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234 results on '"Liu, J.Q."'

31. Microstructure and properties of FeCoNiCrMn and Al2O3hybrid particle-reinforced aluminum matrix composites fabricated by microwave sintering

Author

Wang, H.M., Su, W.X., Liu, J.Q., Li, G.R., Liu, Y.J., and Zhou, P.J.

Abstract

In this paper, multiscale Al2O3micro/nanoparticles (0–14 wt%) mixed with FeCoNiCrMn high-entropy alloy (HEA) particles (15 wt%) were used as reinforcements to prepare dual-phase-reinforced aluminum matrix composites (AMCs) through microwave sintering. The strengthening effects of doping different weight fractions of Al2O3micro/nanoparticles on the microstructure, mechanical properties, and strengthening mechanisms of the mixed-phase particle-reinforced AMCs were investigated. The performance after 11 wt% Al2O3+HEA microparticles was similar to that obtained by adding 2 wt% and 5 wt% Al2O3+HEA nanoparticles. The hardness, yield strength, and compressive strength of the 2 wt% nano-Al2O3composite were 109.7 HV, 286.5 MPa, and 506.7 MPa, respectively, which were 70.9%, 98.5%, and 94.7% higher than those of the single HEA-reinforced sample. In terms of the strengthening and toughening mechanisms, Orowan strengthening, dislocation strengthening, and thermal mismatch strengthening were the main strengthening mechanisms of particles species mixed in the metal matrix composites. Hall-Petch strengthening and load-transfer effects were mainly attributed to the cross-scale mixing of particles. The hybrid particles of HEA and Al2O3synergistically delayed interfacial crack propagation. This study provides a new preparation method for high-performance metal matrix composites.

Published
2023
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41. Hypoxic constriction and reactive oxygen species in porcine distal pulmonary arteries

Author

Liu, J.Q., Sham, J.S.K., Shimoda, L.A., Kuppusamy, P., and Sylvester, J.T.

Subjects
Smooth muscle -- Research, Biological sciences
Abstract

To determine whether reactive oxygen species (ROS) play an essential role in hypoxic pulmonary vasoconstriction (HPV) and the cellular locus of ROS production and action during HPV, we measured internal diameter (ID) at constant transmural pressure, lucigenin-derived chemiluminescence (LDCL), and electron paramagnetic resonance (EPR) spin adduct spectra in small distal porcine pulmonary arteries, and dichlorofluorescein (DCF) fluorescence in myocytes isolated from these arteries. Hypoxia (4% [O.sub.2]) decreased ID, increased DCF fluorescence, tended to increase LDCL, and in some preparations produced EPR spectra consistent with hydroxyl and alkyl radicals. Superoxide dismutase (SOD, 150 U/ml) or SOD + catalase (CAT, 200 U/ml) did not alter ID during normoxia but reduced or abolished the constriction induced by hypoxia. SOD also blocked HPV in endothelium-denuded arteries after restoration of the response by exposure to [10.sup.-10] M endothelin-1. Confocal fluorescence microscopy demonstrated that labeled SOD and CAT entered pulmonary arterial myocytes. SOD, SOD + CAT, and CAT blocked the increase in DCF fluorescence induced by hypoxia, but SOD + CAT and CAT also caused a stable increase in fluorescence during normoxia, suggesting that CAT diminished efflux of DCF from cells or oxidized the dye directly. We conclude that HPV required increased concentrations of ROS produced by and acting on pulmonary arterial smooth muscle rather than endothelium. vascular smooth muscle; endothelium; electron paramagnetic resonance; dichlorofluorescein; lucigenin; superoxide dismutase; catalase

Published
2003

43. Recombination-enhanced defect motion in forward-biased 4H-SiC p-n diodes

Author

Skowronski, M., Liu, J.Q., Vetter, W.M., Dudley, M., Hallin, C., and Lendenmann, H.

Subjects
Electroluminescence -- Analysis, Synchrotron -- Usage, Silicon carbide -- Electric properties, Physics
Abstract

The generation and evolution of defects in 4H-SiC p-n junctions due to carrier injection under forward bias are investigated by synchrotron white beam x-ray topography, electroluminescence imaging, and KOH etching. Low angle grain boundaries are observed to act as one of a number of possible nucleation sites of stacking faults.

Published
2002

50. Effect of TiB2content on microstructure and mechanical properties of (TiB2p+B4Cp)/Al composites fabricated by microwave sintering

Author

Wang, H.M., Liu, J.Q., Li, G.R., Tang, F., Yan, Y.W., Gao, L.P., and Zhao, Y.T.

Abstract

This study demonstrates a novel method to improve the density, interface bonding strength and mechanical properties of the B4Cp/Al composites by directly adding TiB2to the material. Specifically, the (TiB2p+B4Cp)/Al composites with different TiB2contents were successfully fabricated by ball milling (BM) and microwave sintering (MS). The results indicate that the developed (TiB2p+B4Cp)/Al possess a clean interface, with the absence of any reaction, thus, confirming microwave sintering as one of the preferred ways to prepare the (TiB2p+B4Cp)/Al composites. On adding TiB2, the densification in the microstructure is noted to initially increase, followed by a decrease. Overall, the TiB2and B4C particles are noted to synergistically improve the densification as well as ameliorate the interfaces and microstructure. As a result, the optimized composites exhibit the compactness and Vickers hardness as high as 94.6% and 153.42HV0.3respectively. The highest value of the compressive strength is determined to be 578.71 MPa at 50.0%. Further, no macroscopic fracture is noted to occur after 50% compression strain.

Published
2021
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