Measurement of Coefficient of Thermal Expansion of Metallic Materials from 20 to 150 K by Speckle Interferometry

The coefficient of thermal expansion (CTE) is a critical physical property of materials, especially in deep-space exploration, where precise determination of material properties is decisive for the performance and reliability of spacecraft, while traditional CTE measurement instruments face significant challenges in achieving CTE measurements below liquid nitrogen temperatures (< 77 K). This study developed a testing system for measuring the CTE of highly thermally conductive materials within the temperature range of 20 K to 150 K using the classical principle of speckle interferometry. The materials were cooled to cryogenic temperatures using a cryostat, and measurements were taken during the warming process as they returned to room temperature. This method completely eliminates the vibrations generated during the operation of cryostat, making it possible to acquire speckle images of the sample at low temperatures. Since the ESPI method directly measures the strain on the sample surface, it eliminates the need for instrument thermal expansion calibration using a reference sample. Detailed measurements were conducted on the two materials: brass and copper. To validate the accuracy and reliability of the developed system, comparative analysis was conducted between the CTE obtained in this study and those reported in other literature, as well as with the measurements from a commercial instrument within the overlapping temperature range. The results reveal that the maximum error of CTE for the above materials using the proposed setup is 2.68% and 4.40%, respectively, indicating good accuracy for engineering applications. Furthermore, the functionality of the proposed setup for measuring the ultra-low temperature CTE of thin-film materials was also validated.