Enhanced high-cycle fatigue behavior of electrodeposited nickel plates with optimized grain-size gradient structures

Gradient structures fabricated using plastic deformation methods have been demonstrated to exhibit excellent fatigue performances. However, achieving an optimal gradient structure remains challenging because of methodological limitations. In this study, nickel plates with varying grain-size gradient structures (GSs) were synthesized in a controllable manner via direct-current electrodeposition. Fatigue tests revealed that the GS samples, ranging from coarse grains (CGs, 4 μm) to nano-grains (NGs, 40 nm), exhibited higher fatigue strengths compared to the homogeneous CG sample. Detailed observations showed that cracks were initiated in the surface layers of the GS samples, while severe plastic deformation was mitigated, demonstrating a superior co-deformation capability. An optimized structure with a linear hardness gradient ranging from 2.3 to 3.4 GPa and grain sizes ranging from CGs to ultrafine grains (UFGs, 170 nm) led to a further enhanced fatigue performance, achieving a fatigue limit of 325 MPa and a fatigue ratio of 0.38. This improved performance was attributed to the ability of the structure to disperse cyclic deformation and suppress stress concentration. These findings highlight the potential of controllably synthesized grain-size gradient structures to enhance the high-cycle fatigue properties of nickel plates.