Avaliação do comportamento em corrosão e tribocorrosão de revestimentos de Inconel 625 depositados pelo processo de soldagem MIG/MAG.

Abstract

Inconel 625 is a nickel-based alloy highly resistant to corrosion at high temperatures. However, due to its high cost, it is commonly deposited onto a less noble substrate, particularly by welding processes. One of the most widely used welding processes in the industry is MIG/MAG (Metal Inert Gas/Metal Active Gas) due to its ease of operation, robotization and production capacity due to high current densities and continuous feed of filler material. However, this process promotes dilutions (mixing of the base material in the coating) above the dilutions promoted by the welding processes conventionally used for this purpose. Thus, this work has as proposal the analysis of the impact of heat input and thermal pulsing in MIG/MAG processes on the dilution, microstructure, corrosion resistance and tribocorrosion of the deposits. For this, welding overlays were produced with the MIG/MAG process in its conventional form by varying the heat input applied at three levels and also with the MIG/MAG-DP derivative process. The welding overlays were evaluated by measuring the dilution; analyzing the microstructure using optical microscopy (OM), electron microscopy (SEM) and X-ray diffraction (XRD); analyzing by cyclic potentiodynamic polarization corrosion test method at temperatures of 25 ° C and 60 ° C and reciprocating ball-ondisk tribocorrosion tests using potentiostatic polarization were carried out at temperatures of 25 ° C and 60 ° C and at passive and transpassive potentials. The results showed that the dilution of the welding overlays was not dependent directly on the value of the heat input, but also on the area and mode of application (continuous or pulsed). The resulting microstructure was typical of Inconel 625 and showed variations in the amount of the precipitates as a function of the applied heat and welding process. Corrosion resistance was temperature-dependent. Polarization tests at 25 °C showed an increase in corrosion resistance with increasing heat input, while at 60 °C no considerable influence of the heat input was observed. Comparing the processes, MIG/MAG-DP produced coatings less resistant to corrosion than MIG/MAG, independent of the temperature used in the test. For the tribocorrosion tests, the results showed that under lower corrosion severity conditions (passive potential and temperature of 25 ° C) the wear caused by the sliding movement induces corrosion due to the cyclic destruction of the passive layer. In the tribocorrosion tests under more severe corrosion conditions sliding had little influence on corrosion. The variations in the welding overlay parameters did not influence mass loss the in tribocorrosion tests.