ON THE ORIGIN OF COMPRESSIVE STRESS IN PVD COATINGS - AN EXPLICATIVE MODEL

Compressive stress in hard plasma vapor deposition coatings - up to values of several gigapascals - is found to be strongly dependent on the process parameters, especially on the energy of ion bombardment on the growing film. Increasing energy usually causes increasing stress. Internal stress influences all other coating properties, e.g. adhesive strength, microhardness and wear resistance. A detailed knowledge of the origin of this stress is therefore of great significance, particularly for practical applications. Experimental work was performed with various coating and substrate materials and various coating processes (d.c. sputtering, r.f. sputtering, arc ion plating) to determine the interrelationships. The creation of internal stress can be explained by a phenomenological model describing the interaction of bombarding ions in the plasma and coating ions, whose mobility is restricted by their position on the substrate or previously deposited layers of the coating. The validity of the model is demonstrated by good agreement with experimental results for both crystalline and amorphous coatings.