Debonding of particles in thin films

Thin composite films consisting of a matrix with embedded particles are currently being developed both as hard, wear resistant coatings and as functional surfaces. The effect of stiff particles in the film are studied for systems where the film is under residual tensile stresses. The particles, when they are fully bonded to the matrix, increase the stiffness of the composite film. In cases where the particles debond from the matrix material, the stiffness of the composite film decreases. The conditions under which the debonding process is stable are studied. For systems properly designed, a controlled debonding process of the particles can thus be used to reduce the stress levels in composite film lowering the risk for delamination of the composite film from the substrate as well as the risk of through cracks in the film. The work includes finite element based unit cell calculations of interface debonding between spherical particles and the film, and the release of residual stresses following this. The three dimensional unit cell calculations assume a periodic distribution of particles in the plane parallel to the substrate interface with equi-biaxial tension and periodicity with zero overall stress perpendicular to the substrate interface.