Microstructure, texture evolution and mechanical properties of pure Ti by friction stir processing with slow rotation speed.

Abstract The microstructure and texture characteristics of commercial pure Ti after friction stir processing (FSP) with a slow rotation speed were studied. The shoulder friction zone (SFZ) which did not exist in the FSPed pure Ti with normal rotation speed (> 250 rpm) was observed in the sample treated with a slow rotation speed of 180 rpm. The texture of SFZ in the pure Ti was affected by shear stress from the shoulder of stir tool and the c-axes of the grains in this zone were nearly parallel to the processing direction. While crystallographic texture in the normal stir zone (SZ) were nearly perpendicular to the processing direction. The maximum depth of SFZ in the sample with 180 rpm was 1.2 mm, which decreased with the increased rotation speed until it disappeared. The grains in the SZ of specimen following FSP at a slow rotation speed were fine and homogeneous. The microhardness increased from 150.2 HV to 191.6 HV after FSP at 180 rpm. The microhardness trends were related to grain sizes, work hardening and texture evolution. The slow rotation speed processed alloy boosted the yield strength by 71.7% after the FSP. Highlights • Shoulder friction zone of pure Ti formed during FSP with a slow rotation speed. • Texture was not uniform in the thickness direction of FSPed pure Ti processed with a slow rotation speed. • Grain size decreased and microstructure homogeneity in thickness increased in pure Ti by FSP with a slow rotation speed. • Mechanical properties of pure Ti were developed after FSP with a slow rotation speed. [ABSTRACT FROM AUTHOR]