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ABSTRACT: Amorphous Ti50Cu28Ni15Sn7 alloy powders were synthesized by a mechanical alloying (MA) technique. Differential scanning calorimetry (DSC) results showed
that, after 7hours of exposure to the milling process, amorphous Ti50Cu28Ni15Sn7 alloy powders exhibit a wide supercooled liquid region of 61K. Consolidation of amorphous powders were performed at a temperature
slightly higher than the glass transition temperature under a pressure of ∼1.2GPa, and bulk metallic glass (BMG) discs can
be prepared successfully. However, we noticed partial crystallization during the hot pressing process and were not able to
achieve full densification of BMG. The Vickers microhardness of Ti50Cu28Ni15Sn7 BMG was 634kg/mm2, and the trace of the indentation revealed that pre-existing particle boundaries or interfaces between nanocrystals and amorphous
matrix may serve as the crack initiation sites. Thus, typical brittle failure of Ti50Cu28Ni15Sn7 BMG was observed and resulted in relatively low fracture stress compared to that estimated by the microhardness.
Metallurgical and Materials Transactions A 04/2012; 39(8):1857-1861. · 1.54 Impact Factor
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Advanced Engineering Materials 11/2008; 10(11):1053 - 1055. · 1.18 Impact Factor
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ABSTRACT: High-speed milling of hardened steels generates high cutting temperature and leads to detrimental effects on tool life and workpiece surface finish. In this paper, feasibility study of the minimum quantity lubrication (MQL) in high-speed end milling of NAK80 hardened steel by coated carbide tool was undertaken. Flood cooling and dry cutting experiments were conducted also for comparison. It is found that cutting under flood cooling condition results in the shortest tool life due to severe thermal cracks while the use of MQL leads to the best performance. MQL is beneficial to tool life both in the lower speed cutting and the higher speed cutting conditions. A less viscous oil of MQL is essential in high cutting speed so that cooling effect can be effective. SEM micrograph of the insert shows that the use of MQL in high-speed cutting can delay welding of chips on the tool and hence prolongs tool life as compared with dry cutting condition. The application of MQL also improves machined surface finish in high-speed milling of die steels.
International Journal of Machine Tools and Manufacture 01/2007; 47:1667-1676. · 2.17 Impact Factor
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ABSTRACT: In the current study, pure elemental powders of Fe and S were mixed to give the desired compositions of Fe 67 S 33 , Fe 50 S 50 and Fe 33 S 67 . A SPEX 8000D high-energy ball mill was used to synthesize iron sulfide powders under an Ar-filled atmosphere. The as-milled powders were examined by conventional X-ray diffraction (XRD) and synchrotron X-ray absorption spectroscopy (XAS). The experimental results showed that mechanochemical reactions occurred during the ball milling process for all the compositions investigated. The Fe 1−x S phase was observed at the end of milling. The formation time of the Fe 1−x S phase increased with increasing sulfur content. Extended X-ray absorption fine structure (EXAFS) results revealed that the nearest neighbor bond lengths of the radial distribution function for iron decreased when iron sulfides formed. X-ray absorption near-edge structure (XANES) of sulfar K-edges distinguished better the structural evolution of these iron sulfides.
Materials Science and Engineering A. 01/2004; 375377:834-838.
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ABSTRACT: Cyclin D1 expression is co-regulated by growth factor and cell adhesion signaling. Cell adhesion to the extracellular matrix activates focal adhesion kinase (FAK), which is essential for cyclin D1 expression. Upon the loss of cell adhesion, cyclin D1 expression is downregulated, followed by apoptosis in normal epithelial cells. Since bcl-2 prevents apoptosis induced by the loss of cell adhesion, we hypothesized that bcl-2 induces survival signaling complementary to cell adhesion-mediated gene regulation. In the present study, we investigated the role of bcl-2 on FAK activity and cyclin D1 expression. We found that bcl-2 overexpression induces cyclin D1 expression in human breast epithelial cell line MCF10A independent of cell anchorage. Increased cyclin D1 expression in stable bcl-2 transfectants is not related to bcl-2-increased G1 duration, but results from cyclin D1 promoter activation. Transient transfection studies confirmed anchorage-independent bcl-2 induction of cyclin D1 promoter activity in human breast epithelial cell lines (MCF10A, BT549, and MCF-7). We provide evidence that bcl-2 induction of cyclin D1 expression involves constitutive activation of focal adhesion kinase, regardless of cell adhesion. The present study suggests a potential oncogenic activity for bcl-2 through cyclin D1 induction, and provides an insight into the distinct proliferation-independent pathway leading to increased cyclin D1 expression in breast cancer.
