Journal of Ultrafine Grained and Nanostructured Materials
Volume:56 Issue: 2, Dec 2023

Developing an effective yet convenient synthesis method to achieve visible light-responsive metal sulfides has been one of the main challenges in the photocatalysis field. In this study, a facile reflux approach has been proposed to synthesize SnS2 nanoflakes for photocatalytic degradation of methylene blue (MB) as an organic pollutant. X-ray diffraction (XRD) pattern and Raman spectroscopy confirmed the formation of SnS2 with hexagonal crystal structure. The results of the nitrogen (N2) adsorption-desorption were analyzed by Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods. BET results exhibited specific surface area, total pore volume, and average pore diameter of 84.3 m2/g, 0.22 cm3/g, and 10.3 nm, respectively. The BJH outcomes indicated a distribution of about 40 nm for pore size with a peak of 1.64 nm. The nanoflake morphology and band gap energy of approximately 2.15 eV were revealed through field emission electron microscope (FESEM) and diffuse reflectance spectroscopy (DRS), proving the successful synthesis of visible light-responsive SnS2 nanoflakes. The efficiency of MB photodegradation over SnS2 nanoflakes was 78% under visible light radiation. The photocatalytic reaction followed a pseudo-first-order kinetic model with the calculated rate constant of 0.0045 min-1. Additionally, the photocatalytic degradation mechanism over SnS2 nanoflakes was investigated, and the results proved the successful contribution of holes and hydroxyl radicals in the mineralization of MB.

Polyvinyl alcohol (PVA)/chitosan (CS) and PVA/ CS/carbon nanotube (CNT) nanofibers were fabricated by electrospinning method. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis and water contact angle (WCA) tests were used to evaluate the morphology and some properties of electrospun fibers. The results showed that the most appropriate mass ratio of PVA/Cs resulting in uniform and smooth nanofibers was 2.8:1, and this morphology was not affected by the addition of CNT. However, the presence of CNT caused a significant decrease in fibers’ diameter from 519 nm to 85 nm. The compatibility of CNT with PVA/Cs and crosslinking between the components was confirmed by the XRD and FTIR analysis. Improving the hydrophilic properties of the fibrous mat was admitted by the WCA test.Keywords: Polyvinyl alcohol (PVA);chitosan (CS); Carbon nanotube (CNT), Electrospinning

In the current study, 316 stainless steel and 4140 steel sheets were successfully joined using friction stir butt welding (FSBW). The tool's rotational speed and the linear welding speed were assumed to be 1400-1700 rpm and 30-50 mm/min, respectively. The weld microstructures were examined by X-ray diffraction (XRD), optical microscopy, and scanning electron microscopy (SEM). In this welding, three zones with different structures relative to the base metals, including thermomechanical zones for each base metal and stir zone, were formed. Observations indicated that in the microstructure of 4140 steel containing martensite, the martensite blades vanished, and the grains extended in the thermomechanical zone. Furthermore, in the 316 stainless steel containing austenite, the austenite grain size was shrunk due to the dynamic recrystallization in the thermomechanical zone. Also, the microhardness test results showed that the stir zones have higher hardness than base metals in all specimens because of the dynamic recrystallization and fine-grained structure. Moreover, the 1550 rpm - 40 mm/min welded specimen in the stir zone has the highest yield strength of 350 MPa in the tensile test, which was higher than the yield strength of 316 stainless steel.

The effect of content in the piezoelectric response of poly (vinylidene fluoride) (PVDF)/BaTiO3 nanocomposites has been investigated in this work. The morphology of PVDF-BaTiO3 composite films was characterized using scanning electron microscopy (SEM). Fourier transforms infrared (FTIR) spectroscopy and X-ray diffractometry (XRD) were used to investigate the phase analysis of samples. Voltage output increases significantly with increasing filler content. The electroactive β-phase of PVDF is nucleated by the presence of the ceramic filler, the effect being strongly dependent on filler content. The results revealed that incorporating the functionalized BaTiO3 nanoparticles within the PVDF layer increases the piezoelectric response of pure PVDF compared to the sample with incorporated pure sample. Increasing concentration caused enhanced piezoelectric response.

Hall-Petch analysis and the effect of the average grain size (D) on the hardness (H) of AISI 309Si stainless steel should be systematically investigated. This aim was achieved by cold rolling (reduction of thickness of 90%) followed by annealing at 1000 °C for different holding times. Cold rolling led to the formation of deformation-induced α΄-martensite and work-hardening of the retained austenite, which led to an increased hardness of 427 HV compared to the hardness of 115 HV for the as-received sample. X-ray diffraction (XRD) analysis revealed the formation of ~30 vol% martensite, which signifies the higher mechanical stability of austenite in this alloy when compared to the metastable grades. At the annealing temperature of 1000 °C, the material is fully austenitic without any intermetallics. Moreover, by occurrence of martensite reversion, recrystallization of the retained austenite, and subsequent grain growth, it is easy to obtain different grain sizes at this temperature. Annealing at 1000 °C for 30 min resulted in a significant increment of hardness (155.1 HV) compared to the as-received sample as well as the formation of a fine-grained microstructure with an average grain size of 6.7 µm, which is equivalent to ~93% refinement of the grain size. Longer annealing times led to the occurrence of grain growth with the resulting decrement of hardness, where D–D0=2.1762×1011exp(–280000/RT)×t0.5 was proposed to predict the grain size during grain coarsening. Moreover, the Hall–Petch relationship of H=140.1/√D+100.7 was proposed for the first time, in which the H0 value of 100.7 HV was also compared to those determined for AISI 316L (130.0 HV) and 304L (160.4 HV) alloys. Furthermore, it was revealed that the increased metastability leads to an increment in the H0 value, which can be correlated with the Md30/50 temperature.

