Evaluation of Microdefects in Thermal Sprayed Alumina Coating by X-ray CT at SPring-8

In recent years, three-dimensional inspection of internal defects using X-ray CT method has become popular. This technology is characterized by its ability to nondestructively acquire three-dimensional images, enabling three-dimensional observation of the internal structure of materials. Quality control of thermal spray coatings is performed by measuring the coating hardness and observing the coating structure so on. There are several methods for measuring porosity in coating, but the measurement conditions affect the results in the method with binarized image processing. Evaluation of microdefects in thermal spray coatings by X-ray CT would be very useful for quality control, but there are few studies on this subject. <BR>In this study, alumina coatings deposited by plasma spraying were evaluated using an X-ray CT system at BL20B2 in SPring-8 synchrotron radiation facility. As a result, clear reconstructed images were obtained, and small pore-like structures were observed. The images of the cortex showed uneven black-and-white contrast. This was thought to be due to pores and unjoined areas between the layers in coating. The linear absorption coefficient map showed locally elevated areas, possibly due to unmelted particles in the coating. X-ray CT at a synchrotron radiation facility may be able to evaluate microdefects in thermal sprayed coatings.