Mechanical Properties of Titanium Nitride Nanocomposites Produced by Chemical Precursor Synthesis Followed by High-P,T Treatment

We investigated the high-P,T annealing and mechanical properties of nanocomposite materials with a highly nitrided bulk composition close to Ti3N4. Amorphous solids were precipitated from solution by ammonolysis of metal dialkylamide precursors followed by heating at 400-700 degrees C in flowing NH3 to produce reddish-brown amorphous/nanocrystalline materials. The precursors were then densified at 2 GPa and 200-700 degrees C to form monolithic ceramics. There was no evidence for N-2 loss during the high-P,T treatment. Micro- and nanoindentation experiments indicate hardness values between 4-20 GPa for loads ranging between 0.005-3 N. Young's modulus values were measured to lie in the range 200-650 GPa. Palmqvist cracks determined from microindentation experiments indicate fracture toughness values between 2-4 MPa.m(1/2) similar to Si3N4, SiC and Al2O3. Significant variations in the hardness may be associated with the distribution of amorphous/crystalline regions and the very fine grained nature (similar to 3 nm grain sizes) of the crystalline component in these materials.