Volume 106, Issue 12

For the traceability of hardness and elasticity measurements with instrumented indenters to SI units, a measuring standard based on a silicon bending spring with a stop limit exists. Besides the bending stiffness of the spring, the bending point of the measured force–displacement curve at the stop limit can be used as an additional calibration point for both the probing force and the displacement. In a round-robin test with six participants and seven devices the bending stiffness, the bending force and the bending deflection were measured and compared. The result of the bending stiffness, the bending force and the bending deflection agree within ±2.8 %, ±4.2 % and ±3.2 %, respectively.

This study investigates the effects of cold working prior to aging on the microstructure and mechanical properties of SP-700 titanium alloy. The results indicate that the microstructure of the quenched alloy comprises blocky primary α, retained β, and acicular α” martensite distributed in the β matrix. The retained β is transformed to denser and finer brittle acicular martensite α” by stress-induced martensitic transformation and the quantity of retained β decreases with higher degrees of cold working. The quenched alloy exhibits not only low yield strength, but the stress-induced martensite leads to a distinct increase in strength with good ductility. Plastic deformation prior to the aging treatment produces a great increase in the yield strength due to refinement of the precipitate microstructure, leading to the ratio of strength increment and ductility being very low.

The applicability of cyclic channel die compression (CCDC) for producing fine grained structure in oxygen free high conductivity (OFHC) copper is investigated in the present work. OFHC copper was severely plastically deformed at room temperature up to an effective plastic strain of 7.2 through three cycles of CCDC. Optical microscopy studies indicated microstructural inhomogeneity after the first cycle followed by considerable improvements in deformation homogeneity during subsequent straining. EBSD analysis of microstructural evolution revealed maximum grain refinement during the initial stages of strainitrun 2176 ng and lower grain refinement rates subsequently. Substantial grain refinement in CCDC processed samples was manifested by the formation of fine grained equiaxed structures (∼1 – 2 μm) from coarse grained (58 μm) starting material after three cycles. Grain boundary characteristics divulged continuous changes in the relative fraction of high-angle and low-angle boundaries with strain. The room temperature tensile behaviour indicated considerable improvement in yield strength by ∼3.5 times from 129 MPa to 422 MPa after the first cycle correlating with the structural refinement observed. Initially degraded room temperature ductility revealed a marginal gain at large strain owing to the restoration of strain hardening ability. Hardening and softening regimes revealed in a Hall–Petch plot are attributed to the relative evolution of grain boundary characteristics.

Al-5Ti-0.6C-1Ce master alloy has been successfully prepared by a method of thermal explosion reaction in pure molten aluminum. The microstructure of the alloy was characterized by means of optical microscopy, X-ray diffraction and scanning electron microscopy equipped with energy-dispersive spectrometry. The results showed that the Al-5Ti-0.6C-1Ce alloy was composed of α-Al, granular TiC, lump-like TiAl 3 and block-like Ti 2 Al 20 Ce. When compared with the Al-5Ti-0.6C master alloy, the formation of Ti 2 Al 20 Ce compounds and the addition of Ce accelerated the formation of TiC. An excellent grain-refining performance was obtained when the addition level of Al-5Ti-0.6C-1Ce reached 0.5 wt.%. The effect of Ce on the synthesis of TiC and refinement mechanism of Al-5Ti-0.6C-1Ce has also been discussed.

Semi-solid TiAl 3 /ZL101 aluminum matrix composite slurry was prepared by ultrasonic vibration. A rotational viscosimeter was used to determine the rheological behavior of the slurry at a constant shear rate. The effects of ultrasonic power, solid fraction and TiAl 3 fraction (vol.%) on the apparent viscosity of the slurry were investigated. Results showed that the apparent viscosity of the slurry increased as the TiAl 3 fraction or solid fraction increased, and decreased with increasing ultrasonic power. Based on the experimental data, this study established a rheological model of semi-solid TiAl 3 /ZL101 composites prepared by ultrasonic vibration.

A scratch-brushing model which is applicable for roll bonding processes is proposed. This model was suggested based on the mechanical energy transfer from a rotating brush to the surface of sheet metal in order to produce a thin brittle layer. There were good agreements between the model predictions and the experimental data from this work and the literature. The effects of annealing temperature and brushing time on the formation of the thin brittle layer and joint strength of the roll bonded sheets were also examined. It was shown that annealing temperature changed the microhardness variation along the thickness direction. The results showed that there was an optimum brushing time for attaining highest bond strength. After the optimum brushing time, the brushed surfaces were examined using scanning electron microscopy. It was also observed that the brushing direction, parallel or normal to the rolling direction, had some influence on the quality of the roll bonded sheets. For clarification of this phenomenon, the adhered interface was examined in the scanning electron microscope.

Cement powder particles of micronic size tend to form agglomerates due to the influence of interparticle forces (Van der Waals forces). The formation of agglomerates results in an increased air-void in the solid structure (aerated powder) requiring an increase in water demand to sustain the feasibility of the structure. Consequently, if the compound formed is not stabilized, it would have low mechanical strength that may result in cracking of hardened cement. In this study, the results of cement powder consolidation and its flow properties show that its behaviour is controlled by internal forces (Van der Waals) and external forces (elastic and plastic). These forces have a direct influence on the powder structure, leading to a variable packing behaviour (void reduction). Consolidated cement powder shows a decrease in the void structure leading to a more efficient material. This study intends to determine the impact of interaction forces between cement particles during consolidation.

