A Study of Speckle Materials for Digital Image Correlation (DIC): Thermal Stability and Color Change Mechanisms at High Temperatures

This study focused on the measurement requirements of Digital Image Correlation (DIC) in high-temperature environments of aero-engines and systematically investigated the applicability and stability of high-temperature speckle materials. Five common coating materials (Ti, TiN, Ta, NiCr alloy, and SiC) were selected. Corresponding thin films were deposited on Al2O3 ceramic substrates using magnetron sputtering technology, and their surface color evolution from room temperature up to 1200 °C was examined. The film compositions were analyzed by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), revealing the mechanisms behind the color changes. The results indicate that Ti, TiN, Ta, and NiCr alloy exhibit significant color variations, which leads to insufficient color contrast for high-temperature speckle patterns. Further investigation shows that depositing an outer SiO2 coating can improve surface scattering and reflection, while also inhibiting oxygen penetration, thereby enhancing oxidation resistance and improving speckle contrast. The SiC/SiO2 composite structure demonstrates excellent thermal stability, making it an ideal speckle material for high-temperature DIC measurements.