ISO 23458:2020 pdf free
ISO 23458:2020 pdf free.Fine ceramics (advanced ceramics, advanced technical ceramics)
The deformation of a coated bar during heating or cooling involves two effect factors, i.e. thermal expansion coefficient and residual stress in the coating and the substrate. The thermal expansion coefficient is a material characteristic. However, the residual stresses in the coating are not only due to a material property but depend also on the size of the component and the cross-sectional area ratio of the coating and substrate.
The thermal expansion coefficient of CVD ceramic coatings is deduced by the relative method, i.e. it is related with the expansion coefficient of the substrate and the coefficient of the coated bar. Two types of test piece, a bar with CVD ceramic coating (composite) and a bar without coating (substrate), shall be used to measure the thermal expansion coefficient according to ISO 17139. After determining the elastic modulus of the substrate and coating, the thermal expansion coefficient of both the composite and the substrate are obtained. The thermal expansion coefficient of CVD ceramic coating shall then be calculated.
The sample length change and environment temperature are measured continuously at regular, frequent intervals during the imposed cycle. The residual stress of CVD ceramic coatings is usually generated due to the mismatch of thermal expansion coefficient between the coating and the substrate.
Based on the uniform strain model, geometric compatibility analysis and internal stress equilibrium, the residual stress calculation formula of CVD ceramic coatings is deduced by the relative method, which is a function of many factors including elastic modulus, expansion coefficient, configurations and temperature. After getting the thermal expansion coefficient of the coating, the residual stress of CVD ceramic coatings shall be calculated from elastic modulus, expansion coefficient, cross-sectional area ratio of the coating to substrate and the temperature during coating preparation.ISO 23458 pdf download.
