The origin and the effect of the fcc phase in sintered HfNbTaTiZr

• Published in: Materials letters Vol. 286; p. 129224
• Main Authors: Lukáč, František, Vilémová, Monika, Klementová, Mariana, Minárik, Peter, Chráska, Tomáš
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.2021; Elsevier BV
• Subjects: Alloy powders; Argon; Heat treating; HfNbTaTiZr; High entropy alloys; Materials science; Mechanical alloying; Mechanical properties; Microstructure; Oxygen compounds; Phase composition; Phase transformation; Plasma sintering; Powder metallurgy; Powder technology; Refractory high-entropy alloys; Spark plasma sintering; Refractory high-entropy alloys; Phase transformation; Powder technology; HfNbTaTiZr
• ISSN: 0167-577X; 1873-4979
• DOI: 10.1016/j.matlet.2020.129224

[Display omitted] •HfNbTaTiZr is sensitive to its environment at HT due to high affinity of Hf, Zr and Ti to O and N.•New fcc phase is prepared in ultrafine-grained HfNbTaTiZr by SPS and MA.•Both ZrHfTi-rich hcp and fcc phases are formed during sintering from the powder milled with air.•Only the fcc and bcc phases are found when N is introduced in mechanical alloying and SPS.•Ultra-high hardness is achieved when MA is performed in nitrogen atmosphere. The growing interest in preparing refractory high entropy alloys via powder metallurgy reveals significant sensitivity to impurities, influencing the phase composition and microstructure and, consequently, the mechanical properties. Mechanical alloying of commercial purity powders is a cost-effective way of material preparation leading to a very fine microstructure when spark plasma sintering is used. However, the atmosphere of the milling process plays a significant role. This study shows that the phase composition of the HfNbTaTiZr alloy may be tailored by milling in ambient atmosphere, in argon or in nitrogen. Formation of a new fcc-ZrHfTi phase as a complex nitrogen and oxygen compound was elucidated and its significant hardening effect was shown. Finally, exceptional hardness was achieved by the synergic effect of nano-grained structure and high volume fraction of fcc-ZrHfTi phase.