A Laser Thermal Cycling Rig As a New Method to Characterize the Evolution of Coating Adhesion Under Thermal Cycle

Thermal sprayed coatings are often used for high temperature applications and, per se, are subjected to transient temperature gradients during operation.  The severe thermal cycles present in applications such as turbines, motors and chemical plants generate thermal stresses that damage the coating with time, and can even lead to its delamination. The most common method to evaluate coating thermal shock resistance is through a burner rig.  However, this technique involves thermal cycling in a combustion atmosphere, which might be non-representative of several applications.  Furthermore, the presence of a flame makes accurate measurement of the temperature profile difficult, and it cannot always match the high heating rates reached in service.  As a consequence, a versatile and robust method to evaluate coating resistance to spalling under thermal cycles is still to be found.  This paper presents the development of a thermal cycling rig where the heat input is supplied by a laser.  After the presentation of the rig design itself, preliminary results are shown regarding the temperature cycles achievable with the rig.  The variations in the adhesion of arc-sprayed metallic coatings subjected to thermal cycling are reported.  Finally, potential delamination identification methods are assessed and compared.