TEM study on chromium nitride coatings deposited by reactive sputter method

Chromium nitride coatings are deposited on stainless steel under different nitrogen pressures by means of the reactive sputtering method. The coatings are investigated using transmission electron microscopy (TEM) and X-ray diffraction. Crystal structure of the coating changes from hexagonal Cr2N to cubic CrN with increasing nitrogen content. The Cr2N and CrN phases grow from substrate along the normal direction of (101¯1) plane forming dendritic structure and of (001) plane forming columnar structure, respectively. Lattice constants of Cr2N phase are analyzed to be a hexagonal structure with lattice constants of 0.28 nm (a-axis) and 0.44 nm (c-axis) and depend upon the nitrogen content. All coatings reveal very fine structure. The grains of Cr2N phase in the coating, which contains nitrogen below the stoichiometric composition of Cr2N (2/1 of Cr2N), are the tiniest ones among the coatings and randomly oriented in regard to normal axis of coating surface. Coating around the stoichiometric composition of Cr2N exhibits rather coarse structure and preferred orientation and it becomes fine structure with the increasing nitrogen content.