Vickers hardness properties of structural materials for superconducting magnet at cryogenic temperatures Original Research Article

In order to estimate the tribological properties of structural materials for superconducting magnet at cryogenic temperatures, we investigated Vickers hardness from 4.2 K in liquid helium to 293 K. The clear change of hardness property was obtained around 77 K. We considered that it would be caused by a transformation of the deformation mechanism from dislocation slip at higher temperature to deformation twinning at lower temperature from the thermal activation process. We also considered that the transition temperature changing hardness property was related to the intersection temperature at which slip stress became equal to twinning stress. The change of deformation mechanism was confirmed experimentally by changing the loading rate, and by the TEM observation of the indentation scar.