Formation Of Nanocrystalline Structure Research Articles

The GMI effect of Fe-based microwires with a partially crystallized near-surface layer

The GMI effect was investigated in microwires based on a Fe70Si18B9Cu1Nb2 alloy (ρ = d/D = 0.5, d = 15 µm) after heat treatment at 550 °C resulting in the formation of a non-uniform nanocrystalline structure. It was shown experimentally that short heat treatments (≤2 min 40 s) led to the emergence of α-Fe(Si) nanocrystals near the surface of a microwire while the central part of the microwire remained amorphous. Simultaneous processes of stress relaxation and formation of the nanocrystalline structure induced an enhancement of the GMI effect. A maximum value of ΔZ/Z = 150 % was observed at a frequency of 200 MHz. With an increase in the heat treatment time, the soft magnetic properties of the surface layer degenerated, resulting in the degradation of the observed GMI effect.

Formation of nanocrystalline and nanolaminate structures in a twinning induced plasticity Ti-12Mo alloy: The role played by {332} 〈113〉 twinning

Grain refinement is an effective strategy to strengthen metastable β titanium alloys. {332}<113> twinning, a typical deformation mode, its role on grain refinement still remains unelucidated. Here, we produced a gradient nanostructured layer with a depth of 800 μm in a metastable twinning induced plasticity β-Ti-12Mo (wt.%) alloy by means of surface mechanical rolling treatment. We found that {332}<113> deformation twinning, mainly dominated the deformation at moderate strain and strain rates, refining coarse grains into submicro-structures. With increasing strain and strain rates, dislocation slip instead of {332}<113> twinning prevailed. These dislocations were first arranged into extended boundaries and then into laminated structures to coordinate deformation. Eventually, shear banding and fragmentation of laminates result in the formation of nanocrystalline with size of 34 ± 8 nm. The nanostructured Ti-12Mo alloy exhibited the high hardness of 4.9 GPa at subsurface. The surface hardness decreased to 4.4 GPa which was mainly caused by the inhibition of stress-induced martensitic transformation α″ and the occurrence of its reversal transformation due to adiabatic heating induced by the high strain rate. This work expands our knowledge on strengthening β titanium alloys by {332}<113> twinning induced grain refinement at different deformation conditions.

Surface integrity and rolling contact fatigue behavior of 18CrNiMo7-6 steel subjected to ultrasonic surface rolling process

In this study, the effect of ultrasonic surface rolling process (USRP) on the surface integrity and rolling contact fatigue (RCF) behavior of 18CrNiMo7-6 steel have been conducted. The different static loads and ultrasonic amplitudes on surface morphology, surface roughness, microstructure, microhardness, and residual stress were examined. Results revealed that USRP treatment resulted in a remarkably smooth surface with the surface roughness value Ra of 0.035 μm. Moreover, USRP treatment induced the formation of nanocrystalline and ultrafine crystalline structures on the surface layer. Additionally, the sample surface was subjected to a significant layer of residual compressive stress, reaching a maximum value of approximately −1243 MPa and extending to a depth of around 1500 μm. The surface microhardness had been increased to 808 HV0.2. The comprehensive integration of grain refinement, the increase of surface microhardness, and the induction of residual compressive stress led to an improvement in RCF life.

Effects of aging and shot peening on surface quality and fatigue properties of material extrusion additive manufactured 17-4PH stainless steel

Material extrusion additive manufacturing (MEX) gains increasing interest due to its cost-effectiveness. However, concerns arise regarding inherent MEX characteristics potentially affecting mechanical properties. This study investigates the effects of shot peening and heat treatment on MEX 17-4PH stainless steel. After shot peening, surface nanocrystalline and compressive residual stress are induced. Aging results in higher hardness and tensile strength with lower elongation, while shot peening results in higher surface hardness with minimal change in elongation. For fatigue properties of as-sintered specimens, Al2O3 particle contamination dominates at high cycle regimes, while other MEX surface inhomogeneities dominate at low cycle regimes. Furthermore, as-aged properties are dominated by all surface inhomogeneities, resulting in the non-improvement of fatigue performance compared to the as-sintered specimens. However, shot peening on the as-sintered specimens significantly enhances fatigue properties through the formation of surface nanocrystalline structures and the induction of compressive residual stress, albeit with the occurrence of wrapped corners acting as fatigue crack initiation sites. Remarkably, the combination of aging and shot peening yields the most improvement in fatigue performance, exhibiting behaviours akin to as-sintered specimens with shot peening but without the generation of wrapped corners. Instead, fatigue crack initiation sites shift to subsurface region’s inhomogeneities.

