Development Of Ultra-High Temperature Testing System For Mechanical Properties And Thermal Shock Experiments Of Conductive Ceramics

Ultra high temperature ceramics(UHTCs), such as diboride zirconium and diboride hafnium, have an extremely high melting point(>3000 °C), metal-like thermal and electrical conductivities, chemical stability, high resistance against oxidation and thermal shock as well as high rupture strength. Because of these properties, UHTCs are extensively used in molten metal crucibles, furnace electrodes, cutting tools, and thermal protection structures for leading edge parts on hypersonic reentry space vehicles.The experiments of UHTCs at ultra high temperature are crucial for the application of these materials and have been receiving increasing attention. A testing device with direct electrical-heating method was developed, and with this device, a series of tensile experiments and thermal shock experiments of Zr B2-Si C at ultra high temperatures were conducted. The main developments achieved in the research of the thesis are listed as follows:① An ultra high temperature testing system for the mechanical properties of UHTCs was developed. It consists of hardware part and software part. The hardware part includes vacuum system, mechanical part, colorimeter and camera assembly and actuator assembly. The vacuum system consisting of vacuum chamber, vacuum pump and filter offers vacuum or protective gas environment for testing; the mechanical part contains electrodes, grips and loading units; the colorimeter and camera assembly is used to measure temperature of the specimen and takes the pictures from the specimen surface for the strain analysis by digital image correlation(DIC) method. The device developed is compact, and has the advantages of good precision, high heating-rate, high testing efficiency, safety, energy saving, etc.② An integrated system is developed for the testing system. It was developed based on VB with the secondary development of the data acquisition card, which can collect the data from force and displacement transducers, galvanometer, colorimeter, and linear stepping motor, and help realizing the servo control of the heating and loading.③ A series of tensile experiments and thermal shock experiments of 2Zr B based UHTCs at ultrahigh temperatures were conducted. The constant current thermal shock, constant heating-rate thermal shock and the thermal shock of preloaded specimens at maximum temperature of 2400 °C were investigated. It shows the preload thermal shock accelerates remarkably the failure of the material.