Cell Death and Differentiation 02/2001; 8(1):44-50. · 8.85 Impact Factor
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ABSTRACT: Many recent studies have focused on potential chemopreventive activities of dietary genistein, a natural isoflavonoid compound found in soy products. Genistein has been implicated in anticancer activities, including differentiation, apoptosis, inhibition of cell growth and inhibition of angiogenesis. In previous studies, genistein was shown to induce apoptosis and cell cycle arrest at G(2)/M in several cancer cell lines in vitro, which is associated with induction of p21(WAF1/CIP1), a universal inhibitor of cyclin-dependent kinases. At present, the molecular basis for diverse genistein-mediated cellular responses is largely unknown. In the present study, we investigated whether galectin-3, an anti-apoptotic gene product, regulates genistein-mediated cellular responses. We show that genistein effectively induces apoptosis without detectable cell cycle arrest in BT549, a human breast epithelial cell line which does not express galectin-3 at a detectable level. In galectin-3 transfected BT549 cells, genistein induced cell cycle arrest at the G(2)/M phase without apoptosis induction. Interestingly, genistein induces p21(WAF1/CIP1) expression in galectin-3-expressing BT549 cells, but not in control BT549 cells undergoing apoptosis. Collectively, the results of the present study suggest that galectin-3, at least in part, is a critical determinant for genistein-mediated cell cycle arrest and apoptosis, and genistein induction of p21(WAF1/CIP1) is associated with cell cycle arrest, but not required for apoptosis induction.
Carcinogenesis 12/2000; 21(11):1941-5. · 5.70 Impact Factor
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ABSTRACT: Galectin-3 is a member of a growing family of animal beta-galactoside-binding proteins shown to be involved in cell growth, differentiation, apoptosis resistance, and tumor progression. In the present study, we investigated whether galectin-3 can protect against apoptosis induced by the loss of cell anchorage (anoikis). Because studies suggest that cellular sensitivity to anoikis is associated with cell cycle regulation, we examined the role of galectin-3 on cell cycle regulation. Although BT549 cells (human breast epithelial cells) undergo anoikis, galectin-3-overexpressing BT549 cells respond to the loss of cell adhesion by inducing G1 arrest without detectable cell death. Galectin-3-mediated G1 arrest involves down-regulation of G1-S cyclin levels (cyclin E and cyclin A) and up-regulation of their inhibitory protein levels (p21(WAF1/CIP1) and p27KIP1). After the loss of cell anchorage, Rb protein becomes hypophosphorylated in galectin-3-overexpressing cells, as predicted from the flow cytometric analysis and immunoblot analysis of cyclins and their inhibitors. Interestingly, galectin-3 induces cyclin D1 expression (an early G1 cyclin) and its associated kinase activity in the absence of cell anchorage. On the basis of these results, we propose that galectin-3 inhibition of anoikis involves cell cycle arrest at an anoikis-insensitive point (late G1) through modulation of gene expression and activities of cell cycle regulators. The present study suggests that galectin-3 may be a critical determinant for anchorage-independent cell survival of disseminating cancer cells in the circulation during metastasis.
Cancer Research 09/1999; 59(16):4148-54. · 7.86 Impact Factor
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ABSTRACT: Members of the bcl-2 gene family encode proteins that function either to promote or to inhibit apoptosis. Despite numerous efforts, the mechanism of action of Bcl-2, an anti-apoptotic protein, is still not clear. In particular, the relation between Bcl-2 and the endoplasmic reticulum (ER) calcium store is not well-understood. In the present work, we examined the effect of Bcl-2 on the ER store. We demonstrate that overexpression of Bcl-2 in breast epithelial cells modulates ER store by upregulating calcium pump (SERCA) expression without affecting the release channel (IP3R). The steady state levels of SERCA2 mRNA and protein were both increased in Bcl-2 expression clones. The increase in SERCA2 protein leads to accelerated calcium uptake and enhanced Ca2+ loading. In addition, we also show the detection of intracellular interaction between Bcl-2 and SERCA molecules by co-immunoprecipitation. Since high lumenal Ca2+ concentration of ER is essential for normal cell functions, the results suggest that Bcl-2 preserves the ER Ca2+ store by upregulating SERCA gene expression as well as by a possible interaction with the pump.
Oncogene 11/1998; 17(15):1903-10. · 6.37 Impact Factor
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ABSTRACT: High-speed milling of hardened steels generates high cutting temperature and leads to detrimental effects on tool life and workpiece surface finish. In this paper, feasibility study of the minimum quantity lubrication (MQL) in high-speed end milling of NAK80 hardened steel by coated carbide tool was undertaken. Flood cooling and dry cutting experiments were conducted also for comparison. It is found that cutting under flood cooling condition results in the shortest tool life due to severe thermal cracks while the use of MQL leads to the best performance. MQL is beneficial to tool life both in the lower speed cutting and the higher speed cutting conditions. A less viscous oil of MQL is essential in high cutting speed so that cooling effect can be effective. SEM micrograph of the insert shows that the use of MQL in high-speed cutting can delay welding of chips on the tool and hence prolongs tool life as compared with dry cutting condition. The application of MQL also improves machined surface finish in high-speed milling of die steels.
International Journal of Machine Tools and Manufacture.
