Volume 36, Issue 2 -

Co 3 O 4 nanostructures have been synthesized via a hydrothermal-assisted thermal treatment process. A new complex formulated as [Co(py) 2 (H 2 O) 2 (NO 3 ) 2 ] was synthesized, and then used to prepare Co 3 O 4 nanostructures. Cubic phase of spinel Co 3 O 4 nanostructures with particle size of about 39 nm could be produced after calcination of the Co(OH) 2 materials prepared with hydrothermal method at 160 °C for 15 h. Using of inorganic precursors decreased the time and temperature of Co 3 O 4 preparation. The effect of pH on the morphology of the product s synthesized by hydrothermal reactions was investigated. It was found that the best morphology was achieved on pH=8, where was not prepared any precipitation. In this method, we could decrease the reaction temperature in synthetic rout to fabricate Co 3 O 4 nanostructures. Nanostructures were characterized by SEM, TEM, X-ray diffraction (XRD), UV–visible, Fourier transformed infrared (FT-IR) spectroscopy and Nuclear magnetic resonance ( 1 H-NMR).

In this study the modification effect of Hf content on the shape memory properties and magnetic permeability of a 75.5-77Ti-20Ta-3-4.5Hf alloy system has been systematically studied by DSC, three-point bend test, vector network analyzer and XRD. The martensitic transformation temperature, heat of reaction and recovery strain increases with the increase of hafnium and tantalum content. A stable high temperature shape memory effect was observed (Ms = 385–390 °C) during the two thermal cycles between 20 °C and 725 °C. Transformation temperatures and heats of reaction were determined by DSC measurements. Recovery strain was determined by three-point bend testing. Also an alloy, 70Ti-26Ta-4Hf, with higher tantalum content was produced to observe the effect of Ta on the shape memory properties. Permeability increases gradually from 1.671 to 1.919 with increasing content of hafnium modification and remains stable in the frequency range of 450 MHz to 1 GHz.

Nickel Chromite nanoparticles were successfully synthesized via a modified sol-gel method using nickel acetate and ammonium dichromate in melted stearic acid as a complexing agent. The diffractograms of the nanoparticles confirmed a pure formation of NiCr 2 O 4 spinel without any minor phase. The coordination structure of as prepared nanoparticles shows a series of absorption bands below 1,000 cm −1 were evidenced the M-O (Cr-O, Ni-O) bond in the sample. Optical band gap, magnetic properties and color parameters ( L*.a*.b *) indicates that the final nanoparticles are optically and magnetically active. The particle size of NiCr 2 O 4 was calculated using Scherrer equation at about 24 nm. Optical band gap obtained at 1.7 eV indicating that NiCr 2 O 4 nanoparticles are semiconductor material and can be used in electrical devices.

The hot rolled 60Si2MnA spring steel was transformed to obtain different proeutectoid ferrite morphologies by different cooling rates after finish rolling through dynamic thermal simulation test. The coexistence relationship between proeutectoid ferrite and pearlite, and the effect of proeutectoid ferrite morphology on mechanical properties were systematically investigated. Results showed that the reticular proeutectoid ferrite could be formed by the cooling rates of 0.5–2 °C/s; the small, dispersed and blocky proeutectoid ferrite could be formed by the increased cooling rates of 3–5 °C/s; and the bulk content of proeutectoid ferrite decreased. The pearlitic colony and interlamellar spacing also decreased, the reciprocal of them both followed a linear relationship with the reciprocal of proeutectoid ferrite bulk content. Besides, the tensile strength, percentage of area reduction, impact energy and microhardness increased, which all follow a Hall–Petch-type relationship with the inverse of square root of proeutectoid ferrite bulk content. The fracture morphologies of tensile and impact tests transformed from intergranular fracture to cleavage and dimple fracture, and the strength and plasticity of spring steel were both improved. The results have been explained on the basis of proeutectoid ferrite morphologies–microstructures–mechanical properties relationship effectively.

