SYNTHESIS AND CHARACTERIZATION OF CHROMIUM BASED HARD COATINGS

Abstract

Hard coatings of transition metal nitride materials (TiN, CrN, TiSiN, CrSiN, etc) are used in tribological applications due to their remarkable physical and mechanical properties such as high hardness, high melting point, excellent wear resistance, chemical inertness, and good thermodynamic stability. Development of hard coatings with superior tribological properties, through various physical and chemical vapor deposition techniques, is ever growing to provide protection and extend service life of the equipments/components used in the actual engineering applications such as in machining and forming tools. The fabrication of transition metal nitride coatings such as CrN, CrSiN, and CrAIN with desirable microstructural characteristics in terms of grain size, crystallographic orientations, lattice defects, and surface morphology as well as phase composition is very important in realizing the improved tribological properties hitherto unachieved in the literature. It- is possible only through the thorough understanding of the influence of process variables, in the physical/chemical vapor deposition techniques, used for the fabrication of hard coatings. Although literature is available on sputter deposited Cr based transition metal nitride coatings, there is no single processing window with the optimized process conditions for achieving the desired microstructural morphology of the hard coatings, probably due to ' their high sensitivity/complexity of the environmental factors manifested in the vacuum chamber employed in various physical vapor deposition techniques. Therefore, it is essential to investigate the influence of sputtering process parameters for achieving the desirable microstructural characteristics with enhanced tribological properties in Cr based metal nitrides coatings. The main objectives of the present work were i) To synthesize CrN, CrSiN, and CrAIN coatings on stainless steel and Si substrates by DC/RF magnetron sputtering technique, ii) To study the effect of various sputtering process parameters on the phase formation and microstructural characteristics of these coatings by XRD, FE-SEM/EDS, and AFM, and iii) To measure the mechanical and tribological properties of CrN, CrSiN, and CrAIN by microhardness, nanoindenter, and pin-on-disc tribotester, respectively. A detailed description of the present work is presented in seven Chapters and it is briefly discussed below. Chapter 1 gives an overview of hard coatings and nanostructured coatings. The growth mechanisms, structural properties of films, and mechanical properties of nanostructured