Volume 107, Issue 11

The aim of this study was to identify the physical processes of nucleation and growth of cube grains by means of in-situ annealing experiments. The calculated nucleation site density at cube bands was found not to be sufficient for a correct computational prediction of the cube recrystallization texture. Growth competition at an early stage of recrystallization has to be taken into account for a better agreement between model and experiment, which necessitates a sufficiently refined grid resolution in discrete computer models of recrystallization. Accounting for these dependencies yields an excellent prediction of both the cube component in the recrystallization texture and the grain size distribution. The contribution of cube nucleation apart from cube bands to the cube recrystallization texture was found to be negligible.

Tensile deformation of single-crystal copper along [001] orientation is modeled. Single crystal is deformed at three sets of high strain rates, ranging from 10 3 to 10 5 s −1 , using the three-dimensional dislocation dynamics technique to simulate dislocation microstructure evolution and the resultant macroscopic response. Two initial dislocation configurations consisting of straight dislocations and Frank–Read sources are randomly distributed over the simulation volume with an edge length of 1 μm. For both initial setups, the mechanical response of the single crystal to the external loading demonstrates a considerable effect of strain rate. In addition, strain rate influences dislocation density evolution and consequently development of the dislocation microstructure. At all applied strain rates for both initial dislocation setups, dislocations evolve into a heterogeneous microstructure and this heterogeneity increases with plastic strain and strain rate.

This manuscript focuses on the mechanical behavior under compressive and bending loadings of tubular aluminum foams. The tubular structures were manufactured using the powder metallurgy technique. Tubular aluminum foams were fabricated by heating foamable precursor materials above their melting temperature in a mould. The influence of important parameters such as wall thickness and density of foam on the mechanical properties was investigated. It was found that the 6 mm thick specimen showed a lower collapse strength than the thicker 9 mm specimen. Despite the decrease in densities of the samples, the collapse strength increased with the increase in wall thickness. The reduction of approximately 33% in wall thickness (from t = 9 mm to 6 mm) decreased the bending performance of the tubular aluminum foams by approximately 50%.

Zn-5.3 wt.% Al-0.8 wt.% Sb alloy was directionally solidified upward at a constant temperature gradient ( G = 2.39 K mm −1 ) with a wide range of growth rates ( V ) (9.70 – 2 013.40 μm s −1 ) by using a Bridgman type directional solidification furnace. The average values of eutectic spacing ( λ ), microhardness ( HV T ), ultimate tensile strength ( σ UTS ) and electrical resistivity ( ρ ) were measured from transverse sections of the directionally solidified samples. The dependency of λ , HV T , σ UTS and ρ on V were experimentally obtained by using linear regression analysis for low, high and all growth rates. The bulk growth rates were also determined by using the measured values of λ and V for low, high and all growth rates. The results obtained in the present work were compared with the Jackson–Hunt eutectic theory and similar experimental results in the literature. Also, the specific heat difference (Δ C P ) and enthalpy of fusion (Δ H ) for the Zn–Al–Sb alloy were determined by means of differential scanning calorimetry.

A 40Cr steel was formed with warm extrusion under different temperatures, and the tensile fatigue limits after the warm extrusion were calculated according to the Roca rule. The metallographic microstructure and chemical compositions of the extrusion samples were analyzed with an optical microscope and photoelectric direct-reading spectrometer, respectively; the residual stress and residual austenite were investigated on a stress tester. The fracture morphologies were analyzed with a field-emission scanning electron microscope, and the mechanism by which the warm extrusion temperatures affected the fatigue fracture of the 40Cr steel was discussed. The results show that the grains are refined by warm extrusion at 550°C, the C weight fraction on the sample surface is 0.39%, and the compressive residual stress and content of residual austenite are −297 MPa and 5.3%, respectively, increasing the fatigue life of the samples. The grain sizes of the extrusion samples at 650 and 750°C are larger than those at 550°C, the corresponding C content of the sample surface is 0.39% and 0.38%, respectively, and the compressive residual stresses and contents of residual austenite decrease, leading to a decrease in the fatigue life. The fatigue strength of the samples by warm extrusion at 550, 650, and 750°C is 382, 412, and 385 MPa, respectively. The fracture morphology of the sample at 550°C is a dimple, while that at 650 and 750°C is a cleavage step and river pattern, respectively.

