Mechanical behavior and microstructural deformation mechanisms of Ti-6Al-4V helix springs under prolonged extreme cryogenic temperatures and constant loading

Abstract

The prolonged mechanical performance degradation and failure of elastic components in mechanical systems can pose significant safety risks and disrupt related operations. While helical compression springs' mechanical behavior and failure mechanisms at high temperatures have been well-studied, their mechanical properties and microstructural deformation mechanisms at extreme cryogenic temperatures remain largely unexplored. This paper conducts experiments to investigate the detailed mechanical properties and microstructural evolution of Ti-6Al-4V helix springs under such conditions. Initially, we examined the mechanical properties at cryogenic temperatures and compared them with those at high temperatures. It was observed that the logarithmic constitutive model applicable at high temperatures does not suitably describe the spring's mechanical behavior at cryogenic temperatures. At extremely low temperatures, the mechanical properties of the spring were enhanced. Furthermore, we characterized the microstructural deformation mechanisms using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), including twinning, slip activation, and dislocation evolution. The findings suggest that the deformation mechanism in Ti-6Al-4V springs under cryogenic conditions is predominantly governed by twinning and basal and prismatic slip. Due to the significant increase in the critical resolved shear stress (CRSS) of the pyramidal slip systems at cryogenic temperatures, these slip systems may not be activated during the deformation process. Additionally, the volume fraction of twinning shows a significant positive correlation with both cryogenic temperature and mechanical stress.