Electro-healing cracks in nickel Zheng, X.G.; Shi, Y.-N.; Lu, K.
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
01/2013, Letnik:
561
Journal Article
Recenzirano
Healing cracks in metallic materials is challenging due to limited atomic mobility in solid state around ambient temperature. In this paper, we developed a novel crack-healing approach by means of an ...electrochemical process in which metallic ions in electrolyte are used as a healing agent. Pure Ni sheets with a through-thickness crack were taken as an example. Cracks with sizes in the micrometer range or larger are successfully healed by electro-healing. The electro-healing process starts with the vertical epitaxial growth of healing crystals from the original crack surfaces followed by lateral growth of healing crystals that bond with each other at atomistic level. Tensile tests exhibited that the healed samples have a comparable tensile strength as the virgin sample and some tensile ductility can be achieved for the sample of 100μm thick. Post-fracture analysis indicated that part of the crack propagated along the substrate instead of healing crystals. The healing efficiency, ranging from 96% to 33% with an increasing sample thickness, is related to the fraction of fully-healed region and the strength difference between the substrate and the healing crystals.
Mesenchymal stromal cells (MSCs) tend to infiltrate into tumors and form a major component of the tumor microenvironment. Our previous work demonstrated that tumor necrosis factor α (TNFα)-activated ...MSCs significantly promoted tumor growth. However, the role of TNFα-treated MSCs in tumor metastasis remains elusive. Employing a lung metastasis model of murine breast cancer, we found that TNFα-activated MSCs strikingly enhanced tumor metastasis compared with normal MSCs. We analyzed the chemokine profiles and found that the expression of CCL5, CCR2 and CXCR2 ligands were enhanced in TNFα-activated MSCs. Using genetic or pharmacological strategies to inhibit CCL5 or CCR2, we demonstrated that CCL5 and CCR2 ligands were indispensable in supporting TNFα-activated MSCs to promote tumor metastasis. Analysis of immune cells revealed that CXCR2 ligands (CXCL1, CXCL 2 and CXCL5) expressed by TNFα-activated MSCs efficiently recruited CXCR2
neutrophils into tumor. These neutrophils were responsible for the pro-metastatic effect of MSCs since inhibition of this chemotaxis abolished increased neutrophil recruitment and tumor metastasis. The interaction between neutrophils and tumor cells resulted in markedly elevated metastasis-related genes by tumor cells, including CXCR4, CXCR7, MMP12, MMP13, IL-6 and TGFβ. Importantly, in IL8
human breast cancer samples, we also observed similar alterations of gene expression. Collectively, our findings demonstrate that TNFα-activated MSCs promote tumor metastasis via CXCR2
neutrophil recruitment.
Astrometric ground-based catalogs usually suffer from varied systematic errors. These systematic errors were hard to detect because there was no independent reference catalog complete to very faint ...limiting magnitudes (∼20 mag). This situation has changed since the second data release of the Gaia mission (Gaia DR2). We aim to investigate positions and the proper-motion (PM) system of two ground-based catalogs, the UCAC5 and PPMXL, referring to the Gaia DR2. The individual position in the Gaia DR2 is transferred by its PM to the epoch of other catalogs for comparison. Systematic errors that depend on the magnitude, color, and sky regions in the UCAC5 and PPMXL could be clearly seen. A different behavior between the northern and southern sky is found in the PPMXL, which is possibly inherited from the imperfect calibration of the PM system. Besides, we perform a quantitative analysis of global differences for positions and PMs by the vector spherical harmonics method in terms of 3 rotation angles, 3 glide parameters, and 10 quadrupole parameters. We find a large glide component of ∼8 mas along Z-axis and a rotation angle of ∼5 mas about Z-axis for positional offsets between the PPMXL and Gaia DR2. These terms are found to be insignificant between the UCAC5 and Gaia DR2. We show that the position and PM system of the UCAC5, a new reduction of ground-based observations in the frame of the Gaia reference system, has been largely improved. This indicates that systematic errors in positions and PMs obtained from ground-based observations are mostly impacted by a relatively poor reference catalog. But these observations can be reconstructed in the frame of a space-based reference catalog. In this sense, our results justify the tradition of space-calibrated ground-based astrometric catalogs.
