Abstract
Problem Statement (Relevance): When zirconium and titanium alloys are used in nuclear power and space industries, it is necessary that they could perform well under heavy duty regimes. It is known that the meta-stable baric ω-phase, which forms in the above materials under severe loading, is characterised with higher density, hardness and brittleness compared with the stable α-phase. To minimize the embrittlement factor of the ω-phase and to prevent fracture in structures made of both pure metals and Zr/Ti alloys, it is necessary to look into the stability of the metastable ω-phase as observed after severe loading. Objectives: The objective of this study is to understand what structural transformations take place in sample zirconium pseudo-single crystals subjected to loading in the Bridgman chamber as the temperature increases from room temperature to 300 °C. Methods Applied (Experiments): With the help of electron beam crucible-free zone melting, original samples of iodide pseudo-single crystal of α-Zr were derived. Disk samples were subjected to plastic deformation in hard-alloy Bridgeman anvils at 8 GPa and the angular speed of ω=1.0 RPM. The tests were conducted at room temperature and at 70, 100, and 300 °C. The anvil turn angle was φ=1080 degrees. The structural phase state of the deformed zirconium samples was analysed through electron microscopy (with a JEM-200CX microscope) and X-ray diffraction (with a DRON-3 diffractometer in the monochromatic CuKα-radiation). Findings: The tests showed that after the loading was stopped and the test samples cooled down from the 70, 100, and 300 °C to room temperature, the ω-phase partially persisted in all the samples, despite the dynamic and post-dynamic recrystallisation processes observed. These tests were also first to prove that 70°C works as a stabilisation temperature for the metastable ω-phase. Practical Relevance: The results obtained may be used to predict the structural durability of equipment used in aerospace and nuclear industries.
Keywords
Pseudo-single crystal of zirconium, deformation, high quasi-hydrostatic pressure, α → ω phase transitions.
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