In this paper, uniaxial material properties, creep resistance and impact energy of the austenitic heat-resistant steel (1.4841) are experimentally determined and analysed. Engineering stress–strain diagrams and uniaxial short-time creep curves are examined with computer-controlled testing machine. Impact energy has been determined and fracture toughness assessed. Investigated data are shown in the form of curves related to ultimate tensile strength, yield strength, modulus of elasticity and creep resistance. All of these experimentally obtained results are analysed and may be used in the design process of the structure where considered material is intended to be applied. Based on these results, considered material may be classified as material of high tensile strength (688 MPa/293 K; 326 MPa/923 K) and high yield strength (498 MPa/293 K; 283 MPa/923 K) as well as satisfactory creep resistance (temperature/stress →$ \to $strain (%) at 1,200 min: 823 K/167 MPa →$ \to $0.25 %; 923 K/85 MPa →$ \to $0.2 %).

Low carbon high manganese steels with different Ce contents were melted in medium frequency vacuum induction furnace. The microstructures and mechanical properties of steels were studied by OM, SEM, EDS and mechanical property testing. The results showed that the microstructures of experimental steels were refined remarkably, inclusions distributed more finely and uniformly, the tensile strength and impact toughness of tested steels both improved greatly after the addition of Ce. Thermodynamic calculation results demonstrated that Ce contained inclusions were Ce 2 O 3 and Ce 3 S 4 , which agreed well with the results observed by SEM and EDS. By analysis of two-dimensional lattice disregistry, it was shown that the lattice misfit parameter between δ-Fe and Ce 2 O 3 , Ce 3 S 4 are less than 6 %, which indicated that Ce 2 O 3 and Ce 3 S 4 could effectively act as the heterogeneous nuclei of initial δ-Fe. Therefore, the microstructures were refined significantly and the mechanical properties were improved correspondingly in Ce-added low carbon high manganese steels.

In this work, the geometry and material constraint effects on creep crack growth (CCG) and behavior in welded joints were investigated. The CCG paths and rates of two kinds of specimen geometry (C(T) and M(T)) with initial cracks located at soft HAZ (heat-affected zone with lower creep strength) and different material mismatches were simulated. The effect of constraint on creep crack initiation (CCI) time was discussed. The results show that there exists interaction between geometry and material constraints in terms of their effects on CCG rate and CCI time of welded joints. Under the condition of low geometry constraint, the effect of material constraint on CCG rate and CCI time becomes more obvious. Higher material constraint can promote CCG due to the formation of higher stress triaxiality around crack tip. Higher geometry constraint can increase CCG rate and reduce CCI time of welded joints. Both geometry and material constraints should be considered in creep life assessment and design for high-temperature welded components.

The nano-sized ZrO 2 reinforced Mo alloys were prepared by hydrothermal synthesis and subsequent sintering. During preparation, the nano-sized ZrO 2 particles were added into the Mo powder via hydrothermal synthesis. This work investigated the differences in mechanical properties and microstructures of the Mo-ZrO 2 alloys prepared by hydrothermal synthesis and the other traditional method. As the amount of ZrO 2 particles increased, the grain size of the Mo powders reduced obviously. The grains were refined obviously after sintering. The ZrO 2 particles added by hydrothermal synthesis can effectively restrain the growth of grains and improve mechanical properties such as strength and hardness.

Mo-0.5Ti and Mo-0.1Zr alloys were prepared by powder metallurgy. In Mo-0.5Ti and Mo-0.1Zr alloys, there appears the second-phase particles of Ti 2 O 3 and ZrO 2 respectively, each of which can effectively prevent the dislocation activity in the process of plastic deformation. The addition of Zr can increase the strength of molybdenum alloys. Meanwhile, the ZrO 2 formed from the alloy element Zr can refine the grains of molybdenum alloys to improve the recrystallization plasticity. After annealing, the tensile strength decreases while the plasticity greatly increases compared to the annealed Mo-0.5Ti and Mo-0.1Zr alloys. With the increase of annealing temperature, both the tensile strength and plasticity of Mo-0.5Ti and Mo-0.1Zr alloys decrease. Compared with pure Mo, after annealing the properties of the Mo-0.5Ti alloy and the plasticity of the Mo-0.1Zr alloy significantly increases.

