Superior fracture toughness with high yield strength in a high-Mn steel induced by heterogeneous grain structure

Heterogeneous grain structures were designed in a high Mn steel (Fe28Mn10Al1.00C), and the tensile properties and fracture toughness were investigated and compared with those for homogeneous structures. The heterogeneous grain structures display larger tensile ductility, stronger strain hardening and higher fracture toughness at the similar yield strength level. Hetero-deformation-induced hardening is found to play an important role in the heterogeneous grain structures, resulting in better mechanical properties. The size of plastic zone and the strain hardening capacity around the crack tip for the heterogeneous grain structures are found to be much larger/higher than those for the homogeneous grain structures at the same level of yield strength, resulting in better fracture toughness. High density of geometrically necessary dislocations and grain refinement are induced at the adjacent area of the main crack path, and numerous microvoids are also observed besides the main crack for the heterogeneous grain structures, resulting in more energy dissipation for higher fracture toughness. The deformation mechanisms around the crack tip are highly dependent on the magnitude of plastic strain and the grain size. The observed higher fracture toughness in the heterogeneous grain structures can be partly attributed to the formation of microbands. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Controlled Cationic Polymerization of p-Methylstyrene in Ionic Liquid and Its Mechanism

Ionic liquid (IL) as a green solvent is entirely composed of ions; thus, it may be more than a simple solvent for ionic polymerization. Here, the cationic polymerization of p-methylstyrene (p-MeSt) initiated by 1-chloro-1-(4-methylphenyl)-ethane (p-MeStCl)/tin tetrachloride (SnCl4) was systematically studied in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim][NTf2]) IL at −25 °C. The results show that IL did not participate in cationic polymerization, but its ionic environment and high polarity were favorable for the polarization of initiator and monomer and facilitate the controllability. The gel permeation chromatography (GPC) trace of the poly(p-methylstyrene) (poly(p-MeSt)) changes from bimodal in dichloromethane (CH2Cl2) to unimodal in IL, and polydispersities Mw/Mn of the polymer in IL showed narrower (1.40–1.59). The reaction rate and heat release rate were milder in IL. The effects of the initiating system, Lewis acid concentration, and 2,6-di-tert-butylpyridine (DTBP) concentration on the polymerization were investigated. The controlled cationic polymerization initiated by p-MeStCl/SnCl4 was obtained. The polymerization mechanism of p-MeSt in [Bmim][NTf2] was also proposed

Extraordinary fracture toughness in nickel induced by heterogeneous grain structure

The tensile properties and fracture toughness of both heterogeneous grain structures and homogeneous structures in pure nickel have been investigated and compared. The heterogeneous samples were found to show much larger uniform elongation and much higher fracture toughness at the similar level of yield strength, compared to the homogeneous structures. The enhanced ductility/toughness can be attributed to the stronger heterodeformation-induced hardening for the heterogeneous structures. In sharp contrast to the cleavage-like and brittle fracture behavior in the homogeneous hot-extruded and cold-rolled samples, the fracture process in the heterogeneous structures shows ductile fracture by microvoid coalescence and dimples. The crack path in the heterogeneous structures was found to display a gourd shape, which can result in longer crack length and dissipate more energy for better fracture toughness. Hardening is obvious across a much larger area around the crack tip in the heterogeneous structures as compared to the homogeneous structures, indicating a much larger plastic zone for the heterogeneous structures. The strong strain hardening at the crack tip was found to be induced by the grain refinement of the coarse grains in the heterogeneous structures, resulting in extraordinary fracture toughness

Transient Global Amnesia following Neural and Cardiac Angiography May Be Related to Ischemia

