Study Damage And Cracking Of Plasma Sprayed Coating Using The Digital Image Correlation Method

Pores existing in the plasma sprayed coatings cause the properties of coatings lower than those of the correspondingly sintered materials. Therefore, the investigation on the damage and cracking of the coating not only has theoretical significance, but also provides the basis for the coating’s application. In this study, the fractures of plasma sprayed copper coatings and Yttria stabilized zirconia coatings (YSZ) are observed through using Scanning Electron Microscope (SEM) coupled with the in situ tensile test. The crack tip deformation field are calculated through using the digital image correlation (DIC) software system.The effect of different parameters of SEM on the deformation results by DIC method is investigated in the present study. The parameters include the imaging mode, scanning time, brightness and contrast. It shows that the calculation results based on the secondary electron imaging mode are less stable than that based on the back-scattering mode. The error of calculation is minimal in the present examining range when the scanning time is60s. Both brightness and contrast have effects on the gray distribution, and further affect the results of DIC. The images obtained at higher brightness and lower contrast have better correlation coefficient.Cracking behavior of the coatings partly depends on the porosity, while the latter is controlled by the plasma spraying parameters directly. The pore size characteristics of plasma sprayed copper coating and YSZ coating are observed by A high-resolution surface morphology instrument. The results show that the pore depth in the two kinds of coatings are predominantly in the size of submicron, occasionally there are some micron pore. Compared with the YSZ coating, the copper coating presents denser structure. The effect of spraying parameters on the pore distribution of YSZ coatings is also studies. It indicates that the the area and number of micron pores in YSZ coatings show increasing tendency with the decreasing in spraying current and spraying distance.Strain field at the crack tip is studied using the DIC software when Cu coating and YSZ coating are in situ tension under SEM.The result shows that with the increasing in loading force, butterfly-shaped plastic zone gradually emerges at the tip of crack in Cu coating. However, a micro-cracking district appears at the crack tip of YSZ ceramic coating. YSZ coating exhibits larger strain in the cracking process. The deformation behavior of the coatings is not only related with the nature of the material, but also related with the pore size in the coating.