Mechanical failure of CrN/Cu/CrN interfacial regions under tensile loading

Abstract

Quantitative assessment of the adhesion strength of ceramic hard coatings on substrates is a subject of great technological and scientific relevance, the achievement of which has proven difficult over the past two decades. Here we show that a micro-pillar tension testing protocol may serve as an effective method for this purpose, and demonstrate its effectiveness through a combination of micro tension testing and crystal plasticity finite element analysis (CPFEA). Tensile loading perpendicular to the interfaces, as well as accompanying CPFEA simulations, was conducted on CrN/Cu/CrN/Si micro-pillar tensile specimens fabricated from vapor phase deposited thin film sandwich structures. All tensile loading induced fracture were observed to occur within the Cu interlayer and near one Cu/CrN interface of the CrN/Cu/CrN sandwich structure. Observations, measurements, and discussions were made regarding the fracture surfaces, fracture stresses, and primary fracture mechanisms. Fracture surface examinations indicated ductile tensile fracture, induced by the formation of voids. It is shown that, due to the geometric constraint imposed by the ceramic layers in the current testing configuration, interlayer plasticity and the critical fracture stress display a strong dependence on the Cu interlayer thickness. It is postulated as a failure criterion that cooperation of deviatoric and hydrostatic stress components is needed to induce the nucleation and growth of voids. The relevance of the present work to the interfacial mechanical integrity of other metal/ceramic interfaces is discussed.