Laser beam welding of titanium nitride coated titanium using pulse-shaping

a new welding method which allows the assembly of two titanium nitride coated titanium parts is proposed. the welding procedure utilizes the possibility for pulse-shaping in order to change the energy distribution profile during the laser pulse. the pulse-shaping is composed of three elements: a) a short high power pulse for partial ablation at the surface; b) a long pulse for thermal penetration; and c) a quenching slope for enhanced weldability. the combination of these three elements produces crack-free welds. the weld microstructure is changed in comparison to normal welding, i.e. with a rectangular pulse, as the nitrogen and the microhardness are more homogenously distributed in the weld under pulse-shaping conditions. this laser pulse dissolves the tin layer and allows nitrogen to diffuse into the melt pool, also contributing to an enhanced weldability by providing suitable thermal conditions.