The relation of material properties, residual stresses, and thermal and mechanical loadings to coating degradation in thermal barrier coatings and tungsten carbide thermal spray coatings

Thermal spray coatings (TSCs) are increasing in industrial applications. Further growth in the industry requires a better understanding of the relation between coating production procedures and in-service failure. This work investigates two types of TSCs: plasma sprayed yttria-stabilized zirconia thermal barrier coatings (TBCs) and high velocity oxy-fuel sprayed tungsten carbide (WC) coatings.; Residual stresses are inherent in thermal spray coatings and can influence in-service performance and life of the coatings. Therefore, the effective design and processing of thermal spray coatings requires knowledge about residual stress generation and the effect of residual stresses on life. The effect of spraying processes and in-service conditions on Young's modulus is investigated. Residual stresses were evaluated by the Modified Layer Removal Method. The Cantilever Beam Bending Method was used to determine Young's modulus.; TBCs were studied to evaluate the effects of (1) substrate temperature during processing, (2) coating powder silica content, and (3) air plasma spraying (APS) versus vacuum plasma spraying (VPS) in conjunction with post-processing thermal cycles (one hour at 1000{dollar}spcirc{dollar}C) on coating residual stresses and Young's modulus of the top coat.; Results show that a higher substrate processing temperature increases top coat compressive residual stress. The initial thermal cycles further increase the compressive residual stresses for both higher and lower substrate processing temperatures, but continued thermal cycling does not further change the residual stresses. A silica content of 1.0% increases the Young's modulus of the coating after ten thermal cycles. As-sprayed, there is no difference in residual stresses in the top coat due to 0.1% and a 1.0% silica content. After ten thermal cycles, the residual stresses increase the same amount for both silica contents. There is no difference in the residual stress in the top coat between APS and VPS methods after ten thermal cycles.; For the tungsten carbide coatings, this study compares the bending fatigue life of three types of WC coatings on 4130 steel to chrome plated 4130. All TSCs had fatigue lives equal to or longer than the chrome plated specimens. Certain levels of residual stress in the coating enhanced the fatigue life of specimens with TSCs.