Topography-engineered sputtered TiN precursor coatings for in situ particle dispersion and microstructural tailoring during laser welded 2205 duplex stainless steel

This study proposes a topography-engineered coating design strategy for regulating fusion-zone microstructure in laser-welded 2205 duplex stainless steel by utilizing sputtered TiN coating as active particle-precursor layer rather than conventional passive protective films. TiN coatings were deposited on substrates with two distinct initial surface topographies, producing a dense coating on the smooth substrate and a porous cauliflower-like coating on the rough substrate. During laser welding, both coatings were incorporated into the weld pool but exhibited distinct fragmentation behaviors. The dense TiN coating yielded predominantly coarse, flake-like residues, whereas the porous architecture underwent extensive disintegration into uniformly dispersed submicron particles. Despite comparable retained TiN area fractions, the mean feature size decreased from 713 ± 24 nm (dense) to 282 ± 15 nm (porous), corresponding a higher population of submicron TiN-derived particles. These differences in particle size and dispersion were associated with distinct solidification structures. Compared to the bare joint, the dense coating reduced the average grain size from 164.6 to 70.4 μm and elevated the austenite fraction from 13.2% to 19.4%; conversely, the porous precursor further refined the grains to 39.9 μm and promoted austenite reformation to 32.5%. Concurrently, the maximum texture intensity decreased from 6.51 to 1.77. Accordingly, the joint produced using the porous TiN precursor exhibited an improved balance of tensile strength, ductility, and corrosion resistance: ultimate tensile strength rose from 801 to 854 MPa, elongation increased from 14.8% to 19.4%, and corrosion current density decreased to 1.86 × 10 −8 A/cm 2 . The results establish a substrate-topography/coating-architecture/fragmentation/microstructure/property relationship for laser welding of duplex stainless steel.