Hi sumant
Quote:I would like to know the test method to test the bond strength (bend test) of wire arc spray coatings.
For tensile bond strength testing you need to follow ASTM C633.
The simple bend test is not quantitative, nor is it a direct measure of bond strength. The results of a bend test are also effected by coating strength, ductility, thickness, shear strength etc. Example: flame sprayed zinc coating ~750 psi bond strength passes bend test, plasma sprayed WC/Co ~11000 psi bond strength fails very similar bend test (not to say WC/Co normally fails
just in this particular case).
The simple bend test has an advantage in that it is quick and easy to perform. Ideal for thermal spray operators to perform to assess their own work and equipment set-up. It is a very qualitative test of general coating quality and to be of any meaning, needs to be set-up as a comparative test (against a known standard coating) for one coating type under very strict conditions of testing. Test piece thickness, coating thickness, angle of bend and coating type are factors that can dramatically effect results. These obviously need very tight control for the test to have any real qualitative meaning.
The simple bend test tends to be going out of favour, as it is seen to be superfluous, when other more quantitative testing is also employed.
A typical bend test set-up would be:
Test piece - 75 x 50 x 0.125 mm
Coating thickness - 0.15 (+/- 0.025) mm
Mandrel - 12.5 mm
Bend angle - 90 degrees (coating on outside of bend)
But really all the above can be changed to suit the circumstances. For instance the test piece could be bent to a point where a certain amount of failure is observed and the angle recorded. Thicker test piece, thicker coating, smaller mandrel, larger angle will all make the test more aggressive.
Quote:It is 1.00 mm thk SS 316L coating on carbon steel. Is bond coat required? (In case of bend test, coating on inner face or outer face?)
I would say a bond coat is advisable for the job. Bend test thin 316 coating only though, as this really can only be used to qualify equipment set-up/operator and not the coating on the job. Coating on outer face of bend during bend test.
Hope that helps
Interesting topic. Does anybody use this test method? Any views on the value of using this test?