Mechanical Properties of Ball-milled Nanoand Microcrystalline (Nix Fe1-x)Al Alloys

Abstract

Compact nanocrystalline samples of (Ni x Fe 1-x )Al (x =0...1) alloys with grain sizes between 30 and 50nm were prepared by mechanical milling of master alloys and subsequent hot compaction. Grain sizes were determined by X-ray diffraction, using the Williamson-Hall method, and scanning electron microscopy. Controlled grain growth was achieved by annealing the samples. Mechanical properties were determined by compression tests at elevated temperatures and Vickers hardness measurements at room temperature. It is shown that there is a clear influence of grain size on Vickers hardness, H v , and flow stress, σ y . The grain size dependence of H v shows a Hall-Petch like behaviour. Grain size hardening is active at low temperatures in nanocrystalline NiAl (d 50 nm). At high temperatures, softening occurs which is explained by the onset of grain boundary sliding and diffusional creep.