Investigating the fatigue behavior of heavily-faulted nickel-based alloy thin films

Abstract

Coherent twin boundary (TB) is a planar defect that offers an ideal balance between strength and ductility in face-centered cubic (fcc) metals. However, albeit scant, it has been reported that specimens with high density of non-TB stacking faults (SFs) also exhibit unique mechanical behavior mediated by the interaction between SFs and dislocations. As an example, heavily-faulted nickel-molybdenum-tungsten (Ni-Mo-W) thin film has recently emerged as a promising structural material due to its exceptional uniaxial tensile strength. However, the practical reliability of a material depends heavily on its resilience against repeated cyclic loading. Therefore, this study delves into the fatigue properties of heavily-faulted Ni-Mo-W thin films prepared by direct-current (DC) sputter deposition. MEMS-fabricated freestanding thin films were subjected to tension-tension loading using a custom-built micro-mechanical tester. Ni-Mo-W thin films last much longer in the high cycle fatigue (HCF) regime compared to conventional nanocrystalline / nanotwinned films. Some conjectures are proposed to explain the hypothetical deformation mechanism that could not be lucidly substantiated in this study.