This work proposes a T6-like heat treatment, including solid-solution treatment at 535 °C and an artificial aging treatment for 10 h at 158 °C, to control the mechanical behavior of selective-laser- ...melting (SLM)-produced AlSi10Mg alloys. The mechanical properties of the AlSi10Mg alloys, such as densification, hardness, and tensile/bending strength, were investigated, and the microstructure of the alloys was analyzed. The results reveal that the tensile strength of the heat-treated samples slightly decreased by 19.97% (from 334 MPa to 267.3 MPa of the as-fabricated samples), while the elongation showed a remarkable increase by up to 155% (from 3.64% to 9.28%). Likewise, the bending strength slightly decreased by 6.1%, while the fracture deflection dramatically increased by up to 122.9% after T6 heat treatment. Thus, the T6 heat treatment can critically enhance plasticity/ductility without any significant loss in the tensile/bending strength of the alloy. The corresponding mechanism is also elucidated based on the spheroidization and diffusion of silicon precipitation during the T6 heat treatment. The results of this study offer an intriguing insight to tailor the mechanical properties of SLM-fabricated AlSi10Mg alloys using suitable solid solutions and artificial aging treatment.
In this work, stress- and fracture mechanics-based criteria are developed to predict initiation and evolution, respectively, of intra- and inter-laminar cracking developed in composite laminates ...subjected to a relatively low energy impact (⩽15J) with consideration of nonlinear shear behaviour. The damage model was implemented in the finite element (FE) code (Abaqus/Explicit) through a user-defined material subroutine (VUMAT). Delamination (or inter-laminar cracking) was modelled using interface cohesive elements while splitting and transverse matrix cracks (intralaminar cracking) that appeared within individual plies were also simulated by inserting cohesive elements along the fibre direction (at a crack spacing determined from experiments for computing efficiency). A good agreement is obtained when the numerically predicted results are compared to both experimentally obtained curves of impact force and absorbed energy versus time and X-ray radiography damage images, provided the interface element stiffness is carefully selected. This gives confidence to selected fracture criteria and assists to identify material fracture parameters that influence damage resistance of modern composite material systems.
Rare-earth (RE) mischmetal modification, homogenous annealing and rolling techniques were used to improve the microstructure and mechanical properties of an Al−1Fe alloy. Al3Fe, Al6Fe and Al3Ce ...intermetallic phases were found in the RE-modified alloys in the as-cast state. The RE modification refined the α-Al grains, resulting in a divorced eutectic and the formation of the Al−Fe phases in the forms of discontinuous networks, flakes and particles. Elemental La dissolved in the Al−Ce phases but did not dissolve in the Al−Fe phases. The dissolution of elemental Ce in the Al−Fe phase along with homogeneous annealing caused the claw-like Al−Fe phases to transform into short flakes and particles, which were uniformly distributed in the matrix by the rolling processes. A 0.3wt% RE modification had the optimized effect on the microstructure and mechanical properties, while a 0.4wt% RE addition resulted in the aggregation of the Al−Ce particles, which then deteriorated the mechanical properties of the alloys.
In this study, we present a method that employed ultrasound to impose vibration on the surfaces of cementitious materials at the early stage of hydration to form a hardening layer and improve the ...surface hardness. The formation mechanism of the ultrasonic hardening layer (UHL) was analyzed, and the density and surface hardness of the UHL were measured. An experimental study was carried out to determine the effect of the UHL on improving the wind-blown sand erosion resistance of cementitious materials. Experimental data show that the UHL has a density 3.3% greater and a hardness 136% greater than that of the contrast samples after 28-days of curing. Wind-blown sand erosion tests data show that to the specimens with 28-days curing age, the UHL can improve the erosion resistance for 12.8–24.1% versus that of the contrast in a 30-min erosion procedure.
•A layer known as the UHL can be formed by ultrasonic vibration applied on the surface of cementitious composites.•UHL had the characteristics of higher density and higher surface hardness.•In the UHL, the micro-structure of the composite was promoted.•The UHL improved the erosion resistance of the cement mortar specimens in a wind-blown sand erosion test.
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