Effect of Cold Deformation on Microstructure and Mechanical Behavior of Commercially Pure Grade 4 Titanium Strip

Abstract

The microstructure and mechanical behavior of commercially pure grade 4 (Gr.4) titanium strips with different deformations were studied by optical microscope (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), uniaxial tensile test, and hardness test. The work-hardening characteristics of a Gr.4 strip were analyzed with a true-stress–strain curve. The results show that cold deformation can significantly improve the strength and hardness of a commercially pure titanium Gr.4 strip, which has significant work hardening characteristics. With the increase in deformation amount, the grain is stretched into a fibrous shape along the longitudinal direction, while the strength and hardness increase and the plasticity decreases. Moreover, there is a significant linear relationship between the tensile strength and hardness. The true-stress–true-strain curves of a Gr.4 strip in different states were analyzed by combining three hardening models. It was found that the true-stress–true-strain curve of an annealed Gr.4 strip can be regressed by the Ludwigson, Voce, and Swift models, the Ludwigson model has a higher fitting accuracy, and the fitting results of the tensile true-stress–true-strain curves of Gr.4 strips after cold deformation hardening are not ideal. The cold deformation mechanism of a Gr.4 strip is mainly based on slippage, with an increase in dislocation density and dislocation tanglement leading to work-hardening behavior during cold deformation.