Effect of thermocycling on the microstructure of Ti-6Al-4V alloy in simulated low Earth orbit space environment

The study of material damage and its physical mechanisms, the deep understanding of material performance degradation processes, and the improvement of key materials and devices used in a space environment are undoubtedly of critical scientific importance. This work investigated the mechanical properties and microstructures of the Ti-6Al-4V alloy subjected to thermocycling in a simulated low Earth orbit (LEO) space environment by using microhardness tests, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results revealed an initial increase in hardness with the number of cycles, followed by a subsequent decrease. After 300 thermal cycles, many cavities were formed at the two-phase interface of the Ti-6Al-4V alloy. The dominating structures were transformed into dislocation cell substructures of larger size. After 500 cycles, the central structures in the sample were subgrains evolving by dislocation cells, as well as intra-granular twins and jogs structures. The relationship between microstructural evolution and thermal fatigue in LEO space environment was discussed, which may help predict the fatigue damage of materials.