Study of structural and optical properties of Gd doped ZnO nanostructures synthesized by one-step, mass-scale productive method

In the present work, one-step, mass-scale productive solid state reaction method has been employed for the preparation of gadolinium (Gd) doped ZnO (GZOx: x = 0, 2, 4, 6, 8 wt%) nanostructures. The prepared GZOx samples have been studies their structural, morphological, elemental diffusion profile and optical properties using P-XRD, FE-SEM, EDS, FTIR, and photoluminescence (PL) spectroscopy. The powder X-ray diffractometer (P-XRD) results clearly indicate strong and sharp diffraction peaks with broadening that confirms the formation of hexagonal nanocrystalline structure of ZnO and Gd doped ZnO. The hexagonal morphology formation of the grains after doping of Gd contents into the ZnO nanostructures system is seen from the FE-SEM micrographs and the sizes of the grains are found to close to the results obtained from XRD patterns. The presence of Gd contents in ZnO matrix confirms its doping by EDS spectrum of 4 wt% Gd doped ZnO nanostructures. Fourier transform infrared (FTIR) results confirm the presence of functional groups and chemical bonding of ZnO at room temperature. Investigation of optical emission is interesting and the PL spectra reveal two emission peaks, one in UV-region located in the range of ∼385 to 395 nm and other is defects related emission centred at ∼450, ∼468, ∼503 and ∼562 nm in visible region for all the samples. The enhanced PL intensity is observed in the higher doped Gd contents in ZnO nanostructures and can be attributed to the presence of Gd ions into ZnO lattice. The detailed structural and luminescence analysis has been carried out and correlated. The study of structural and optical properties GZOx samples suggest the luminescent optoelectronic applications.

Generation of viable nanocrystalline structures using the melt-cool method: the influence of force field selection

ABSTRACT The influence of force field selection on the formation of nanocrystalline structures of pure copper using the Melt-Cool method within Molecular Dynamics (MD) was investigated. This is of utmost importance since the use of MD to investigate nanocrystalline materials is critical due to the ability to study on the appropriate length scale. The Melt-Cool simulation method involves annealing the starting single crystal structure to temperatures exceeding the melting point of the material, followed by rapid quenching and equilibration to room temperature. The heating and rapid quenching allows for the mixture of atoms to randomised orientations with realistic microstructures and randomised defects, such as interstitial or vacancy atoms. Due to the requirement of the mathematical model (force field) to predict the nanocrystalline structure, the influence of force field selection is of paramount importance – a major gap found in currently available literature. The current investigation was performed in two phases: initial investigation to understand influence of force field parameterisation on formation of nanocrystalline structures, followed with an investigation to enhance predictions of mechanical properties of nanocrystalline copper found in currently available literature. The initial phase demonstrated a clear dependence on force field selection for the formation of viable nanocrystalline structures. The second phase demonstrated that the most accurate force field for mechanical properties may not be the ideal selection for use with the Melt-Cool method. The most ideal force field selection when performing the Melt-Cool method with the goal of obtaining accurate mechanical properties for pure copper was determined.

Magneto-Optical Properties of Ni0.4Cu0.3Zn0.3Gd0.125Fe1.875O4 Nano Ferrite for Application of Soft Magnetic Material

Abstract: Ni0.4Cu0.3Zn0.3Gd0.125Fe1.875O4 spinel ferrite powder is successfully synthesized using sol-gel auto combustion technique. The structural, optical and magnetic properties investigated by using X-ray Diffractometer, FTIR Spectrometer, Scanning Electron Microscope and Vibrating Sample Magnetometer (VSM). XRD analysis confirmed that formation of Nano crystalline cubic spinel structure of the sample. The crystallite size of synthesized nanoparticles is about 29.45nm. The IR study support the confirmation spinel structure of Ni0.4Cu0.3Zn0.3Gd0.125Fe1.875O4 sample. Band gap energy Eg obtained using UV-Visible absorption data is about 2.4238 eV. The magnetic properties have been studied from VSM data shows that

