copper-zinc alloys containing alumina particles I. Macroscopic properties and workhardening theory

The stress-strain curves of Cu and Cu+ Zn alloys containing alumina particles have been measured as a function of temperature, strain rate, composition, volume fraction and radius of the particles. Around room temperature the stress-strain curves of the Cu alloys are strongly temperature dependent and there is a marked recovery effect. A theory of workhardening is developed based on a model deduced from the electron microscope observations in which the glide dislocations generate rows of loops at the particles which act as parallel linear obstacles, leading to 'self-hardening' of a slip line. In addition, the interaction of other dislocations on parallel glide planes is considered, and the slip line spacing and the number of dislocations per slip line are adjusted to minimize the flow stress for! a given strain. The theory predicts a parabolic stress-strain curve following an initial region of relatively low hardening rate, in good quantitative agreement with the stress-strain curves for the Cu alloys at 77 K. The predicted slip line spacing agrees with electron microscope observations. The behaviour of the Cu+ Zn alloys, the temperature and strain rate dependence of the stressstrain curve, and the recovery effect are discussed qualitatively and are correlated with observed changes in the microstructure.