Due to their light weight, high corrosion resistance and good heat conductivity, aluminium alloys are used in many industries today. They are suitable for manufacturing many automotive components such as clutch housin...
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Due to their light weight, high corrosion resistance and good heat conductivity, aluminium alloys are used in many industries today. They are suitable for manufacturing many automotive components such as clutch housings. These alloys can be fabricated by powder metallurgy and casting methods, in which porosity is a common feature. The presence of pores is responsible for reducing their strength, ductility and wear resistance. The present study aims to establish an understanding of the tribological behavior of high pressure die cast Al A380M and powder metallurgy synthesized Al 6061. In this study, dry sliding wear behavior of Al A380M and Al 6061 alloys was investigated under low loads (1.5 N – 5 N) against AISI 52100 bearing steel ball using a reciprocating ball-on-flat configuration and frequency of 10 Hz. Wear mechanisms were studied through microscopic examination of the wear tracks. This study revealed that due to combined effect of real area of contact and subsurface cracking, wear rate increased with increasing porosity content. The difference in friction and wear behavior between received Al A380M and Al 6061 is attributed to their hardness differences.
Indentation and reciprocating wear tests are carried out to study dent and wear resistance of superelastic Ti-Ni alloys. The effect of loading rate on the superelastic behavior of TiNi under indentation loading is inv...
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Indentation and reciprocating wear tests are carried out to study dent and wear resistance of superelastic Ti-Ni alloys. The effect of loading rate on the superelastic behavior of TiNi under indentation loading is investigated and compared to a new generation of shape memory alloys, i.e., 60NiTi. Only limited amount of work has been done to investigate the dependency of superelasticity on loading rate of TiNi under localized compressive loads, but much work is directed towards understanding the effect of strain rate on tensile properties. Understanding the superelastic behavior helps to employ superelastic alloys in applications where high impact loading is expected as in bearings and gears. In the present study, it is found that dent resistance of Ti-Ni alloy is not significantly affected by loading rate (within the employed loading conditions). It has also been found that new-generation 60NiTi alloy exhibits superior wear and dent resistance, as well as higher hardness compared to equiatomic TiNi.
Due to light weight, high specific strength, high corrosion resistance and good heat transfer ability, aluminium alloys are becoming attractive for critical structural applications. These alloys can be manufactured us...
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Due to light weight, high specific strength, high corrosion resistance and good heat transfer ability, aluminium alloys are becoming attractive for critical structural applications. These alloys can be manufactured using powder metallurgy techniques in which porosity is a common characteristic. The presence of pores is responsible for decreasing effective load bearing cross sectional area and inducing stress concentration sites for strain localization and damage, decreasing both strength and ductility. The present study aims to establish a better understanding of the relationship between surface porosity and corresponding wear behavior. In this study, porous specimens were produced using powder metallurgy technique and the extent of wear damage and the type of wear was investigated under low load range of 1.5 - 5 N against AISI 52100 bearing steel ball using a reciprocating ball-on-flat configuration and frequency of 10 Hz. Scanning electron microscopy of the wear tracks and wear debris was carried out to understand wear mechanisms. This study revealed that due to combined effect of high stress intensity and subsurface cracking, wear rate increases with increasing porosity content. The friction and wear behavior of pure Al and Al 6061 as a function of porosity content can be attributed to their hardness and corresponding wear mechanism.
Electrical resistivity, magnetization, and specific heat measurements were performed on polycrystalline samples of the filled-skutterudite systems La1−xMxPt4Ge12(M=Ce and Th). Superconductivity in LaPt4Ge12 was quickl...
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Electrical resistivity, magnetization, and specific heat measurements were performed on polycrystalline samples of the filled-skutterudite systems La1−xMxPt4Ge12(M=Ce and Th). Superconductivity in LaPt4Ge12 was quickly suppressed with Ce substitution and no evidence for superconductivity was found down to 1.1 K for x>0.2. Temperature-dependent specific heat data at low temperatures for La1−xCexPt4Ge12 show a change from power-law to exponential behavior, which may be an indication for multiband superconductivity in LaPt4Ge12. A similar crossover was observed in the Pr1−xCexPt4Ge12 system. However, the suppression rates of the superconducting transition temperatures Tc(x) in the two systems are quite disparate, indicating a difference in the nature of superconductivity, which is conventional in LaPt4Ge12 and unconventional in PrPt4Ge12. In comparison, a nearly linear and smooth evolution of Tc with increasing Th was observed in the La1−xThxPt4Ge12 system, with no change of the superconducting energy gap in the temperature dependence of the specific heat, suggesting similar types of superconductivity in both the LaPt4Ge12 and ThPt4Ge12 compounds.
