Structure Stability Study on a Newly Developed Nickel-Base Superalloy - Allvac 718Plus

Abstract

Recently a new Ni base superalloy to be used at 700°C has been developed by ATI Allvac designated as Allvac ® 718Plus TM .The critical criterion for this alloy is long time structure stability at 700°C that is closely related to the nature of phases and their stability in this alloy.In this study phase identification of 718Plus at as-heat treated and long-term thermal exposed conditions was conducted by various means.Phase prediction of 718Plus was calculated by Thermo-Calc software and the detailed phase identification was conducted by SEM, TEM, EDS, SAD and XRD.Quantitative determination of different phases were conducted by electrolytic phase isolation and followed by micro-chemical analyses.The results show that alloy 718Plus is predominantly γ' strengthened alloy with very good structure stability at 700°C.The formation of δ phase occurred during heat treatment and thermal exposure.A new phase Ni 3 Al 0.5 Nb 0.5 with HCP structure was found.The phase precipitation behavior in combination with good mechanical properties makes 718Plus a very good candidate superalloy to be used at 700°C.