Effect of nitrogen on the microstructures and mechanical behavior of Ti-6Al-4 V alloy additively manufactured via tungsten inert gas welding

Using tungsten inert gas welding, a simple technique to additively construct single-channel multilayer Ti alloy (Ti-6Al-4V) was developed. In the manufacturing process, the flow rate of nitrogen is used to control the microstructure and composition of each individual layer. The use of nitrogen leads to the formation of TiN particles, whose amount increases with the flow rate of nitrogen. There is no significant difference in the elastic moduli among individual layers. Increasing the flow rate of nitrogen results in an increase in the compression strength of the individual layers and a decrease in the ductility of individual layers. The Vickers hardness increases gradually from 300 to 400 HV for the base metal to ∼1000 HV for the top layer of the Ti alloy, and the compressive strength of the Ti alloy reaches 1.92 GPa at a 1.5 L/min nitrogen flow rate. The technique developed in this work provides a feasible route to additively construct single-channel multilayer structures with spatial distributions of the composition and microstructures.