Efeitos do gás de proteção e da espessura do substrato na usinabilidade de revestimentos de Inconel® 625 soldados pelo processo MIG/MAG

Abstract

Inconel® 625 alloy is considered a nickel-based superalloy, very resistant to corrosion and difficult to machine due to its high degree of hardening and low thermal conductivity. Commercially, the main disadvantage of Inconel® 625 is its high cost and for this reason, research is increasingly advancing in the use of this alloy as a coating on a less noble substrate. In this research, the MIG/MAG (Metal Inert Gas/Metal Active Gas) welding process was used due to its ease of operation, automation and productivity. However, as many applications require machining after the deposition of the coating, a greater knowledge about its machinability is fundamental for the wider use of Inconel®. The interaction between the tool and the workpiece in the machining process of nickel superalloys causes severe plastic deformation in the workpiece, which, together with the low thermal conductivity of the material, generates high temperatures and cutting forces. Thus, the main purpose of this work is to evaluate the machining forces in coatings of Inconel® 625 welded by the MIG/MAG process and the effects that microstructure and dilution cause in the machinability of the weld overlays. For that, it was evaluated how the shielding gas and substrate thickness affect the microstructure, dilution, microhardness, roughness, machining forces and wear on cutting tools. The coatings were evaluated by measuring the cooling rate through thermocouples, dilution through Image J software, analyzing the microstructure through SEM/EDS (Scanning Electron Microscope/Energy Dispersive Spectroscopy) and X-ray diffraction (XRD), tracing microhardness profiles in the machining region, measuring the machining forces via signal acquisition system and LabVIEW® software, analyzing the types and mechanisms of wear found during the milling machining process and also measuring the surface roughness of the samples after machined. The results showed that cooling rates were higher in the plates welded with Ar + 25% He. Dilution was lower in the plates welded with Ar + 25% He. In the microstructure, a γ-Ni matrix with precipitated phases of Mo and Nb was identified. In the samples welded with Ar + 25% He obtained higher average machining forces. When compared in relation to the variation in substrate thickness, it is clear that in sheets welded with Ar + 25% He, the 9.5 mm thick samples had the highest average machining forces in relation to the 25.4 mm thick substrates. mm. The average microhardness and wear of the cutting tools were higher in samples welded with Ar + 25% He. The roughness values were independent of the shielding gas and substrate thickness variables. The addition of CO2 to the shielding gas, although it increases dilution, improves general machining conditions, thus obtaining lower machining forces during milling and consequently less wear on cutting tools, generally optimizing the entire process.