ISO 27307:2015 pdf download

ISO 27307:2015 pdf download.Thermal spraying一Evaluation of adhesion/cohesion of thermal sprayed ceramic coatings by transverse scratch testing
4 Principle
Scratch testing involves drawing an indenter of known geometry across a coating-substrate system. In this test, the indenter is of a known material, size, and geometry such as a Rockwell conical diamond indenter. Testing is performed over a given length under a constant load. If the coating is removed from the substrate, then the adhesion of the coating-substrate system can be evaluated and the adhesion level may be ranked against similar coating-substrate system combinations. If the failure occurs only in the thermal sprayed ceramic coating, it reveals the cohesion of coatings itself. In the case of no observed failure, the test load may be increased until the coating failure occurs. The various coating failure modes during scratch testing are shown in Annex A. During scratch testing, cracks can form as a result of the tensile stress induced behind indenter and these stresses could balance the compressive frictional stresses ahead. Crack formation can be detected by means of an acoustic emission (AE) sensor attached to the indenter holder of scratch testing machine. In addition, the tangential force between the indenter and test surface can be monitored to provide more information on the failure conditions. This tangential force, often incorrectly referred to as a frictional force, is the result of both friction between the indenter and the test specimen and the ploughing force required to deform the coating substrate system.
Set the scratch length to 2 mm to 3 mm and the indenter traverse speed to 0,1 mm min-1 to 10 mm min-1. Mount one of the previously prepared test samples rigidly in the sample holder and bring the diamond indenter, recommended tip radius of 20 μm, into contact with the substrate portion of the sample such that the scratch, of selected length, will lie perpendicular to the coating-substrate interface and will traverse the coating and end in the mounting medium. Scratch the sample using a constant normal load of 3 N. Lift the indenter, reposition the sample such that the next scratch will be made a minimum of 4 mm away from the previous one in order to avoid interaction of the stress fields from adjacent scratches, reposition the indenter as for the first scratch, and produce a second scratch. Repeat this procedures until the required number of scratches under the initial load have been produced, normally at least 5, changing test samples as necessary. Inspect the diamond to ensure that it is clean and free from debris and clean as necessary. Repeat the above procedure for constant normal loads of5 N, 10 N, 13 N, 15 N and 20 N (or more), inspecting the diamond and recleaning as necessary before each change of load, until all scratches under the highest load produce adhesive failure, as observed under an optical microscope with a magnification of 100:1. NOTE The need for at least 5 scratches to be made at each load is related to the heterogeneity of thermal sprayed ceramic coatings, which results in large variations in the response of the coating to scratch testing. Using an optical microscope, take images of each of the scratches, using a magnification of >100:1, ensuring that the substrate, coating and mounting medium are all in the field of view.