Order and domain hardening in Cu 3Au type superlattice alloys

Abstract

An X-ray study has been made of the change of degree of order and domain size during the isothermal ordering of a series of Ni 3Fe, Ni 3Mn and Cu 3Au alloys, all of which form the same type of superlattice. It is shown that the ordering process varies with composition within an alloy system as well as from one alloy system to another. Hardness measurements were made upon the same samples as used in the X-ray investigation. From this combined X-ray and mechanical properties study it is concluded that an initial increase in strength during isothermal ordering is due to a combination of short range order strengthening and the strengthening produced when an antiphase boundary has to be created. A new strengthening mechanism involving the cutting of ordered domains by single dislocations is shown to contribute to this initial increase in strength. After a continuous domain structure has developed, a softening, as predicted by Cottrell and Flinn, is observed.