Avaliação mecânica e microestrutural pós forjamento da liga de níquel 718 com adição de ítrio

Abstract

The influence of Y addition on the microstructural and mechanical properties of the alloy 718 was examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and tensile tests. Two alloys with nominal yttrium contents of 0.1% and 1% in weight and a reference alloy with no yttrium addition were melted, forged, solubilized and aged. It was observed that an initial Y addition, after melted, led to a final Y content of 50 and 60%. The Yttrium addition decrease the oxygen, nitrogen and sulfur contents. The low-Y alloy presented an increase of the grain size, while the high-Y alloy presented a refined grain size due to the intense precipitation of second phase particles. The microstructural analysis also revealed that the yttrium promoted carbide fragmentation. The Ni19Y2 and Y2O3 phases were evidenced in the low-Y alloy, while in the high-Y alloy, Ni17Y2, Y2S3 and Y2O3 phases were observed. Concerning the influence of the Y addition on the mechanical properties, it was observed that there is an optimal yttrium value addition. The low-Y alloy showed improved ductility and no relevant variation to strength, both in solubilized and aged conditions. However, the high-Y alloy, despite increased strength, there was a significant weakening of the alloy, influenced by the massive second phase precipitation.