Precipitation Hardening in Fe-Cu Binary and Quaternary Alloys.

The behavior of precipitation hardening in two types of Fe-Cu alloys has been investigated by means of mechanical tests as well as small angle neutron scattering measurements.The integrated intensity increased first and reached a constant corresponding to the completion of precipitation reaction, while particle radius increased monotonically with aging time, where Vickers hardness and yield stress increased and reached maxima, then decreased. The interaction force with a dislocation due to each precipitate was very small comparedwith the force by the Orowanmechanism.After discussion based on three possible mechanisms in terms of coherency strain. elastic moduluschangeand interfacial energy, the strengthening was suggested to be caused from the coherency strain effect. The first increase of yield stress during aging is attributed to the growth in size of clusters and the decrease of yield stress after the maximum is mainly related to the decrease of numberdensity of precipitates. It was found that the loss of coherency with the matrix greatly lowers the strengthening effect, wherebythe structure of precipitates changesfrom bcc to fcc during aging.