Investigation into plastic damage behavior of the CO2 laser deep penetration welded joint for Ti–6Al–4V alloy

There are great nonlinear gradient distributions of microstructures in CO2 laser deep penetration welded joints of Ti–6Al–4V alloy. Although there are great developments on the damage behavior of titanium alloy, there is a few to investigate the plastic damage behavior of the laser welded joint with heterogeneous microstructures. In order to understand the effects of nonlinear microstructures on the plastic damage behavior of CO2 laser deep penetration welded joint, a multi-specimen tensile method by measuring the microvoid density was applied to estimate the plastic damage behavior for Ti–6Al–4V alloy. The damage mechanism presents the pattern of microvoid nucleation, growth and coalescence. The microvoid density under different loading has a great relationship with the gradient distribution of microstructure in the welded joint. The growth rate of microvoids in the weld metal, heat affected zone and base metal is also related to the loads. When the load is lower, the damage in the weld metal is larger than that in the heat affected zone and base metal, and when the load is higher, the growth rate of the microvoid in heat affected zone and base metal is higher than that in weld metal. The grain size in weld metal has small effects on plastic damage, but the great gradient of the grain size in heat affected zone may delay the plastic damage evolution.