Peel strength of thermal sprayed coatings

Abstract

For the thermal spray industry to progress, informative and reliable coating evaluation techniques are needed. Measurement of adhesion is an important function, and existing tests have severe limitations. The peel adhesion test (PAT) was adapted to thermal spray coatings (TSC) from the adhesives industry. In this test, a thin metal foil is coated by thermal spraying. The foil is then peeled off the coating at a constant speed. The force required for separation is monitored as a function of crack position. The force is than converted into a peel strength that is equivalent to the energy required for separation. The adhesion of a range of different TSCs was measured in the form of spray pattern profiles and uniform coatings. Results were compared with the ASTM standard for TSC adhesion measurement, the expected range of interface toughness, and the Vickers hardness of the coating. Comparisons indicate that the PAT is self consistent, and it produces results comparable to other toughness measurements. The peel test was used to determine interface toughness in the range of 10 to 60 J/m2 for ceramic coatings, 150 to 250 J/m2 for cermet coatings, and 160 to 300 J/m2 for metal coatings.