Notched Tensile Strength and Fatigue Crack Growth Behavior of Ti-6Al-6V-2Sn Laser Welds

Abstract

Notched tensile and fatigue crack growth tests were performed on Ti-6Al-6V-2Sn laser welds which were subjected to post-weld heat treatments (PWHTs) at various temperatures. In comparison with the mill-annealed base metal (BM), Ti-6Al-6V-2Sn laser welds showed notch brittleness at different degrees. Generally, the weld metal (WM) had a lower fatigue crack growth rates (FCGRs) than the BM. Fine acicular α distributed uniformly in the β matrix could account for the high hardness of the as-welded WM relative to the BM. With the PWHTs at higher temperatures, the coarsened microstructures of the welds reduced not only the hardness but also the sensitivity to notch brittleness. The fatigue fracture morphology of the WM was much rougher and irregular than that of the BM. A tortuous crack path in the WM as compared to the relatively straight path in the BM resulted in reduced FCGRs in the WM, particularly for the welds subjected to PWHTs at 704°C or higher.