A graded SiC coating was prepared on a graphite substrate by a pack cementation technique at 1 873 K to improve the oxidation resistance. The HSC Chemistry software was used for thermodynamics calculations. The coating was characterized by means of X-ray diffraction and scanning electron microscopy. Isothermal oxidation testing of the samples was performed at 1 773 K in air. The modeling analysis indicated that aluminum oxide can be reduced and an SiC coating can be formed due to the reaction of silicon with CO and carbon with SiO. The growth of the SiC nanofibers was attributed to the gaseous reaction of SiO with CO. A 600 μm thick SiC layer can be observed at the graphite–coating interface. The simulation and experimental results were consistent with each other. The mass loss of the SiC coated sample was 1.1 % after oxidation for 10 h, whereas the graphite was fully oxidized after 1 h.

A nanocrystalline surface layer with average grain size of 77 nm was produced on mild steel through a wire brushing process. Its corrosion behavior was studied in the absence and presence of 3-amino-1,2,4-triazole (3-AT) as corrosion inhibitor. Although the increase in the inhibitor concentration shows a positive effect on inhibition efficiency of micro- and nano-grained surfaces, this effect is more remarkable for the sample with a nanocrystalline surface layer. In addition, in the presence of the optimum concentration of 3-AT, temperature increment has a more negative effect on the sample with a microcrystalline surface layer. The results also revealed that due to enhanced adsorption of 3-AT inhibitor and formation of a protective layer with a high polarization resistance, the inhibition effect of 3-AT increased as the grain size decreased from microcrystalline to nanocrystalline.

Use of rare earths, high silicon and carbon contents, and low cooling rates are reported as possible reasons for formation of chunky graphite in ductile iron castings. The understanding of this graphite degeneration is however limited, and the above conclusions are still controversial. To get further insight into this topic, ductile cast iron melts have been prepared with various carbon and silicon contents and using nodularizing alloys with various rare earth levels. These melts have been cast in blocks with different sizes to include also the effect of cooling rate on graphite degeneration. Metallographic investigation revealed that the chunky-affected areas enlarge when decreasing the cooling rate, when increasing the silicon content and without low-level addition of rare earth. In the discussion, a schematic based on change of liquid/graphite interfacial energy with alloying elements is proposed which describes the conditions for the formation of chunky graphite instead of nodular graphite.

Three-dimensional (3D) nanocomposite monolith containing MoS 2 nanoflakes, graphene oxide (GO) and amorphous SiO 2 was fabricated through a simple mixing process and hydrothermal treatment. Compared with GO monolith prepared under identical conditions, the MoS 2 –GO monolith had larger specific surface area, smaller pore diameter, as well as much higher adsorption capacity for Cu 2+ and Rhodamine B. Introducing amorphous SiO 2 into the end monolith by using tetraethyl orthosilicate as a reactant in the synthesis reduced shrinkage and produced a greater number of large pores (>1 μm pore diameter) in the monolith. The specific surface area and pore diameter of the MoS 2 –GO monolith were 321.4 m 2 g −1 and 11.71 nm, respectively. The higher adsorption capacity was ascribed to the presence of many S atoms in the MoS 2 nanoflakes inside the monolith.

In this article a new method of synthesizing ultrafine powder of α-phase metallic cobalt is proposed, synthesis by a combination of two methods, liquid-phase precipitation on a carbon support and low-temperature microwave heat treatment in the stream of argon. An entire spectrum of intermediates obtained during thermolysis and reduction of cobalt precursors during heat treatment by electromagnetic field to the final product is presented. Sample structure, morphology and particle size as well as phase composition and the size of specific surface areas are shown.

The aim of this work is to develop a multifunctional composite based on β-tricalcium phosphate (β-TCP) working as a single carrier that has a therapeutic function, as a calcium supplement, together with the capability for carrying low-dose drugs. The composite was prepared by blending synthetic β-TCP powder, sodium silicate, and citric acid. The synthetic β-TCP and its composite were characterized using X-ray powder diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques. Mechanical testing and in-vitro drug release testing, using atenolol, of the fabricated tablets was conducted. The results revealed the synthesis of pure β-TCP powder and fabrication of optimal dense β-TCP-based composite. The β-TCP-based composite exhibited an optimal release behavior of atenolol together with releasing of synthetic β-TCP particles, a calcium supplement.