This study investigates the ductile fracture mechanisms in as-quenched (As-Q) and quenched-and-tempered (Q-T) dual-phase steels. Using in-situ tensile testing combined with synchrotron X-ray tomography, we performed four-dimensional quantitative analysis of void evolution to reveal how heat treatment fundamentally alters damage behavior. The high-strength, low-ductility As-Q steel exhibited premature failure. Its significant phase-hardness mismatch between ferrite and martensite phases induced continuous and widespread void nucleation via martensite cracking after reaching the ultimate tensile strength. The subsequent rapid, isotropic growth and coalescence of these numerous voids led to early fracture. In contrast, tempering the Q-T steel reduced the hardness mismatch among phases, yielding superior ductility with lower strength. The Q-T steel, in particular, exhibited a two-stage damage process. Throughout most of the deformation, voids grew anisotropically by elongating along the tensile axis. This stable growth, however, gave way to a drastic change just before fracture, characterized by a rapid proliferation of voids oriented perpendicular to the loading direction. This final phase is attributed to damage in the martensite, suggesting the quantitative and qualitative differences in void evolution between the As-Q and Q-T steels.
The damage initiation and evolution behaviors of ferrite-martensite dual phase (DP), transformation-induced plasticity (TRIP)-aided dual-phase (TDP), quenched and tempered (QT), and TRIP-aided martensitic (TM) steels during tensile deformation were investigated. Voids were initiated at the phase boundaries and inside the martensite in the DP and TDP steels, whereas fine voids were observed at the prior austenite, packet, and block boundaries in the QT and TM steels. In the DP and TDP steels, the size of the voids remarkably increased with the plastic strain, even though the number of voids increased slightly. By contrast, the QT and TM steels exhibited a drastic increase in the number of voids, whereas a slight increase in the size of the voids was observed. The voids in the TM steel hardly extended as the plastic strain increased unlike those in the QT steel. The extent of voids in the DP and TDP steels might be attributed to stress and plastic strain partitioning between the different phases during tensile deformation. In addition, the promotion of void initiation and suppression of void growth might be attributed to the fine and uniform martensite matrix in the QT and TM steels. The suppression of void initiation in the TDP steel and void growth in the TM steel might be attributed to the stress and plastic strain relaxations at the void initiation site and the vicinity of voids owing to the effective martensitic transformation of retained austenite.
We study Gibbs measures on high-dimensional Haar-random unimodular lattices, where the energy of a lattice vector is its squared Euclidean norm. The random lattice is viewed as quenched geometric disorder, and c>0 denotes the scaled inverse temperature. We first analyze the edge window of vectors whose length is within the factor e^a/n of the shortest length, with fixed a as n→∞. For the full sign-class Gibbs ensemble, we prove a Poisson point process limit theorem for the Gibbs mass of this window. The mass vanishes in probability for 01 it has a nontrivial Poisson limit, and the ranked Gibbs weights converge to the Poisson-Dirichlet distribution with parameter 1/c. We then pass to a primitive-direction Gibbs ensemble and consider a fixed approximation factor γ>1. For this modified ensemble, we prove a weighted moment formula and a quenched thermal concentration result in the high-temperature range 0
Structural and magnetic properties of the quaternary Heusler alloy CoFeTiSn were investigated. The crystal structure was found to be a cubic LiMgPdSn-type with a lattice parameter a = 0.605 77(9) nm at 300 K. The magnetization curve of CoFeTiSn exhibited the ferromagnetic behavior with a spontaneous magnetization Ms = 1.06 μB/f.u. and a Curie temperature TC = 173.6 K. The obtained Ms value is close to the value predicted by the Slater-Pauling rule and first-principles band calculations for half-metallic ferromagnets. The determination of spectral parameters T0 and TA based on Takahashi’s spin fluctuation theory suggests that spin fluctuations were suppressed relative to those in typical itinerant ferromagnets. The square of the spontaneous magnetic moment ps2(T) was proportional to T4/3 in wide temperature range up to TC. The experimental results reveal that the spin fluctuation theory for weak itinerant electron ferromagnets is applicable even to CoFeTiSn with moderately localized Co and Fe atoms.
Ultraviolet (UV) emissions from molecular hydrogen in Saturn's atmosphere consist of bright auroral emission over the poles and disk-wide airglow. The dayside disk emits substantial intensities (dayglow) previously detected by various instruments. Exploration of dayside disk emissions provides insight into the interaction between the solar flux and planetary atmosphere. The respective contributions from the dayglow and the aurorae has not yet been evaluated, and the daily variability of the H-2 dayglow over timescales of weeks remains somewhat unexplored. For three weeks in 2014, the low-Earth orbiting telescope, Hisaki, monitored Saturn while Cassini concurrently observed Saturn's northern hemisphere from within the magnetosphere. The total emitted power varies by a factor of 2.26 over 23 days as observed by Hisaki, and 1.29 over 17 days by Cassini. Cassini data allow separation of the auroral power; the total power is dominated by that from the dayglow emission, with the northern aurora contributing similar to 10%-26%. The disk-wide dayglow component displays strong correlation with solar activity, with Pearson correlation coefficients >0.8. The Cassini data further show that the global power at longer wavelengths (155-162 nm) depends more strongly on the solar spectrum than shorter wavelengths (70-148 nm). The auroral contribution to the total H-2 emission (70-170 nm) is similar to 2%-14%. It is concluded that the total power is dominated by the dayglow from the disk, with solar photons controlling the H-2 dayglow emission.
