Syntheses of full-density nanocrystalline titanium nitride compacts by plasma-activated sintering of mechanically reacted powder |
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Authors: | M Sherif El-Eskandarany M Omori T Hirai T J Konno K Sumiyama K Suzuki |
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Affiliation: | (1) Present address: Department of Chemical Physics of Non Crystalline Materials, Institute for Materials Research, Tohoku University, Japan;(2) Materials Science and Metallurgy, Mining and Petroleum Engineering Department, Faculty of Engineering, Al-Azhar University, Nasr City, 11371 Cairo, Egypt;(3) Department of High-Temperature Materials Science, Tohoku University, 980-77 Sendai, Japan;(4) Department of Chemical Physics of Non-Crystalline Materials, Tohoku University, 980-77 Sendai, Japan;(5) Present address: Department of Chemical Physics of Non-crystalline Materials, Tohoku University, Japan;(6) Sumitomo Metal Industries, Advanced Materials Research, 660-0891 Husocho 1–8, Amagasaki, Japan |
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Abstract: | Nearly equiatomic nanocrystalline titanium nitride (Ti56N44) powder with an average grain size of 5 nm has been synthesized by ball milling elemental Ti powder under nitrogen gas flow
at room temperature. During the first stage of reactive ball milling (RBM) (time <3.6 ks), the metallic Ti powder tends to
agglomerate to form powder particles with a larger diameter. At the second stage (3.6 to 22.0 ks), the agglomerated particles
of Ti fragment to form smaller particles. These smaller particles that have new or fresh surfaces begin to react with the
milling atmosphere (nitrogen) during the third stage of milling (22 to 86 ks) to form TiN powder coexisting with unreacted
Ti powder. Toward the end of milling (86 to 173 ks), a single phase of nanocrystalline TiN (NaCl structure) is obtained. The
powder of this end-product has a spherical-like morphology with an average particle size of about 0.4 μm diameter. A sintering
procedure using plasma activation has been employed to consolidate the powder particles at several stages of the RBM. The
as-milled and as-consolidated powders have been characterized as a function of the RBM time by means of X-ray diffraction
(XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), optical metallography, and chemical analyses.
Density measurements of the consolidated samples show that after 86 to 173 ks of the RBM time, the compacted samples are essentially
fully dense (above 96 pct of the theoretical density for TiN). The results also show that the consolidated TiN compacts still
maintain their unique nanocrystalline properties with an average grain size of about 65 nm. The hardness and some mechanical
properties of the consolidated TiN compacts have been determined as a function of the RBM time. |
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