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The ASTM Test for Adhesion or Cohesive Strength of Flame-Sprayed Coatings (C 633-69) is a bond test consisting of coating a flat end face of a 2.5-cm-diameter rod of substrate material, attaching this coating with an epoxy adhesive to the face of another rod, and subjecting the assembly to tensile load normal to the plane of the coating. Flame-sprayed coatings include wire, rod, or powder sprayed by combustion flame, plasma spray, arc gun, and detonation processes. Bond strengths of such coatings range from about 0.05 N/m2 to greater than 0.7 N/m2. A problem with the test method is a tendency for some adhesives to penetrate the porosity of these coatings and thereby influence strength results. An attempt to determine adhesive penetration by testing different thicknesses of coating is described. Tests of bond strength versus thickness of the thinner coatings gave erratic results. To avoid penetration the procedures require a coating thickness minimum of 0.4 mm, and there is a list of recommended adhesives in the standard method. Other related test procedures, as well as round-robin testing which led to the prescribed procedures of ASTM Method C 633-69, also will be described.
adhesion, coatings, cohesion, bonding strength, adhesive strength, epoxy, flame spray, plasma spray
Manager, R&D Department, METCO Inc., Westbury, N.Y.