Fe5Cu5V30Ti30Nb30 High-Entropy Alloy Films as Cr- and Al-Free Sensing Layers for Thin-Film Strain Gauges in High-Pressure Hydrogen

A Fe5Cu5V30Ti30Nb30 high-entropy alloy film was designed as a Cr- and Al-free metallic sensing layer for thin-film strain gauges in high-pressure hydrogen environments. CALPHAD calculations predicted a BCC/B2-type phase field, while XRD, EBSD and GIXRD results supported a BCC-type structure without direct confirmation of long-range B2 ordering. Fe5Cu5V30Ti30Nb30 films deposited on Si reference substrates at 150 and 300 W retained broad BCC-type diffraction features. The 300 W film showed a more continuous cross-sectional morphology, good metallic conductivity and a comparable nanomechanical response with slightly higher hardness. Device-level tests were then performed using Cr/AlN/Fe5Cu5V30Ti30Nb30 TFSGs on 316L stainless-steel substrates. The devices exhibited average absolute apparent zero shifts of 16.08 με in 12 MPa N2 and 17.79 με in 12 MPa H2, with an additional H2-associated apparent response of only 1.71 με. Static tensile tests in 12 MPa H2 confirmed a linear strain response with a gauge factor of 1.72 ± 0.01.