The steel alloys of the current study contain 0.3% carbon with different amounts of Cr, and Mo, in addition to W. The alloys were cast as Y-blocks. Cast slabs with 150x100x35 mm dimensions were then subjected to 4-steps directional hot forging into 15 mm diameter round bars in the temperature range 1200-830 oC.Austenite grain refinement was taken place by the 4-steps cross-sectional reductions, where it secures extreme fine lath martensite combined with crammed nano needle- like Cr23W2C6 carbides between the martensite laths.A quenching tempering cycle was carried on the forged bars at 250 oC for 25 min. and then air cooled to modify the martensite laths and reorganize the nano needle-like carbides to modify the mechanical properties. The optical microscopic investigation confirms extensive grain refining of the martensite laths. However, scanning electron microscope (SEM) photos at high magnifications reveal. The structure composed mainly of extreme fine laths martensite with nano needle-like structured carbides with 50 nm diameter crammed between the martensite laths. Little amounts of retained austenite (RA) phase was located tightening on the boundaries of martensite laths as white nano films. A blend of extreme-fine laths martensite and nano films of retained austenite (RA) phases in addition to the crammed nano needle-like structured carbides are working cooperatively for ultra-high strength creation. The tensile test specimens possessed continuous yielding, as the predominant microstructure contains a martensite phase. Strength increases continuously due to tungsten (W) addition up to 1.6%. During tempering, some of the nano needle-like Cr21W2C6 carbides, which were crammed between the martensite laths have a chance to migrate out from the martensite laths. The migrated nano needle carbides favor to coagulate and stick to each other to form 3D nano bulk-size spheroidal shaped carbides sizing 200 nm and precipitating on the martensite laths surface.

This study investigated the influence of three different frequencies (100, 1000, and 2000 Hz) during the PEO process on the characteristics of ceramic coatings fabricated on Ti-6Al-4V alloys in the presence of 12 g/L Na3PO4.12H2O and 3 g/L ZrO2 nanoparticles. The microstructure, surface roughness, wettability, chemical composition, and corrosion performance of the coatings were thoroughly examined to assess their performance. The microstructural results revealed that increasing frequencies led to a reduction in the porosity size, as well as a decrease in coating thickness, wettability, and surface roughness. Additionally, the corrosion performance of the coatings was evaluated in Hank's solution using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) methods. As the frequency rose from 100 to 2000 Hz, the corrosion current density dropped significantly from 47.35 to 13.75 nA/cm2 and the corrosion potential increased from 218 to 684 mV versus Ag/AgCl electrode. These findings indicated that the coating produced at a frequency of 2000 Hz exhibited the lowest corrosion density, thereby demonstrating superior corrosion resistance compared to the coatings produced at lower frequencies. The corrosion resistance of the optimum coating (coating formed at a frequency of 2000 Hz) was found to be approximately 0.8 times higher compared to the uncoated metal.

In this article, effects of annealing treatment on the evolution of microstructure, tensile properties and electrical resistivity of copper-graphene nanocomposites are investigated. In order to fabricate the nanocomposite, graphene nanopowder was ball-milled after being mixed with copper powder to form a mixture of copper-graphene powder (CuG). Hot rolled copper sheets were used as the matrix of the composite which were annealed prior to accumulative roll bonding (ARB). The nanocomposite was fabricated using 2, 4 and 6 cycles of ARB leading to 20, 40 and 160 multi-layered nanocomposites. Despite increased mechanical strength, the elongation to failure and the electrical conductivity were significantly reduced which were attributed to the high defect density after severe cold deformation and strength-ductility trade-off. The effect of cold deformation on increasing electrical resistivity was so significant that no positive effects of addition of 1% CuG on reducing resistivity was observed but a slight improvement was found in the sample with 2% CuG. However, after annealing at 500 C for 2 h, ductility was fully recovered to the initial value and the electrical resistivity was significantly reduced in the nanocomposite. This was attributed to the fact that a fully recrystallized grain structure was achieved after annealing. Percentage of reinforcing agent and the thickness of the stacking layers were found to determine the final grain size. Electrical conductivity of the nanocomposite was found to significantly improve with annealing. Indeed, the electrical conductivity of the annealed 6ARB-2%CuG composite was higher than the initially annealed copper sheet while the strength and ductility were increased, as well. This determines that the combination of ARB and annealing can be used as an effective method for fabrication of copper-graphene nanocomposites.

