[en] Self-propagating high-temperature synthesis (SHS) was used to fabricate a Fe(Cr)-Al₂O₃ nanocomposite. The composite was fabricated by the reactions between the powders of Fe, Fe₂O₃, Cr₂O₃, and Al. The effect of blending ratio and mechanical activation of the initial powders and the precursor compressing pressure on the microstructure of the final product was studied by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The significance of the effect of each of the aforementioned parameters on the quality of the composite (assessed by measuring the compressive strength and wear resistance) was determined using a full-factorial design of experiments method. The results showed that the best molar powder ratio that produced the most homogeneous product through a sustainable SHS reaction was Fe:Fe₂O₃:Cr₂O₃:Al = 10:1:1:4. A lower Fe content caused the Fe(Cr) phase to melt and separate from the rest of the materials.

[en] In this work, mechanochemical reduction of CuO/ZnO powder mixture by Al and C has been investigated. Powder mixture was milled up to 20 h in a planetary ball mill. X-ray diffraction, transmission electron microscopy, thermo gravimetric analyzer, and differential scanning calorimeter have been used to study products phases and activation of redox reactions took place during ball milling. Results showed that the highly exothermic reduction reaction caused by aluminum provided the required heat for the endothermic reduction reactions by carbon. Consequently, the oxide powders were entirely reduced during ball-milling process and α-brass-Al₂O₃ nanostructured composite was obtained after 3 h milling. By utilizing the Scherrer's method, the mean grain size of the brass was found to be in the nanometer range which was later confirmed by TEM observations.

[en] Highlights: ► Combustion synthesis reactions were utilized for welding of aluminum alloys. ► A composite joint reinforced by different intermetallic compounds was obtained. ► Using metal oxides as a part of raw materials makes the welding process economical. ► Furthermore, this process introduces new applications for thermite reactions. - Abstract: In this work, first, a metastable composite powder of “14Al–3CuO–Ni” with a decreased ignition temperature was obtained via Arrested Reactive Milling (ARM), then this exothermic blend was used for welding of 1100 Aluminum alloy. The reactive media and the weld zones were investigated using scanning electron microscope. X-ray diffraction experiment and morphological investigations accompanied with the EDS analyses were carried out in order to evaluate the reactions’ products. Vickers microhardness profile across the joint and the shear strength of the joints were determined. The weld zone thickness in each of the parent alloys was measured to be 750 μm, approximately. Results showed that different reactions occurring during the process lead to the in situ formation of different intermetallic compounds such as Al₃Ni₂ and Al₇Cu₄Ni as well as Al₂O₃ nanoparticles at the interface. Thus, this area has the maximum hardness (80–90 VHN) and the minimum hardness of 35 VHN belongs to the parent alloys. The mean shear strength of the obtained joints was 27 MPa.

[en] Graphical abstract: Display Omitted Highlights: ► Nano particles of WC are synthesized by mechanochemical process. ► Zn was used to reduce WO₃. ► By removing ZnO from the milling products with an acid leaching, WC will be the final products. ► XRD results showed that the reduction reactions were completed after 36 h. ► TEM and SEM images showed that the morphology of produced powder is nearly spherical like. -- Abstract: In this research we introduce a new, facile, and economical system for fabrication of tungsten carbide (WC) nano particle powder. In this system WO₃, Zn, and C have been ball-milled for several hours, which led to the synthesis of tungsten carbide nano particles. The synthesized WC can successfully be separated from the ball-milled product by subjecting the product powder to diluted HCl for removing ZnO and obtaining WC. X-ray diffraction (XRD) analysis indicates that the reduction of WO₃ will be completed gradually by increasing milling time up to 36 h. Scanning electron microscope (SEM), and transmission electron microscope (TEM) images show that after 36 h of milling the particle size of the fabricated powder is nano metric (about 20 nm). Results have shown that this system can surmount some main problems occurred in previous similar WC synthesizing systems. For example carbothermic reduction reactions, which lead to the synthesis of W₂C instead of WC, would not be activated because in this system reactions take place gradually.

