Modelling the Coupling Effects of Residual and Diffusion Induced Stresses on the Nucleation and Propagation of Circular Coating Blisters in the Presence of Coating Micro-cracks
Authors: Nazir, H., Khan, Z. and Stokes, K.
Journal: Surface Science Reports
Publisher: Elsevier
ISSN: 0167-5729
Abstract:This paper presents the delamination of coating bonded to the substrate under the condition in which coating with micro-cracks is subjected to compressive residual stress coupled with diffusion induced stress. The micro-cracks in coating provide passage for the corrosive specie towards the coating-substrate interface which in turn produces diffusion induced stress in the coating. The micro-cracks contract gradually with increasing compressive residual stress in coating due to thermal expansion mismatch which blocks the specie diffusion towards interface. This behaviour reduces the diffusion induced stress in the coating while the compressive residual stress is increasing. With the further increase in compressive residual stress, the micro-cracks reach to the point, where they cannot be constricted any further and high compressive residual stress causes the coating to buckle away from substrate producing delamination and therefore initiating blistering. Blistering causes the contracted micro-cracks to open wide again increasing diffusion induces stress along with high compressive residual stress. The high resultant stress in coating causes the blister to propagate in an axis-symmetric circular pattern. A two-part prediction model has been developed coupling thermodynamic concepts with solid mechanics concepts. The thermodynamic concepts involve the corrosive specie transport through micro-cracks under increasing compression, eventually causing blistering, while the fracture mechanics concepts are used to treat the blister growth as circular defect propagation. The influences of moduli ratio, thickness ratio, thermal mismatch ratio, poisson’s ratio and interface roughness on blister growth are discussed. Experiment is reported for blistering to allow visualisation of interface and to permit coupled (diffusion and residual) stresses in the coating over a full range of interest. The predictions from model show excellent, quantitative agreement with the experimental results. Furthermore, a comparative study with the existing blistering models is also carried out.
http://www.journals.elsevier.com/surface-science-reports
Source: Manual