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ABSTRACT: The rapid wear rate of cutting tools due to high cutting temperature is a critical problem to be solved in high-speed machining (HSM) of hardened steels. Near-dry machining such as minimum quantity lubrication (MQL) is regarded as one of the solutions to this difficulty. However, the function of MQL in HSM is still uncertain so far which prevents MQL from widely being utilized in the machining of hardened steels. In this paper, the mechanism of MQL in HSM of hardened steel is investigated more comprehensively. Comparing with dry cutting, the tool performance can be enhanced by MQL under all cutting speeds in this study. It is found that MQL can provide extra oxygen to promote the formation of a protective oxide layer in between the chip–tool interface. This layer is basically quaternary compound oxides of Fe, Mn, Si, and Al, and is proved to act as diffusion barriers effectively. Hence, the strength and wear resistance of a cutting tool can be retained which leads to a significant improvement of tool life. It is found that there exists an optimal cutting speed at which a stable protective oxide layer can be formed. When cutting speed is lower than this speed, there is less oxide layer and the improvement of tool life is less apparent. As the cutting speed is far beyond the optimal value, the protective layer is absent and the thermal cracks are apt to occur at the cutting edge due to large fluctuation of temperature. Resultantly, application of MQL is inappropriate in the extreme high-speed cutting condition irrespective of its little increase in tool life. Based on this study, it is concluded that the tool life can be effectively improved by MQL in HSM of NAK80 hardened steels when cutting parameters are chosen properly.
International Journal of Machine Tools and Manufacture.
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ABSTRACT: End milling of Inconel 718 under various cutting speeds by cemented carbide tools was conducted. For slot milling, it is found that the increase of cutting temperature and strain hardening are responsible for the difficulty at low speed cutting. Tool failure is mainly in the form of chipping and breakage of the cutting edge. At medium cutting speeds, softening of work material due to special thermal stability property of γ′ precipitation of Inconel 718 leads to a reduction of cutting force, and tool life is improved with the increase of speed. But when cutting speed is further increased, most of the chips are welded on both sides of the slot, and chip flow is retarded. The cutting temperature would rise drastically and plastic deformation of cutting tool takes place eventually. Cutting speed plays a less important role in side milling since chips can flow more smoothly. Based on this study, it is found that high cutting temperature and difficult chip disposal are two main problems encountered in high-speed end milling of Inconel 718. It is also concluded that there exists an appropriate range of cutting speed in end milling of Inconel 718 by cemented carbide tools. On the contrary, feed does not have a significant effect for both kinds of milling operations.
Journal of Materials Processing Technology.
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ABSTRACT: The ultrasonic vibration assisted drilling of Inconel 718 superalloy is studied in this paper. The tool holder of a machining center is retrofitted so that axial resonant vibration can be provided. Experimental results show that the chip size is reduced, and the variation of torque in drilling becomes smaller. These phenomena are particularly apparent at the final stage of a drill's usable life. It is also found that there is little improvement in drilling performance when the frequency of the ultrasonic vibration is varied. On the contrary, a drill's life is greatly increased when the vibration with a smaller amplitude is applied. But too large a vibration amplitude, such as over 12 μm in this study, could lead to negative effects. For the testing conditions, the frequency of 31.8 kHz and the amplitude of 4 μm result in the best drill life and quality of the drilled hole in this study. Under this condition a drill's life is prolonged by as much as 2.7 times of that without vibration assisted drilling process. Concerning drilling efficiency, it is found that by applying ultrasonic vibration assisted drilling, lifting of the drill for chip removal as commonly employed in conventional drilling of a high aspect ratio hole is not necessary, and saving of the working time is obtained.
International Journal of Machine Tools and Manufacture 47:1988-1996. · 2.17 Impact Factor
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ABSTRACT: In the current study, pure elemental powders of Fe and S were mixed to give the desired compositions of Fe67S33, Fe50S50 and Fe33S67. A SPEX 8000D high-energy ball mill was used to synthesize iron sulfide powders under an Ar-filled atmosphere. The as-milled powders were examined by conventional X-ray diffraction (XRD) and synchrotron X-ray absorption spectroscopy (XAS). The experimental results showed that mechanochemical reactions occurred during the ball milling process for all the compositions investigated. The Fe1−xS phase was observed at the end of milling. The formation time of the Fe1−xS phase increased with increasing sulfur content. Extended X-ray absorption fine structure (EXAFS) results revealed that the nearest neighbor bond lengths of the radial distribution function for iron decreased when iron sulfides formed. X-ray absorption near-edge structure (XANES) of sulfar K-edge distinguished better the structural evolution of these iron sulfides.
Materials Science and Engineering: A.
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ABSTRACT: This study investigated the tensile properties of spray-formed (SF) and ingot-cast (IC) high-Si aluminum alloys which suffered from cyclic heating/cooling. Due to the breakup of massive primary Si particles, the strength of the IC specimens descends gradually with an increasing number of thermal cycles. The uniform and refined structure of the SF specimens displays ductile fracture pattern and retains a similar tensile behavior even after a great number of heating and water quenching.
Scripta Materialia.
