Modified tensile adhesion test for evaluation of interfacial toughness of HVOF sprayed coatings

Tensile adhesion test is widely used to evaluate the adhesion strength of coatings sprayed by High Velocity Oxy-Fuel (HVOF) technique. But there are two issues to be improved. Firstly, when the coatings have high adhesion strength, failure occurs in an adhesive layer, and secondary, the edge of a substrate is heavily deformed and rounded due to the high impact energy of sprayed particles. This deformation causes large scatter of adhesion test results. In this paper, a new technique to evaluate the interfacial fracture toughness has been proposed by introducing pre-crack at the interface of a conventional tensile adhesion test specimen. The asymptotic analytical formula was derived for interfacial toughness evaluation. Numerical analysis was also carried out for comparison. The difference between the numerical and the theoretical data was less than 5%. The developed procedure was applied for the SUS316 L steel coatings and the significant effects of the surface roughness and preheating temperature on adhesion strength were reconfirmed quantitatively.