Structure and mechanical properties of welded joints from alloy based on VTI-4 orthorhombic titanium aluminide produced by pulse laser welding

Abstract

Ti2AlNb-based alloys are promising materials for operation at high temperatures in aerospace industry. Meanwhile, the existing difficulties of weldability restrict opportunities of their application. This work is devoted to studies of welded joints from Ti2AlNb-based VTI-4 alloy, obtained using pulsed laser welding (PLW). The optimum PLW modes have been determined providing uniform faultless joint. The features of formation of external defects, internal pores, cracks and non-uniform penetration depth were detected depending on welding conditions. The main PLW parameters influencing on formation of welded joint are voltage and duration of laser pulse. It was demonstrated that at insufficient medium and high peak powers sawtooth seam roots and internal pores can be formed. However, at higher rates of energy input thermal hydraulic processes in welding bathe are violated, accompanied by metal splashing (spattering), heterogeneity of pulse imposition is observed. This leads to formation of cracks, higher porosity, heterogeneity of melting zone, and as a consequence, poor mechanical properties. Microstructure analysis of the welded joints obtained by means of PLW has demonstrated that the melting area is comprised of long dendritic grains of β phase, and the heat affected zone from two regions of β + α2 phases and β + α2 + O phases. Herewith, the achieved joint strength equals to ~80 % of the base metal produced using the optimum PLW mode.