Average Grain Size Values Research Articles

Effects of Ni cation ratio and sintering temperature on microstructure and electrical properties of NiMnCoO4-based ceramics

Negative temperature coefficient (NTC) thermistors as temperature sensors play an important role in various electrical/electronic devices and are widely applied in the fields such as, automotive sensor modules, home appliances and control applications. The electrical properties of NTC thermistors can be effectively controlled by regulating the content of their chemical components or changing the microstructures. Therefore, this study investigated the effects of Ni cation ratio and sintering temperature on microstructures, crystal structures, and electrical properties of NiMnCoO4-based ceramics. With increasing Ni content, it was found that sinterability of NiMnCoO4-based ceramics was decreased with forming rock-salt phase of NiO, resulting in degrading resistivity. Furthermore, the spinel structures were detected by X-ray diffraction analysis regardless of sintering temperatures. Notably, values of average grain size for sintered samples were increased with increasing sintering temperature. Besides, it was clarified that electrical properties were significantly influenced by average grain size. The room temperature resistivity was increased from approximately 300 kΩ⋅cm for the sintered sample at 1100°C to about 600 kΩ⋅cm for for the sintered sample at 1300oC. On the other hand, the B(25/85) constant was not significantly influenced by the sintering temperature. Accordingly, it is expected that the results of this study are useful for controlling electrical properties of MnCoNiO4-based ceramics.

Phase-field simulation of dynamic recrystallization in friction stir weld nugget zone of dissimilar Al/Mg alloys

In friction stir welding (FSW) of dissimilar Al/Mg alloys, the materials on both sides in weld nugget zone (WNZ) undergo extremely uneven high temperature and plastic deformation, resulting in a great difference in dynamic recrystallization (DRX) which determines the weld microstructure evolution. In this study, the multi-phase field model coupled with the dislocation density model is developed to conduct numerical simulation of DRX behavior in WNZ of Al/Mg alloys FSW with Mg placed on advancing side. It is found that during welding process, the grain size at the checking points in WNZ always decreases rapidly at first and then increases slowly to a stable value, while the dislocation density always increases first and then decreases to a stable level. After welding, the final grain size on Al's side is lower than that on Mg's side. As the welding speed decreases, the DRX becomes more intense, and the dislocation density curve fluctuates more frequently. The calculated final values of average grain size at both Al's and Mg's sides are in good agreement with the experimentally measured ones.

Microstructure evolution mechanisms and a physically-based constitutive model for an Al–Zn–Mg–Cu–Zr aluminum alloy during hot deformation

High-temperature flow features of the Al−Zn−Mg−Cu−Zr aluminum alloy was revealed by hot compression tests. The evolution mechanisms of dislocation clusters, subgrain, and dynamic recrystallization (DRX) grains, are thoroughly explored by EBSD and TEM analysis. Experimental results suggest that the high strain rate can exacerbate dislocation clusters formation, as well as subgrain nucleation/accumulation, inducing the increasing of flow stress. Nevertheless, the noticeable annihilation of substructures, as well as the growth of DRX grains, emerge at the higher temperature, causing the descending of flow stress. Three types of DRX nucleating mechanisms, i.e., discontinuous DRX (DDRX), geometric DRX (GDRX) and continuous DRX (CDRX) are activated in the Al−Zn−Mg−Cu−Zr aluminum alloy during hot compression. Simultaneously, the GDRX often appears at a high compressed temperature or a low strain rate. A physically-based (PB) model is proposed to collaboratively reconstruct true stresses and microstructure evolution features. The estimated values of true stress, DRX fractions and average grain size preferably fit the experimental data, indicating the proposed PB model can precisely catch the thermal compression behaviors and microstructure evolution characteristics of the Al−Zn−Mg−Cu−Zr aluminum alloy.

