Cobalt/BSA co-regulation enables near-zero-stress and high-strength Ni-Co electrodeposits

Achieving near-zero internal stress without sacrificing strength remains a key challenge in Ni-based electroforming. Here, a Co/BSA co-regulation strategy is developed using benzenesulfonamide (BSA) as a dual-functional additive. Theoretical calculations and electrochemical measurements show that the benzene ring promotes interfacial adsorption, while activation of the sulfonamide group facilitates S incorporation, shifting the internal stress from tensile to compressive. Dynamic BSA adsorption suppresses lateral and through-thickness grain growth, promotes nucleation, and drives the transition from columnar grains to refined equiaxed grains. Meanwhile, facet-dependent BSA adsorption drives a concentration-dependent texture transition by shifting the deposition mode from grain-growth-dominated at low BSA concentrations to nucleation-dominated at high concentrations, favoring (200)- and (111)-oriented grains, respectively. The resulting texture evolution and S segregation cause a mismatch between the low-stress and high-hardness windows. To overcome this trade-off, Co is introduced for synergistic regulation. Co incorporation provides tensile-stress compensation and solid-solution strengthening, shifting the near-zero-stress state toward the high-strength region. Consequently, Co/BSA co-regulation enables the fabrication of near-zero-stress Ni-Co deposits with a hardness of 549.3 HV 0.1 and a tensile strength of 1598.2 MPa. This work provides a strategy for designing low-stress and high-strength electroformed Ni-based materials.