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| 1.
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Watanabe, Chihiro ; Monzen, Ryoichi ; Ueji, Rintaro ; Miura, Hiromi ; 渡邊, 千尋 ; 門前, 亮一
概要:
金沢大学理工研究域機械工学系<br />Strain-rate and temperature dependences of deformation behavior of ultrafine-grained (UFGed) AZ61Mg
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alloy were examined. For this purpose, AZ61Mg alloy specimens were subjected to multi-directional forging (MDFing) under decreasing temperature conditions to have various grain sizes. The average grain sizes attained by MDFing to 1, 3, 6 and 9 passes were approximately 8, 2, 0.5 and 0.3 μm, respectively. A superior balance of the mechanical properties of strength and ductility at room temperature was achieved by MDFing to three passes and over. The strain-rate sensitivity of mechanical properties of the MDFed specimens increased with decreasing grain size. The specimens with grain sizes of 0.5 and 0.3 μm (0.5 or 0.3 specimen) exhibited stronger strain-rate and temperature dependences of total elongation than those with grain sizes of 8 and 2 μm (8 or 2 specimen). This can be partially ascribed to grain-boundary sliding, since an AFM observation revealed the occurrence of room-temperature grain-boundary sliding in the 0.3 specimen. The activation volume V* for the 8, 2 and 0.5 specimen increased with increasing temperature, while the 0.3 specimen exhibited an inverse temperature dependence of V*. This suggests a change in deformation mechanism with decreasing grain size as well as the occurrence of grain-boundary sliding. © 2017 The Minerals, Metals & Materials Society and ASM International<br />Embargo Period 12 months<br />The final publication is available at www.springerlink.com/article/10.1007/s11661-017-4303-7
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| 2.
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Watanabe, Chihiro ; Monzen, Ryoichi
概要:
The precipitation process in an aged Cu-1.9wt%Ni-0.3wt%Be alloy has been examined by high-resolution transmission electr
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on microscopy. The precipitation sequence found is: Guinier-Preston (G.P.) zones → γ″ → γ′ → stable γ. The disk-shaped G.P. zones and the disk-shaped γ″, γ′ and γ precipitated phases are composed of monolayers of Be atoms on {100}α of the Cu matrix and alternative Be and Ni matrix layers parallel to {100}α. The γ′' phases consisting of two to eight Be-layers has a body-centered tetragonal (bct) lattice with a=b=0.24 nm and c=0.28 nm. The γ′ or γ phase is bct with a=b=0.24 nm and c=0.26 nm or a=b=0.26 nm and c=0.27 nm. The γ′', γ′ or γ phase aligns with the matrix according to the Bain orientation relationship. The growth kinetics of disk-shaped γ precipitates on aging at 500°C has been also investigated. The {001}α habit planes of the γ precipitates migrate by a ledge mechanism. The average thickness of the γ disks increases with aging time t as t1/2. An analysis of experimental data using a kinetic model yields the diffusivity of solute in the Cu matrix, which is in agreement with the reported diffusivity of Ni in Cu. © (2011) Trans Tech Publications.
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| 3.
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Monzen, Ryoichi ; Hasegawa, Tomoyuki ; Watanabe, Chihiro
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金沢大学理工研究域機械工学系<br />The influence of prior cold work (90% reduction) on the length change and precipitation behaviour of
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a Cu-1.8wt%Be-0.2wt%Co alloy aged at 320C up to 350 h has been investigated. The alloy gradually expands to a maximum and then contracts during ageing. The maximum expansion is attributable to both the expansion due to the loss of Be solute atoms and the contraction due to precipitation of the [image omitted], I, m and ' phases. The subsequent contraction results from the decrease in amounts of the [image omitted] and m phases and the increase in amount of the ' phase. The new-found m phase, consisting of alternate Be and Cu matrix layers parallel to the matrix {001}, is body-centred monoclinic with a = b = 0.263 nm and c = 0.279 nm and = 83, and aligns with the matrix according to the Bain orientation relationship. The Guinier-Preston (GP) zone transforms continuously to the m or I phase via '' and [image omitted]. The transformation from the GP zone to ' via '', [image omitted] and I is retarded in comparison with that for the un-deformed alloy.全文公開201002
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| 4.
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Monzen, Ryoichi ; Hosoda, Takasumi ; Takagawa, Yusaku ; Watanabe, Chihiro
概要:
金沢大学理工研究域機械工学系<br />The effects of addition of 0.01 and 0.03 wt% Mg on the bend formability and strength of a Cu-1.8 wt%
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Be-0.21 wt% Co alloy aged at 320 °C for 30 min have been investigated metallographically. The addition of Mg to the Cu-Be-Co alloy enhances the bend formability and strength of the alloy. The enhancement of strength is caused by the increase in volume fraction of γ I′ precipitates in the Cu matrix. In bending of the alloys with and without 0.01 and 0.03 wt% Mg, a number of micro necks first arise along grain boundaries, and part of them grows, resulting in surface wrinkles, which finally lead to surface cracking. The cracking is initiated from voids formed by destruction of bar-like γ precipitates in discontinuous precipitation (DP) cells and propagates along grain boundaries. The addition of Mg decreases the width of DP cells, resulting in better bend formability. This arises because smaller stress concentration due to less inhomogeneous deformation develops in cells and, as a result, destruction of the γ precipitates in cells occurs less easily as the cell width decreases. © 2011 Springer Science+Business Media, LLC.
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| 5.
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Monzen, Ryoichi ; Takagawa, Yusaku ; Watanabe, Chihiro ; Terada, Daisuke ; Tsuji, N.
