Acoustic emission analysis of hard coatings cracking during indentation test

Hard coatings are widely used in industries where the good behaviours of surface properties play the main role in a life cycle of machine components. The main material characteristic of coatings which determines behaviour of surface is Hardness. In the past, Hardness of materials was considered to be the most important material property, which influences wear properties of coatings as well as value of maximal elastic tension needed for initiation of cracks. However, Adhesion of hard coatings depends on mechanical properties such as Young modulus E, hardness H and fracture toughness R. Initiation/Formation of fractures and their propagation in hard coatings is commonly investigated using indentation tests. Creation of Hard coating crack during indentation is usually detected as a wide frequency AE signal. In this article, the initiation of cracks is investigated using data measured during the indentation. The cracks formation/propagation and spalling in hard coatings during indentation were observed and quantified by using AE. AE frequency analysis was calculated from the signals measured during the indentation and it was evaluated from recorded AE signals.