Cu–Ce substituted cobalt nano ferrite - Structural, morphological, and magnetic behavior prepared by sol-gel auto-combustion

Sol-gel auto-combustion synthesized Co1-xCuxFe2-yCeyO4 (x = 0.0, 0.25, 0.5 and 0.75; y = 0.0, 0.03, 0.06, and 0.09), Cu–Ce substituted Co ferrite nanopowders. Investigations have been done on how Cu–Ce substitution affects the structural and magnetic characteristics. The Cu–Ce substitution variation effect on structural and magnetic properties is studied with X-ray diffraction (XRD), Field effect scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and Vibrating sample magnetometer (VSM). The XRD was used to identify the crystal phase, and the role of Cu–Ce substituted for Co indicates how it formed. There is no change in the crystal structure, and no additional characteristic peak linked to Cu2+ and Ce3+ ions substitution was found in the XRD. The powder was sintered at 1100 °C. The crystallite sizes were found in between 33 and 62 nm. Increasing the Cu–Ce content decreases the lattice constant and is found between 8.4044 and 8.3309 Å. The FESEM images were used to analyze the nanostructural properties. The range of 110–128 nm is the value of average grain size. Two vibrational bands can be seen in FTIR spectra at about 600 cm−1 (v1) and 400 cm−1 (v2). They are attributed to the spinel lattices A and B sites, respectively. The tetrahedral site has a greater vibrational frequency of 566.09 cm−1, while the octahedral site has a lower vibrational frequency of 420.09 cm−1. FTIR spectra show the tetrahedral stretching peaks shifting towards lower frequencies with increasing Cu2+ and Ce3+ ions content. At ambient temperature, the magnetic properties of Cu–Ce substituted cobalt ferrites revealed a strong hysteresis loop. There was a decrease in magnetic saturation and an increase in coercivity.

The Performance of V2O5:Ag Nanoparticles as Thin Film and Bulk Pellet Sensor for NO2 and NH3 Detection

A comparison of gas sensing performance of V2O5:Ag nanoparticles as thin film and as bulk pellet toward NO2 and NH3 is presented. V2O5:Ag nanoparticles thin films were deposited by vacuum thermal evaporation method on glass substrates while the pellets were prepared by powder technology. XRD patterns of thin film and pellet were polycrystalline with an orthorhombic structure. The value of average grain size is about 60 nm. The morphological properties of the samples have been distinguished by atomic force microscopy (AFM) and field effect scanning electron microscopy (FESEM) which indicated that the films showed homogeneous surfaces morphology and contained pores between the grains. Sensing results showed a various response to NO2 and NH3 gases. It was found that the sensitivity of thin films sensor is superior to that of the pellets sensor.

GRAIN SIZE EVOLUTION, MECHANICAL AND CORROSION BEHAVIOUR OF PRECIPITATE STRENGTHENED Cu-Ni ALLOY

Grain size characteristics, mechanical properties, and corrosion resistance of Cu-10%Ni alloy heat treated at three different temperatures and times were investigated and compared with the synthesized alloy. Mechanical properties such as UTS, ductility, hardness, and impact strength were determined. An optical metallurgical microscope was used to examine the structural properties. ImageJ software was also used to measure the grain size distribution of the alloys. The corrosion behaviour of the produced Cu-10%Ni alloys is analyzed by potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS). After corrosion testing, the surface morphology of the exposed samples is analyzed by scanning electron microscope (SEM) equipped with energy dispersive spectroscopy. The corrosion rate of precipitate strengthened Cu-10%Ni alloy decreases and ultimate tensile strength, ductility, and hardness increase as the average grain size distribution decreases. The non-heat treated Cu-10%Ni alloy showed a peak value of corrosion rate and average grain size, but a lower value of mechanical properties. An increase in residual stress follows an increase in grain size distribution, which lowers the strength and increases corrosion rates due to more active sites. The research outcome has enabled the improvement of the mechanical and corrosion properties of Cu-10%Ni alloys as a component for marine and automobile applications.

STUDY OF THE WELDABILITY OF STEELS OF DIFFERENT ALLOYING COMPOSITIONS FOR THE LARGE-DIAMETER PIPES TRANSPORTING HYDROGEN SULPHIDE-CONTAINING GAS

