Nonlinear ultrasonic assessment of precipitation hardening in ASTM A710 steel

We investigated several specimens of ASTM A710 steel containing copper-rich precipitates with variations in the final aging treatment. X-ray diffraction line-broadening and small-angle neutron-scattering experiments revealed the existence of the precipitates and associated coherency strain. We determined the nonlinear ultrasonic parameter β for each specimen by harmonic-generation experiments and measured the ultrasonic longitudinal velocity v_L and attenuation α_L. Although v_L and a_L showed no consistent trends, β increased with increasing strain. This correlation is compared to a microstructural model for harmonic generation that includes a contribution from precipitate-inned dislocations.