Effect of two-step solid solution on microstructure and δ phase precipitation of Inconel 718 alloy

Abstract

Inconel 718 is the most popular nickel-based superalloy and is extensively used in aerospace, automotive, and energy industries owing to its extraordinary thermomechanical properties. The effects of different two-step solid solution treatments on microstructure and δ phase precipitation of Inconel 718 alloy were studied, and the transformation mechanism from γ″ metastable phase to δ phase was clarified. The precipitates were statistically analyzed by X-ray diffractometry. The results show that the δ phase content firstly increased, and then decreased with the temperature of the second-step solid solution. The changes in microstructure and δ phase were studied by scanning electron microscopy and transmission electron microscopy. An intragranular δ phase formed in Inconel 718 alloy at the second-step solid solution temperature of 925°C, and its orientation relationship with γ matrix was determined as

[ \overline{1} 00 {]}_{\delta } / / [ 01 \overline{1} {]}_{\gamma }

\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$[\bar{1}00]_{\delta}//[01\bar{1}]_{\gamma}$$\end{document}

and (010)_δ//(111)_γ. Furthermore, the Vickers hardness of different heat treatment samples was measured, and the sample treated by second-step solid solution at 1010°C reached the maximum hardness of HV 446.84.

Keywords

Inconel 718 alloy / two-step solid solution treatment / δ phase / γ″–δ transformation

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