Improving the strength-ductility synergy and surface properties of NiFe ₂₉ Cr ₂₁ CuMo-based alloy laser welding subsequent deep cryogenic treatment and vacuum plasma WC ₂₀ Cr ₃ C ₂ Ni <sub>X</sub

The novel research work focused on enhancing the mechanical properties and joining strengths of laser welding (LW) procedures on a sample of NiFe29Cr21CuMo-based alloy. Moreover, the surface properties and microstructure were improved by vacuum plasma spraying the WC20Cr3C2NiX coating (vacuum plasma spray coating (VPSC)) and deep cryogenic treatment (DCT). Based on temperature, two DCTs (DCT-(L)–(H)) were carried out: −180°C and 250°C on twin boundaries structure, NiFeCr phase, CrMo structure, and µ-austenite lattice structure was observed of the inner surface layer. The plasma spray WC 20 Cr 3 C 2 NiX coating technology was used to improve the outer layer and residual stress. The DCT and VPSC process investigations using electron backscatter diffraction demonstrated unambiguously that the inner and outer surface layer of the µ′(Ni–Fe 2 Cr 3 ), Fe–CrC, β′-Fe 2 Cr 4 , CrCoMn structure, and twin boundary's structure were present. Heat inputs on plasma spray coating samples were more affected in the inner and outer surface layer to the formation of strong crystallographic NiCr phase, β′-Ni / Cr, and CrC/Mn structure. Moreover, the CrMn structure, Fe(AsO 4 ) phase, and NiFeBCr phase abruptly increased the hardness value of DCT-(L) samples of the outer surface. The DCT-(H)–VPSC method yielded a hardness value of 18% highly present. Peak profile investigation revealed the various ranges: 0 to −600 µm for LW + DCT-(H) coating samples, 225–350 µm for LW + DCT-(L) coating samples, and −100 to −200 µm for LW + DCT-(L)–(H) coating. Electrochemical analysis employing potential dynamic polarization was used to assess each sample's corrosion resistance. The corrosion resistance and surface characteristics of DCT and VPSC were superior.