Structure determination in a new type of amorphous molecular solids with different nonlinear optical properties: a comparative structural analysis

The microscopic structures of two amorphous molecular solids with extremely nonlinear optical properties have been studied. They consist of organotetrel chalcogenide clusters with the chemical formula [(RSn)4S6]. The basic molecular building blocks are adamantane-like {Sn4S6} cores with organic ligands R attached to the Sn atoms. While the material equipped with R=naphthyl generates frequency doubling upon irradiation with a simple infrared laser diode, the material decorated with R=phenyl responds by emitting brilliant white light. The structural differences were investigated using x-ray scattering and extended x-ray absorption fine structure combined with molecular Reverse Monte Carlo. Transmission electron microscopy and scanning precession electron diffraction were used to examine structural differences from mesoscopic down to microscopic scales. Characteristic differences were found on all scales. While close core-to-core distances between {Sn4S6} cluster cores and molecular distortions are found in the white light emitting material, undistorted molecules and significantly larger core distances characterize the material showing frequency doubling. Here however, results of scanning precession electron diffraction reveal the formation of nanocrystalline structures in the amorphous matrix, which we identify as cause for the suppression of white light emission.

Enhanced surface properties and contact fatigue performance of Cr4Mo4V bearing steel subjected to ultrasonic surface rolling processing

AbstractThe paper presents the experimental studies on the enhanced comprehensive properties of Cr4Mo4V bearing steel using ultrasonic surface rolling process. Considerable improvements in mechanical properties and rolling contact fatigue performance are achieved in the present study, accompanied by the characterization of surface microstructures. The ultrasonic surface rolling process promotes the formation of fine nanocrystalline structures and nano‐sized elongated grains with severe deformation, leading to the increasing residual stress, micro‐hardness and high temperatures hardness. The crack propagation and delamination pit in the surface after ultrasonic surface rolling process is inhibited, further enhancing the rolling contact fatigue life of Cr4Mo4V bearing steel.

Synthesis and utilization of mesoporous alumina as a supporting material of Ce‐promoted Ni‐based catalysts in the methane reforming process

AbstractDue to the large applications of hydrogen as a feedstock of chemical industries and as an energy carrier, its production on large scales with low costs has attracted researchers. Steam reforming of methane (SRM) is the most common process for producing H2‐rich syngas over Ni/Al2O3 catalysts, which suffer from coke deposition and Ni particles agglomeration. For overcoming these issues, we have synthesized mesoporous alumina (MA) as a supporting material of Ni particles, structure, and activity, which were compared with the bulk alumina (BA) supported catalysts in the SRM process for the first time. Besides, cerium as an appropriate promoter for lowering deposited coke was added to all prepared catalysts. The reaction temperature (600–700°C), Ni loading (10–25 wt.%), and Ce loading (1–5 wt.%) were the parameters that were optimized for maximizing H2 yield and CH4 conversion. Prepared samples were characterized by various techniques before and/or after reaction. The results of TEM and XRD depicted the formation of nanocrystalline and mesoporous structure for Ni‐MA catalysts compare to Ni‐BA samples. The observations indicated that 20Ni‐3Ce/MA had the highest catalytic performance, achieving a CH4 conversion of 91.0% and H2 yield of 92.8% at 700°C.

The Mode Deformation Effect on Surface Nanocrystalline Structure Formation and Wear Resistance of Steel 41Cr4

A surface nanocrystalline steel layer in the low alloy steel 41Cr4 was fabricated by using mechanical-pulse treatment (MPT) with different deformation modes. The structure parameters, the physical and mechanical properties, the wear resistance, and the surface topography parameters of the treated steel depending on the deformation mode were investigated. A tool with a smooth working surface was used for inducing unidirectional deformation in the top surface layer (shear), and a tool with the oppositely directed grooves was used for generating multidirectional deformation. The surface layer with a nanocrystalline structure formed by MPT using both of the tools was characterised by enhanced mechanical properties and wear resistance compared with those of the untreated or heat-treated steels. Inducing multidirectional deformation during the MPT resulted in a decrease in the grain size and an increase in the depth and microhardness of the surface layer due to it facilitating the generation of dislocations compared to those formed under unidirectional deformation. The results also demonstrated that favourable surface topography parameters providing the highest wear resistance of the steel were obtained at MPT using multidirectional deformation.

