Understanding the role of Ca segregation on thermal stability, electrical resistivity and mechanical strength of nanostructured aluminum

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:798

Article

Sauvage, Xavier¹  Cuvilly, Fabien¹  Russell, Alan²  Edalati, Kaveh³ 

[1] Normandie Univ, UNIROUEN, INSA Rouen, CNRS,Grp Phys Mat, F-76000 Rouen, France

[2] Iowa State Univ, Dept Mat Sci & Engn, Ames, IA 50011 USA

[3] Kyushu Univ, WPI, Int Inst Carbon Neutral Energy Res WPI I2CNER, Fukuoka, Japan

关键词: Aluminum;    Nanostructure;    Grain boundary segregation;    Electrical resistivity;    Severe plastic deformation;   

DOI  :  10.1016/j.msea.2020.140108

来源: Elsevier

【 摘 要 】

Achieving a combination of high mechanical strength and high electrical conductivity in low-weight Al alloys requires a full understanding of the relationships between nanoscaled features and physical properties. Grain boundary strengthening through grain size reduction offers some interesting possibilities but is limited by thermal stability issues. Zener pinning by stable nanoscaled particles or grain boundary segregation are wellknown strategies for stabilizing grain boundaries. In this study, the Al-Ca system has been selected to investigate the way segregation affects the combination of mechanical strength and electrical resistivity. For this purpose, an Al-Ca composite material was severely deformed by high-pressure torsion to achieve a nanoscaled structure with a mean grain size of only 25 nm. X-ray diffraction, transmission electron microscopy and atom probe tomography data revealed that the fcc Ca phase was dissolved for large levels of plastic deformation leading mainly to Ca segregations along crystalline defects. The resulting microhardness of about 300 HV is much higher than predictions based on Hall and Petch Law and is attributed to limited grain boundary mediated plasticity due to Ca segregation. The electrical resistivity is also much higher than that expected for nanostructured Al. The main contribution comes from Ca segregations that lead to a fraction of electrons reflected or trapped by grain boundaries twice larger than in pure Al. The two-phase state was investigated by in-situ and exsitu microscopy after annealing at 200 degrees C for 30 min, where precipitation of nanoscaled Al4Ca particles occurred and the mean grain size reached 35 nm. Annealing also significantly decreased electrical resistivity, but it remained much higher than that of nanostructured pure Al, due to Al/Al4Ca interfaces that reflect or trap more than 85% of electrons.

【 授权许可】

Free