Microstructural Evolution in Ti-5111 Friction Stir Weids

摘要

The microstructural evolution occurring during friction stir welding of a near-á titanium alloy, Ti-5111, has been examined by backscattered electron imaging and electron backscatter diffraction. The unaffected baseplate (BP) microstructure consists of millimeter-scale prior ? grains containing -100 ìm large colonies of aligned a laths, related to each other by a strain-accommodating Burgers orientation relationship. The a laths are separated by fine, 100 to 150-nm-thick, interlath ? ribs. A heat-affected zone (HAZ) is observed -1.5 to 2.5 mm from the tool surface, characterized by a thickening of the ? ribs and the formation of secondary a platelets within them closer to the tool.