Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Titanium aluminides find application in modern light-weight, high-temperature turbines, such as aircraft engines, but suffer from poor plasticity during manufacturing and processing. Huge forging presses enable materials processing in the 10-GPa range, and hence, it is necessary to investigate the phase diagrams of candidate materials under these extreme conditions. Here, we report on an in situ synchrotron X-ray diffraction study in a large-volume press of a modern (α2 + γ) two-phase material, Ti-45Al-7.5Nb-0.25C, under pressures up to 9.6 GPa and temperatures up to 1686 K. At room temperature, the volume response to pressure is accommodated by the transformation γ → α2, rather than volumetric strain, expressed by the apparently high bulk moduli of both constituent phases. Crystallographic aspects, specifically lattice strain and atomic order, are discussed in detail. It is interesting to note that this transformation takes place despite an increase in atomic volume, which is due to the high ordering energy of γ. Upon heating under high pressure, both the eutectoid and γ-solvus transition temperatures are elevated, and a third, cubic β-phase is stabilized above 1350 K. Earlier research has shown that this β-phase is very ductile during plastic deformation, essential in near-conventional forging processes. Here, we were able to identify an ideal processing window for near-conventional forging, while the presence of the detrimental β-phase is not present under operating conditions. Novel processing routes can be defined from these findings. © 2016, Creative Commons

Bifurcations in Globally Coupled Map Lattices

The dynamics of globally coupled map lattices can be described in terms of a nonlinear Frobenius--Perron equation in the limit of large system size. This approach allows for an analytical computation of stationary states and their stability. The complete bifurcation behaviour of coupled tent maps near the chaotic band merging point is presented. Furthermore the time independent states of coupled logistic equations are analyzed. The bifurcation diagram of the uncoupled map carries over to the map lattice. The analytical results are supplemented with numerical simulations.Comment: 19 pages, .dvi and postscrip

Cell Cycle-Dependent Induction of Homologous Recombination by a Tightly Regulated I-SceI Fusion Protein

Double-strand break repair is executed by two major repair pathways: non-homologous end joining (NHEJ) and homologous recombination (HR). Whereas NHEJ contributes to the repair of ionizing radiation (IR)-induced double strand breaks (DSBs) throughout the cell cycle, HR acts predominantly during the S and G2 phases of the cell cycle. The rare-cutting restriction endonuclease, I-SceI, is in common use to study the repair of site-specific chromosomal DSBs in vertebrate cells. To facilitate analysis of I-SceI-induced DSB repair, we have developed a stably expressed I-SceI fusion protein that enables precise temporal control of I-SceI activation, and correspondingly tight control of the timing of onset of site-specific chromosome breakage. I-SceI-induced HR showed a strong, positive linear correlation with the percentage of cells in S phase, and was negatively correlated with the G1 fraction. Acute depletion of BRCA1, a key regulator of HR, disrupted the relationship between S phase fraction and I-SceI-induced HR, consistent with the hypothesis that BRCA1 regulates HR during S phase

In situ synchrotron X-ray diffraction line-profile analysis of additively manufactured Ti−6Al−4V alloy under tensile deformation

In this study, the tensile deformation behavior of an electron beam melted Ti−6Al−4V alloy was examined by in situ X-ray diffraction (XRD) line-profile analysis. The as-built Ti−6Al−4V alloy specimen showed a fine acicular microstructure that was produced through the decomposition of the α′-martensite during the post-melt exposure to high temperatures. Using high-energy synchrotron radiation, XRD line-profile analysis was successfully applied for examining the evolution of dislocation structures not only in the α-matrix but also in the nanosized, low-fraction β-phase precipitates located at the interfaces between the α-laths. The results indicated that the dislocation density was initially higher in the β-phase and an increased dislocation density with increasing applied tensile strain was quantitatively captured in each constitutive phase. It can be thus concluded that the EBM Ti−6Al−4V alloy undergoes a cooperative plastic deformation between the constituent phases in the duplex microstructure. These results also suggested that XRD line-profile analysis combined with highenergy synchrotron XRD measurements can be utilized as a powerful tool for characterizing duplex microstructures in titanium alloys

Uniaxial strain dependence of the critical current of Di-BSCCO tapes

In order to explain the effect of uniaxial strain on the critical current of DI-BSCCO-Bi2223 tapes, we employed a springboard sample holder that can smoothly and continuously apply both tensile and compressive strains to tape samples. Over a narrow tensile strain region, the critical current in the tapes decreased linearly with increasing strain and returned reversibly with decreasing strain. When compressive strain was applied, the critical current first increased and then reached a weak maximum. Thereafter, it decreased monotonically with further increases in compressive strain. At room temperature, the local strain exerted on BSCCO filaments was measured by means of a quantum beam diffraction technique. Over the whole tensile strain region up to 0.2% and the small compressive strain range, the local strain changed linearly with applied strain. When the compressive strain was applied beyond the relaxation strain, the local strain (measured by diffraction) versus the applied strain (measured using a strain gauge) deviated from linearity, which is characteristic of strain relaxation and the onset of BSCCO filament fracture. Thus, the strain at the maximum critical current corresponds to a crossover point in strain, above which the critical current decreased linearly and reversibly with increasing applied strain, and below which the critical current decreased due to the BSCCO filament fracture. In this paper, we clearly characterize the reversible range terminated by both compressive and tensile strains, in which filaments do not fracture. Our analysis of the compressive regime beyond the relaxation strain suggests that although BSCCO filament fracture is the primary factor that leads to a decrease in critical current, the critical current in those regions of filaments that are not fractured increases linearly and reversibly with decreasing applied strain at compressive strains well beyond the reversible region for the tape

Development of CdTe pixel detectors combined with an aluminum Schottky diode sensor and photon-counting ASICs

We have been developing CdTe pixel detectors combined with a Schottky diode sensor and photon-counting ASICs. The hybrid pixel detector was designed with a pixel size of 200"μm by 200 μm and an area of 19 mm by 20 mm or 38.2 mm by 40.2 mm. The photon-counting ASIC, SP8-04F10K, has a preamplifier, a shaper, 3-level window-type discriminators and a 24-bits counter in each pixel. The single-chip detector with 100 by 95 pixels successfully operated with a photoncounting mode selectingX-ray energy with the windowcomparator and stable operationwas realized at 20 degrees C. We have performed a feasibility study for a white X-ray microbeam experiment. Laue diffraction patterns were measured during the scan of the irradiated position in a silicon steel sample. The grain boundaries were identified by using the differentials between adjacent images at each position