Soaring upwards

金沢大学理工研究域機械工学系本研究では，高い強度，優れた耐応力緩和特性，適切な導電性を持つ時効硬化型Cu-Ni-Sn合金の作製を目的とした．市販合金と組成がほぼ同じCu-9%Ni-6%Sn，Cu-15%Ni-8%Sn，Cu-21%Ni-5.5%Sn合金，並びに今回提案するCu-9%Ni-9%Sn合金に400℃でピーク時効後圧延し，応力緩和率を向上のため400℃で焼鈍を行った．この加工熱処理は筆者独自のものである．いずれの合金も，市販合金に比べ引張強さは100～200MPaも高く，導電性は同程度であるが，耐応力緩和特性は劣る．Cu-9%Ni-9%Sn合金が強度，耐応力緩和特性，導電性の面で最もバランスが取れている．In this study, we aimed to fabricate an age-hardened Cu-Ni-Sn alloy with a high strength, an excellent stress relaxation resistance and a suitable conductivity. A Cu-9wt%Ni-9wt%Sn alloy with proposed compositions of Ni and Sn, and Cu-9wt%Ni-6wt%Sn, Cu-15wt%Ni-8wt%Sn, and Cu-21wt%Ni-5.5wt%Sn alloys with almost the same compositions of Ni and Sn as commercial Cu-Ni-Sn alloys were first peak-aged at 400°C, then cold-rolled, and finally annealed at 400°C to improve the stress relaxation resistance of the four cold-rolled alloys. This thermomechanical heat treatment is the author\u27s unique method. The four alloys have tensile strengths higher than those of commercially available alloys by about 100 to 200 MPa, and their conductivities are comparable, but their resistances to stress relaxation are smaller. Among the four alloys, the balance of strength, stress relaxation resistance, and conductivity of the Cu-9%Ni-9%Sn alloy is the most excellent.研究課題/領域番号:15K06480, 研究期間(年度):2015-04-01 - 2018-03-3

Coarsening of δ-Ni2Si precipitates in a Cu-Ni-Si alloy

金沢大学理工研究域機械工学系The coarsening behavior of rod-shaped and spherical δ-Ni 2Si precipitates in a Cu-1.86 wt% Ni-0.45 wt% Si alloy during aging at 823-948 K has been investigated by measuring both precipitate size by transmission electron microscopy (TEM) and solute concentration in the Cu matrix by electrical resistivity. The rod-shaped δ precipitates have an elongated shape along 〈5̄58〉m and a {110}m habit-plane facet. The coarsening theory of a spherical precipitate in a ternary alloy developed by Kuehmann and Voorhees (KV) has been modified to a case of rod-shaped precipitates. The coarsening kinetics of average size of the rod-shaped and spherical δ precipitates with aging time t obey the t 1/3 time law, as predicted by the modified KV theory. The kinetics of depletion of the supersaturation with t are coincident with the predicted t -1/3 time law. Application of the modified KV theory has enabled calculation of the energies of sphere, {110}m and rod-end interfaces from the data on coarsening alone. The energy of the {110}m interface having a high degree of coherency to the Cu matrix is estimated to be 0.4 J m-2, the incoherent sphere-interface energy 0.6 J m-2, and the rod-end interface energy 5.2 J m-2. © 2011 Springer Science+Business Media, LLC

Fatigue behavior and microstructure of an Al-Mg-Sc alloy at an elevated temperature

金沢大学理工研究域機械工学系Al-Mg-Sc alloy polycrystals bearing Al3Sc particles with different sizes, i.e. 4, 6 and 11 nm in diameter, have been cyclically deformed at 423 K under constant plastic-strain amplitudes, and the microstructural evolution has been investigated in relation to the stress-strain response. Cyclic softening after initial hardening is found in specimens with small particles of 4 and 6 nm, but no cyclic softening takes place in specimens with larger particles of 11 nm. These features of cyclic deformation behavior are similar to the results previously obtained at room temperature. Transmission electron microscopy observations reveal that dislocations are uniformly distributed under all applied strain amplitudes in the specimens containing large particles of 11 nm, whereas slip bands are formed in the cyclically softened specimens bearing smaller particles. The cyclic softening is explained by a loss of particle strength through particle shearing within strongly strained slip bands. The 6 and 11 nm Al3Sc particles have a stronger retardation effect on the formation of fatigue-induced stable dislocation structure than 4 nm particles at 423 K. © 2010 IOP Publishing Ltd

Effects of microstructures on fatigue behavior of an Al-Mg-Sc alloy at an elevated temperature

Polycrystalline Al-1wt%Mg-0.27wt%Sc alloys bearing Al3Sc particles with different average sizes of 4 and 11nm Polycrystalline 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

Precipitation process in a Cu-Ni-Be alloy

The precipitation process in an aged Cu-1.9wt%Ni-0.3wt%Be alloy has been examined by high-resolution transmission electron 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′\u27 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′\u27, 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

Face-centred cubic to body-centred cubic martensitic transformation of Fe-Co particles in a copper matrix

金沢大学大学院自然科学研究科機能創成システム金沢大学工学

Misorientation dependence of intergranular embrittlement of Cu-2.0 wt.% Sb bicrystals

Bicrystals of a Cu–2.0 wt.% Sb alloy with different [0 0 1] symmetric tilt boundaries were tensile tested at several temperatures from 77 to 743 K. The dependence of Sb segregation level at [0 0 1] tilt boundaries on the misorientation angle also was examined by energy-dispersive X-ray spectroscopy. The fracture behavior was sensitive to the misorientation angle and test temperature. Both the fracture behavior at 77 K and the Sb segregation level showed a good correlation with the grain-boundary energy of pure Cu. The higher the grain-boundary energy, the higher the Sb segregation level and the higher the degree of grain-boundary embrittlement

Mechanical Properties of Cu-Cr system alloys with and without Zr and Ag

金沢大学大学院自然科学研究科機能創成システムThe effects of addition of Zr and Ag on the mechanical properties of a Cu-0.5 wt%Cr alloy have been investigated. The addition of 0.15 wt%Zr enhances the strength and resistance to stress relaxation of the Cu-Cr alloy. The increase in strength is caused by both the decrease in inter-precipitate spacing of Cr precipitates and the precipitation of Cu5Zr phase. The stress relaxation resistance is improved by the preferentially forming Cu5Zr precipitates on dislocations, in addition to Cr precipitates on dislocations. The addition of 0.1 wt%Ag to the Cu-Cr and Cu-Cr-Zr alloys improves the strength, stress relaxation resistance and bend formability of these alloys. The increase in strength and stress relaxation resistance is ascribed to the decrease in inter-precipitate spacing of Cr precipitates and the suppression of recovery during aging, and to the Ag-atom-drag effect on dislocation motion. The better bend formability of the Ag-added alloys is explained in terms of the larger post-uniform elongation of the alloys. © 2007 Springer Science+Business Media, LLC