Increased resistance to brittle fracture in any zone of the welded joint is one of the main requirements for quality of steel pipes for transportation of the hydrogen sulphide gas, which determines the relevance of identification of the reasons of the impact toughness decrease of the welded joint area. The purpose of the study was to investigate the microstructure formation features of the seam zone of pipes made of low-carbon steels of different chemical composition. The effect of microstructure of the coarse-grained area of the heat affected zone on toughness of welded joint has been estimated by the laboratory thermal cycling testing complex Gleeble 3180. The samples with cross-section of 10×10×110 mm made of commercially available steel grades 04ХНДБ, 06ГНФБ and 05ХГБ (Russian Standard) with different contents of niobium and manganese were used as material for the research. To eliminate the effect of heating rate and holding time in austenitic region on the microstructure, the simulation was carried out in a cyclic mode with the same heating rate up to 1350 °С and subsequent cooling to 800 °С. The cooling rate in the interval 800–500 °C varied from 2 to 64 °C/s. The microstructure formation of the seam zone was studied by scanning electron microscopy and reflected electron diffraction. Despite the differences in chemical composition, the studied steels showed similar microstructure after simulation of the coarse-grained area of the heat-affected zone. For all the steels an increase in the share of rack bainite and the density of high angle boundaries with increasing cooling rate was found. It was established that at close values of average grain size of ferrite in the samples from steel 04ХНДБ the grain homogeneity is higher due to decrease in size and quantity of the largest grains. In specimens made of 05ХГБ and 06ГНФБ steel grades, the impact toughness of simulated coarse-grained area of the heat affected zone stabilizes at high level due to formation of more favorable dispersed structure when cooling rate increases more than 8 °C/s.

Features of the formation of structure and mechanical properties in rolled products of various thicknesses from low-carbon microalloyed steel produced by casting and rolling complex

The article considers results of the study of microstructure parameters effect on the impact strength in temperature range from 0 to –80 °C in 20 °C increments of Charpy samples with a sharp stress concentrator and Mesnager test pieces with a circular stress concentrator from rolled coils of low-carbon microalloyed steel with various thicknesses. The used roll products were produced in conditions of JSC “Vyksa Metallurgical Plant”. The tests were performed using optical and scanning electron microscopy. It is shown that with the same chemical composition and thermomechanical treatment modes, the metal of smaller thickness (6, 8 mm) is characterized by higher strength properties (on average, by 10 MPa for temporary resistance, by 30 MPa for yield strength) and a margin for viscous properties at negative temperatures at close values of grain score and average grain size corresponding to 10 – 11 numbers according to the State standard GOST 5639. The metal with a thickness of 12 mm has the lowest level of cold resistance, and the temperature of brittle transition is minus 50 °C. Structure of rolled products of various thicknesses has a variation in grain size. Rolled metal of smaller thicknesses have a smaller grains corresponding to number 14, rolled metal of larger thicknesses has a larger grains corresponding to number 8. By conducting electron microscopic studies using the backscattered electron method, it was found that a greater number of large-angle boundaries, which are barriers for brittle cracks propagation, are observed in the 6, 8 mm thick rolled products. The constructed orientation maps of the microstructure showed the presence of pronounced deformation texture corresponding to the orientations <110>||RD (rolling direction) and (<113>...<112>)||RD for rolled products with a thickness of 6 mm.

Microstructure and Mechanical Properties of Heat-affected Zone of Repeated Welding on 304 Stainless Steel

The effect of the repeated welding on the microstructure and mechanical properties of the heat-affected zone (HAZ) for 304 stainless steel were investigated under repeated welding up to five times by automatic gas tungsten arc welding using an optical microscope, a x-ray diffraction, a scanning electron microscope and an electron back-scattered diffraction. The repeated welding specimens were consisted with the microstructures of austenitic matrices with lath δ-ferrite. With the increasing of the repeated welding times, the average values of the austenitic grain size increased, and the δ-ferrite content decreased then increased. The preferred orientation of the HAZ changed from to . The values of location misorientation increased monotonically with the increasing number of repeated welding. The variation of the ultimate tensile strength and elongation was affected by the grain size mainly. Due to the hardening rate increasing, the yield tensile strength was increasing.