概要:
The enhancement of strength of Cu-1.2wt%Ni-0.2wt%Be-0.1wt%Zr and Cu-1.4wt%Ni-0.25wt%P-0.1wt%Zr alloys has been tried by
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the combination of ARB process by 5 cycles and aging treatment at 350 to 450°C. The grain sizes of the alloys, severely deformed by 5-cycle ARB process, were refined down to about 0.4μm. The Cu-Ni-Be-Zr alloy, ARB-processed and peak-aged at 375°C, exhibited a tensile strength σu of 810MPa, an elongation εt of 9% up to failure and an electrical conductivity σ of 62%IACS. The Cu-Ni-P-Zr alloy, initially aged at 450°C, then ARB-processed and peak-aged at 400°C, had the values of σu=780MPa, εt =6% and σ=56%IACS. © 2011 Published by Elsevier Ltd.
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| 6.
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Watanabe, Chihiro ; Monzen, Ryoichi
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Polycrystalline Al-1wt%Mg-0.27wt%Sc alloys bearing Al3Sc particles with different average sizes of 4 and 11nm Polycrysta
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lline Al-1wt%Mg-0.27wt%Sc alloys bearing Al3Sc particles with different average sizes of 4 and 11nm in diameter have been cyclically deformed at 423K under various constant stress amplitudes, and the relationship between fatigue characteristics and microstructure of the alloy has been investigated. The specimen bearing 11 nm particles exhibited a cyclic hardening to saturation, while in specimens with the small particles a cyclic softening was observed after initial hardening. In the specimen with large particles, dislocations were uniformly distributed under all applied stress amplitudes, whereas the specimens bearing small particles, in which cyclic softening occurred exhibited clearly developed slip bands. The cyclic softening for the latter specimen was explained by particle shearing within the strongly strained slip bands. The width of precipitate free zones (PFZs) has been found to be one of the factors affecting the fatigue life of the specimens at 423K. The two-step aging decreases the width of PFZs, resulting in increase in the fatigue life. © 2012 Trans Tech Publications, Switzerland.
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| 7.
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Monzen, Ryoichi ; Okawara, Syoichi ; Watanabe, Chihiro
概要:
An investigation by high-resolution transmission electron microscopy of the precipitation process during ageing a Cu-1.2
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wt%Be-0.1wt%Co alloy at 320°C has revealed that the transition phases follow a γ″ → γ″+ γ′ → γ sequence. The γ′ phase heterogeneously precipitates on the γ″ phase. The effects of an external stress on the nucleation and growth of disc-shaped γ″ and plate-shaped precipitates have been examined for the alloy aged at 320°C. A compressive stress applied in the [001] direction during ageing preferentially accelerates the nucleation and growth of the γ″ variant normal to the [001] axis among three crystallographically equivalent variants and the specific four γ′ variants formed on the γ″ variant normal to the [001] axis. A tensile stress does not significantly affect those of and precipitates. The critical diameter of the disc-shaped γ″ nucleus is estimated as about 1nm from evaluation of the interaction energy between the applied stress and the misfit strains γ″ of precipitates. It is proposed that applied external stress does not affect the diffusion rate but the interphase boundary velocity. © 2012 Taylor & Francis.
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| 8.
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Monzen, Ryoichi ; Kawai, Ryutaro ; Watanabe, Chihiro
概要:
The effects of an external stress on the formation of ellipsoidal ω phase precipitates have been examined for a Ti–20 wt
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% Mo alloy aged at 300 °C. Application of a tensile stress accelerates the nucleation of ω precipitates but a compressive stress does not significantly affect it. Estimates of the average misfit strains along the loading and the transverse directions, based on the misfit strains of ω precipitates, from measurements of the length change and the lattice parameter reveal preferential formation of specific ω variants among crystallographically equivalent four ones, which depends on the sense of the applied stress. This is supported by the result of the dependence of the number density of an ω variant on its misfit strain along the loading direction. This result, together with the dependence of the formation of ω precipitates on the sense of the applied stress, can be well understood through the interaction energy due to the presence of misfit strains between the applied stress and ω precipitate.
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| 9.
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Watanabe, Chihiro ; Monzen, Ryoichi ; Ii, Seiichiro ; Tsuchiya, Koichi
概要:
The microstructure and aging behavior of Cu-1.8wt%Be-0.2wt%Co alloy specimens processed by high-pressure torsion (HPT) a
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t room temperature (RT) and 150°C after solution treatment have been studied. Application of HPT processing at RT and 150°C under an applied pressure of 5 GPa for 10 revolutions at 1 rpm to alloy specimens (RT- and 150°C-specimen) produces an ultra-fine grained structure with a grain size of 70 nm. The hardnesses of the RT- and 150°C-specimens increase with equivalent strain up to 7 and then saturate at constant values of 400 and 430 Hv, respectively. Annealing the RT-specimen at 150°C for 10 min increases the hardness from 400 to 430 Hv. Transmission electron microscopy observations of the 150°C-specimen and the RT-specimen annealed at 150°C reveal that there are no intragranular and intergranular precipitates. It is suggested that the higher hardness of the 150°C-specimen than the RT-specimen is ascribed to the segregation of Be atoms on dislocations during HPT processing at 150°C. The RT- and 150°Cspecimens harden rapidly and exhibit maximum values of hardness at 3 min during aging at 320°C. The increase in the hardness is attributed to the precipitation of finely dispersed G.P. zones. © (2014) Trans Tech Publications, Switzerland.
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| 10.
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Watanabe, Chihiro ; Monzen, Ryoichi ; Ii, Seiichiro ; Tsuchiya, Koichi
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