Growth rates of grain boundary cavities during high temperature fatigue of copper

A simple technique for measuring cavity growth and nucleation rates has been used to study cavitation during high temperature deformation in 99.999% Cu. By combining precision density and small angle neutron scattering experiments, a characteristic cavity volume and cavity number density can be obtained. Under a static stress, the measured cavity growth rate is close to that predicted by theory for unconstrained diffusion-controlled cavity growth. The growth rate of the characteristic cavity volume during fully reversed fatigue is independent of time. The cavity nucleation rate is high initially, but by the time a specimen has cycled through 10-20% of its life the number density of voids has leveled off. Cavity density is only weakly frequency-dependent. The growth rate of the characteristic volume during fatigue depends on the square root of the cycling frequency. Neither stress-driven vacancy diffusion nor plastic strain growth mechanisms can explain the observed frequency dependence of cavity growth during fatigue. Graphs. 23 ref.--M.W.C.