CALCULATION OF DIFFUSION-COEFFICIENTS AND CORRELATION FACTORS IN GRAIN-BOUNDARY DIFFUSION

A random-walk approach is developed for tracer diffusion by a point-de fect mechanism in grain boundaries with a periodic structure. Such bou ndaries are characterized by a finite spectrum of possible atomic jump s. The effective (macroscopically measured) diffusion coefficient is e xpressed in terms of the different jump frequencies and the associated partial correlation factors. The partial correlation factors are calc ulated by a matrix method, the matrix elements (i.e. next jump probabi lities) being obtained by Monte Carlo simulations of individual point- defect-tracer encounters. In such simulations, the walk of the point d efect is followed until it induces a tracer jump or randomizes after e xecuting a large number of jumps. Together with the tracer jumps induc ed by the same defect as the previous jump, the possibility of the nex t tracer jump by interaction with a 'fresh' defect is taken into accou nt. The method is applied for the calculation of tracer self-diffusion by the vacancy mechanism parallel and perpendicular to the [001] tilt axis in a Sigma = 5, (310) grain boundary in silver.