Effect of yttrium addition on phase transformations in alloy 718

Abstract

The nickel-base alloy 718 is widely used due to its superior performance at high temperatures, combining properties such as high strength, high corrosion and oxidation resistances and good formability and weldability. Its properties can be further improved by controlled additions of alloying elements such as Ce, W, Mo, P, B and Y. The present work aims to evaluate the effect of the yttrium alloying on the phase transformation in alloy 718. Thermodynamic calculation, scanning electron microscopy, electron backscattered diffraction, hardness measurements and differential scanning calorimetry tests were conducted. The Ni17Y2 phase was observed in two situations: associated with the Nb-rich particles or as single particles. The addition of yttrium has a remarkable effect on grain size control. The differential scanning calorimetry tests indicated that the alloy with the high Y content showed earlier precipitation of the γ” phase (Ni3Nb), which is the main hardening contributor, resulting in an increase in hardness.