Mechanical Properties of Cu+CuO Coatings Determined by Nanoindentation and Laugier Model

Nanoindentation-based fracture toughness measurements of three different materials based on copper oxide with a Berkovich indenter are fascinating topics in material science. The main purpose of this study was to calculate the fracture toughness in mode I (<i>K_Ic</i>) for three copper oxide coatings (Cu+CuO) deposited on a steel substrate by the DC magnetron sputtering method. The parameter <i>K_Ic</i> can be referred to as the critical load (P_critical), where the cracking process is initiated uncontrollably. The basic mechanical parameters, such as the hardness and Young's modulus of Cu+CuO coatings, were determined using a Berkovich nanoindenter operated with the continuous contact stiffness measurement (CSM) option. Structural observation was performed by scanning electron microscopy (Helios). Using the nanohardness tester from Anton Paar with a Berkovich diamond indenter with experimentally selected load allowed generation of visible and measurable cracks, which were necessary for <i>K_Ic</i> calculation. Crack lengths were measured by scanning electron microscopy (SEM Hitachi TM3000). The obtained results indicated that the values of hardness and Young's modulus of Cu+CuO coatings decreased as the power of the magnetron source and the fracture toughness coefficient increased. In the case of the presented study, the Laugier model was chosen for <i>K_Ic</i> determination.