An examination of class A to class M transition in Pb-9Sn and other alloys

Abstract

High-temperature creep has been studied in Pb-9Sn solid solution alloy at temperatures in the range 489 to 539 K and in the stress region of 3 × 1⁻⁶ to 4 x 10⁻⁵ G using double-shear type specimens. There are two distinct deformation regions in the plot of γvs τ: region II, at low stresses and the stress exponent being about 5, reveals the dislocation climb creep behavior; region I, at intermediate stresses and the stress exponentn being 3.5, is consistent with viscous-glide. It is shown here that inclusion of the appropriate diffusivities in lieu of Darken diffusivity in glide-controlled creep region (Cottrell-Jaswon interaction) and Herring diffusivity in climb-controlled region along with proper constant (B ≈ 6 × 10¹⁴) is adequate to bring Zn-40 Al alloy in line with other solid solution alloys. Importance of solute concentration, normalized stacking fault energy, temperature and diffusivities for climb and glide on transitional stress are also discussed.