Microstructure，properties and first principles calculation of titanium alloy/steel by Nd:YAG laser self-fluxing welding

The experiment of Nd:YAG pulsed laser self-fluxing welding for 304 stainless steel/Ti6Al4V titanium alloy dissimilar metal was carried out．The microstructure properties of welded joint were analyzed by SEM，EDS and XRD．The equilibrium lattice constants，enthalpies of formation，cohesive energies，mechanical properties，Debye temperatures and valence electron structures of Ti－Fe intermetallic compounds(IMCs)were calculated by the first principle pseudopotential plane wave method based on density functional theory(DFT)．According to the thermodynamic data of Ti－Fe－Cr compounds，the Gibbs free energy per mole of compound at different temperatures was calculated and their thermal stability was compared．The results show that there are no macroscopic cracks in the welded joints，and the IMCs distributed evenly along the welding interface exhibits 3 distinct layers of microstructure with different colors．The welds interface generates IMCs of TiFe，TiFe2and a small amount of Ti5Cr7Fe17IMCs．Ti－ Fe IMCs with high thermodynamic stability and easy alloying formation．The results of Gibbs free energies show that the sequence of precipitates in the interface is Ti5Cr7Fe17，TiFe2and TiFe in high temperature during the metallurgical reaction．The G/B values of Ti－ Fe IMCs are greater than the critical value of 0．5，indicating that it is an intrinsic brittleness．