Strain Rate Sensitivity and Fatigue Properties of an Al-fe Nanocrystalline Alloy Produced by Cryogenic Ball Milling

Abstract

The tensile strength and fatigue properties of metals are strongly related to grain size. An Al-Fe alloy with 4.5% of iron was produced by cryogenic ball milling and subsequent compaction and extrusion. The material showed mean sub-grain size in the order of 100 nm. During room temperature tensile and nanoindentation tests (0.1-0.01 s −1 ) the material showed positive strain rate sensitivity. In all the strain rate conditions, the alloys exhibited high tensile strength higher than 1000 MPa. The fatigue properties and the fatigue crack grow rate were analysed in the present study and compared with those of an Al-Mg alloy with 4.5% of magnesium produced via the same route. An increase in fatigue endurance of the nanocrystalline alloys was recorded, in comparison with the common commercial aluminium alloys. This phenomenon was accompanied with pronounced reduction in Δ K th and an increase in fatigue crack growth rate. The morphology of fracture surfaces was examined by employing a FEGSEM microscope, leading to the explanation of the described behaviour.