Microstructural factors determining mechanical properties of laser-welded Ti-4.5Al-2.5Cr-1.2Fe-0.1C alloy for use in next-generation aircraft

The complex microstructure of a high hot-workable α + β-type titanium alloy, Ti-4.5Al-2.5Cr-1.2Fe-0.1C with a continuously varying α phase in terms of its size, distribution, morphology, and crystal orientation from the welded zone to the matrix, including a trace amount of welding defect, was investigated by several microstructural and crystallographical analysis techniques such as optical microscopy, scanning electron microscopy, and X-ray diffraction to elucidate the crucial factors determining its mechanical properties such as tensile properties and fatigue etc. The alloy was processed with laser welding to prepare parts for use in next-generation aircraft. The tensile properties of welded samples exhibit a strength-ductility balance similar to that of non-welded sample. All the failures in these samples occur at their matrices because the hardness values of welded zone on the cross section perpendicular to loading direction of the welded samples are higher than that on the same plane of non-welded sample, which is related to crystal texture of α phase. However, the fatigue strengths of welded samples are lower than that of non-welded sample. Such the decrease in fatigue strength of welded samples is caused by the presence of pores formed during welding.