Effect of extrusion ratios on hardness, microstructure, and crystal texture anisotropy in pure niobium tubes subjected to hydrostatic extrusion
(1. Advanced Materials and Process R&D Department, Korea Institute of Industrial Technology, Incheon City, 21999, Korea;
2. Department of Advanced Materials Science and Engineering, Inha University, Incheon City, 22212, Korea)
2. Department of Advanced Materials Science and Engineering, Inha University, Incheon City, 22212, Korea)
Abstract: Nb tubes were fabricated through hydrostatic extrusion at extrusion ratios of 3.1 and 6.1 at ambient temperature, and then their microstructure, texture, and Vickers hardness were investigated based on electron back-scattered diffraction (EBSD) data. The fraction of low-angle boundaries (LABs) largely decreased with a sharp decrease in mean grain sizes after hydrostatic extrusion and was not proportional to extrusion ratios, assuming that mixed-asymmetrical junctions forming LABs dissociate at high extrusion ratios from the external stress (>981 MPa) with thermal activation by the generated heat. The correlation between grain size and Vickers hardness followed the Hall-Petch relationship despite the texture gradient of the á111？ cyclic fiber textural microstructure at low extrusion ratios and the á100？ true fiber textural microstructure at high extrusion ratios. The increase in hydrostatic pressure on the Nb tubes contributed to texture evolution in terms of extrusion ratios due to the difference between {110}á111？ and {112}á111？ components based on EBSD data.
Key words: niobium tube; hydrostatic extrusion; microstructure characterization; mechanical properties; texture evolution