Strain rate sensitivity and Hall-Petch behavior of ultrafine-grained gold wires

The strain rate sensitivity and Hall-Petch behavior of ultrafine-grained gold (Au) wires were evaluated and compared to results outlined in a similar study conducted on both coarse and ultrafine-grained Au films by Emery [R.D. Emery, G.L. Povirk, Acta Mater. 51 (2003) 2067; R.D. Emery, G.L. Povirk, Acta Mater. 51 (2003) 2079]. The results showed that the strain rate sensitivity (m) of fine-grained Au films is ∼ 0.2, whereas coarse-grained Au films are strain-rate insensitive. In comparison, fine-grained Au wires have a weak m of only 0.02. The Hall-Petch coefficient (k) of Au wires range between 0.02 and 0.06 MPa m1/2, while the k value of Au film is higher (k ∼ 0.25 MPa m1/2). These results imply that Au films have a larger strength contribution from the grain boundaries than wires. Addition of calcium in Au wires does not change m, but increases the k value. The difference in k could possibly be attributed to the ability of Ca to increase dislocation density along the grain boundaries.