Ion beam assisted deposition in the synthesis and fracture of metal-ceramic microlaminates

Al2O3/Al/Al2O3 microlaminates of nominal thickness 750 nm were formed by physical vapor deposition (PVD) and ion beam assisted deposition (IBAD). IBAD influences the residual stress in the layers, their strength and mixing of the metal-ceramic interface. Different combinations of PVD- and IBAD-synthesized layers were used in trilayer microlaminates which were then tested in tension for cracking behavior, Residual stress states of the microlaminates are reproducible and follow a rule-of-mixtures of the constituents. IBAD of monolithic oxide causes an increased residual compressive stress and results in a slightly larger strain to fracture over the PVD oxide. Trilayer microlaminates exhibit lower saturation crack densities compared to monolithic oxides due primarily to the introduction of a ductile layer. The variation in strength of the ductile layer (by IBAD) and mixing of the interfaces do not appear to affect the fracture behavior, which is understandable in a strong bond-forming system. Observations are consistent with a cracking mechanism that is controlled by the flaw distribution in the brittle oxide layer.