The porosity assessment of thermal barrier coatings obtained by APS method

Purpose: The article presents the outline of methods and range of microstructural assessment of ceramic coatings, using the example of thermal barrier coatings. The major structural parameters describing the quality of the barrier layers have been characterised as well as the problems related to the correct metallographic specimen preparation and the methodology of their assessment. Design/methodology/approach: A procedure of porosity assessment, employing quantative metallographic principles and automatic image analysis has been propounded, together with types of quantitative parameters and methods of their application. Findings: It was found that the application of the quantitative metallographic methods combined with automatic image analysis can form an effective tool of both quantitative and qualitative assessment such parameters of structural ceramic layers as porosity. Research limitations/implications: This type of assessment enables obtaining more than just the absolute value of the porosity of the given area: it provides the means for determining a number of other quantitative parameters, e.g. the surface area of the pores, their elongation and shape together with the whole statistical analysis. Practical implications: The application of scanning microscopy, especially observation techniques such as BSE, BSETOPO or BSE3D enables a precise differentiation of the areas constituting pores from other artefacts. Originality/value: Description of procedure of porosity assessments in APS TBC system by use of the quantitative metallographic methods combined with automatic image analysis, and possibility of applications special techniques of scanning microscopy.