Control of grain boundary microstructures in molybdenum polycrystals by thermomechanical processing of single crystals

Abstract

The formation of grain structures and grain boundary microstructures in polycrystalline molybdenum, produced by thermomechanical processing from cylindrical single crystals with different initial surface normal orientations of ⟨110⟩, ⟨111⟩ and ⟨112⟩, were investigated with the objective of controlling grain boundary microstructures. The polycrystalline specimens displayed different microstructures depending on the initial orientation of the single crystal and the deformed microstructure. The recrystallized microstructure was composed of some oriented-grain clusters, in which grains possessing a similar orientation were assembled. The frequency of low-angle boundaries was very high in the oriented-grain clusters. A close relationship also existed between the grain boundary character distribution (GBCD) and the triple junction distribution. Grain boundary microstructures were compared of bcc molybdenum and fcc polycrystalline materials with reference to path-dependent percolation resistance.

Acknowledgements

The authors thank Dr T. Nagano of Japan Fine Ceramics Center (JFCC) for his help in X-ray measurements of compressive deformed specimens. This work was supported by the Ministry of Education, Science, Sports and Culture through the Grant in Aid for Fundamental Research (Grant No. 08405046).