Microstructure and wear performance of NiCr-B hardfacing on AISI 316L(N) stainless steel via Ar + CO ₂ shielded cold metal transfer

Hardfacing deposits of ER NiCr-B alloy were fabricated in single and double layer configurations on 12 mm thick AISI 316L(N) stainless steel substrate using the cold metal transfer process (CMT) with an 80% Ar + 20% CO ₂ shielding gas mixture. Microstructural analysis revealed that the precipitate (carbide and boride) fractions increased from 13.12% in the first layer to 17.84% in the second layer, yielding corresponding hardness values of ∼482 VHN and ∼602 VHN. Tribological performance of the hardface deposits was evaluated under a 2 N load across ambient, 25 °C-vacuum, and 550 °C-vacuum conditions. For the first layer deposit, friction coefficients of 0.62, 0.72, and 0.38 were observed in three different test conditions, with corresponding wear rates of 6.17 × 10 ⁻¹⁶ , 9.4 × 10 ⁻¹⁶ and 4.72 × 10 ⁻¹⁶  m ³ /N·m. The second layer deposit exhibited lower friction coefficients (0.58, 0.59, and 0.48) and reduced wear rates (2.44 × 10 ⁻¹⁶ , 2.95 × 10 ⁻¹⁶ , and 2.07 × 10 ⁻¹⁶  m ³ /N·m). Detailed investigation was performed using electron microscopy, Raman spectroscopy, and profilometry of the wear tracks . Wear mechanism in ambient condition was predominantly abrasive, whereas at 550 °C-vacuum condition adhesive wear was significant. At 25 °C-vacuum condition, wear was governed by both abrasive and adhesive mechanisms, characterized by highest wear rate. The results indicate that the addition of CO ₂ in the argon shielding gas promotes crack-free, low-dilution deposits with enhanced hardness and favorable wear resistance, emphasizing the effectiveness of CMT process for producing durable NiCr-B hardface deposits on stainless steel substrates.