Evolution of Structure and Properties of Nickel-Enriched NiTi Shape Memory Alloy Subjected to Bi-Axial Deformation.

The effect of a promising method of performing a thermomechanical treatment which provides the nanocrystalline structure formation in bulk NiTi shape memory alloy samples and a corresponding improvement to their properties was studied in the present work. The bi-axial severe plastic deformation of Ti-50.7at.%Ni alloy was carried out on the MaxStrain module of the Gleeble system at 350 and 330 °C with accumulated true strains of e = 6.6-9.5. The obtained structure and its mechanical and functional properties and martensitic transformations were studied using DSC, X-ray diffractometry, and TEM. A nanocrystalline structure with a grain/subgrain size of below 80 nm was formed in bulk nickel-enriched NiTi alloy after the MaxStrain deformation at 330 °C with e = 9.5. The application of MaxStrain leads to the formation of a nanocrystalline structure that is characterized by the appearance of a nano-sized grains and subgrains with equiaxed and elongated shapes and a high free dislocation density. After the MaxStrain deformation at 330 °C with e = 9.5 was performed, the completely nanocrystalline structure with the grain/subgrain size of below 80 nm was formed in bulk nickel-enriched NiTi alloy for the first time. The resulting structure provides a total recoverable strain of 12%, which exceeds the highest values that have been reported for bulk nickel-enriched NiTi samples.

Effects of TiMoTa nano-crystalline interlayer on nucleation, adhesion and tribological behaviors of diamond coating

To investigate the influence of the transition layer on diamond nucleation and growth, the TiMoTa multi-alloy interlayers were firstly prepared on WC-6%Co cemented carbide by double glow plasma surface alloying technique, and diamond was then deposited using microwave plasma chemical vapor deposition system. The thickness of the TiMoTa interlayers increased from 1.2 μm to 2.7 μm with the deposition temperature increasing from 800 to 900 °C. Due to the formation of nano-crystalline structure and hard phase, the as-prepared TiMoTa interlayer exhibited high micro-hardness. In the diamond deposition process, the nano-carbide particles preferentially formed at the TiMoTa interlayers can effectively prevent the further diffusion of C, so the surface carbon concentration rapidly accumulates to the critical value required for the nucleation and growth of diamond microcrystals. Finally, a microscale wear-resistant diamond coating with good adhesion was grown on the transition layer, the crack propagation radius of the diamond coating is ∼162 μm, and can reach Hf 2–3 grade. Therefore, our prepared TiMoTa nano-crystalline interlayer provides a new path for the development of a high-quality diamond coating with good adhesion on cemented carbide.

Effect of self-ion with high-energy irradiation on the surface morphology, microstructure and mechanical properties of nanocrystalline TiAlN coating

TiAlN coating are used as nuclear reactor cladding protective materials due to their good corrosion resistance. However, long-term exposure to an extremely harsh nuclear environment will cause degradation, and the threshold irradiation fluence is not clear. In this work, a nanocrystalline TiAlN coating was successfully deposited on 304 L stainless steel and silicon wafers by filtered cathodic vacuum arc (FCVA) technology. The effects of different fluences of Al 3+ irradiation performed by the GIC4117 tandem accelerator on the structure and mechanical properties of TiAlN coatings were studied. After irradiation with a fluence of 4.0 × 10 14 ions/cm 2 , the refinement of grain size and columnar structure of nanocrystalline TiAlN coatings was confirmed, which improved the hardness. The irradiation fluence of 4.0 × 10 16 ions/cm 2 reduces all mechanical properties and can be taken as the threshold for the degradation of the TiAlN coating. These nanocrystalline TiAlN coatings have high surface integrity with no destruction, such as flacking, exfoliation and blistering, and good mechanical properties after irradiation. • Ultra-hardness (>40 GPa) was obtained by the formation of nanocrystalline structure and solid solution phase. • The crystallites refined from the average size of 23 ± 2 nm for the initial state up to a size of 18 ± 2 nm. • The hardening effect was confirmed under ion irradiation and the hardness increases from 42.5 ± 1.3 GPa to 46.4 ± 1.4 GPa. • The TiAlN coating with nano-polycrystalline structure exhibits structural integrity without blistering or flaking effects after irradiation.

