Densification Kinetics and Structural Evolution During Microwave and Pressureless Sintering of 15 nm Titanium Nitride Powder

Microwave sintering (MWS) of commercially available 15-nm-size nanocrystalline TiN powder was studied. Densification kinetics and grain growth mechanisms of nano-TiN were evaluated using non-isothermal heating up to 1500 degrees C with variable heating rates. A true nanocrystalline ceramic with similar to 80-nm-size grains and 94.5 % theoretical density was obtained via MWS consolidation at 1400 degrees C. At higher temperatures, however, an uncontrolled grain growth and a formation of bimodal microstructure were noticed. A temperature dependence of grain growth suggested grain boundary sliding as a primary mechanism of densification below 1100-1200 degrees C. An activation energy of nano-TiN densification under MWS varied from 26 +/- 3 kJ/mol at the initial stage of sintering (900-1200 degrees C) to 162 +/- 22 kJ/mol at higher temperatures. In addition, a relationship coupling microstructural characteristics (grain size, grain boundary) with mechanical properties of titanium nitride ceramics obtained via both microwave and pressureless sintering techniques was discussed.