Nanomechanical Testing of Gum Metal

“Gum Metal” is a newly developed β-Ti alloy that, in the cold-worked condition, has exceptional elastic elongation and high strength. The available evidence suggests that Gum Metal does not yield until the applied stress approaches the ideal strength, and then deforms by mechanisms that do not involve conventional crystal dislocations. To study its behavior, submicron-sized pillars of solution-treated and cold-worked Gum Metal were compressed in situ in a quantitative compression stage in a transmission electron microscope. Solution-treated specimens and half of the cold-worked specimens exhibited essentially monotonic hardening during compression, but with serrated load-deflection curves that included periodic partial relaxations of the stress. The other cold-worked specimens exhibited pronounced shear instability. These samples deformed by a stick-slip motion along a well-defined shear plane, with a serrated load-deflection curve demonstrating partial stress relaxation at each sliding event. The pattern of deformation is consistent with prior work showing deformation by the formation and growth of shear bands and faults in a matrix that is densely decorated with defects.