In situ XRD study of stress- and cooling-induced martensitic transformations in ultrafine- and nano-grained superelastic Ti-18Zr-14Nb alloy

In this study, a superelastic Ti-18Zr-14Nb shape memory alloy was subjected to a thermomechanical treatment, combining moderate or severe cold rolling and post-deformation annealing in the 500–600 °С temperature range for 5–30 min, in order to characterize the features of nanocrystalline structure formation, stress- and cooling-induced martensitic transformations, and determine a critical grain size for these transformations. A moderate (e = 0.3) cold rolling and annealing at 500 °C (30 min) forms a predominantly polygonized nanosubgrained β-phase substructure with a small amount of α-phase. An increase in the annealing temperature to 550 °C leads to the development of the polygonization process and the growth of the β-phase nano- to submicrometer-sized subgrains. As a result of severe cold rolling (e = 3), a predominantly nanograined structure with inclusions of amorphized and nanosubgrained structures is formed. Subsequent annealing at 500 °C (5 min) forms a nanograined structure of β-phase with some amounts of α-phase. An increase in holding time at 500 °C to 15 min increases the average grain size. After annealing at 525 °C, a submicrocrystalline structure forms. The smallest Young’s modulus values and the highest total recovery strains (E = 37–39 GPa and εr = 3.0–3.5%, respectively) are observed after post-deformation annealing in the 525–550 °C temperature range. A critical average grain size for the stress-induced β→α'' martensitic transformation of this alloy at room temperature is defined as 36 ± 13 nm, while for the cooling-induced transformation, this value is almost one order of magnitude greater (~ 250 nm).

Brief Communications on the Limiting Minimum Grain Sizes and Mechanism of В2→В19′→В2-Transformation during Formation of Nanocrystalline Structure in Titanium Nickelide

Brief Communications on the Limiting Minimum Grain Sizes and Mechanism of В2→В19′→В2-Transformation during Formation of Nanocrystalline Structure in Titanium Nickelide

Study on Properties and Heat Treatment Process of Fe75.9Cu1Si13B8Nb1.5Mo0.5Dy0.1

The soft magnetic properties of Fe[Formula: see text]Cu1Si[Formula: see text]B8Nb[Formula: see text]Mo[Formula: see text]Dy[Formula: see text] nanocrystalline alloy were studied which is designed on the basis of the Finemet type alloys. The X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), electric inductance measuring-testing instrument and MATS soft magnetic material AC/DC tester were used to study the effects of the effective permeability ([Formula: see text], saturation magnetic induction ([Formula: see text]), coercivity ([Formula: see text]), and hysteresis losses ([Formula: see text]) at 100[Formula: see text]kHz and 0.2[Formula: see text]T under factors such as different annealing temperatures, different thicknesses, and whether there is a need for transverse field for annealing. The results show that the commercial amorphous alloy ribbons Fe[Formula: see text] Cu1Si[Formula: see text]B8Nb[Formula: see text]Mo[Formula: see text]Dy[Formula: see text] have complete amorphous structure in as-cast state, and [Formula: see text]-Fe nanocrystalline phase precipitates on the amorphous matrix after vacuum annealing. Fe[Formula: see text] Cu1Si[Formula: see text]B8Nb[Formula: see text]Mo[Formula: see text]Dy[Formula: see text] alloy has high [Formula: see text] value and good thermal stability, which can better control the formation of nanocrystalline structure. The transverse magnetic field annealing can greatly increase the [Formula: see text] of the material and reduce the [Formula: see text], which is more significant for the ribbons. The optimum annealing process of Fe[Formula: see text]Cu1Si[Formula: see text]B8Nb[Formula: see text]Mo[Formula: see text]Dy[Formula: see text] alloy is that the transverse magnetic field of 1000[Formula: see text]Gs is applied and the temperature is kept at 833[Formula: see text]k for 30[Formula: see text]min. And the best properties for [Formula: see text] are 1.39[Formula: see text]T, for [Formula: see text] is 4.6[Formula: see text]A/m and [Formula: see text]@1[Formula: see text]kHz, [Formula: see text]@100[Formula: see text]kHz. With the high frequency and miniaturization of electronic components, this material has potential application value.

