Band 35, Heft 10 -

In this paper, the effects of extrusion–shear (ES) on the microstructures and mechanical properties of AZ31 magnesium alloy has been studied, which has been achieved by conducting a lot of experiments and tests, including ES process, direct extrusion with different billet temperatures, microstructure analysis, hardness test, tensile & compression tests. The results show that the ES-processed rods has higher strengths (yield strength and tensile strength) than the direct extrusion ones with the same billet temperature, which contributed to their lower averaged grain size obtained from microstructure analysis according to Hall–Petch relation. Besides, the hardness of ES-processed AZ31 magnesium alloy decreases with the increasing of billet temperature. By comparing the two processes, it can be seen that the ES process could refine the microstructure and improve the mechanical properties of magnesium alloy.

The degradation of titanium diboride (TiB 2 )/titanium carbide (TiC) composites in the liquid Nd and molten NdF 3 –Nd 2 O 3 –LiF salts is investigated at 1,060 °C, respectively. The penetration of TiB 2 /TiC composites by liquid Nd mainly depended on the grain boundaries and residual pores, even if the coherent interface is formed between TiB 2 and TiC. The oxidation of TiB 2 led to further interfacial chemistry reactions, which speeded up the degradation of TiB 2 /TiC composites at the initial stage in NdF 3 –LiF–Nd 2 O 3 system. After that, the degradation was slowed because of the formation of diffusion boundary layer, and then chemical penetration was replaced gradually by the physical penetration. The dissolved Ti in liquid Nd and NdF 3 –LiF–Nd 2 O 3 melts are used to evaluate the corrosion rate of TiB 2 /TiC composites, and the calculated values were about 0.56 and 7.8 mm/year, respectively. After the penetration by liquid Nd and NdF 3 –LiF–Nd 2 O 3 melts, the bending strengths of TiB 2 /TiC composites decreased and the fracture mode changed from transgranular to intergranular due to the decreased grain boundary force.

In this study, irradiated UO 2 is analyzed by atomistic simulation method to obtain diffusion coefficient of oxygen ions. For this purpose, a couple of molecular dynamics (MD) supercells containing Frenkel, Schottky, vacancy and interstitial types for both anion and cation defects is constructed individually. Each of their contribution is used to calculate the total oxygen diffusion for both intrinsic and extrinsic ranges. The results display that irradiation-induced defects contribute the most to the overall oxygen diffusion at temperatures below 800–1,200 K. This result is quite sensible because experimental data shows that, from room temperature to about 1,500 K, irradiation-induced swelling decreases and irradiated UO 2 lattice parameter is gradually recovered because defects annihilate each other. Another point is that, concentration of defects enhances the irradiation-induced oxygen diffusion. Irradiation type also has the similar effect, namely oxygen diffusion in crystals irradiated with α-particles is more than the crystals irradiated with neutrons. Dynamic Frenkel defects dominate the oxygen diffusion data above 1,500—1,800 K. In all these temperature ranges, thermally induced Frenkel defects make no significant contribution to overall oxygen diffusion.

Change in mechanical parts from macro-size to micro-size has become a trend in the metal- and alloy-forming process, with an increasing demand on micro-parts in the last decades. The material mechanical behaviors of micro-size parts are quite different from the conventional ones of macro-size parts due to size effect. It is necessary to further investigate the effects of grain size on material mechanisms in micro-scales, especially fracture behaviors. The fracture behaviors of Inconel 718 sheet with the thickness of 300 μm are studied by uniaxial tensile tests in different grain sizes ranging from 18 to 130 μm. The results show that fracture stress and strain decrease with the increase of grain size. A critical value in the specimen thickness ( t ) to grain size ( d ) ratio divides the strength levels into separate stages on the basis of an increase of the inverse of grain size. In addition, the grain size-dependent fracture morphology is changed in the number of dimples and micro-voids decreasing on the fracture surfaces and the sizes of micro-voids changing larger with the increase of grain size.

The Bredig transition to the superionic phase indicated with the λ$$\lambda $$-peak in Cp$${C_p}$$ was highly expected for plutonium dioxide (PuO2$${\rm{Pu}}{{\rm{O}}_2}$$) as other actinide dioxides. However, least-square fit and local smoothing techniques applied to the experimental enthalpy data of PuO 2 in 1980s could not detect a λ$$\lambda $$-peak in specific heat that might be due to too scattered and insufficient experimental data. Therefore, this issue has not been yet put beyond the doubts. In the current article, a superionic model of PuO2$${\rm{Pu}}{{\rm{O}}_2}$$ is developed with partially ionic model of a rigid ion potential. Thermophysical properties were calculated in constant pressure–temperature ensemble using molecular dynamics simulation. The Bredig transition with vicinity of a λ$$\lambda $$-peak in specific heat was successfully observed for the model system at about 2,100 K. Moreover, the experimental enthalpy change was well reproduced before and after the estimated transition temperature.

