Morphology Evolution of γ′ Precipitates during Isothermal Exposure in Wrought Ni-Based Superalloy Inconel X-750

The morphological evolution of γ′ precipitates and lattice misfit with isothermal aging were closely investigated in wrought Ni-based superalloy Inconel X-750. The γ′ morphology dramatically changes in terms of shape, distribution, coalescence and coherency at the γ/γ′ interface. These processes and their dependence on temperature are summarized as a γ′ morphology map together with a time–temperature–precipitation (TTP) diagram through quantifying relevant morphological parameters. The lattice misfit was measured by X-ray diffraction and is positive; it decreases from 0.6% at room temperature to 0.1% at the aging temperature. These results suggest that the morphological changes of the γ′ precipitates are attributable to very low lattice misfit, the interaction of the elastic field, the volume fraction of the precipitates and incoherence in γ/γ′ interface

Improving the tensile properties of additively manufactured β-containing tial alloys via microstructure control focusing on cellular precipitation reaction

The effect of a two-step heat treatment on the microstructure and high-temperature tensile properties of β-containing Ti-44Al-4Cr (at%) alloys fabricated by electron beam powder bed fusion were examined by focusing on the morphology of α2/γ lamellar grains and β/γ cells precipitated at the lamellar grain boundaries by a cellular precipitation reaction. The alloys subjected to the first heat treatment step at 1573 K in the α + β two-phase region exhibit a non-equilibrium microstructure consisting of the α2/γ lamellar grains with a fine lamellar spacing and a β/γ duplex structure located at the grain boundaries. In the second step of heat treatment, i.e., aging at 1273 K in the β + γ two-phase region, the β/γ cells are discontinuously precipitated from the lamellar grain boundaries due to excess Cr supersaturation in the lamellae. The volume fraction of the cells and lamellar spacing increase with increasing aging time and affect the tensile properties of the alloys. The aged alloys exhibit higher strength and comparable elongation at 1023 K when compared to the as-built alloys. The strength of these alloys is strongly dependent on the volume fraction and lamellar spacing of the α2/γ lamellae. In addition, the morphology of the β/γ cells is also an important factor controlling the fracture mode and ductility of these alloys.Cho K., Odo H., Okamoto K., et al. Improving the tensile properties of additively manufactured β-containing tial alloys via microstructure control focusing on cellular precipitation reaction. Crystals, 11, 7, 809. https://doi.org/10.3390/cryst11070809

Peculiar microstructural evolution and tensile properties of β-containing γ-TiAl alloys fabricated by electron beam melting

The microstructure and tensile properties of β-containing Ti–44Al–4Cr alloy rods additively manufactured by electron beam melting (EBM) process were examined as a function of input energy density determined by the processing parameters. To the best of our knowledge, this is the first report to demonstrate that two types of fine microstructures have been obtained in the β-containing γ-TiAl alloys by varying the energy density during the EBM process. A uniform α2/β/γ mixed structure containing an α2/γ lamellar region and a β/γ dual-phase region is formed at high energy density conditions. On the other hand, a lower energy density leads to the formation of a peculiar layered microstructure perpendicular to the building direction, consisting of a ultrafine α2/γ lamellar grain layer and a α2/β/γ mixed structure layer. The difference in the microstructures originates from the difference in the solidification microstructure and the temperature distribution from the melt pool, which are dependent on the energy density. Furthermore, it was found that the strength of the alloys is closely related to the volume fractions of the β phase and the ultrafine α2/γ lamellar grains which originates from the massive α grains formed by rapid cooling under low energy density conditions. The alloys with high amounts of these peculiar microstructures exhibit high strength comparable to and higher than the conventional β-containing γ-TiAl at room temperature and 1023 K, respectively.Cho K., Kawabata H., Hayashi T., et al. Peculiar microstructural evolution and tensile properties of β-containing γ-TiAl alloys fabricated by electron beam melting. Additive Manufacturing, 46, 102091. https://doi.org/10.1016/j.addma.2021.102091

Influence of Input Energy Density on Morphology of Unique Layered Microstructure of γ-TiAl Alloys Fabricated by Electron Beam Powder Bed Fusion

Microstructure and tensile properties of Ti–48Al–2Cr–2Nb (at%) rods fabricated by electron beam powder bed fusion (EB-PBF) process were investigated by changing input energy density (ED) which is one of the important factors affecting formation of the melt pool. We found that unique layered microstructure consisting of an equiaxed γ grain layer (γ band) and a duplex region can be formed by EB-PBF with ED in the range of 13 to 31 J/mm3. It is interesting to note that the width of the γ band and the volume fraction of the γ phase in the duplex region decrease with increasing ED. On the other hand, the α2/γ lamellar grain in the duplex region increases with increasing ED. These morphological changes in the layered microstructure are attributed to variation of temperature distribution from melt pool caused by increasing ED. Moreover, we also found for the first time the strength of the alloys can be improved by decreasing width of the γ band and increasing of the α2/γ lamellar grain in the duplex region. Whereas, the width of the γ band and the fraction of the equiaxed γ grain in the duplex region should be increased to enhance ductility of the alloys.Cho Ken, Morita Naohide, Matsuoka Hiromasa, et al. Influence of Input Energy Density on Morphology of Unique Layered Microstructure of γ-TiAl Alloys Fabricated by Electron Beam Powder Cho Ken, Morita Naohide, Matsuoka Hiromasa, et al. Influence of Input Energy Density on Morphology of Unique Layered Microstructure of γ-TiAl Alloys Fabricated by Electron Beam Powder Bed Fusion. MATERIALS TRANSACTIONS 64, 44 (2023); https://doi.org/10.2320/matertrans.MT-MLA2022015

Numerical changes in blood monocytes in bronchial asthma.

