Effect of Texture on Microstructural Developments: Some Case Studies

Abstract

In the present study, effect of texture on microstrutural developments in Zirconium based alloys and electrical steels were exploited. Three important alloys were considered: single-phase zircaloy 2, two-phase Zr-2.5Nb alloy and cold rolled non-oriented electrical steel. Zircaloy 2 was subjected to near plane strain deformation. The deformed structure had two types of grains – (i) deforming or fragmenting grains & (ii) non-deforming or non-fragmenting grains. Typically grains of the non-fragmenting type were larger and remained nearly equiaxed even after 50% deformation. They also had low grain average misorientation and were estimated to be elastically harder. Residual stress developments were mostly concentrated in the near basal orientations as obtained from plots of residual stress orientation distribution function. The same Zircaloy 2, when deformed at higher temperature (≥200°C), the equiaxed non-fragmenting grains got elongated. It has also been found that the misorientation developments and grain size refinement in such grains were higher than those in cold rolled samples. Dislocation dynamics simulations could capture such an effect during plane strain deformation of zircaloy 2. Two types of Zr-2.5Nb samples were subjected to uniaxial cold compression tests. Both type of samples consisted of two phases – hcp  and grain boundary bcc . However, the hardness of the second phase  differed between the samples – respectively being hard and soft relative to the primary phase. The relative hardness of an effect caused by the presence of fine precipitates, determined almost all aspects of microstructural developments. With hard , the primary phase had higher lattice strain and in-grain misorientation developments. On the other hand, softer second phase was clearly linked to more deformation twinning and associated grain size refinement and textural changes in hcp . Applications of cold rolled non-oriented (CRNO) electrical steels demand uniform magnetic property in all directions. To investigate the magnetic properties of CRNO steel in different directions, four different sets of samples were made from CRNO steel sheets - (1) samples along rolling direction, (2) samples at 30° to the rolling direction, (3) samples at 60° to the rolling direction and (4) samples at 90° to the rolling direction. The textural and magnetic properties were investigated using standard techniques. The results showed different textural and magnetic properties in all the CRNO samples. However, the properties were always better in rolling direction where the texture was more.