TY - JOUR
T1 - Examination of inverse Hall-Petch relation in nanostructured aluminum alloys by ultra-severe plastic deformation
AU - Mohammadi, Abbas
AU - Enikeev, Nariman A.
AU - Murashkin, Maxim Yu
AU - Arita, Makoto
AU - Edalati, Kaveh
N1 - Funding Information:
This work was financially supported by the Light Metals Educational Foundation of Japan, the Ministry of Education, Culture, Sports, Science and Technology ( MEXT ) of Japan (No. 19H05176 , 21H00150 ) and the Russian Science Foundation (No. 17-19-01311 ).
Publisher Copyright:
© 2021
PY - 2021/11/20
Y1 - 2021/11/20
N2 - To have an insight into the occurrence of inverse Hall-Petch relationship in ultrafine-grained (UFG) aluminum alloys produced by severe plastic deformation (SPD), ultra-SPD (i.e. inducing several ten thousand shear strains via high-pressure torsion, HPT) followed by aging is applied to an Al-La-Ce alloy. Average nanograin sizes of 40 and 80 nm are successfully achieved together with strain-induced Lomer-Cottrell dislocation lock formation and aging-induced semi-coherent Al11(La,Ce)3 precipitation. Analysis of hardening mechanisms in this alloy compared to SPD-processed pure aluminum with micrometer grain sizes, SPD-processed Al-based alloys with submicrometer grain sizes and ultra-SPD-processed Al-Ca alloy with nanograin sizes reveals the presence of two breaks in the Hall-Petch relationship. First, a positive up-break appears when the grain sizes decrease from micrometer to submicrometer which is due to extra hardening by solute-dislocation interactions. Second, a negative down-break and softening occur by decreasing the grain sizes from submicrometer to nanometer which is caused by weakening the dislocation hardening mechanism with minor contribution of the inverse Hall-Petch mechanism. Detailed analyses confirm that nanograin formation is not necessarily a solution for extra hardening of Al-based alloys and other accompanying strategies such as grain-boundary segregation and precipitation are required to overcome such a down-break and softening.
AB - To have an insight into the occurrence of inverse Hall-Petch relationship in ultrafine-grained (UFG) aluminum alloys produced by severe plastic deformation (SPD), ultra-SPD (i.e. inducing several ten thousand shear strains via high-pressure torsion, HPT) followed by aging is applied to an Al-La-Ce alloy. Average nanograin sizes of 40 and 80 nm are successfully achieved together with strain-induced Lomer-Cottrell dislocation lock formation and aging-induced semi-coherent Al11(La,Ce)3 precipitation. Analysis of hardening mechanisms in this alloy compared to SPD-processed pure aluminum with micrometer grain sizes, SPD-processed Al-based alloys with submicrometer grain sizes and ultra-SPD-processed Al-Ca alloy with nanograin sizes reveals the presence of two breaks in the Hall-Petch relationship. First, a positive up-break appears when the grain sizes decrease from micrometer to submicrometer which is due to extra hardening by solute-dislocation interactions. Second, a negative down-break and softening occur by decreasing the grain sizes from submicrometer to nanometer which is caused by weakening the dislocation hardening mechanism with minor contribution of the inverse Hall-Petch mechanism. Detailed analyses confirm that nanograin formation is not necessarily a solution for extra hardening of Al-based alloys and other accompanying strategies such as grain-boundary segregation and precipitation are required to overcome such a down-break and softening.
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U2 - 10.1016/j.jmst.2021.01.096
DO - 10.1016/j.jmst.2021.01.096
M3 - Article
AN - SCOPUS:85105730387
SN - 1005-0302
VL - 91
SP - 78
EP - 89
JO - Journal of Materials Science and Technology
JF - Journal of Materials Science and Technology
ER -