Investigation On Oxidation And Ablation Testing Method And Mechanism Of Ultra-high Temperature Composites Based On In-situ Spectroscopic Technology

Ultra-high temperature composite materials are particularly suitable for hightemperature structural components in aerospace equipment,and these composite materials can be used in extreme environments such as high heat flux,high enthalpy,and high pressure.In the assessment of the service performance of high-temperature resistant composite materials,oxidation and phase transformation of the composite materials are important issues.Therefore,the study of the oxidation mechanism and thermodynamic ablation of composite materials is of great significance.Spectroscopic detection technology is an important method for studying the oxidation,phase transformation,and structural behavior of composite materials.It is widely used to determine the composition of oxidation products and measure residual stress of large-area coatings.In addition to offline detection after hightemperature treatment,in-situ spectroscopic technology allows monitoring of oxidation kinetics during processing and provides time-resolved information on structural changes during processing.This paper designs and constructs a high-temperature spectroscopic measurement system for in-situ spectroscopic detection of the oxidation and ablation process of high-temperature resistant composite materials.The system can be applied to various test platforms for the assessment of the service performance of high-temperature resistant composite materials,including combustion wind tunnels,plasma wind tunnels,oxygen-acetylene torches,and others.The spectroscopic measurement system is mainly composed of a high-temperature Raman spectroscopic measurement system and a laser-induced breakdown spectroscopic measurement system.The high-temperature Raman system successfully performed in-situ Raman spectroscopic measurements on samples subjected to 5 Mach airflow heating and over 2000 K high-temperature conditions in the hypersonic aerothermodynamics and thermomechanics testing chamber of the Center for Material Service at the University of Science and Technology Beijing.The laser-induced breakdown spectroscopic measurement system shares a laser as the excitation light source with the high-temperature Raman spectroscopic measurement system and can achieve synchronous measurements of Raman spectroscopy and LIBS during the high-temperature oxidation and ablation process of the material.Therefore,by combining the sample surface composition and phase detection of Raman with the deep element composition identification function of LIBS,the material’s oxidation and ablation process can be studied from multiple angles.This paper presents a series of methods for data processing and error suppression of the spectra obtained by high-temperature in-situ measurements.The methods include using reference light to correct the energy fluctuations to reducing the influence of laser energy instability caused by complex optical paths;using a combination of experimental measurements and blackbody radiation theory to subtract the thermal radiation background of high-temperature Raman spectra;theoretically deriving and calculating the influence of the instrument response function on Raman spectral peaks,and the intensity ratio between peaks with large and small linewidths will increase with the increase of the instrument spectral width.Therefore,for quantitative or semi-quantitative analysis of Raman,convolution fitting should be combined with the instrument response function.This paper uses the designed high-temperature spectroscopic measurement system to perform in-situ spectroscopic measurement and analysis of the ablation process of typical C/SiC and ZrB2-SiC composite materials.Through in-situ Raman spectroscopic analysis of the oxidation and ablation process of C/SiC composite materials,it is concluded that the oxidation process of SiC in a plasma environment is a combination of the process of SiC reacting with atomic oxygen to generate SiO2 and the process of SiO2 reacting with atomic oxygen being consumed.The different changes in the reaction rates of the two processes result in different ablation results.When the heating temperature increases,the process of SiO2 consumption becomes dominant,resulting in less SiO2 layer compared to when the temperature is low.When the SiO2 layer is completely consumed,the SiC surface temperature jumps and undergoes severe ablation.Meanwhile,based on this mechanism,when other external factors such as airflow scouring can also affect the state of the surface SiO2 layer,the critical temperature at which the temperature of SiC jumps will be changed.In addition,the oxidation process of ZrB2-SiC was studied by detecting the oxidation products of ZrB2 using a LIBS measurement system,and the measurement results of ZrB2 and ZrB2-SiC were compared to analyze the role of SiC in the composite system.