Improvement of microstructure and initial permeability of Mn0.5Ni0.1Zn0.4GdxFe2-xO4 with sintering temperature

This article reports the effect of sintering temperatures on microstructure and magnetic properties of Mn0.5Ni0.1Zn0.4GdxFe2-xO4 synthesized by conventional solid state reaction technique and the sintering was performed in the temperature range of 1150 to 1350 °C. The sintered samples were characterized using several techniques. Initial permeability, RQF and magnetic loss factor were measured using impedance spectroscopy. Microstructural analysis and phase identification were analyzed using field emission scanning electron microscope and X-ray diffractometer, respectively. XRD patterns reveal the formation of spinel ferrites phase of all the compositions sintered at 1300 °C, as optimum TS. Average grain size and relative quality factor are found increased with the rise of TS and the highest value of average grain size and RQF are observed for TS = 1300 °C, beyond this temperature average grain size and RQF are found decreased slightly. Magnetic loss factor (tanδ) decreases gradually with the rise of TS. The initial permeability increases with TS and it is found that the value of initial permeability for TS = 1350 °C is more than 5 times higher than that of the value obtained for TS = 1150 °C.

Effect of Cu Incorporation on Structure, Densification and Magnetic Properties of Polycrystalline Li<sub><i>x</i></sub>Ni<sub>0.2</sub>Zn<sub>0.8-2<i>x</i></sub>Fe<sub>2+<i>x</i></sub>O<sub>4</sub> Ceramics

The polycrystalline LixNi0.2Zn0.8-2xFex+2O4 and LixNi0.1Cu0.1Zn0.8-2xFex+2O4 (x = 0.0, 0.1, 0.2, and 0.3) ferrites were synthesized by the standard solid-state reaction method. The compound was sintered at 1150˚C for 5 hours. The effect of Cu substitution and its impact on the crystal structure, microstructure, complex initial permeability and magnetization of the Ni-Zn ferrites were studied. The effect of Li+ incorporation on the properties mentioned above was also investigated. X-ray diffraction patterns of the samples indicated a single cubic spinel structure for both the compound. No effect of Cu addition on crystal structure was observed. The density of the ferrites was found to be enhanced because of adding Li whereas the porosity of the samples decreased with the content of Li ions. The average value of grain size increased with the addition of Li content. The samples having Cu ions formed bigger size grains. Frequency-dependent complex initial permeability, loss tangent, and relative quality factor were studied at room temperature using an Impedance analyzer in the range of 100 Hz - 120 MHz regions. In the low-frequency region, the prepared samples exhibited a high value of permeability and after a certain frequency, the permeability falls. The value of permeability enhanced with the increase in Li whereas loss tangent was found to be reduced. The relative quality factor graphs described that the compound has excellent frequency stability up to a certain frequency which is suitable to be used in inductors, resistors, capacitors, etc. Initial permeability for LixNi0.1Cu0.1Zn0.8-2xFex+2O4 ferrites was found high than LixNi0.2Zn0.8-2xFex+2O4 which might be attributed to having bigger size grains of Cu containing samples because of easy movement of domain wall in bigger size grains. The values of saturation magnetization (Ms) were calculated for both compounds from M-H hysteresis loops and it enhanced with the increase in Li content which might be related to the modification of predominant exchange interactions between the cations. The Cu-containing compound exhibited higher values of saturation magnetization. The cation distribution reflects this increment because ferromagnetic Ni2+ and paramagnetic Cu2+ ions occupied in the B-sites and the diamagnetic Zn and paramagnetic Li occupied in the A-sites; therefore, net magnetic moments increased gradually. The studied materials might be used as an alternative to Pb-based compounds and would be environment friendly.

Вплив розміру зерна в полікристалічних матеріалах на механізми пластичної деформації та границю плинності

The influence of grain size on the physical yield strength of the polycrystal is considered by the method of cellular automata. The physical yield strength of the polycrystal in this model is defined as the stress at which, the plastic deformation covers the entire cross section of the sample from one edge to another. Three mechanisms of plastic deformation are considered. The first one is an initiation of plastic flow from grain to grain by dislocation pile-ups. The second one is plastic flow in different grains independently of each other under the action of external stress and the third one is intergranular slippage. Computer simulations have shown that at large grain sizes (d > 200 nm) deformation propagates from grain to grain by initiating dislocations pile-ups, since in this case pile-ups are quite powerful and have a large effect on neighboring grains. At average values of grain size (20 nm <d <200 nm) plastic deformation occurs in the grains independently of each other, and the external strain give a major influence on plastic deformation. With further reduction of the grain sizes (d <20 nm) the main mechanism of deformation is intergranular slippage. because in grains of this size are quite large image stresses that do not allow large dislocation clusters. In small grains the image forces are quite large to prevent large dislocation pile-ups formation, but the mass and volume of grain are quite small to turn or slip its under the action of external stresses. In accordance with these mechanisms, on the calculated dependence of the physical yield strength vs grain size, there are three areas with different angles of inclination in logarithmic coordinates. Keywords: yield point, grain size, Hall―Petch low.

