Structure of As-Cast Hafnium

• Published in: Physics of metals and metallography Vol. 119; no. 6; pp. 558 - 568
• Main Authors: Khlebnikova, Yu. V., Rodionov, D. P., Akshentsev, Yu. N., Egorova, L. Yu, Suaridze, T. R.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01-06-2018; Springer; Springer Nature B.V
• Subjects: Analysis; Chemistry and Materials Science; Crystal growth; Crystal structure; Diffusion; Floating structures; Grains; Hafnium; Materials Science; Metallic Materials; Metallography; Orientation relationships; Phase Transformations; Phase transitions; Residual stress; Smooth boundaries; Solid phases; Structure; Temperature gradients; Twinning; Twinning (Crystallography); Twins; Zone melting; Burgers orientation relationships; twinning; dihydrides; lath packet; polymorphic transformation; EBSD analysis; hafnium; fracture
• ISSN: 0031-918X; 1555-6190
• DOI: 10.1134/S0031918X1806008X

The structure of a hafnium crystal grown by the method of floating zone melting which underwent upon cooling the β → α (bcc → hcp) polymorphic transformation has been studied using the metallography, EBSD analysis, and electron microscopy. It has been shown that the α-phase structure of as-cast hafnium consists of lath-shaped crystals grouped into packets. As a rule, the α-phase grains contain several packets of different orientations from 12 orientations that can arise according to the Burgers orientation relationships. The boundaries of the α-phase grains and packets differ significantly. The grains have smooth boundaries, whereas the boundaries of packets are wavy. The misorientations between separate laths in a packet are less than 1°. Extended twins with a
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2
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α
twinning plane have been discovered in the structure of hafnium. The presence of twins in the hafnium crystal is due to the influence of the total internal stresses caused by the temperature gradient that arise upon zone melting and by the β → α phase transformation. The fracture of the hafnium crystal at room temperature occurs along the basal (0001) plane. The typical fracture is brittle-viscous with a predominance of the brittle component.