Strength and fracture of tensile Ti49.8Ni50.2 alloy specimens after isothermal abc forging

Abstract

The study explores the effect of grain-subgrain structure refinement in Ti49.8Ni50.2 alloy subjected to isothermal abc (multiaxial) forging on its tensile strength and fracture behavior in tensile tests. It is found that the size reduction of grain-subgrain structure elements down to ∼1 µm does not affect the tensile strength value and the type of fracture surfaces. This is probably explained by the formation of a critical dislocation-disclination microstructure during tension. The tensile strain value before the critical microstructure formation is determined by the microstructure produced by abc forging. The magnitude of internal stresses in the presence of the critical microstructure is independent of the degree of abc deformation. The internal stresses induce the formation of stable incipient cracks in specimens and macroscopic strain localization with necking at approximately the same external stress for all specified degrees of abc deformation, which can be due to the presence of second phase particles in the specimens. The tensile fracture of the specimens occurs by nucleation and growth of voids in their bulk, which further coalesce and form a main crack.