Volume 37, Issue 7 -

Aluminum matrix composites that were reinforced by in situ zirconium diboride nanoparticles were fabricated from an aluminum-potassium tetrafluoroborate-potassium hexafluorozirconate system via a direct-melt reaction. The morphologies of the in situ particles and the mechanical properties of the composite were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffractometry, optical microscopy and tensile tests. X-ray diffractometry and energy-dispersive X-ray spectroscopy showed the existence of zirconium diboride in the composite. Multidirectional forging and heat treatment were used to determine the effect of plastic deformation and heat treatment for the highest tensile strength applied to the composite. Multidirectional forging and heat treatment have a positive influence on the composite microstructure and tensile strength, which increase by 21.81 % and 13.43 %, respectively. The mechanism of multidirectional forging and heat treatment that affects the composite mechanical properties has been discussed. The heat-treatment parameters that affect the tensile strength include the solution-treatment temperature, aging temperature and aging time. The highest tensile strength with moderate extensibility loss was achieved for a specimen that was solution treated for 4 h at 793 K and with aging at 423 K for 4 h.

Hydroxyapatite was synthesized via sol-gel and solid-state reaction. Both compounds were investigated using high-temperature X-ray diffraction and differential scanning calorimetry. For sol-gel hydroxyapatite, we observed a phase transition, confirmed by character of changing of unit-cell parameters, thermal expansion coefficients and endothermic effect on DTA curve. In the process of obtaining ceramics using spark-plasma sintering both compounds manifested an unexpected shrinkage rate. All effects were explained on the basis of changings in crystal structure during distortion polymorphic transition.

This study investigates the wear behavior of Al hybrid composites produced by adding 4 % Ti and different amounts of B 4 C ( ex situ ) to the AA7075 alloy produced by powder metallurgy method in order to obtain TiAl 3 ( in situ ) reinforcement phase. Different amounts of B 4 C (3 %, 6 % and 9 %) were added to the 4 % Ti added AA7075 alloy. Preformed parts were sintered in controlled atmosphere (argon) heat treatment furnace at 580 °C for 4 hours and then cooled. After the sintering process, the samples were characterized with scanning electron microscopy, X-ray diffraction and density and hardness measurements. Wear tests of the samples were conducted at 1ms -1 sliding speed, under 30N load for 6 different sliding distances (500–3000 m). As a result of the study, the density of the AA7075 alloys, added 4 % Ti and different amounts of B 4 C, was observed to decrease by the increasing amount of reinforcement elements. Also, the highest hardness value was measured for the 9 % B 4 C added AA7075 alloy. Wear test results showed that the weight loss of the aluminum hybrid composites increased with the increasing sliding distance. On the other hand, it was observed that weight losses of composites decreased with increasing amount of B 4 C.

The double-slag converter steelmaking process can smelt low- and ultra-low-phosphorus steel and reduce lime and dolomite consumption and the amount of final slag simultaneously. Industrial steelmaking tests on a 150-metric ton converter at the Tangsteel Company were carried out to study this principle and its effect on the dephosphorization ratio and material consumption. The results showed that low-temperature stage could be used with a reduced amount of slag in the double-slag steelmaking process to achieve rapid and efficient dephosphorization. A low-basicity slag (~1.5–2.0) in the dephosphorization stage is required in double-slag process. The dephosphorization ratio reached a maximum of 71 % when the slag basicity was 1.7. The end-point phosphorus content after the smelting process was reduced from an average of 0.018 mass% to an average of 0.011 mass% and the dephosphorization efficiency increased by more than 6 %. The dephosphorization slag could be poured out rapidly when the FeO content was controlled at ~16–20 mass% in the double-slag smelting process. Based on key factors such as an efficient dephosphorization and a rapid iron–slag separation, the production efficiency was improved and the smelting cycle increased by only four minutes over the conventional process.

In order to study dynamic recrystallization behavior of the as-extruded 3Cr20Ni10W2 under isothermal compression conditions, a cellular automaton (CA) model was applied to simulate hot compression. Analysis on the strain–stress curves indicates that dynamic recrystallization is the main softening mechanism for the 3Cr20Ni10W2 when the deformation occurred in the temperature range of 1203–1303 K with an interval of 50 K and strain rate range of 0.01–10 s −1 . The deformation temperature and strain rate have a significant influence on the dynamically recrystallized grain size. Subsequently, a CA model is established to simulate the dynamic recrystallization behaviors of the studied alloy. The simulated results show that the mean grain size increases with the increased deformation temperature and decreases with the increased strain rate, which is consistent with the experimental result. In addition, the average absolute relative error, which is 13.14%, indicates that the process of the dynamic recrystallization and the dynamically recrystallized grain size can be well predicted by the present CA model.