Diffusion behavior and diffusion kinetics of chromium (Cr) from the pure chromium coating in the matrix of Super304H and TP304H steels were investigated in a temperature range of 600–900 ℃ by using energy-dispersive spectrum (EDS) quantitative line scanning and Fick’s second law of diffusion. Pure Cr coating was obtained by electroplating. Experimental results show that the diffusion depth and diffusivity of Cr increase gradually with the increase in temperature. The diffusion activation energy of Cr is found to be lower and the diffusion coefficient of Cr to be higher in the Super304H steel than those in the TP304H steel at the same temperature. Furthermore, the diffusion equation of Cr in the Super304H and TP304H steels is DCr/Super304H=1.08×10−15exp (−6.08×104/RT)${D_{{\rm{Cr/Super304H}}}} \, {\rm{=\, 1}}{\rm{. 08 \times 1}}{{\rm{0}}^{{\rm{- 15}}}}{\rm{exp\ (- 6}}{\rm{. 08 \, \times \, 1}}{{\rm{0}}^{\rm{4}}}{\rm{/RT)}}$ and DCr/TP304H=2.29×10−15exp (−7.44×104/RT)${D_{{\rm{Cr/TP304H}}}}{\rm{= 2}}{\rm{. 29 \times 1}}{{\rm{0}}^{{\rm{- 15}}}}{\rm{exp\ (- 7}}{\rm{. 44 \times 1}}{{\rm{0}}^{\rm{4}}}{\rm{/RT)}}$, respectively.

Iron ore sintering is an important part during the ironmaking process, and a large amount of SO 2 is also generated. Our previous research shows that it is an effective way to reduce SO 2 content of flue gas by adding urea to a special sintering material zone position. In this paper, the mechanism of selective desulphurization by adding urea during the iron ore sintering was carried out. The results show that 88.14 % desulphurization rate was obtained with the addition of 0.05 % urea particles at 100 mm height from the feed bottom. During the sintering process, when drying zone reached the added position of urea, large amounts of NH 3 were generated by urea decomposition, and then reacted with SO 2 to produce (NH 4 ) 2 SO 4 in the wetting zone. With the accumulated desulphurization reactions during the sintering, the low SO 2 emission in the flue gas was achieved. Moreover, the addition of urea in the bottom zone avoided the ammonia present in the sintering ore and promoted the urea utilization efficiency.

The characteristics of large precipitates in H13 tool steel with 0.015wt% Ti were studied. The result shows that three types of phases larger than 1 μm exist in the as-cast ingot, that is, (Ti, V) (C, N) type phase, (V, Mo, Cr)C type phase and sulfide. (Ti, V) (C, N) type phase could be further classified as the homogeneous Ti-rich one and the Ti-V-rich one in which Ti/V ratio gradually changes. (V, Mo, Cr)C type phase contains the V-rich one and the Mo-Cr-rich one. The compositional characteristics in all of them have little relation with the cutting position or cooling rate. The precipitating process could be well described through calculation by Thermo-Calc software. During solidification, the primary phase (Ti, V)(C, N) first starts to precipitate in the form of Ti-rich carbonitride. With the development of solidification, the ratio of Ti decreases and that of V increases. Then the primary phase Ti-V-rich (Ti, V)(C, N) and V-rich (V, Mo, Cr)C appears successively. Mo-Cr-rich (V, Mo, Cr)C phase does not precipitate until the solidification process reaches to the end. Sulfide precipitates before (V, Mo, Cr)C type phase and it could act as the nucleus of (V, Mo, Cr)C.