Experimental investigations for a postweld heat treatment on Ti-6Al-4V titanium welds with a defocused laser beam

¹ Université de Toulouse, LGP, ENIT/INPT, 47 Avenue d’Azereix, 65016 Tarbes, France
² Université de Toulouse, Institut CARNOT CIRIMAT, UPS/CNRS/INPT, ENSIACET, 4 allée Emile Monso, 31030 Toulouse France

Corresponding author : Jean-denis Beguin, jean-denis.beguin@enit.fr

Abstract

The purpose of this study is to apply a local heat treatment (LHT), in-situ, on the weld bead, using a defocused Yb: YAG laser beam on a continuous regime, in order to reduce residual stresses and decompose the brittle a’ martensite, into a lamellae and fine β phase. Laser scan experiments were firstly performed on a commercially pure titanium grade 2, with a wide range of parameters, in order to provide a “heat treatment window” without titanium melting. After optimization of the processing parameters, to obtain a sufficient width and depth for the scanning zone, experiments have been performed on a β-treated, fully martensitic Ti-6Al-4V sheet. For each processing experiments, the decomposition of a’, was studied based on metallographic cross sections. A local heating with a minimum energy density at 700 J.cm^-2, has a sufficient effect to destabilize a’, while for an energy density at 1000 J.cm^-2 , a diffusional transformation take place, with the formation of Widmanstätten microstructure. Finally, these optimized conditions were applied on a full penetration Ti-6Al-4V welds. The results of the LHT will be described in terms of the microstructural changes observed in the welded zone and hardness evolution.