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Mechanical Behavior of Liquid Route Processed SiCf/Ti Composites Under Longitudinal and Transverse Loadings

  • Valle, Roger
  • Daux, Jean-Claude
Publication Date
Jan 28, 2016
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Due to the high melting point and strong chemical reactivity of titanium alloys, titanium matrix composites (TMCs) are usually processed through solid state routes such as the foil-fiber-foil (FFF) technique. An alternative method consists in the deposition of the matrix on the fibers. However, techniques such as physical vapor deposition (PVD) lead to a very low deposition rate, contrary to liquid route processing using a levitating liquid alloy sphere held in a cold crucible. In order to investigate the effects of the resulting thermal shock on carbon coated SiC fibers, and select an appropriate fiber, fibers are subjected to a pure thermal shock using a laser bench facility. These fibers are then tensile tested to failure in order to evaluate the resulting fiber strength degradation and, thus, the maximum acceptable temperature. Mechanical characterization of the liquid route processed TMC is then investigated through longitudinal and transverse tensile and creep tests at temperatures representative of aeronautical applications. The specimens, unbroken after long duration creep tests, are then subjected to tensile loading to failure: conditions representative of service i.e. short time over-speeding of a gas turbine. Finally, interpretation of the mechanical tests through micrographical and microfractographical examinations is focused on the identification of the deformation and failure mechanisms specific to the liquid route processed composite, e.g. nucleation, under either longitudinal or transverse loadings, of internal cracks in the alpha phase of the titanium-based matrix, explained through a physical model involving a high shear stress and normal stress combination, leading to cleavage.

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