Mechanical behavior and fracture mechanisms of titanium alloy welded joints made by pulsed laser beam welding

Component parts made of a commercial two-phase alpha + beta Ti-6Al-4V alloy can be assembled by Nd:YAG pulsed laser beam welding. Welding processes are known to result in strong heterogeneities, i.e. strength mismatch and residual stresses and are also accompanied by a great variety of flaws, which is why the failure behavior of welded joints is still difficult to predict. The present work aims at gaining insights into the mechanical behavior of Ti-6Al-4V welds and also investigates the effect of defects such as the welding joint/weld root misalignment and pore size distribution. Comprehensive metallurgical analyses in the weld region are first carried on on the basis of optical, X-ray diffraction and SEM analyses. Then, the overmatch is highlighted from hardness measurements of a weld cross section. Next, tensile testing of both the base metal and fusion zone are performed. The tensile specimens are taken along and parallel to a partial penetration weld and also in the base metal. Two different thicknesses are chosen for weld embedding specimens, respectively 1.5mm and 2.5mm The latter one embeds the notch coming from the partial penetration. Tensile tests displayed a slight overmatch, which effect is underlined by digital image correlation on transversal 1.5mm tensile specimens. Nevertheless, high-speed camera data acquisition revealed that such a slight overmatch was not sufficient to prevent the occurrence of plasticity within the weld in the case of the 2.5mm tensile specimens. It also highlighted the influence of plasticity on the crack path, which tends to bifurcate from the hardest to the softest area. Further aspects of the weld structure and mechanical behavior heterogeneities are finally discussed. Copyright (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license.