Evaluation of the strength of diffusion bonded joints in continuous fiber reinforced metal matrix composites

Abstract

SiC continuous fiber reinforced Ti6Al4V composites with various fiber volume fractions were fabricated by the vacuum hot pressing process and were joined to a Ti6Al4V alloy plate by solid state diffusion bonding processes. The matrix alloy was perfectly joined to the Ti6Al4V plate within the bonding condition. The joint strength decreased with increasing fiber volume fraction. The joint strength was not directly proportional the matrix area fraction. A joint efficiency over 90% could be obtained when the fiber volume fraction was less than 30%. The SiC fibers were debonded from the matrix and cylindrical defects were formed at the end of the fiber under tensile stress. The defects produced a triaxial stress state at the matrix alloy and thus higher joint strengths than the values simply calculated from the area fraction of the matrix at the bonding interface. The composite was transient liquid phase bonded to itself using TiCuZr filler metal. The joint strength was degraded using thin interlayer less than 80 μm thick. An interlayer thickenss over 80 μm was found to be necessary to obtain a sound joint.