No abstract

In this study, the optimal process parameters for a high-velocity oxygen fuel spray, which was used to deposit WC-12Co coating on a 16Mn steel substrate, were studied to simultaneously improve the microhardness, adhesion strength, and porosity of the coating. To this end, trial tests were conducted to determine the feasible ranges of the spray parameters: powder feed rate ( A), spray distance ( B), and oxygen/propane mixture ratio ( C). Taguchi orthogonal array (L9) experimental design was used to determine regression formulae for the microhardness, adhesion strength, and porosity. Then, based on a method using the multiple regression-based weighted signal-to-noise ratio, the optimal spray parameters were identified. To verify the optimization results, confirmation experiments were carried out. An analysis of variance was also conducted to check the proportion of contribution of the spray parameters on the output quality characteristics. The confirmation test results proved that the predicted and measured results were in good agreement. The optimal conditions of the high-velocity oxygen fuel spray were: A = 32 g/min, B = 0.35 m, and C = 5. The estimated optimal coating properties were: microhardness = 1335.784 HV, adhesion strength = 64.659 MPa, and porosity = 1.797%. The oxygen/propane ratio showed the highest contribution to the microhardness, whereas the most influential factor for both adhesion strength and porosity was the spraying distance.

Research in building materials has increasingly been focused upon procedures for service life prediction. For coatings, improved service life prediction will aid in the effective selection and use of materials and in the development of cost-effective maintenance strategies. However, quantitative measures of degradation are essential in predicting service life. Standard procedures are available to quantitatively measure small changes in the appearance properties of coatings, one of the two primary functions of coatings, the other being protection. However, quantitative measurements of early changes associated with the protective function usually are not possible. Hence, the objective of this report is to ascertain, based upon the literature, whether changes in appearance properties of coatings can be used to predict changes in the protective properties of the film. It was concluded, that for the most part, changes in appearance properties are not related to changes in the protective properties of a coating film.