On May 12, 2020, the international standard ISO 23458:2020 "Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for determining thermal expansion coefficient and residual stress of CVD ceramic coatings," led by CTC, was officially released at ISO headquarters. The Chinese title is "Fine Ceramics (High-Performance Ceramics, High-Tech Ceramics) — Test Method for Thermal Expansion Coefficient and Residual Stress of CVD Ceramic Coatings." 

The international standard was proposed in May 2018 by Dr. Wan Detian of the Central Research Institute of CTC and successfully approved as a project in ISO/TC 206, the ISO technical committee for fine ceramics, through voting. Working group member countries included China, France, Austria, the United Kingdom, Italy, Japan, South Korea, Malaysia, and others. After more than two years, it went through multiple stages including NP, WD, CD, DIS, and FDIS. Through three international meeting discussions and dozens of email exchanges, the working group analyzed the feedback from peer experts and revised the standard text, ultimately gaining unanimous recognition.

The coefficient of thermal expansion is one of the important thermal properties of ceramic coatings, and its accurate evaluation is of great significance for coating design and application. At present, homogeneous bulk materials are mostly used for testing. However, due to differences in the preparation processes of the tested materials and the neglect of the influence of the substrate, the measured results have large errors. The technology in this standard adopts the relative method theoretical modeling proposed by Professor Bao Yiwang, Chief Scientist of CTC. The core innovation is the establishment of an analytical relationship for the thermal expansion coefficient of ceramic coatings among the substrate, composite body, and coating, and the creation of a "three-step method" testing technology: the first step is to test the substrate performance, the second step is to test the composite body performance, and the third step is to calculate the coating performance.

Residual stress is one of the most important mechanical parameters of ceramic coatings. It is not a material constant, and the residual stress of the coating measured on a small specimen cannot represent the residual stress of the coating on an actual component. How to accurately test the residual stress of coatings is extremely important for engineering applications and optimized design. Based on the preparation process of CVD ceramic coatings, a calculation formula and test method for the residual stress of coatings were established. The substrate sample and the composite body sample are placed on two parallel platforms to simultaneously test the thermal expansion coefficients of the two samples, thereby calculating the thermal expansion coefficient of the coating and further calculating the residual stress of the coating. This international standard is applicable to the evaluation of residual stress of coatings on components of any shape and size, solving the problem that the residual stress of ceramic coatings on in-service components could not be evaluated.

Based on the new technology of international standard ISO 23458, CTC signed a strategic cooperation agreement with the German company Linseis to turn the testing technology into equipment and promote its application globally. As a high-tech enterprise in the inspection and certification field, CTC has always attached great importance to international standardization work. The successful publication of this international standard has enhanced China's international discourse power, effectively improved the scientific and technological influence, innovation capability, and core competitiveness of CTC's testing services, and promoted the better and stronger future development of CTC.