ON THE RELATIONS BETWEEN PORTEVIN LE CHATELIER PLASTIC INSTABILITIES AND PRECIPITATION

This paper concerns the interplay between dynamic strain ageing and precipitation. The classical behaviour of critical strains (dependence with strain rate and temperature) in the Portevin Le Chatelier effect is briefly reviewed together with its modelling in the Estrin-Kubin-Penning model, The so called ''inverse Portevin Le Chatelier effect'', known to occur in concentrated solutions, is often attributed to precipitation. A model for the influence of precipitation on dynamic strain ageing is proposed. Both homogeneous and heterogeneous precipitation is considered. It is shown that as a result of precipitation the critical strains for the occurrence of the Portevin-LeChatelier effect should exhibit an 'inverse' behaviour with temperature and strain rate as compared to the behaviour observed in dilute solid solutions. It is also shown that plasticity induced reversion or disordering can lead,in alloys with a strain rate sensitivity which would be positive, to an apparent negative strain rate sensitivity and to a ''pseudo Portevin Le Chatelier effect''.