Anneal hardening in single phase nanostructured metals
Research output: Contribution to journal › Review article › peer-review
Standard
In: Materials transactions, Vol. 64.2023, No. 7, 2023, p. 1464-1473.
Research output: Contribution to journal › Review article › peer-review
Harvard
APA
Vancouver
Author
Bibtex - Download
}
RIS (suitable for import to EndNote) - Download
TY - JOUR
T1 - Anneal hardening in single phase nanostructured metals
AU - Renk, Oliver
AU - Pippan, Reinhard
N1 - Publisher Copyright: ©2023 The Japan Institute of Metals and Materials.
PY - 2023
Y1 - 2023
N2 - Recovery of cold worked metals is associated with a loss of strength due to the reduction of the defect density. However, already in the 1960s analytical models and few experiments suggested that this may not generally be the case and even a hardening rather than a softening might occur. With the availability of severe plastic deformation and deposition techniques this anneal hardening phenomenon has been observed frequently. In this overview we summarize early findings on this topic before focusing on general observations and potential origins, with a special focus to show the similarities for nanostructures across different grain size scales (i.e., structures prepared by deposition and severe plastic deformation techniques, respectively). Comparison of different results indicate a grain size dependent hardening increment that could be additionally affected by segregation or the processing variables. Considering the agreement of the peak hardening temperatures with that for dislocation annihilation at grain boundaries, anneal hardening can be rationalized by the loss of intragranular defects and grain boundary relaxation. Grain boundary diffusivity hence plays a crucial role and particular solutes could amplify the hardening process even further. As anneal hardening already occurs for grain sizes at the micron scale, its effect on properties is even of technological relevance. Beneficial effects on the fatigue strength are evident, but the strain softening of anneal hardened specimens drastically shorten ductility. Nevertheless, some strategies to overcome this adverse effect seem promising to create metallic structures with exceptional combinations of strength and ductility.
AB - Recovery of cold worked metals is associated with a loss of strength due to the reduction of the defect density. However, already in the 1960s analytical models and few experiments suggested that this may not generally be the case and even a hardening rather than a softening might occur. With the availability of severe plastic deformation and deposition techniques this anneal hardening phenomenon has been observed frequently. In this overview we summarize early findings on this topic before focusing on general observations and potential origins, with a special focus to show the similarities for nanostructures across different grain size scales (i.e., structures prepared by deposition and severe plastic deformation techniques, respectively). Comparison of different results indicate a grain size dependent hardening increment that could be additionally affected by segregation or the processing variables. Considering the agreement of the peak hardening temperatures with that for dislocation annihilation at grain boundaries, anneal hardening can be rationalized by the loss of intragranular defects and grain boundary relaxation. Grain boundary diffusivity hence plays a crucial role and particular solutes could amplify the hardening process even further. As anneal hardening already occurs for grain sizes at the micron scale, its effect on properties is even of technological relevance. Beneficial effects on the fatigue strength are evident, but the strain softening of anneal hardened specimens drastically shorten ductility. Nevertheless, some strategies to overcome this adverse effect seem promising to create metallic structures with exceptional combinations of strength and ductility.
KW - dislocation annihilation
KW - grain boundary relaxation
KW - nanocrystalline
KW - recovery
KW - severe plastic deformation
UR - http://www.scopus.com/inward/record.url?scp=85164538788&partnerID=8YFLogxK
U2 - 10.2320/matertrans.MT-MF2022029
DO - 10.2320/matertrans.MT-MF2022029
M3 - Review article
VL - 64.2023
SP - 1464
EP - 1473
JO - Materials transactions
JF - Materials transactions
SN - 1345-9678
IS - 7
ER -