Band 107, Heft 8

The indentation behavior of carbon microspheres was examined. The indentation load was in the range of 50 μN to 500 μN for the carbon microspheres with a diameter of ∼5 μm, and 15 μN to 100 μN for the carbon microspheres with a diameter of 1 μm. For the same ratio of the maximum indentation depth to the diameter of the carbon microspheres, both the contact modulus and indentation hardness for the carbon microspheres with a diameter of ∼5 μm are larger than the corresponding values for the carbon microspheres with a diameter of ∼1 μm. The carbon microspheres of ∼5 μm in diameter exhibited a larger resistance to the mechanical deformation than the carbon microspheres of ∼1 μm in diameter. The plastic energy dissipated in the nanoindentation increases with the increase of the indentation depth (load) and is a power function of the indentation depth.

Single walled and multi walled carbon nanotubes were incorporated into a high molar mass polycarbonate polyurethane via ultrasonication. The polycarbonate polyurethane which is free of any healing additives has the capacity to partially re-heal after rupture. The formation of the polyurethane/carbon nanotube composites has been shown to greatly improve the self-healing characteristics. Moreover, there is an increase in the thermal and mechanical properties of the thermoplastic composites. Herein we investigate the thermal and mechanical properties of the elastomeric material with a focus of the interface of the carbon nanotubes. Additionally, the self-healing polymer is probed using Raman techniques in order to provide an insight into how the self-healing actions are improved upon addition of carbon nanotubes.

Using a low temperature hydrothermal method, zinc oxide (ZnO) nanorod arrays were grown from seed layers coated on silicon substrates. The grown morphologies of the nanorod arrays heavily depend on the seed layer preparation methods. The grown nanorod arrays are of high density and good crystallinity with <002> preferred orientation for the nanorod arrays growing from uniformly distributed nucleation sites which are prepared on the seed layers by using the solvent ethanol. Using a conductive atomic force microscope, the dependence of the output current generated from the piezoelectric effect of bending a single nanorod was characterized. The output current increases with increasing the free bending lengths and applied force due to the increase in the deformation of the ZnO nanorods, and the maximum output current is 2.6 nA. The dependence of the bending-induced output current on the growth parameters, the nanorod array morphology and inclined orientation feature is discussed.

The 620 °C isothermal section of the Al–Zn–Fe–V quaternary system with the Al content fixed at 55 wt.% and the Al-rich corner of the Al–Fe–Zn ternary system at 620 °C have been determined by means of scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffractometry. Two four-phase regions are identified in the isothermal section of the Al–Zn–Fe–V quaternary system. Two three-phase regions are found in the Al-rich corner of the Al–Fe–Zn ternary system. No new ternary and quaternary phases have been found in the present work.

A continuous casting technique was developed to fabricate lotus-type porous alloys. This type of porous Cu–Zn (2, 6, and 10 wt.%) alloy was successfully fabricated by using the continuous casting technique under a hydrogen gas pressure of 0.6 MPa at various withdrawal rates. The influences of processing parameters on the pore structure and morphology were investigated. For the porous Cu-2Zn alloys, an increased withdrawal rate will result in slightly increased porosity, but a decreased average pore diameter. The pore morphology becomes more and more inhomogeneous with increasing Zn content, and the porosity tends to firstly decrease and subsequently increase. Such tendencies are correlated with the Zn content and corresponding width of the mushy zone.

In this work, plasma–target interactions on tungsten samples, carried out in a Mather-type plasma focus PF-1000 device, were investigated. The experimental results have been compared to 1D model computer simulations. Samples were studied by means of scanning electron microscopy, focused ion beam microscopy and precise measurements of weight loss. Additionally, simulations based on the numerical solution of a 1D heat conductivity equation were carried out. The samples exhibited relatively high resistance to the generated plasma streams. The practical work indicated a loss of about 1.54 mg per plasma focus discharge. The computer model calculations gave a weight loss one magnitude greater. An attempt to explain this discrepancy is given in the paper.

