Hall–Petch effect and strain gradient effect in the torsion of thin gold wires

Gold wires with diameters of 20 and 50 μm were annealed in the temperature range 330–750 °C to obtain different grain sizes. Torsion and tension experiments on these wires confirm that the Hall–Petch effect is stronger than the strain gradient effect in the small grain size region (below 5 μm). With the grain size becomes larger, the strain gradient effect is evident. We find that these two mechanisms are synergistic, and this interaction strongly depends upon the grain size.