend on the fiber-matrix interface-strength. However, almost no attention has been given to the pre-fracture behavior dictating this interface-strength. This study reports structural changes caused by inelastic energy dissipated prior to fracture, under flat-punch Nanoindentation. This test is coupled ex-situ with Transmission Electron Microscopy (TEM) to obtain electron-diffraction signatures. An "axis-alignment" procedure for semi-crystalline carbon structures in the composite is proposed to obtain accurate diffraction data. Results reveal that the dissipated energy "graphitizes" the composite, evidenced by a reduction in basal interplanar spacing of graphitic crystallites within fiber and matrix regions. Furthermore, a drastic reduction in the relative "Orientation Angle" (OA) between crystallites of both regions is observed. Both these structural changes imply a progressive weakening of the interface leading toward fracture. A first hypothesis for interface-strength is forwarded proposing that a higher initial OA-mismatch allows more scope for energy-dissipation by the observed mechanisms to yield higher interface-strength. The proposed hypothesis is successfully corroborated by comparing two C/C materials having distinct heat-treatment histories. Thus, this study establishes the role of pre-fracture microstructural evolution mechanisms in dictating interface-strength and proposes a novel hypothesis for informed design of C/C mechanical properties. Graphical abstract: Image, graphical abstract