Chiral molecules display a unique interaction with light. Here, the synthesis of two types of chiral structures based on spiro compounds is presented, each of which show remarkable chiroptical activity. The structure ...
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Chiral molecules display a unique interaction with light. Here, the synthesis of two types of chiral structures based on spiro compounds is presented, each of which show remarkable chiroptical activity. The structure of the (P2)‐1 molecule shows a double helix formed by all‐carbon atoms, whereas the (P4)‐2 molecule revealed a flexible configuration that modifies its chiroptical activity, but keeps its overall peculiar structure. More information can be found in the Communication by A. Qin, J. Ling and B. Z. Tang et al. on page 10725 ff.
We regioselectively localize protein hydrogels over the hot spots of single gold nanotriangle using MPPL, and track the immobilization using dark-field scattering spectroscopy. This technique can be exploited to study...
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Adding nanophase defects to YBa2Cu3O7-δ (YBCO) superconductor thin films is well-known to enhance flux pinning, resulting in an increase in current density (J ct ). While many previous studies focused on single phase...
Adding nanophase defects to YBa2Cu3O7-δ (YBCO) superconductor thin films is well-known to enhance flux pinning, resulting in an increase in current density (J ct ). While many previous studies focused on single phase additions, the addition of several phases simultaneously shows promise in improving current density by combining different pinning mechanisms. This paper compares the effect of the addition of two insulating, nonreactive phases of barium zirconium oxide (BZO) and yttrium oxide Y2O3, both as a single addition of BZO and as a double addition in conjunction with Y2O3. Processing parameters vary the target composition volume percent of BZO from 2-6 vol. %, while maintaining 3 vol. % Y2O3, and the remaining vol. % YBCO. Pulsed laser deposition produced thin films on LaAlO3 (LAO) and SrTiO3 (STO) substrates at various deposition temperatures. Comparison of strong and weak flux pinning mechanisms, current densities, critical temperatures, and microstructures of the resulting films will be presented. Films produced from the 2 vol. % BZO + 3 vol. Y2O3 doped YBCO target at a deposition temperature of 825 °C attained the highest current density. The addition of second phase Y2O3 impacted the film microstructure, resulting in more isotropic behavior when compared to the YBCO films doped with only BZO.
A new class of high‐temperature dipolar polymers based on sulfonylated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (SO 2 ‐PPO) was synthesized by post‐polymer functionalization. Owing to the efficient rotation of hig...
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A new class of high‐temperature dipolar polymers based on sulfonylated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (SO 2 ‐PPO) was synthesized by post‐polymer functionalization. Owing to the efficient rotation of highly polar methylsulfonyl side groups below the glass transition temperature ( T g ≈220 °C), the dipolar polarization of these SO 2 ‐PPOs was enhanced, and thus the dielectric constant was high. Consequently, the discharge energy density reached up to 22 J cm −3 . Owing to its high T g , the SO 2 ‐PPO 25 sample also exhibited a low dielectric loss. For example, the dissipation factor (tan δ) was 0.003, and the discharge efficiency at 800 MV m −1 was 92 %. Therefore, these dipolar glass polymers are promising for high‐temperature, high‐energy‐density, and low‐loss electrical energy storage applications.
The assembly of nanocrystals into ordered structures called supercrystals or superstructures has become a pivotal frontier owing to numerous useful applications such as correlating the arrangements of atoms in macrosc...
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The assembly of nanocrystals into ordered structures called supercrystals or superstructures has become a pivotal frontier owing to numerous useful applications such as correlating the arrangements of atoms in macroscopic crystals and tuning the collective properties to meet the demands of various applications. In this article, recent progress in the preparation of three-dimensional superlattices of nanocrystals is outlined, with a particular emphasis on the driving forces and evolutionary routes beyond orderly assembly. First, the leading or repulsive forces that internally and externally govern the formation of three-dimensional supercrystals are systematically identified and discussed with respect to their origins and functions in three-dimensional self-organization. Then a synoptic introduction of commonly applied means of nanocrystal self-assembly based on growth scenarios such as droplet evaporation and a liquid/liquid interface is presented with specific cases and detailed analyses. Finally, the existing challenges and prospects for this field are briefly highlighted.
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