High-strength ultrafine-grained titanium 99.99 manufactured by large strain plastic working

Abstract

In this research, high-purity titanium (hp-Ti, 99.99 wt%) was subjected to a large strain via a cold plastic working process. To accumulate a relatively large plastic deformation in the workpiece, the hydrostatic extrusion (HE) technique was applied. The initial rod with a diameter of ∅50 mm was subjected to a multi-pass extrusion process, and, this way, rods with a diameter of ∅8 mm and ∅7 mm were obtained. In this paper, the results of an investigation of the structure and mechanical properties of the hp-Ti are presented. The size and shape of the grains of the as-received and extruded samples were examined, and an effective way of refining grain and strengthening hp-Ti using plastic working was demonstrated. Thanks to the process applied, an ultrafine-grained structure was obtained. In the transverse section, the average grain size determined by transmission electron microscopy was 117 nm on average. As a result of the extrusion, a significant increase in yield stress, tensile strength and microhardness was observed. Moreover, in this paper the overall potential of the HE technique was demonstrated. The results of this work confirm that it is possible to manufacture high-strength, ultrafine-grained high-purity titanium via cold plastic working.