Microstructure and aging behavior of Cu-Be alloy processed by high-pressure torsion

The microstructure and aging behavior of Cu-1.8wt%Be-0.2wt%Co alloy specimens processed by high-pressure torsion (HPT) at 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

Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae

We systematically surveyed period variations of superhumps in SU UMa-type dwarf novae based on newly obtained data and past publications. In many systems, the evolution of superhump period are found to be composed of three distinct stages: early evolutionary stage with a longer superhump period, middle stage with systematically varying periods, final stage with a shorter, stable superhump period. During the middle stage, many systems with superhump periods less than 0.08 d show positive period derivatives. Contrary to the earlier claim, we found no clear evidence for variation of period derivatives between superoutburst of the same object. We present an interpretation that the lengthening of the superhump period is a result of outward propagation of the eccentricity wave and is limited by the radius near the tidal truncation. We interpret that late stage superhumps are rejuvenized excitation of 3:1 resonance when the superhumps in the outer disk is effectively quenched. Many of WZ Sge-type dwarf novae showed long-enduring superhumps during the post-superoutburst stage having periods longer than those during the main superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to be strongly correlated with the fractional superhump excess, or consequently, mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with multiple rebrightenings tend to have smaller period derivatives and are excellent candidate for the systems around or after the period minimum of evolution of cataclysmic variables (abridged).Comment: 239 pages, 225 figures, PASJ accepte

Mechanical and Spectroscopic Characterization of Solute Elements in Aluminum

We characterized the distribution of minor elements such as Si and Fe in Al utilizing a nanoindentation and electron microscopy with an energy dispersed X-ray spectroscopy (EDS) system. Nanoindentation can detect the dislocation nucleation known as “pop-in” event, the critical load (Pc) depends on the solute amount of Fe. However, that in Si-doped Al is rarely changed up to 1.0 at% of Si. That independent Pc in Al-Si is caused by the inhomogeneity of the Si, which is the grain boundary segregation, in Al. The grain boundary segregation of Si was clearly detected by using a newly developed microcalorimeter type EDS system, even at the 0.1 at% Si

Mechanical and Spectroscopic Characterization of Solute Elements in Aluminum

We characterized the distribution of minor elements such as Si and Fe in Al utilizing a nanoindentation and electron microscopy with an energy dispersed X-ray spectroscopy (EDS) system. Nanoindentation can detect the dislocation nucleation known as “pop-in” event, the critical load (Pc) depends on the solute amount of Fe. However, that in Si-doped Al is rarely changed up to 1.0 at% of Si. That independent Pc in Al-Si is caused by the inhomogeneity of the Si, which is the grain boundary segregation, in Al. The grain boundary segregation of Si was clearly detected by using a newly developed microcalorimeter type EDS system, even at the 0.1 at% Si

Transmission electron microscopy/electron energy loss spectroscopy measurements and ab initio calculation of local magnetic moments at nickel grain boundaries

We have determined local magnetic moments at nickel grain boundaries using a transmission electron microscopy/electron energy loss spectroscopy method assuming that the magnetic moment of Ni atoms is a linear function of the L3/L2 (white-line ratio) in the energy loss spectrum. The average magnetic moment measured in the grain interior was 0.55 μB, which agrees well with the calculated magnetic moment of pure nickel (0.62 μB). The local magnetic moments at the grain boundaries increased up to approximately 1.0 μB as the mis-orientation angle increased, and showed a maximum around 50°. The respective enhancement of local magnetic moments at the Σ5 (0.63 μB) and random (0.90 μB) grain boundaries in pure nickel was approximately 14 and 64% of the grain interior. In contrast, the average local magnetic moment at the (111) Σ3 grain boundary was found to be 0.55 μB and almost the same as that of the grain interior. These results are in good agreement with available ab initio calculations