Effect of serrated grain boundary on tensile and creep properties of a precipitation strengthened high entropy alloy

Jhuo-Lun Lee; Pei-Te Wang; Kai-Chi Lo; Pai-Keng Shen; Nien-Ti Tsou; Koji Kakehi; Hideyuki Murakami; Che-Wei Tsai; Stéphane Gorsse; An-Chou Yeh

doi:10.1080/14686996.2022.2158043

Effect of serrated grain boundary on tensile and creep properties of a precipitation strengthened high entropy alloy

Sci Technol Adv Mater. 2023 Jan 10;24(1):2158043. doi: 10.1080/14686996.2022.2158043. eCollection 2023.

Authors

Jhuo-Lun Lee^{1

2

3}, Pei-Te Wang⁴, Kai-Chi Lo¹, Pai-Keng Shen³, Nien-Ti Tsou⁴, Koji Kakehi⁵, Hideyuki Murakami^{6

7}, Che-Wei Tsai^{1

2

3}, Stéphane Gorsse⁸, An-Chou Yeh^{1

2

3}

Affiliations

¹ High Entropy Materials Center, National Tsing Hua University, Hsinchu, Taiwan (ROC).
² Program in Prospective Functional Materials Industry, National Tsing Hua University, Hsinchu, Taiwan (ROC).
³ Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan (ROC).
⁴ Department of Materials Science and Engineering, National Yang Ming Chiao Tung University, Hsinchu, Taiwan (ROC).
⁵ Department of Mechanical Engineering, Tokyo Metropolitan University, Hachiojishi, Tokyo, Japan.
⁶ Research Center for Structural Materials, National Institute for Materials Science, Tsukuba, Japan.
⁷ Department of Nanoscience and Nanoengineering, Waseda University, Shinjuku, Tokyo, Japan.
⁸ CNRS, University of Bordeaux, Bordeaux INP, ICMCB, UMR 5026, Pessac, France.

Abstract

In this study, tensile and creep deformation of a high-entropy alloy processed by selective laser melting (SLM) has been investigated; hot ductility drop was identified at first, and the loss of ductility at elevated temperature was associated with intergranular fracture. By modifying the grain boundary morphology from straight to serration, the hot ductility drop issue has been resolved successfully. The serrated grain boundary could be achieved by reducing the cooling rate of solution heat treatment, which allowed the coarsening of L1₂ structured γ' precipitates to interfere with mobile grain boundaries, resulting in undulation of the grain boundary morphology. Tensile and creep tests at 650°C were conducted, and serrated grain boundary could render a significant increase in tensile fracture strain and creep rupture life by a factor of 3.5 and 400, respectively. Detailed microstructure analysis has indicated that serrated grain boundary could distribute strains more evenly than that of straight morphology. The underlying mechanism of deformation with grain boundary serration was further demonstrated by molecular dynamic simulation, which has indicated that serrated grain boundaries could reduce local strain concentration and provide resistance against intergranular cracking. This is the first study to tackle the hot ductility drop issue in a high-entropy alloy fabricated by SLM; it can provide a guideline to develop future high-entropy alloys and design post heat treatment for elevated temperature applications.

Keywords: Selective laser melting; high-entropy alloys; hot ductility drops; serrated grain boundary; tensile creep properties.

Grants and funding

The work was supported by the National Science and Technology Council, Taiwan [110-2221-E-007-020-MY3,111-2224-E-007-003,111-2634-F-007-008].