In-situ observation of reversible twinning in U3Si

Abstract

The intermetallic compound U3Si has the cubic δ' structure between 765-900°C, and the tetragonal δ structure at lower temperatures. The δ' → δ transition always results in a twinned martensitic structure. Double shear causes the appearance of bands and sub-bands (1).Plastic deformation of martensitic U3Si is accompanied by detwinning, since only one of the twins is usually favorable from the point of view of the external stress. This was confirmed by optical metallography as well as by texture analysis (2).The present work describes a memory effect observed during a study of plastically deformed (⩽2%) martensitic U3Si.TEM specimens were prepared from lateral sections of standard tensile test samples. The principal stress direction was thus perpendicular to the foil.Fig. 1 shows the twinned structure of the martensite before deformation.Primary and secondary twins can be seen. The twinning systems are {101}<101> in FCT coordinates ({112}<111> in BCT coordinates). This was inferred from trace analyses.