[en] Highlights: ► ANNs and ANFIS fairly predicted UTS and YS of warm compacted molybdenum prealloy. ► Effects of composition, temperature, compaction pressure on output were studied. ► ANFIS model was in better agreement with experimental data from published article. ► Sintering temperature had the most significant effect on UTS and YS. -- Abstract: Predictive models using artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS) were successfully developed to predict yield strength and ultimate tensile strength of warm compacted 0.85 wt.% molybdenum prealloy samples. To construct these models, 48 different experimental data were gathered from the literature. A portion of the data set was randomly chosen to train both ANN with back propagation (BP) learning algorithm and ANFIS model with Gaussian membership function and the rest was implemented to verify the performance of the trained network against the unseen data. The generalization capability of the networks was also evaluated by applying new input data within the domain covered by the training pattern. To compare the obtained results, coefficient of determination (R²), root mean squared error (RMSE) and average absolute error (AAE) indexes were chosen and calculated for both of the models. The results showed that artificial neural network and adaptive neuro-fuzzy system were both potentially strong for prediction of the mechanical properties of warm compacted 0.85 wt.% molybdenum prealloy; however, the proposed ANFIS showed better performance than the ANN model. Also, the ANFIS model was subjected to a sensitivity analysis to find the significant inputs affecting mechanical properties of the samples.

[en] Highlights: • We synthesized ZnO nanorods by a simple hydrothermal process at 60 °C. • Effects of zinc salt concentration, solvent and alkaline mineralizer was studied. • Increasing concentration of zinc salt changed ZnO nucleation system. • NaOH yielded better results in the production of nanorods in both solvents. • Methanol performed better in the formation of nanorods using the two mineralizers. - Abstract: ZnO has been produced using various methods in the solid, gaseous, and liquid states, and the hydrothermal synthesis at low temperatures has been shown to be an environmentally-friendly one. The current work utilizes a low reaction temperature (60 °C) for the simple hydrothermal synthesis of ZnO nanorod morphologies. Furthermore, the effects of zinc salt concentration, solvent type and alkaline mineralizer type on ZnO nanorods synthesis at a low reaction temperature by hydrothermal processing was studied. Obtained samples were analyzed using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Increasing the concentration of the starting zinc salt from 0.02 to 0.2 M changed ZnO nucleation system from the homogeneous to the heterogeneous state. The XRD results confirmed the production hexagonal ZnO nanostructures of with a crystallite size of 40.4 nm. Varying the experimental parameters (mineralizer and solvent) yielded ZnO nanorods with diameters ranging from 90–250 nm and lengths of 1–2 μm.

[en] The main goal of the current study is to clarify the effect of TiO₂ particles size (micro and nano) on the crystallite size of microwave-combustion synthesized Al₂O₃/TiC composite. Al, C, both nano- and micron TiO₂ have been mixed mechanically and milled using a planetary ball mill. The milled samples have been pressed before exposing to microwave with different powers. In order to validate the formation of Al₂O₃ and TiC phases, the samples have been analyzed by X-ray diffraction. Crystallite sizes of produced TiC and Al₂O₃ in samples containing micron TiO₂ are about 46.6-87.9 and 63.8-208.8 nm respectively and in samples containing nano-TiO₂ are about 38.2-68.7 and 54.4-99.5 nm respectively. It means that using nano-TiO₂ as one of the raw materials leads to formation of nano-structure Al₂O₃/TiC composite. Microstructure of produced composites has been evaluated using a scanning electron microscope (SEM). Microscopic evaluations show that Al₂O₃ phase in micron samples has a regular shape, unlike needle shape in nano-samples.

[en] Highlights: • Joining of a Ti-based strong glass former using friction stir spot welding process was studied. • Effects of welding parameters on the fracture load and fractured surfaces were analyzed. • Different zones in the weld spot were characterized and stir zone, TMAZ and base metal were identified. • Nano crystal/BMG's composite formation in the stir zone under the tool shoulder was the reason for higher fracture load. • Stir zone under the tool tip and the TMAZ had similar hardness and shear bands pattern with different structural reasons. In this study, TiZrFeBeCu bulk metallic glass plates have been welded together by using the friction stir spot welding method. The effects of processing parameters on the microstructure and mechanical properties of the joints have been studied. It has been found that the plunge depth has a crucial effect on the fracture mode and fracture strength of the joint. Both tool rotation speed and holding time significantly influence the tensile/shear fracture load and the fracture toughness. The correlation between fracture surface and the fracture toughness have been analyzed. The results revealed that there exist three regions in the spot welding of bulk metallic glass plates: stirring zone, thermo mechanically affected zone and base metal. It shows that stirring zone under the tool shoulder and around the tool tip possesses different structures and micro-hardness from that beneath the tool tip. The thermo mechanically affected zone and the stirring zone under the tool tip have similar hardness and structure. Stress relief annealing was used to clarify the reason for the hardness difference at different regions. Changes in the hardness in different areas of the welding spot can be correlated with the shear bands pattern and plastic zone size around the Vickers indents.