Nitrogen Influence on Indentation Fracture Toughness of Stainless Steel Coatings

Abstract

This paper studies some aspects of coatings fracture theory and the possibility of extending Lawn’s equation from Vickers indenter geometry to the Rockwell one. Indentation tests were performed on stainless steel coatings deposited on 35.CD.4 steel substrate. The stainless steel coatings were nitrogen added in order to improve the fracture toughness. A comparison between different nitrogen concentrations has been made, based on the normal critical load at the first crack appearance. This load was very accurate measured with an acoustic emission state-of-the-art device, Vallen System AMSY4. Based on measured diameters of the ring cracks, the crack length was calculated. The normal critical load was precisely measured, due to acoustic emission method. Thus, it was calculated the fracture coefficient, K. A fracture pattern diagram as a function of normal load was plotted for stainlessnitrogen coating deposited on 35.CD.4 steel substrate.