Nanostructured tungsten through cryogenic attrition. (September 2015)

• Record Type: Journal Article
• Authors: Zhou, Le; Kellogg, Frank; Hofmeister, Clara; Giri, Anit; Cho, Kyu; Sohn, Yongho
• Is Part Of: International journal of refractory metals & hard materials. Volume 52(2015:Sep.)
• Page Start: 70
• Page End: 77
• Publication Date: 2015-09
• Subjects: Nanocrystalline -- Tungsten -- Cryomilling -- Microstructure -- Grain size; 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.2015.05.016
• Languages: English
• ISSNs: 0263-4368

Abstract

Abstract: Nanostructured pure tungsten (W) powders have been fabricated through cryogenic attrition (i.e., cryomilling) in a liquid nitrogen medium for the first time. The microstructure and chemistry of W powders before and after 4 and 12 h of cryomilling were thoroughly examined by gas fusion chemical analysis, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy (TEM). Cryomilling in liquid nitrogen protected the tungsten from oxygen and hydrogen contamination while introducing nitrogen. Results showed that the W grain size decreased with cryomilling time, and reached approximately 5 nm after 12 h of cryomilling. High resolution TEM suggested that nitrogen reacted with W to form tungsten nitride (WN). Additionally, amorphous W was identified in the 12 h cryomilled W powder. Tungsten carbide (WC) contamination from the milling media and minor Fe–Cr–Ni-containing impurities from the stainless steel vessel were also documented. The WC had grain size ranging from 20 nm to 150 nm, and was homogeneously dispersed in W matrix. Highlights: Pure nanocrystalline tungsten powder was fabricated by cryomilling. Tungsten grain size decreased to ~ 15 nm after 4 h of cryomilling. Tungsten grain size decreased down to ~ 5 nm after 12 h of cryomilling. Nitrogen content increased with increasing cryomilling time. Tungsten carbide and FeNiCr-rich phase was observed as contamination phases.