Grain boundary relaxation induced ultrastrong-and-ductile bulk pure Ni. (December 2022)

• Record Type: Journal Article
• Authors: Hu, Kai; Yi, Jun; Huang, Bo; Bian, Xilei; Wang, Gang
• Is Part Of: Applied materials today. Volume 29(2022)
• Publication Date: 2022-12
• Subjects: Grain boundary softening -- Partial dislocation -- Grain boundary relaxation -- Grain size; Materials science -- Periodicals; Materials -- Research -- Periodicals; 620.1105
• DOI: 10.1016/j.apmt.2022.101653
• Languages: English
• ISSNs: 2352-9407

Abstract

Highlights: Grain boundary relaxation was found to effectively enhance strength and ductility simultaneously of nanocrystalline Ni with a grain size of 13.9 nm which was close to its critical value (12 nm) of the inverse Hall-Petch effect. The combination of the strength of 2013 MPa and the ductility of 5.17% accessible to bulk pure Ni after grain boundary relaxation in this work extended beyond the benchmark range established by Ni in references, and they were even higher than some Ni alloys and comparable to some ultra-high-strength steels. Grain boundary relaxation facilitated the suppression of softening due to grain boundary sliding and thus increased the strength of Ni. At the same time, it adjusted the deformation mechanism from grain boundary sliding to dislocation sliding, which facilitated the improvement of strain hardening rate and strain rate sensitivity of nanocrystalline Ni and the improvement of ductility of nanocrystalline Ni. Graphical abstract: Abstract: Both strength and ductility are essential for high-performance engineering structural materials, thus great endeavors have been invested to solve the strength-ductility trade-off of them during recent two decades. Here, we utilized grain boundary (GB) relaxation to circumvent the trade-off in bulk pure Ni through optimizing grain size when literatures tells that GB relaxation can improve strength but ductility. Both tensile strength and uniform elongation of Ni were elevated from 1450 MPa to 2013 MPa and from 2.33% to 5.17%, respectively. The combination of strength and ductility extends beyond the range established by the strongest bulk pure Ni known. Our investigation unraveled that the increased strength was produced by GB relaxation which remarkably mitigated GB softening produced by GB sliding, and that partial dislocation emission from GBs became the dominant plastic deformation mechanism. The dislocation activities inside the grains increased the strain hardening rate ( θ ). At the same time, enhanced probability of interaction between dislocations and GBs improved the strain rate sensitivity ( m ). It was the GB relaxation induced dislocation activities that improved θ and m, which stabilized the plastic deformation to enhance ductility. The present work offers a foundation for the ongoing of more advanced engineering structural materials with the advisable design of GB complexion.