Hierarchical microstructure strengthening in a single crystal high entropy superalloy

Yung-Ta Chen,Jien-Wei Yeh,Koji Kakehi,Hideyuki Murakami,An-Chou Yeh,Chen-Wei Li,Taisuke Sasaki,Yao-Jen Chang,Kazuhiro Hono

doi:10.1038/s41598-020-69257-8

Abstract

A hierarchical microstructure strengthened high entropy superalloy (HESA) with superior cost specific yield strength from room temperature up to 1,023 K is presented. By phase transformation pathway through metastability, HESA possesses a hierarchical microstructure containing a dispersion of nano size disordered FCC particles inside ordered L12 precipitates that are within the FCC matrix. The average tensile yield strength of HESA from room temperature to 1,023 K could be 120 MPa higher than that of advanced single crystal superalloy, while HESA could still exhibit an elongation greater than 20%. Furthermore, the cost specific yield strength of HESA can be 8 times that of some superalloys. A template for lighter, stronger, cheaper, and more ductile high temperature alloy is proposed.

Highlights

Concept of High Entropy Superalloys (HESA) has been adopted by Zhang et al.29, Ni45 − x(Fe, Co, Cr)40(Al, Ti)15Hfx based alloys were studied in as-cast condition; the tensile strength of these HESAs could reach 960 MPa at 1,023 K
After an additional heat treatment at 1,023 K for 20 h followed by water quenching, the HT-2 process caused the L 12 phase to grow from 143 to 153 nm in average and secondary L12 particles to coarsen into an average of 14 nm as shown in Fig. 1c; there were nano size particles appeared inside the cuboidal L12 precipitates
This article uniquely addresses the issue of high temperature tensile strength of high-entropy alloys (HEAs), especially the HESA in the HT-2 condition has performed exceptionally well comparing reported HEAs and advanced superalloys, Fig. 4

Summary

Introduction

Concept of HESA has been adopted by Zhang et al.29, Ni45 − x(Fe, Co, Cr)40(Al, Ti)15Hfx based alloys were studied in as-cast condition; the tensile strength of these HESAs could reach 960 MPa at 1,023 K. The HESA (HESA-327) of interest is shown in Table 1; it is a cast-type alloy with a density of 7.96 g/cm[3], comparing to advanced cast superalloys such as CMSX-430, the raw materials cost of this HESA was 84% cheaper due to the absence of Re element content. This HESA in directionally solidified form[27] had been reported to possess a tensile yield strength of 855 MPa at 1,023 K, which was slightly lower than that of CMSX-4 prepared by the standard process[24]. The aim of this article is to present a microstructure template for developing future advanced high temperature alloys with improved cost-performance

Objectives

Methods

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Conclusion