Studies of Grain Boundary Cavitation by Small-Angle Neutron Scattering

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Abstract
Small-angle neutron scattering has been used to study the process of fatigue-induced grain boundary cavitation in two model materials, pure copper and a Cu-7A1 alloy, fatigued at elevated temperature. Values have been obtained from the scattering data for void volume fraction, and number density of the voids and their size distribution, as a function of fatigue time. The growth rate of individual voids has been calculated and found to be in good agreement with a recent theory of fatigue-induced cavitation. Copper and copper-aluminum show opposite responses to the effect of fatigue temperature on cavitation. An increase in the temperature of fatigue produces an increase in the total void volume growth rate and the void nucleation rate in the case of copper, a decrease in copper-aluminum. The process of grain boundary cavitation is shown to be very sensitive to the movement of the grain boundaries. Grain boundary migration can cause cavitated boundaries to shed their voids into the matrix. The number and size distribution of cavities in a specimen appear to be related to the extent of grain growth which occurs during fatigue.