Effect of solute segregation on the strength of nanocrystalline alloys: Inverse Hall–Petch relation

✍ Scribed by T.D. Shen; R.B. Schwarz; S. Feng; J.G. Swadener; J.Y. Huang; M. Tang; Jianzhong Zhang; S.C. Vogel; Yusheng Zhao

• Publisher: Elsevier Science
• Year: 2007
• Tongue: English
• Weight: 789 KB
• Volume: 55
• Category: Article
• ISSN: 1359-6454
• DOI: 10.1016/j.actamat.2007.05.018

✦ Synopsis

We have used a high-energy ball mill to prepare single-phased nanocrystalline Fe, Fe 90 Ni 10 , Fe 85 Al 4 Si 11 , Ni 99 Fe 1 and Ni 90 Fe 10 powders. We then increased their grain sizes by annealing. We found that a low-temperature anneal (T < 0.4 T m ) softens the elemental nanocrystalline Fe but hardens both the body-centered cubic iron-and face-centered cubic nickel-based solid solutions, leading in these alloys to an inverse Hall-Petch relationship. We explain this abnormal Hall-Petch effect in terms of solute segregation to the grain boundaries of the nanocrystalline alloys. Our analysis can also explain the inverse Hall-Petch relationship found in previous studies during the thermal anneal of ball-milled nanocrystalline Fe (containing $1.5 at.% impurities) and electrodeposited nanocrystalline Ni (containing $1.0 at.% impurities).