Investigation on the microstructure of as-deformed NiCr microwires using TEM

Abstract

Ultra-fine NiCr (80/20 wt%) wires with a nanocrystalline (nc) grain and diameters that range from 21 μm to 25 μm were fabricated using a cold-drawing method. The engineering strains were 8.8%, 17.3%, 26.4%, 36.1%, and 46.6%. The microstructures of the drawn direction and wire cross-section were characterized using transmission electron microscopy (TEM). Two thinning preparation techniques were used in preparing the TEM specimens. The grain size was approximately 3 nm to 20 nm. The deformed microstructures include amorphous GBs, crystal GBs, edge dislocations and twins. Amorphous boundaries may be produced by phase transition or dislocation pile-up. Several edge dislocations existed at the grain boundaries (GBs) and grain interior. Twinning deformation microstructures were found in cross-sections with an asymmetrical relationship. The possible deformation mechanism for the formation of the microstructure is discussed.