The oxidation behavior of grain-refined Cu–7.0 Cr alloy (GR Cu–7.0 Cr) in air at 973–1,073 K was investigated in comparison with normal casting Cu–7.0 Cr alloy (CA Cu–7.0 Cr). The oxidation of CA Cu–7.0 Cr alloy nearly followed parabolic law, while the oxidation kinetics of GR Cu–7.0 Cr slightly deviated from parabolic law. Both alloys almost produced multi-layered scales consisting of the outer layer of CuO and the inner layer of mixed Cr 2 O 3 and Cu 2 O oxides plus internal oxidation zones of chromium. The grain-refined Cu–7.0 Cr alloy produced a more amount of Cr 2 O 3 in the inner layer of the scale, and thus was oxidized at much lower oxidation rate than that of CA Cu–7.0 Cr with normal grain size. The experimental results indicated that the differences in oxidation behavior between two alloys may be ascribed to the different size and spatial distribution of the second-phase particles and the reactive component contents in localized zone.

In this work, cadmium sulfide (CdS) nanoparticles were synthesized from a new Cd-octanoate complex via a simple thermal decompose method. The crystallinity of the product was obtained from X-ray diffraction (XRD) pattern. The morphology and product size were analyzed via scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Also Fourier transform infrared (FT-IR) spectroscopy was used to investigate the CdS surface purity. Finally, the optical properties of the product were obtained from photoluminescence (PL) spectroscopy.

In this work, a simple thermal decompose method was served to synthesize NiS 2 nanostructures via a nickel complex. Also polyethylene glycol (PEG) was used as surfactant to increase the steric effect around nanostructure surfaces and decrease the particles size. The product was characterized with different analysis methods. The crystal structure of the product was studied by X-ray diffraction (XRD) pattern. The particle size and morphology were investigated by scanning electron microscopy (SEM). To study the nanostructures surface purity, Fourier transform infrared spectroscopy (FT-IR) was used. And finally to study the optical properties of the product photoluminescence (PL) spectroscopy was served.

Dynamic recrystallization (DRX) of Ti22Al25Nb alloy has been investigated based on the analysis of hot compression experimental data in this paper. The true stress–strain curves of Ti22Al25Nb can be divided into two types: the single-peak conventional dynamic recrystallization (CDRX) curves and the multi-peak discontinuous dynamic recrystallization (DDRX) curves. The multi-peak curves indicate the alternate dominance of hardening mechanism and softening mechanism. A critical Zener–Hollomon parameter ln Z C has been proposed to divide CDRX from DDRX. The hardening rate and DRX volume fraction of CDRX and DDRX have been analyzed. In addition, the effect of the second-phase particle on the DRX has been studied. DRX process was enhanced by the second-phase particles, but the growth process of recrystallized grains was restrained.

The research of smelting low ferronickel from pre-concentrate nickel-iron ore with 2.76 % Ni and 38.00 % Fe total was carried out to find an effective way for stainless steel enterprises to use the low-nickel laterite reasonable. The results show that Ni and Fe both have a certain degree of enrichment, and impurities and harm elements have different degrees of reduction after pre-concentration of nickel-iron ore. Most valuable metal did not compound with impurities which greatly accelerated the speed and extent of melt separation reduction. Good alloy of 6.58 % Ni with the overall recoveries of 93.38 % and 89.95 % Fe total with the overall recoveries of 89.57 % was manufactured under the following conditions: 10 % coke, 1.0 binary basicity, 18 % MgO and 3 % Al 2 O 3 in slag, melting at 1,550 °C for 10 min. The product can be used for the feed of producing stainless steel.

The hot deformation behavior of BFe10-1-2 cupronickel alloy was investigated over wide ranges of deformation temperature and strain rate. The physics-based constitutive model was developed to predict the dynamic recovery (DRV) behavior of BFe10-1-2 cupronickel alloy at elevated temperatures. In order to verify the validity of the developed constitutive equation, the correlation coefficient ( R ) and average absolute relative error ( AARE ) were introduced to make statistics. The results indicated that the developed constitutive equation lead a good agreement between the calculated and experimental data and can accurately characterize the hot DRV behaviors for the BFe10-1-2 cupronickel alloy.

A comprehensive investigation was conducted into the effect of oxides on penetrations, microstructures and mechanical properties of BS700MC super steel weld bead. Boron oxide changed the penetration of weld bead by changing the Marangoni convection in the weld pool and contracting the welding arc. Chromium oxide only changed the Marangoni convection in the weld pool to increase the penetration of super steel. Thus, the super steel weld bead has higher penetration coated with flux boron oxide than that coated with chromium oxide. In other words, the activating flux TIG (A-TIG) welding with flux boron oxide has less welding heat input than the A-TIG welding with flux chromium oxide. As a result, on the one hand, there existed more fine and homogeneous acicular ferrites in the microstructure of welding heat-affected zone when the super steel was welded by A-TIG with flux boron oxide. Thus, the weld beads have higher value of low-temperature impact toughness. On the other hand, the softening degree of welding heat-affected zone, welded by A-TIG with flux boron oxide, will be decreased for the minimum value of welding heat input.