Reactive Ball Milling to Fabricate Nanocrystalline Titanium Nitride Powders and Their Subsequent Consolidation Using SPS
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JMEPEG DOI: 10.1007/s11665-017-2709-4
Reactive Ball Milling to Fabricate Nanocrystalline Titanium Nitride Powders and Their Subsequent Consolidation Using SPS M. Sherif El-Eskandarany (Submitted February 17, 2017; in revised form April 24, 2017) The room-temperature reactive ball milling (RBM) approach was employed to synthesize nanostructured fcc-titanium nitride (TiN) powders, starting from milling hcp-titanium (Ti) powders under 10 bar of a nitrogen gas atmosphere, using a roller mill. During the first and intermediate stage of milling, the agglomerated Ti powders were continuously disintegrated into smaller particles with fresh surfaces. Increasing the RBM time led to an increase in the active-fresh surfaces of Ti, resulting increasing of the mole fraction of TiN against unreacted hcp-Ti. Toward the end of the RBM time (20 h), ultrafine spherical powder (with particles 0.5 lm in diameter) of the fcc-TiN phase was obtained, composed of nanocrystalline grains with an average diameter of 8 nm. The samples obtained after different stages of RBM time were consolidated under vacuum at 1600 °C into cylindrical bulk compacts of 20 mm diameter, using spark plasma sintering technique. These compacts that maintained their nanocrystalline characteristics with an average grain size of 56 nm in diameter, possessed high relative density (above 99% of the theoretical density). The Vickers hardness of the as-consolidated TiN was measured and found to be 22.9 GPa. The modulus of elasticity and shear modulus of bulk TiN were measured by a nondestructive test and found to be 384 and 189 GPa, respectively. In addition, the coefficient of friction of the end-product TiN bulk sample was measured and found to be 0.35. Keywords
FE-SEM, FETEM, gas-solid reaction, high-energy ball milling, nondestructive test
1. Introduction Owing to its high hardness, stability at high temperatures, chemical inertness, corrosion resistance, excellent thermal conductivity, and electrical and optical properties, TiN has become a desirable material for tremendous advanced applications in different areas (Ref 1-3). The nanocrystalline powder form of TiN can be used as wear-resistance surface protective coating for cutting and machinery tools and for solar control films, and it is also a potential candidate for fusion reactors (Ref 4). Different routes can be used to prepare TiN such as a sol-gel approach (Ref 5), direct reaction of TiCl4 with ammonia (Ref 6), activated reactive evaporation (Ref 7), a self-propagating combustion method under high nitrogen pressure and high temperature (Ref 8). Chemical vapor deposition (CVD) can also be used to prepare TiN by reacting the TiCl4 with ammonia at temperatures above 1000 °C (Ref 2). In addition, the lowtemperature physical vapor deposition (PVD) approach allows the deposition of TiN on metallized wafers (Ref 2). The high
M. Sherif El-Eskandarany, Nanotechnology and Advanced Materials Program, Energy and Building Research Center, Kuwait Institute for Scientific Research, 13109 Safat, Kuwait. Contact e-mails: msher
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