Transient nucleation of cavities under coupled lattice and boundary diffusion

摘要

A diffusive process is proposed and examined for the nucleation of a cavity above half the melting point of a material and under low applied tensile stresses at which stress assisted diffusion occurs. An equation is developed for the diffusion of N atoms at a time into a bimaterial boundary to begin the nucleation. The stability of the solution of the equation is examined for a copper-sapphire interface, resulting in an activation energy for boundary diffusion that is in excellent agreement with a range of values previously recorded for metals. A calculation of the time taken for diffusion to create a small cavity is also obtained from the equation developed for the nucleation process. A mechanism for a supersaturation of vacancies that could result in final cavity formation is also developed, with the amount of calculated supersaturation in the range found in other studies. An incubation time before final stable cavitation is calculated and is also found to agree very well with experimental data.