Microstructures and mechanical properties of ultrafine grained pure Ti produced by severe plastic deformation

Abstract

Microstructure evolution and mechanical behavior of ultrafine grained (UFG) commercially pure Ti produced by equal channel angular pressing (ECAP) were investigated. Repetitive pressings of the same sample were performed to six passes at 683 K, using the procedure designated as route Bc. After the sixth pass was finished, recrystallized grains were observed as similar as the fourth pass. The average size of the recrystallized grains was approximately 0.3 μm. The hardness value (Hv) continuously increases with decreasing grain size. The Hv values are in good agreement with the other experimental data of Ti produced by severe plastic deformation processes. The similar slop kH suggests that these microstructures have similar density of dislocations in the grains produced by the severe plastic deformation processes such as torsion straining, multiple forging, and ECAP. The grain size dependence of ky in the present samples is 7.9 \( MPa\sqrt m \). After six-pass ECAP, the ultimate tensile strength was increased by 60%. This is most likely due to considerable grain refinement through severe deformation by ECAP. The standard Hall–Petch relation for yield strength and hardness in the ECAPed Ti implies that the ECAPed Ti samples have similar texture and that the effect of grain size on strength may prevail over the effect of texture on the strength in Ti.