The microstructures and mechanical properties of dissimilar weld joints between T92 and Super 304H steels were investigated. Dissimilar weld joints with four groove angles were constructed using gas tungsten arc welding. The results showed that post-weld heat treatment improved the mechanical properties of the dissimilar weld joints. The optimal groove angle for T92/Super 304H dissimilar weld joints was found to be 20°, considering mechanical properties. Furthermore, the transformation from equiaxed dendrites to columnar dendrites was observed in the weld metal. Epitaxial growth and delta ferrites were found around the fusion line between the Super 304H and the weld metal.

To recycle the phosphorus in P-bearing steelmaking slag and use the slag as phosphate fertilizer, it is necessary to study the distribution of P 2 O 5 between the P-rich phase and matrix phase in P-bearing steelmaking slag. The addition of MgO and MnO into the slag has no effect on the phosphorus form of existence in the slag and has little effect on the %(P 2 O 5 ) SS . In contrast, Na 2 O and CaF 2 in the slag change the phosphorus form of existence in the slag and increase %(P 2 O 5 ) SS obviously. L p ’, γP2O5(SS)${\gamma _{{{\rm{P}}_2}{{\rm{O}}_5}(SS)}}$, γP2O5(M)${\gamma _{{{\rm{P}}_2}{{\rm{O}}_5}(M)}}$, C P(M) and C P(SS) were calculated, and it was found that %(CaO), %(T.Fe) and %(P 2 O 5 ) in the P-rich phase and matrix phase significantly affect L p ’. MnO and MgO in the slag have little effect on the distribution of P 2 O 5 between the P-rich phase and matrix phase, whereas Na 2 O and CaF 2 affect the distribution of P 2 O 5 between the P-rich phase and matrix phase.

Precise control of inclusion and molten steel compositions during ladle-furnace refining is important to obtain high-quality steel. Mass-transfer behavior affects these compositions. A model was developed to investigate the mass transfer occurring between molten steel, slag, inclusions, and the refractory during ladle-furnace refining, using two-film theory to describe the reactions. A coupled-reaction model based on the CaO–Al 2 O 3 –MgO–SiO 2 –FeO–P 2 O 5 slag and Mn–Si–Al–Ca–Mg–P–S–O steel systems was applied to describe the reactions between molten steel and slag; the reactions between the refractory lining and slag or steel were described using average industrial erosion rate data. The model was used to calculate changes in the compositions of molten steel and slag, oxygen activity at the slag–molten steel interface, and composition of the inclusions. The calculated results agreed with operational results for a 100 t ladle furnace at the Tangsteel plant in China.

The tunnel defect formed in friction stir weld would dramatically push the mechanical properties of joints into deterioration. In this study, friction stir welding process was adopted to repair the joints of 7N01 aluminum alloy with tunnel defect. The effects of friction stir repair welding process on the microstructure and mechanical properties were comprehensively investigated. Microstructure of the repaired joints shows that the grain size in nugget zone decreases slightly while the recrystallization in the retreating side of thermo-mechanically affected zone is intensified as the joints are repaired. The microhardness of the repaired joints declined slightly compared with the defective joint. However, the yield strength and tensile strength increase and recover to the values of the joints free of defect. The longitudinal residual stress in weld zone increased remarkably as the repair times increase. Compared with the once repaired joint, yield strength and tensile strength of the twice repaired joint reduced slightly, and the throat thickness also reduced during the repeated repair welding process. Therefore, the times of repair welding applied should be limited actually.

The reaction zones between pure titanium and iron-nickel and pure nickel at 1173 K have been characterized. Two alloys with different initial composition were analyzed. When Ni80Fe20 is used the layer sequence at the reaction interface is: Ni80Fe20 → Ni 3 Ti → NiTi → NiTi 2 →Ti, while for Ni48Fe52 the sequence is: Ni48Fe52 → Ni 3 Ti → TiFe 2 → TiFe → NiTi 2 → Ti. The difference is in formation of NiTi, TiFe 2 and TiFe phases. The reaction zone remains very thin independently of time due to the fast dissolution rate of Ti in the alloy. The two different elementary chemical interaction processes have been identified in this article, namely the growth of the reaction layers by solid state diffusion and chemical conversion of the compounds by reaction-diffusion in the solid state. The mathematical description combining these processes is presented for description of the diffusion path generated during diffusion process.

In this work, friction stir processing (FSP) was used to modify the microstructure of A356 cast aluminum alloy under air cooling and water cooling conditions. The microstructure and mechanical properties of air cooling and water cooling FSP specimens and their differences were mainly discussed. Results show that the grains can be significantly refined after FSP under both air cooling and water cooling conditions. The water cooling FSP specimen shows much smaller grains than the air cooling FSP specimen due to lower temperature. Similarly, the Si particles of water cooling FSP specimen show much smaller sizes and better distribution. Both the air cooling FSP specimen and water cooling FSP specimen own much higher tensile strength and elongation than A356 base material (BM). In particular, the tensile strength and elongation of water cooling specimen are respectively 231 Mpa and 14.15%, which are equal to 186.3% and 1088.5% of the BM. Furthermore, the microhardness of water cooling FSP specimen is lower than that of the air cooling FSP specimen.