Experimental study on atomic-scale strengthening mechanism of the â £B transition-metal nitrides

For deeply understanding on the atomic-scale strengthening mechanism of the ⅣB transition-metal nitrides, three groups of the ⅣB transition-metal nitrides TMN (TiN, ZrN, and HfN) films with different nitrogen contents were synthesized on the Si (100) substrates by enhanced magnetic filtering arc ion plating. The morphologies, microstructures, compositions, chemical states, residual stress, hardness and elastic modulus of as-deposited films were characterized by field emission scanning electron microscope, X-ray diffraction, X-ray photoelectron spectrometry, and Nanoindenter measurements. The results showed that TMNx films exhibited B1NaCl single-phase structure within the large composition ranges. The preferred orientation, thickness, grain size and residual stress of the TMNx films were kept constant at different nitrogen contents. Both nanohardness and elastic modulus first increased and then decreased with the increase of nitrogen content, reaching the peak at x around 0.82. The composition dependent hardness enhancement may be attributed to different atomic-scale chemical bonding states and electronic structures in this work, rather than conventional meso-scale factors, such as preferred orientation, grain size and residual stress.