Effects of Grain Size and Grain Boundary Stability on Mechanical and Fatigue Properties of Nanocrystalline Nickel Thin Films

Nakai, Yoshikazu; Takeshige, Ryota; Kikuchi, Shinichi

doi:10.2320/matertrans.z-m2021837

Cited by 7 publications

(1 citation statement)

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“…Subduing fatigue induced grain growth and a reduced crack growth rate of the recovered condition seem to be responsible for this exceptional fatigue strength. 81,93) Results obtained on nanostructured nickel with ³170 nm grain size, demonstrating a 10% increase of the fatigue strength for the recovered condition 94) suggest a general applicability of this strategy to develop extremely fatigue resistant metallic structures. It should be noted that the positive effect of anneal hardening on the fatigue strength is more pronounced than that on quasi-static strength.…”

Section: Effect Of Recovery Hardening On Propertiesmentioning

confidence: 91%

Anneal Hardening in Single Phase Nanostructured Metals

Renk

Pippan

2023

Mater. Trans.

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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.

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Section: Effect Of Recovery Hardening On Propertiesmentioning

confidence: 91%