Numerical changes in peripheral blood monocytes were examined in 125 patients with bronchial asthma using a new direct method of counting blood monocytes. The number of monocytes in non-attack stages of bronchial asthma was similar to that of healthy controls. The monocyte count observed in overall cases showed a significantly higher value both in pre-attack and attack stages than in non-attack stages. Changes in the number of monocytes in an individual spontaneous asthmatic cycle tended to increase in pre-attack stages, increase more markedly during asthma attacks, then to decrease after the attack was alleviated. Monocytes in cases with a positive test for bronchial challenge to house dust extract changed in almost the same manner as for spontaneous asthma attacks. The number of monocytes did not change during bronchospasm provoked by inhalation of acetylcholine. Exercise-induced asthma patients exhibited indefinite changes of monocytes; that is, some cases showed a significant increase in the number of monocytes related to the asthma cycle, but other cases did not show any appreciable change. These findings suggest that the number of monocytes in the peripheral blood may change in close relation to asthma attacks elicited by allergic reactions.</p

Influence of unique layered microstructure on fatigue properties of Ti-48Al-2Cr-2Nb alloys fabricated by electron beam melting

The influence of a unique layered microstructure consisting of duplex-like region and equiaxed γ grain layers (γ bands) on the fatigue properties of Ti-48Al-2Cr-2Nb alloy bars fabricated by electron beam melting (EBM) was investigated at room temperature (RT) and 1023 K focusing on the angle (θ) between the building direction and cylinder (loading) axis. We found for the first time the fatigue strengths of the alloy bars with the layered microstructure depend strongly on the angle θ. Particularly, the fatigue strength of the alloy bars fabricated at θ = 45° is comparable to that of the hot isostatic pressing (HIP) treated cast alloys, even without HIP treatment. We also found the alloy bars fabricated at θ = 0° and 45° exhibit high fatigue strengths in the low-cycle fatigue life region at 1023 K similar to θ = 45° alloy bars at RT. These high fatigue strengths are caused by inhibition of the brittle main crack initiation by stress relaxation due to shear deformation at the γ bands and large plasticity of the alloys. These findings indicate that the alloys fabricated by EBM at θ = 45° with the unique layered microstructure have a great potential for aerospace and automobile applications.Cho K., Kobayashi R., Oh J.Y., et al. Influence of unique layered microstructure on fatigue properties of Ti-48Al-2Cr-2Nb alloys fabricated by electron beam melting. Intermetallics 95, 1 (2018); https://doi.org/https://doi.org/10.1016/j.intermet.2018.01.009

Distinct connectivity patterns in human medial parietal cortices: Evidence from standardized connectivity map using cortico-cortical evoked potential

The medial parietal cortices are components of the default mode network (DMN), which are active in the resting state. The medial parietal cortices include the precuneus and the dorsal posterior cingulate cortex (dPCC). Few studies have mentioned differences in the connectivity in the medial parietal cortices, and these differences have not yet been precisely elucidated. Electrophysiological connectivity is essential for understanding cortical function or functional differences. Since little is known about electrophysiological connections from the medial parietal cortices in humans, we evaluated distinct connectivity patterns in the medial parietal cortices by constructing a standardized connectivity map using cortico-cortical evoked potential (CCEP). This study included nine patients with partial epilepsy or a brain tumor who underwent chronic intracranial electrode placement covering the medial parietal cortices. Single-pulse electrical stimuli were delivered to the medial parietal cortices (38 pairs of electrodes). Responses were standardized using the z-score of the baseline activity, and a response density map was constructed in the Montreal Neurological Institutes (MNI) space. The precuneus tended to connect with the inferior parietal lobule (IPL), the occipital cortex, superior parietal lobule (SPL), and the dorsal premotor area (PMd) (the four most active regions, in descending order), while the dPCC tended to connect to the middle cingulate cortex, SPL, precuneus, and IPL. The connectivity pattern differs significantly between the precuneus and dPCC stimulation (p<0.05). Regarding each part of the medial parietal cortices, the distributions of parts of CCEP responses resembled those of the functional connectivity database. Based on how the dPCC was connected to the medial frontal area, SPL, and IPL, its connectivity pattern could not be explained by DMN alone, but suggested a mixture of DMN and the frontoparietal cognitive network. These findings improve our understanding of the connectivity profile within the medial parietal cortices. The electrophysiological connectivity is the basis of propagation of electrical activities in patients with epilepsy. In addition, it helps us to better understand the epileptic network arising from the medial parietal cortices