The adhesion/cohesion of the coating was evaluated by the scratch test method, using a Revetest system (CSM Instruments SA, Switzerland) equipped with a H-270 diamond indentor (200μm diameter). Six scratch indentations were carried out under previously optimized conditions (linear progressive load mode 1–4N, 4Nmin−1). In order to aid in determination of location of spallation/delamination, an extended scratch length of 6mm was employed. The scratch tracks were subsequently observed by SEM to determine the locations of the first coating failure and to understand the nature of the coating failure. During the scratch tests, the loading force and penetration depth were recorded and their respective values were correlated with the observed failure locations. The surface roughness of the coating was evaluated using a surface roughness tester (TR200, Timegroup Inc.) according to ISO standard [29]. Due to the presence of the open porosity in the outer layer of the coating, a measurement length for determination of the roughness (Ra) of 0.8mm was used. In total, eight measurements were carried out in different directions.
