Realization of Enhanced Mechanical Properties of Solid-State Welded Ti Alloy with Commercial Purity

Abstract

In this study, we investigated the solid-state weldability of Ti alloys with commercial purity (grade 2). First, as a solid-state welding approach, we conducted friction welding at a rotation speed of 1600 rpm and a friction pressure of 15 kgf on rodtype specimens with a size of 15 mm (dia.) × 50 mm (length). Subsequently, the grain boundary characteristic distributions such as the grain size, shape, orientation, and misorientation angle of the welds were clarified by means of the electron backscatter diffraction method. To study the mechanical properties of the welds, we conducted Vickers microhardness and tensile tests. We found that the application of friction welding to Ti alloy led to a significantly refined grain size in the weld zone (0.84 μm) relative to that in the base material (11.4 μm), accompanied by an orientation change from <0001> in the base material to <2-1-10> in the weld zone. In addition, the mechanical properties of the welds were more enhanced than those of the base material: the microhardness and yield strength of the weld were approximately 20% and 2% higher, respectively, than those of base material. These enhanced mechanical properties are mainly due to grain refinement and orientation development during welding.