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Zirconium Phase Transformation under Static High Pressure and ω-Zr Phase Stability at High Temperatures

1
Faculty of Non-Ferrous Metals, AGH University of Science and Technology, A. Mickiewicza Av. 30, 30-059 Krakow, Poland
2
Lukasiewicz Research Network—Institute of Advanced Manufacturing Technology, Wroclawska St. 37a, 30-011 Krakow, Poland
*
Author to whom correspondence should be addressed.
Materials 2019, 12(14), 2244; https://doi.org/10.3390/ma12142244
Received: 11 June 2019 / Revised: 8 July 2019 / Accepted: 10 July 2019 / Published: 12 July 2019
(This article belongs to the Special Issue High-Pressure Materials)
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Abstract

High-purity Zr has been observed to undergo a phase transformation from the α-phase to the hexagonal ω-phase under high pressure generated either statically or by shock loading. The transition pressure from α-Zr to ω-Zr at 300 K is 2.10 GPa. The main aim of this research was to determine the conditions of α-Zr in ω-Zr transformation and the state of stresses after the high-pressure pressing and sintering of zirconium powders. Commercially acquired zirconium powders of 99.9% and 98.8% purity were used in this study. Qualitative and quantitative phase analysis of the materials was carried out using X-ray diffraction. The materials were statically pressed and sintered using a Bridgman-type toroidal apparatus at under 4.0 and 7.8 GPa. After pressing, the transformation proceeded for the zirconium powder containing 98.8% purity (with hydrides admixture) but did not occur for the high-purity zirconium powders with 99.9% purity. The zirconium powders were sintered using the HPHT (High Pressure—High Temperature) method at temperatures of 1273 K and 1473 K. The transformation proceeded for both powders. The highest contribution of the ω-Zr phase was obtained in the zirconium (98.8% purity with the hydrides contents) sintered for 1 min at a temperature of 1473 K and a pressure of 7.8. The ω-phase content was 87 wt.%. The stress measurement was performed for the pressed and sintered materials using the sin2ψ X-ray diffraction method. The higher sintering temperature resulted in a decrease of the residual stresses in the ω-Zr phase for the sintered zirconium. The higher levels of stress limited the transformation of the α-Zr phase into the ω-Zr phase. Investigated materials characterized by higher compressive macrostresses were also typical of the greater stability of the ω-Zr phase at high temperatures. View Full-Text
Keywords: zirconium powders; HPHT pressing and sintering; phase composition; residual stresses; stability zirconium powders; HPHT pressing and sintering; phase composition; residual stresses; stability
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Jaworska, L.; Cyboron, J.; Cygan, S.; Zwolinski, A.; Onderka, B.; Skrzekut, T. Zirconium Phase Transformation under Static High Pressure and ω-Zr Phase Stability at High Temperatures. Materials 2019, 12, 2244.

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