Abstract: When the diameter (D) and grain size (d) of fibers are of the same order of magnitude, size variations may have an unexpected impact on their cyclic performance. In this study, CoCrFeNi high-entropy alloy fibers with different D and d were fabricated and then tested under monotonic and tension-tension cyclic loading (R = 0.1). For the case of D/d < 10, both smaller diameters and larger grain sizes largely deteriorate the cyclic performance of the fibers, which can be mainly attributed to the weakened monotonic tensile properties caused by the increased surface grain fraction. The shortened crack propagation path and more serious strain localization make thinner fibers more sensitive to stress variations during cyclic deformation. In addition, fibers undergo fatigue and ratcheting damage in accordance with the tension-tension cyclic loading. The findings may offer theoretical guidance for the dimensional design and dependable service of microscale components.

Key words: High-entropy alloys, Fibers, Cyclic loading, Fatigue behavior