Introduction. Transient global amnesia (TGA) following angiography is rare, and the pathogenesis has not been illustrated clearly till now. The aim of this research is to explore the pathogenesis of TGA following angiography by analyzing our data and reviewing the literature. Methods. We retrospectively studied 20836 cases with angiography in our hospital between 2007 and 2015 and found 9 cases with TGA following angiography. The data of these 9 cases were analyzed. Results. We found all 9 cases with TGA following neural angiography (5 in 4360) or cardiac angiography (4 in 8817) and no case with TGA following peripheral angiography (0 in 7659). Statistical difference was found when comparing the neural and cardiac angiography group with peripheral group (p=0.022). Two cases with TGA were confirmed with small acute infarctions in hippocampus after angiography. This might be related to the microemboli which were rushed into vertebral artery following blood flow during neural angiography or cardiac angiography. There was no statistical difference when comparing the different approaches for angiography (p=0.82) and different contrast agents (p=0.619). Conclusion. Based on the positive findings of imaging study and our analysis, we speculate that ischemia in the medial temporal lobe with the involvement of the hippocampus might be an important reason of TGA following angiography

Development and Prospect of Vacuum High-Pressure Gas Quenching Technology

As industrial modernization surges forward, the heat treatment industry strives for lower pollution, reduced oxidation and defects, minimized waste, and automatization. This paper reviews the mechanisms, processes, equipment, and simulations of the vacuum gas quenching technology, presenting a comprehensive account of the structure and working principle of a typical vacuum gas quenching furnace. Firstly, the mechanism of the heat transfer process, flow process, and flow–heat transfer–phase transition coupling were summarized. Then, the influences of process parameters on the mechanical properties and distortion of vacuum gas quenched workpieces, as well as the process optimization methods, were discussed. Finally, the advantages of vacuum gas quenching in energy saving, low pollution, and high efficiency were introduced, with the future development directions figured out

Excellent dynamic properties and corresponding deformation mechanisms in a microband-induced plasticity steel with dual-heterogeneous structure

A dual-heterogeneous structure with dual phases and heterogeneous grains was designed in a high Mn microband-induced-plasticity (MBIP) steel. The heterogeneous structured sample exhibits similar dynamic shear yield strength, while exhibiting enhanced dynamic uniform shear strain and dynamic shear toughness by 36 % and 47 %, respectively, as compared to the homogeneous structured sample. The strain hardening mechanisms contributing to the excellent dynamic shear properties in the heterogeneous structured sample have been revealed. Firstly, the superior hetero-deformation-induced hardening capability of the heterogeneous structured sample arises from a higher density of geometrically necessary dislocations induced in each phase. Secondly, a pronounced strain rate effect is observed in body-centered cubic (BCC) grains and face-centered cubic (FCC) ultra-fine grains, leading to an elevated level of strain rate sensitivity. Finally, the MBIP effect is also observed in FCC coarse grains under dynamic loading. Moreover, the MBIP effect in FCC ultra-fine grains is more likely to occur at high strain rates due to the emergence of single-wall domain boundaries, which is not observed during quasi-static tensile testing. The present results provide new routes for designing impact-tolerant structures in advanced metals and alloys

Tensile Behaviors and Strain Hardening Mechanisms in a High-Mn Steel with Heterogeneous Microstructure

Heterogeneous structures with both heterogeneous grain structure and dual phases have been designed and obtained in a high-Mn microband-induced plasticity (MBIP) steel. The heterogeneous structures show better synergy of strength and ductility as compared to the homogeneous structures. Higher contribution of hetero-deformation induced hardening to the overall strain hardening was observed and higher density of geometrically necessary dislocations were found to be induced at various domain boundaries in the heterogeneous structures, resulting in higher extra strain hardening for the observed better tensile properties as compared to the homogeneous structures. MBIP effect is found to be still effective in the coarse austenite grains of heterogeneous structures, while the typical Taylor lattice structure and the formation of microband are not observed in the ultra-fine austenite grains of heterogeneous structures, indicating that decreasing grain size might inhibit the occurrence of microbands. High density of dislocation is also observed in the interiors of BCC grains, indicating that both phases are deformable and can accommodate plastic deformation. It is interesting to note that the deformation mechanisms are highly dependent on the phase and grain size for the present MBIP steel with heterogeneous structures

Additional file 1 of Claudin-18.2 mediated interaction of gastric Cancer cells and Cancer-associated fibroblasts drives tumor progression

Additional file 1