In the present work, the effects of Al and Nb elements on the formation of glassy phase in Cu-Zr based bulk metallic glasses (BMGs) have been investigated. In this regards, different Cu50Zr50-xAlx and (Cu50Zr43Al7)100-xNbx samples with 2 mm in diameter were prepared using arc melting followed by injection casting in water-cooled copper mold. The results illustrated that Al has positive effect on increasing the glass forming ability (GFA) of Cu-Zr system, and it is possible to create a completely glassy structure in Cu50Zr43Al7 sample. In contrast, the addition of Nb has destructive effects on glass forming ability, the homogeneity and final mechanical properties of Cu-Zr-Al BMGs. The segregation of Nb during solidification process and precipitation of brittle B2-CuZr and Cu10Zr7 phases are the main reasons of lower ductility and compressive strength in the presence of Nb element. As-solidified samples containing Nb showed compressive fracture strength in the range of 1000-1650 MPa, which was much lower than Nb-free alloy (2050 MPa).

Formation of strong texture, columnar grains, and chemical inhomogeneity are some of the serious challenges associated with SLM of metallic alloys. This paper deals with in-situ SLM manufacturing of Ti-5Cu (wt.%) samples from pure Ti and Cu powders at a constant volumetric energy density (VED) of 50.26 J/mm3. The heat treatment of samples was carried out by heating at 1050 °C (above the β-transus temperature) for 3hr followed by furnace cooling. Then the effects of Cu addition to pure Ti and heat treatment on β-columnar to equiaxed transition (CET) morphology and size of the α phase as well as microhardness of pure Ti and Ti-5Cu samples were investigated. The results showed that the β columnar grains with an average equivalent diameter (deq) of 80 μm in SLMed pure Ti were effectively converted to equiaxed grains with an average deq of ~15 μm in the SLMed Ti-5Cu samples. The Cu addition increased the average microhardness from ~290 HV for pure Ti to ~415 HV for Ti-5Cu samples. This was attributed to the formation of equiaxed grains, increased lattice micro-strain resulting from Cu addition and decreased size of the lath-like α phase. The applied heat treatment led to the formation of equiaxed β grains with an average diameter of ~125 μm, dissolution of unmelted titanium particles and the non-dissolution zones of Cu and Ti, and a rather homogeneous structure in Ti-5Cu samples. It also resulted in the decomposition of α´ martensitic structure and the formation of different morphologies of Ti2Cu precipitates. Reduction of the average microhardness of the Ti-5Cu samples to ~312 HV after heat treatment was also related to the increase in deq of the equiaxed β grains, in addition to the increase in the size of the α laths phase and decrease in micro-strain.

Gene editing has many promising applications for the treatment of diseases with unmet clinical needs, including cancers and autoimmune. There are two main routes for gene delivery: viral and non-viral. Recent research shows viral methods are emerging in clinical trials. Nevertheless, there are still a couple of technological obstacles that require further improvements, these include virus concentration and low efficiency of transduction. This research aimed to employ superparamagnetic iron oxide nanoparticles (SPION) to solve these problems. Three sizes of 10, 40, and 120 nm SPION were synthesized by co-precipitation and Sol-Gel methods, and characterized by XRD, FTIR, FESEM, and VSM. Conjugating SPION to viruses by polyethylene glycol (PEG) can increase the sedimentation of viruses due to magnetic and gravity forces even without ultracentrifuge. Moreover, this magnetic force can guide viruses toward cells and tremendously facilitate the transduction process. As shown, average size SPION (40 nm) revealed the best performance, especially in combination with salting-out precipitation and increased transduction efficiency of more than 20-fold. SPION size has significant effects and should be considered for this application. The combination of the salting-out method and SPION has a synergic effect and elevates transduction results tremendously.

Nearly two decades have passed since the introduction of high entropy alloys, which can be synthesized using solid, liquid, or gas methods. This study focuses on the solid-state method of mechanical alloying to create high entropy alloy AlCoCuFeNi and examines the properties of the material at various stages of synthesis. The solid-state method of mechanical alloying was utilized in this research to synthesize a high entropy alloy, with samples taken at regular intervals of 10, 20, 30, 40, and 50 hours. X-ray diffraction (XRD) was used to characterize the alloys, with further XRD analysis performed to determine crystallite size and lattice strain. In this study, high entropy alloys were successfully synthesized as two-phase solid solutions with a two-phase crystal (FCC) structure. The resulting alloy had a crystallite size of 8.4 nm and a residual strain of 1.7%. Elemental mapping image revealed that after 50 hours of mechanical alloying, all elements in the high entropy alloy were dissolved into each other with nearly identical atomic ratios, a finding confirmed by XRD analysis. The solid solution alloys synthesized in this research exhibited an intriguing phase separation phenomenon at the nano scale. The observation of two phases with different lattice constants highlights the versatility of high entropy alloys and their potential for diverse applications.