The Strength–Grain Size Relationship in Ultrafine-Grained Metals

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• 作者：N. Balasubramanian ; Terence G. Langdon
• 刊名：Metallurgical and Materials Transactions A
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：47
• 期：12
• 页码：5827-5838
• 全文大小：1,848 KB
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Chemistry
  Materials Science
  Metallic Materials
  Structural Materials
  Physical Chemistry
  Ceramics,Glass,Composites,Natural Materials
  
• 出版者：Springer Boston
• ISSN：1543-1940
• 卷排序：47

文摘

Metals processed by severe plastic deformation (SPD) techniques, such as equal-channel angular pressing (ECAP) and high-pressure torsion (HPT), generally have submicrometer grain sizes. Consequently, they exhibit high strength as expected on the basis of the Hall–Petch (H–P) relationship. Examples of this behavior are discussed using experimental data for Ti, Al, and Ni. These materials typically have grain sizes greater than ~50 nm where softening is not expected. An increase in strength is usually accompanied by a decrease in ductility. However, both high strength and high ductility may be achieved simultaneously by imposing high strain to obtain ultrafine-grain sizes and high fractions of high-angle grain boundaries. This facilitates grain boundary sliding, and an example is presented for a cast Al-7 pct Si alloy processed by HPT. In some materials, SPD may result in a weakening even with a very fine grain size, and this is due to microstructural changes during processing. Examples are presented for an Al-7034 alloy processed by ECAP and a Zn-22 pct Al alloy processed by HPT. In some SPD-processed materials, it is possible that grain boundary segregation and other features are present leading to higher strengths than predicted by the H–P relationship.