A new-curvature cellular automata model of austenite grain growth

A new-curvature three dimensional cellular automata model for grain coarsening is proposed. The model takes account of the effects of grain size on the local-curvature. The simulation results are analyzed from four aspects: grain growth kinetics, grain size distribution, dynamics of single grain, and topological properties. The grain growth kinetics of the present model is proved to agree well with the theoretical model of normal grain growth. The absolute values of average grain size are compared to the experimental results of a low alloy steel. The simulated grain size distribution can be satisfactorily described by the Werbull’s formula. The simulation results of single grain growth kinetics matches well with the Hillert’s theoretical model, and the topological properties are similar to Ding’s simulation results.

Microstructural refinement of 355 aluminium alloys by ultrasonic melt treatment (UST)

Chemical grain refining of high-silicon-content aluminium alloys, such as 355 alloy, is impaired by the high silicon content. One solution is the use of ultrasonic melt treatment (UST). This study sought to determine the duration of UST and type of horn (steel or Ti) required to achieve optimal grain refining in these alloys. Samples produced by conventional casting underwent UST for different times with steel and Ti horns and were compared with as-cast samples. For all the conditions studied, analysis of the samples showed that UST is an effective grain refining technique and yields satisfactory values of average grain size and primary and secondary dendrite arm spacing (λ1, λ2) as well as low porosity. The chemical composition of the samples was analysed by SEM–EDS mapping and point analysis to identify the intermetallic phases before and after UST. Best results were achieved after only 20 s of UST with a steel horn. UST for this length of time with a steel horn produced a homogeneous microstructure and possible homogeneous mechanical properties. Grain size was 160 µm; primary dendrite arm spacing, or dendrite cell size, was 130 µm; secondary arm spacing was approximately 18 µm; and Vickers hardness was approximately 95 HV.

An effect of La doping on physical properties of CdO films facilely casted by spin coater for optoelectronic applications

Transparent conductive oxides (TCOs) are having emerging applications in optoelectronic technology. Hence, herein, we have designed and fabricated the cadmium oxide (CdO/FTO) TCO films with different concentrations of Lanthanum (La) through a facile spin coating technique. The crystal system and phase confirmation of fabricated films was analyzed by X-ray diffraction analysis. The values of D200 are found in the range of 25–31 nm indicates nanostructured thin films fabrication. EDX/SEM mapping revealed the presence of La and its homogeneity in CdO film. Atomic force microscopy was carried out to investigate the effect of La doping on surface topography of CdO films. The average values of grain size were estimated in the range of 7.56–10.95 nm along with surface roughness in range of 15.25–17.56 for pure and La-doped CdO films. The optical transparency of films was noticed in range of 75–85% in the NIR region. Direct and indirect band gap values are found in the range of 2.55–2.8 eV and 2.0–2.4 eV, respectively. The dielectric constant, loss, refractive and absorption indices were also calculated. Moreover, the linear, nonlinear susceptibilities and refractive index values were estimated and found in the range of 0.1–3, 1 × 10−12 to 1.6 × 10−7 esu and 2 × 10−12 to 1.28 × 10−8 esu, correspondingly.

Effect of the AgO content on the surface morphology and electrical properties of SnO2 thin films prepared by PLD technique

Tin dioxide doped silver oxide thin films with different x content (0, 0.03, 0.05, 0.07) have been prepared by pulse laser deposition technique (PLD) at room temperatures (RT). The effect of doping concentration on the structural and electrical properties of the films were studied. Atomic Force Measurement (AFM) measurements found that the average value of grain size for all films at RT decrease with increasing of AgO content. While an average roughness values increase with increasing x content. The electrical properties of these films were studied with different x content. The D.C conductivity for all films increases with increasing x content. Also, it found that activation energies decrease with increasing of AgO content for all films. Hall measurements confirmed that all the intrinsic films are n-type charge carriers. The variation of carriers concentration increase with increasing x content. Hall mobility decreasing with increasing x content for all films. Also the variation of Drift velocity, carrier life time and free mean path decrease with increasing of x content.

