Analysis of the effect of bending, fatigue, erosion-corrosion and tensile stresses on HVOF coating of metallic surfaces
Al Fadhli, Hussain (2006) Analysis of the effect of bending, fatigue, erosion-corrosion and tensile stresses on HVOF coating of metallic surfaces. PhD thesis, Dublin City University.
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The aim of the present study was to evaluate the bending, fatigue, tensile stresses and erosion-coiTosion characteristics o f HVOF thermally sprayed Inconel-625 powder coatings when deposited on three different metallic surfaces: (a) plain stainless steel (SS), (b) spot-welded stainless steel (SW-SS), and (c) a composite surface o f stainless steel and carbon steel welded together (C-SS-CS) under three conditions: (i) surface as-coated, (ii) surface as-coated and subjected to aqueous static corrosion for two weeks, and (iii) surface as-coated and subjected to aqueous static corrosion for four weeks.
The predictions of the residual stresses generated during the deposition of the coating over the different metallic surfaces were also performed using analytical and numerical model studies. Validation o f the models was earned out by comparing the results to experimental data. The surface morphology and the elemental composition of the coatings before and after each test were examined using SEM and EDS techniques.
The results indicate that the presence of weld or having a composite substrate formed by two different materials does affect the residual stresses at the interface, as it lowers bending, tensile, fatigue strength and enhancing corrosion effect, as observed by the analytical and experimental analyses carried out in this research. Microscopic obseivation of the fractured surfaces showed that the cracks were formed at the interface between the coating and substrate material as well as within the coating. Presence of non-melted particles in the coating enhanced crack propagation and erosion rates. The presence o f oxides, namely AI2O3 at the interface between the coating and the substrate material left over from the surface preparation process also had an effect. Hence careful control is required when applying welds beneath surface coatings.
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