An ultrasonic study of relaxation processes in pure and mechanically alloyed tungsten. (August 2020)

• Record Type: Journal Article
• Authors: Koller, Martin; Vilémová, Monika; Lukáč, František; Beran, Přemysl; Čížek, Jakub; Hadraba, Hynek; Matějíček, Jiří; Veverka, Jakub; Seiner, Hanuš
• Is Part Of: International journal of refractory metals & hard materials. Volume 90(2020)
• Publication Date: 2020-08
• Subjects: Fine-grained tungsten -- Oxide dispersion -- Resonant ultrasound spectroscopy -- Ductile-to-brittle transition temperature -- Internal friction -- Dislocation density; Heat resistant alloys -- Periodicals; Refractory materials -- Periodicals; Metallography -- Periodicals; Alliages réfractaires -- Périodiques; Matériaux réfractaires -- Périodiques; Métallographie -- Périodiques; Heat resistant alloys; Metallography; Refractory materials; Periodicals; Electronic journals; 669.73
• DOI: 10.1016/j.ijrmhm.2020.105233
• Languages: English
• ISSNs: 0263-4368

Abstract

Abstract: High-temperature internal friction in a pure tungsten single crystal, polycrystals with different grain sizes, and mechanically alloyed tungsten polycrystals was studied. Positron annihilation spectroscopy was used to prove that all studied materials contain a detectable amount of dislocations. Then, resonant ultrasound spectroscopy was applied to determine the internal friction evolution with temperature from room temperature up to 740 °C. For the pure tungsten samples, a sharp increase of internal friction was observed for temperatures above 470 °C (for the single crystal) or above 400 °C (for the polycrystals); the activation energy corresponding to this increase was the same as the activation energy for the ductile-to-brittle transition in tungsten reported in the literature. For the alloyed materials, direct observation of the onset of this relaxation mechanism was impossible due to additional effects resulting from the secondary phases in the material. Highlights: Tungsten-based materials are studied by resonant ultrasound spectroscopy up to 740 °C. A single crystal of pure tungsten and pure and alloyed polycrystals are examined. In pure tungsten, dislocation damping rapidly grows above ~400 °C (knee temperature). The corresponding activation energy is the same as for ductile-to-brittle transition. The sharp knee temperature disappears for materials with second-phase particles.