Fabrication of p-Type Co₃O₄ Nanofiber Sensors for Ultra-Low H₂S Gas Detection at Low Temperature.

In the current work, we report the on-chip fabrication of a low-temperature H₂S sensor based on p-type Co₃O₄ nanofibers (NFs) using the electrospinning method. The FESEM images show the typical spider-net like morphologies of synthesized Co₃O₄ NFs with an average diameter of 90 nm formed on the comb-like electrodes. The EDX data indicate the presence of Co and O elements in the NFs. The XRD analysis results confirm the formation of single-phase cubic spinel nanocrystalline structures (Fd3 m) for the synthesized Co₃O₄ NFs. The Raman results are in agreement with the XRD data through the presence of five typical vibration modes of the nanocrystalline Co₃O₄. The gas sensing properties of the fabricated Co₃O₄ NF sensors are tested to 1 ppm H₂S within a temperature range of 150 °C to 450 °C. The results indicate a highest sensor response to 1 ppm H₂S with the gas response of aproximately 2.1 times and the gas response/recovery times of 75 s/258 s at a low temperature of 250 °C. The fabricated sensor also demonstrates good selectivity and a low detection limit of 18 ppb. The overall results suggest a simple and effective fabrication process for the p-type Co₃O₄ NF sensor for practical applications in detecting H₂S gas at low temperature.

Lanthanum doped [formula omitted] spinel ferrites synthesized via co-precipitation route to evaluate structural, vibrational, electrical, optical, dielectric, and thermoelectric properties

Lanthanum doped Zn0.5Co0.5LaxFe2−xO4 spinel ferrites were synthesized through the co-precipitation technique. To characterize the structural, vibrational, electro-optical, dielectric, and thermoelectric properties, the following characterization techniques X-ray diffraction (XRD), Fourier transformation infrared (FTIR) and Raman spectroscopy, I–V measurement analysis, UV–vis spectroscopy, LCR meter, Seebeck analysis, and Energy dispersive X-ray analysis (EDX) were used. The XRD patterns showed nano-crystalline single-phase structure formation. Moreover, the lattice constant increased from 8.3909 ± 0.0042 Å to 8.3994 ± 0.0042 Å, and the crystallite size reduced from 33.6 to 17.5 nm with increasing La3+ cations. The bond angles showed stronger A–A and A–B interactions and weak B–B interactions with the addition of La3+. FTIR spectra showed the existence of the M − O stretching band and functional group study. The resistivity, optical band gap, and activation energy had maximum values at x = 0.1. At room temperature (RT), the dielectric parameters were recorded between the range of 8 Hz to 8 MHz. The Seebeck voltage coefficient was obtained for the as-prepared nano-ferrites to determine the charge carrier type. The EDX spectra showed a compositional distribution of the elements in all the samples.

Structure formation, optical properties and energy loss functions of meso-tetraphenylporphyrin manganese(III) chloride complex thin films for energy conversion applications

Abstract Thin films of meso-tetraphenylporphyrin manganese chloride complex (MnClTPP) have been prepared by evacuated thermal evaporation technique. The structure formation of MnClTPP films has been identified using atomic force microscopy and X-ray diffraction techniques. The pristine MnClTPP films revealed amorphous structure, whereas after annealing temperature up to 490 K, the films turned to nanocrystalline structure formation. The spectrophotometric measurements of transmittance, absorbance and reflectance of pristine and annealed films have been carried out in spectral range 200–2000 nm. The absorbance revealed many electronic transition bands including high intense Soret band (B), Q-band, and two other weaker (M and N) bands extended in UV–visible spectrum. Optical constants (refractive index and absorption index) of pristine and annealed films were determined. The absorption edge analysis was performed to estimate the type of electronic transitions and the value of optical band gap. Additionally, the surface and volume energy loss functions of pristine and annealed MnClTPP films have been estimated. The annealing process improved the performance of those films and reduced the values of energy loss functions that would be utilized a potential material in energy conversion applications.