Effect of Point Defects on the Interface Strength of Joint Materials

Abstract

The paper proposes a nonequilibrium thermodynamic model of quasi-static crack growth at the interface of perfectly elastic materials which are either free of defects or contain nonequilibrium point defects like vacancies or interstitial/substitutional impurity atoms. Considering that the interface of joint materials is a point-defect adsorber from their bulk, the model establishes a crack growth criterion in terms of the defect adsorbability at the interface of two materials and at their free surfaces formed by an open crack, work of reversible interface separation dependent on the defect concentration in the materials, and crack growth rate. The criterion suggests that varying the defect concentration can provide one or another crack mode: growth or healing. The model is supported by a detailed mathematical analysis of the crack growth in the presence of nonequilibrium vacancies. Assuming that only one of the joint materials contains vacancies, the analysis gives an equation for the vacancy concentration which can change the crack mode, shows its analytical solution for two limiting concentrations, and demonstrates how the crack mode is changed as the vacancy concentration increases. The analysis is supplemented with quantitative estimates of the range of external and internal parameters (temperature, tensile stress, parameters of two joint materials, vacancy adsorbability at their interface and free surfaces) that admit of the two limiting cases in actual multilayer structures under typical operating conditions. The research results can be useful for modeling and optimizing the adhesion characteristics and assessing the service life of multilayer structures employed in modern micro- and nanoelectronics.