Comparative study on microstructure and oxidation resistance of Inconel 625 superalloy coatings on 12CrMoV steel surfaces prepared by CMT and MIG cladding

Inconel 625 superalloy coatings were prepared on 12CrMoV steel plates by CMT process and MIG process respectively. The microstructures, the mechanical properties and oxidation resistance of the coatings were tested and analyzed. The results show that the heat input of CMT process is obviously lower than that of MIG process, and the forming quality of the coating is better, with smooth surface, no splash, no internal porosity and no other defects. The average weld penetration depth of CMT process coating is 0.51 mm and the dilution ratio is 6.8 %, which are much lower than that of the MIG process. Both coatings are mainly composed of coarse columnar crystals, however, the dendrites in the CMT process coating are finer and have better alignment consistency. The microstructure of two process coatings shows significant differences, and a large amount of Laves phase presents in the coating of the MIG process. The presence of Laves phase was not found in the coating of CMT process, but was replaced by element segregation region. In terms of mechanical properties, the CMT process coating has a higher hardness of about 221 HV and it is higher than the MIG process coating which is about 204 HV. Oxidation resistance testing of the coatings shows that the outer Cr₂O₃ film plays key role to the oxidation resistance. More compact and stable outer oxide film is formed in the oxidation process of the coating prepared by CMT process, which resulted in a better oxidation resistance.