Cracking behavior of AIP-coated metal nitrides under tensile stress

A series of metal nitrides (TiN, CrN and AITiN) were deposited by the ace-ion plating method onto AISI-304 stainless steel, and their cracking behavior under uni-axial external tensile stresswas investigated. The cracking initiation and propagation of the coating were observed in situwith an optical microscope during the tensile force loading. The strain of the as-deposited coating was evaluated by the iso-inclination X-ray diffraction method, and the actual strain of thecoating during the tensile test was calculated from the applied and initial strain of theas-deposited coating. The cracking density was measured in terms of the applied strain of thecoating during the tensile test. Coatings started to crack between 1.3 and 1.9 % of appliedstrain and 0.22 to 0.79 % of actual strain, depending on the coating material and depositioncondition. This suggests that the initial strain of the as-deposited coating has a significant effectin increasing the tensile fracture limit of coat ed material. Additional cross-sectional SEMobservations revealed that coatings with a poorly densified morphology tend to crack at a lowertensile stress, and the effect of the coating morphology is also suggested as a contributory factor.