In this work, nano-sized manganese ferrite (MnFe 2 O 4 ) was synthesized through the decomposition of the mixed oxalates. The formation of the spinel manganese ferrite was confirmed by X-ray diffraction analysis. The morphology of the ferrite products was studied by scanning electron microscopy. The particle size, which was determined using the Scherrer formula, ranged from 25 to 30 nm. Magnetic properties of the manganese ferrite were analyzed using a vibrating sample magnetometry technique; a narrow hysteresis loop indicated the MnFe 2 O 4 obtained was a soft ferromagnet. Magnetic properties of the manganese ferrite produced were in agreement with those reported in literature for MnFe 2 O 4 nanoparticles prepared by conventional methods, including co-precipitation and mechanochemical processes. By plotting a series of literature data determined by different authors and techniques, a correlation between saturation magnetisation and particle size has been noted regardless of the synthesis methods. In general, the oxalate method seems to be able to produce nano-manganese ferrite in a shorter time (2–3 h) as compared to other conventional techniques reported in literature (up to 54 h).

Alumina–mullite–zirconia composites were prepared using alumina and zircon powders pressed uniaxially at 250 MPa and sintered in a microwave furnace held at 1 550 °C for 90 min. The effects of short milling and sintering time on the density, phase evaluation and mechanical strength of the sintered composites were analyzed and compared with composites sintered in a conventional furnace. The goal was to decrease sintering time and temperature over that for conventional heating. The results showed that, although the densities were similar for both methods, the hardness, mechanical strength and fraction of the tetragonal zirconia phase of the microwave-sintered composites were much higher. The milling time yielded better densification and higher mechanical properties. It was found that the shorter sintering time in a microwave furnace requires longer milling time of the powders to obtain the same composite properties.

2–2 piezoelectric composites were fabricated using PZT-51 as the functional filler and epoxy resin as the matrix using the cutting–filling technique. The influences of PZT-51 volume fraction and the ceramic plate thickness on the damping performance, piezoelectric and dielectric properties were studied. The results showed that the piezoelectric constant and dielectric constant of the composite increased nonlinearly with the increase of PZT-51 volume fraction when the ceramic plate thickness was constant. The maximum loss factor tan δ max increased initially and then decreased with the increase of PZT-51 volume fraction, which reached a maximum value of 0.71 when PZT-51 volume fraction was 50 %. When the PZT-51 content was constant, the ceramic plate thickness had little influence on the piezoelectric strain constant d̅ 33 . The maximum loss factor tan δ max reached 0.73 when the ceramic plate thickness was 0.4 mm, which was 0.30 higher than that of the pure epoxy.

This work began with preparing hydroxyapatite from bovine bones and continued with doping fluorine into hydroxyapatite matrix to produce fluorine-doped hydroxyapatite in optimum conditions. At the end a fluorine hydroxyapatite–zircon nanocomposite ceramic with good bioactivity and good chemical stability was synthesized through a mechano-chemical route and subsequent two step sintering process. The ability of apatite formation on the produced nanocomposite samples, as a yardstick for evaluation of the bioactivity, was estimated by using simulated body fluid. According to the results obtained, after soaking the nanocomposite samples in the fluid solution, the pH value was increased during the first week of experiments. Furthermore, the concentration of the Ca ions at the end of the second week in the fluid solution was dependent on the Si – OH nucleation sites on the surface of nanocomposite.

Aligned high-density Fe 2 O 3 nanowires were successfully obtained by thermal oxidation of Fe foil, with pre-annealing at 300 °C for 30 min. Pre-annealing in this two-step oxidation process improved the nanowire alignment and increased the density from 5.0 × 10 8 to 2.5 × 10 9 nanowires cm −2 . The X-ray diffraction pattern of the Fe 2 O 3 nanowires had a dominant (110) peak, with crystalline Fe and iron oxide phases. The improved properties are the result of formation of smaller grains during the first oxidation step.

Ag-8CuO (wt.%) nanocomposite powders were synthesized by calcination at 600 °C of precipitates of copper and silver nitrates and ammonium carbonate. The calcination temperature was determined according to the results of simultaneous thermal analysis of the precipitates. The particle size of the powders was about 50 nm; the crystallite size and the lattice strain of the calcined powders were 34 nm and 0.04 %, respectively. The nanocomposite powders were cold pressed and solid state sintered at 900 °C for 2 and 6 h. It was shown that the sintering duration has more influence on densification of the sintered samples than the cold pressure magnitude. The sintered compacts were re-pressed under 1 GPa. The relative density, hardness and electrical conductivity of the re-pressed samples were 94 %, 65 HRF and 69 % international annealed copper standard conductivity, respectively.

In the present study, results revealed that hybrid (0.7 % yttria + 0.3 % copper) nano-particle reinforcement has a significant strengthening effect on commercially pure magnesium reaching 100 °C, which gradually diminishes with further increase in temperature. Due to the presence of reinforcement particles, magnesium matrix also completely recrystallizes at 100 °C. Hybrid nano-reinforcement also assisted in the deformation process and achieved large ductility at a relatively low temperature.