SiC-coated h-BN powders ((h-BN)/SiC) were used to substitute h-BN as solid lubricant to prepare Al 2 O 3 /TiC/(h-BN)/SiC self-lubricating ceramic cutting tool materials using hot pressing. Microstructure and mechanical properties of the material were studied. Overall improvements in Vickers hardness and fracture toughness were obtained compared with that of Al 2 O 3 /TiC/h-BN. The coating of SiC blocks direct contact between h-BN and Al 2 O 3 /TiC and hence enables h-BN particles to bond more closely with Al 2 O 3 /TiC. The density of the material was dramatically improved because of the decrement of voids around h-BN particles. Dry turning tests were carried out to investigate the wear resistance of the materials when cutting 40Cr quenched and tempered steel. Enhancement in wear resistance, which may result from the improvement in mechanical properties, was observed.

In the present study, Al 2 O 3 -5 wt.% ZrO 2 nanocomposite powder was fabricated via the sol–gel method, and then the sintering behavior was investigated using various sintering aids (MgO, TiO 2 and MgO/TiO 2 ) at different temperatures. In this regard, the size and structure of fabricated powder, and hardness, fracture toughness and density of sintered samples were studied. The results of X-ray diffraction indicated the presence of α-alumina and tetragonal zirconia. Scanning electron micrographs revealed agglomerated nanometer-sized spherical particles ranging in size from 60 to 150 nm. Energy-dispersive X-ray mapping micrographs also demonstrated the homogeneous dispersion of zirconia in alumina. Moreover, density results indicated that using 0.5 wt.% MgO/0.5 wt.% TiO 2 produced the best results, as the relative density reached 95 % at 1 500 °C. Finally, it was observed that the presence of MgO and TiO 2 induces higher hardness and lower fracture toughness.

In this work, mixed mode fatigue crack propagation in the welding zone of 06Cr19Ni10 austenitic stainless steel was experimentally investigated. The effects of strain strengthening on crack growth paths and growth rates were studied. The experimental results demonstrated that a new crack initiated from the notch-crack tip and propagated in the direction perpendicular to the loading direction, suggesting a change of the crack mode from mixed mode to Mode I. Strain strengthening has no effect on the crack growth paths, while it does have some effect on the crack growth rates. The metallographic results indicate that the fraction of transformed martensite increases with strain-strengthening level. Finite element analysis results reveal that strain strengthening can significantly change the distribution of the residual welding stress.

This paper investigates the influence of rotational and travel speed on the structure and mechanical properties of different regions of friction stir welded dissimilar AA5251–AA5083 joints. It was observed that increasing rotational speed from 800 to 1 250 rpm, at a fixed travel speed, increased the grain size from 6.31 μm to 10.64 μm. This stemmed from higher heat input which is generated at higher rotational speed. Furthermore, it was discovered that at 1 000 rpm, 115 mm min −1 and also 1 250 rpm, 85 mm min −1 , defect-free welds were produced. The results of tensile testing revealed that the best consistent tensile strength was produced at 1 000 rpm rotational speed and 115 mm min −1 travel speed with an average value of about 200 MPa. Further, the results clearly showed that the hardness values gradually increase from the 5251 aluminum side to the 5083 aluminum side.

A methodology for in-situ micro-compression testing of fiber composites has been developed. The tests were performed on carbon fiber reinforced bismaleimide matrix unidirectional composite, IM7/BMI 5250-4. Micro-size specimens were prepared from the bulk composite plaque through a two-step micro-fabrication process and then tested by using a micro-mechanical testing device placed inside the scanning electron microscope chamber. Results show that the fundamental properties (modulus and strength) of the fiber composites obtained from micro-size specimens are consistent with the theoretical estimations and significantly higher than those from macro-size specimens, which may have revealed the presence of size-scale effects in composite materials. The in-situ testing shows that the overall failure mode of the present composite is caused by “micro-buckling” of fibers in shear-mode. High shear strains are seen to occur at the fiber–matrix interfaces, which lead to the micro-cracking and ultimate failure of the composite.

Cu 6 Sn 5 intermetallic nanoparticles have been successfully prepared by a simple reduction method. The crystallinity and morphology of the synthesized products were characterized by means of X-ray diffraction and scanning electron microscopy, respectively. When used as anode material, Cu 6 Sn 5 intermetallic nanoparticles demonstrated an initial discharge capacity of 3368.2 mAh · g −1 and stable capacities of 840 mAh · g −1 after 70 cycles between 0.05 and 2.5 V at a current density of 100 mA · g −1 . The charge–discharge process of Cu 6 Sn 5 intermetallic nanoparticles was also evaluated using cyclic voltammetry. The results indicated Cu 6 Sn 5 intermetallic nanoparticles may be an ideal anode material for Li ion batteries.