Structural and optical characterization of cobalt-doped zinc oxide thin films deposited by chemical spray pyrolysis

In our experimental pure and cobalt (Co) doped Zinc oxide (ZnO) thin film were prepared onto glass substrate chemical spray pyrolysis technique at 400 oC, X-ray diffraction, Atomic force microscope and optical properties were all investigated for each prepared films. Nanocrystalline films with hexagonal structure and strong (100) and (002) preferred orientation were obtained. The maximum value of average grain size is (15.7) nm with 6% Co-doping concentration. The optical transmission spectra have shown that both pure and doped ZnO films were transparent in UV-Vis wavelength region. The energy band gap of 0% Co is about 3.28 eV and decrease to 3.2 eV after 4% doping. The excellent-estimated structure, the optical results are accomplished in doped ZnO film with (4 and 6) % Co.

Facile microwave-assisted synthesis of tungsten-doped hydroxyapatite nanorods: A systematic structural, morphological, dielectric, radiation and microbial activity studies

Abstract Herein we report a low temperature, rapid microwave-assisted synthesis of pure and tungsten (W) doped hydroxyapatite (HAp) nanorods. X-ray diffraction study confirmed the good crystalline nature of synthesized product and various key parameters such as: grain size, dislocation density, lattice strain, degree of crystallinity and lattice parameters were estimated. The average value of grain size is found to be in the range of 11–32 nm and the highest degree of crystallinity was observed for 40 wt% W doped HAp (viz. ~ 67.3%). Functional groups and modes of vibrations were analyzed by FT-IR and FT-Raman spectroscopic studies. Morphology and elemental compositions of synthesized nanostructures were analyzed by FE-SEM/EDX measurements that confirms the formation of very low dimension nanorods (diameter 137 Cs) radioactive source and shows an enhancement in radiation absorption with an increase of doping which makes it useful in radiation shielding. Furthermore, the synthesized nanorods were applied to test their catalytic activity for methyl orange-removal in the presence of bacteria. The W doped HAp exhibited a great catalytic activity in presence of Enterococcus feacalis bacteria which indicates its applications in waste water treatment.

Structural and optical characterization of (Sn/Li) co-doped ZnO thin films deposited by spray pyrolysis technique

(Sn/Li) co-doped ZnO (LTZO) thin films have been deposited by spray pyrolysis technique and their structural, morphological and optical properties have been investigated. The films were characterized by X-ray diffractometer (XRD), field-emission scanning electron micrograph (FESEM), (UV–Vis) spectroscopy and photoluminescence spectroscopy. XRD results revealed that all thin films (LTZO) are polycrystalline with a hexagonal wurtzite structure, moreover when the Li reach (5 at.%) content, the surface thin films of (LTZO5) become covered with bigger and clear nano-sized crystallites and the average value of grain size is 147 nm with mainly hexagonal grains. The (UV–Vis) spectroscopy showed high transmittance in the visible region, which varied between 84% and 93% and the doping of 5 at.% for all the films of Li content thin films (LTZO5) red shifted. The doping ZnO with lithium and tin were eliminates the deep-level emission in orange/red bands (around to 600 nm).

Modeling and simulation of dynamic recrystallization behaviors of magnesium alloy AZ31B using cellular automaton method

In this study, a 2D Cellular automaton (CA) model was developed to visually and quantitatively predict the microstructural evolution of magnesium alloy AZ31B during hot deformation. Hot compressive and metallographic tests were carried out to evaluate the CA model parameters including the work hardening (WH) coefficient, dynamic recovery (DRV) coefficient, nucleation rate and grain boundary mobility. Firstly, the values of CA model parameters under tested conditions were identified based on the experimental true stress-strain curves. Then, the functional relationships between the model parameters and deformation conditions (deformation temperature and strain rate) were established. Using the developed CA model, the flow behaviors and microstructural evolution of magnesium alloy AZ31B during hot deformation were simulated and discussed. The agreement between CA simulated and experimental results indicates that the developed CA model can accurately predict the microstructural evolution of magnesium alloy AZ31B. In addition, a new method to calculate the CA simulated average grain size was proposed. The new proposed method can effectively decrease the effects of DRX nuclei on the calculated value of average grain size.