Formation Of Nanocrystalline Structure Research Articles

Structural study of amorphous and nanocrystalline Mg-based metallic glass examined by neutron diffraction, X-ray photoelectron spectroscopy, Reverse Monte Carlo calculations and high-resolution electron microscopy

The microstructure of amorphous and nanocrystalline Mg65Cu20Y10Zn5 alloy in as-quenched and post-annealed state was examined using neutron diffraction (ND), Reverse Monte Carlo modeling (RMC) and high-resolution transmission electron microscopy (HRTEM). The surface characteristic of Mg-based glass was investigated by X-ray photoelectron spectroscopy (XPS) method. The corrosion activity of alloy in glassy and nanocrystalline state was determined by electrochemical polarization measurements conducted in 3.5% NaCl solution. It was found that the structure of the melt-spun glass is homogeneous, but some medium-range order (MRO) regions as small as 1–2 nm were observed. The RMC analysis of ND data was used for local atomic structure and coordination numbers of the Mg65Cu20Y10Zn5 alloy in as-quenched state. The three-dimensional model representing a simulation box with atomic arrangements was also proposed. An average coordination number for Mg-Mg and Mg-Cu atoms is 8.1 and 2.5, adequately. The formation of nanocrystalline structure after annealing was confirmed by X-ray diffraction (XRD) and HRTEM observations. The TEM and HRTEM techniques allowed to observe regions containing very small particles in the amorphous matrix with size of 4–10 nm. The selected area electron diffraction (SAED) patterns allowed to identified hexagonal Mg and orthorhombic Mg2Cu phases. XPS results indicated the co-existence of MgO and Mg(OH)2 on the surface film formed on glassy ribbon in as-quenched state. The electrochemical polarization measurements revealed that the glassy ribbon exhibited lower corrosion current density than nanocrystalline sample.

Gas hydrogen absorption and electrochemical properties of Mg24Ni10Cu2 alloys improved by Y substitution, ball milling and Ni addition

Mg24Ni10Cu2 and Mg22Y2Ni10Cu2 alloys were prepared via vacuum induction melting, and the nanocrystalline/amorphous Mg24Ni10Cu2 and Mg24Ni10Cu2 + 100 wt% Ni alloys were synthesized through ball milling method. Microstructure and hydrogen storage properties of the alloys were investigated and compared as well. The results suggest that adding Ni in the milling process significantly promotes formation of amorphous and nanocrystalline structure. For these four alloys, the as-milled Mg24Ni10Cu2 with 100 wt% Ni shows the best hydrogen storage performances that 2.03 wt% hydrogen content can be absorbed just in 1 min, and the electrochemical capacity reaches to 899.2 mAh/g. Furthermore, ball milling with Ni promotes the charge transfer reaction and hydrogen diffusion ability which is advantageous to the high rate discharge ability.

Radiation Defects in HCC Materials at Atomic Spatial Level

Diagnostics of the irradiated structure was carried out using the field ion microscopy technique. Modes of radiation exposure for development of amorphized states in subsurface regions of platinum are determined. It is shown that radiation exposure of pure metals with an energy of E = 30 keV under variation of the fluence of the charged argon ion beams by two orders of magnitude (1016 to 1018 ions/cm2) produces a significant effect on the kinetics of defect formation in the subsurface regions of irradiated materials. As a result of irradiation up to a higher fluence (F = 1017 ions/cm2), the effect of formation of the block nanocrystalline structure (at the block size of 1–5 nm) is observed in subsurface regions at a depth of at least 20 nm from the irradiated surface. It is found that the phenomenon of metal amorphization in the subsurface regions occurs up to a sample depth of 12 nm under an increase in the fluence to 1018 ions/cm2 and the above irradiation energies. Experimental results on atomic–spatial investigation of radiative defect formation in surface layers of materials, initiated by ion implantation (in Cu3Au: E = 40 keV, F = 1020 ion/m2, j = 10–3 A/cm2), are considered. The experimentally established average size of a radiation cluster (disordered zone) in the alloy after ion bombardment is 4 × 4 × 1.5 nm.

Effect of heat treatments on crystallization behavior, thermal ability and magnetic properties of Fe85Si1.4B9P4Cu0.5C0.1 amorphous alloy

The influence of heat treatments on the crystallization behavior and magnetic properties of Fe85Si1.4B9Cu0.5P4C0.1 amorphous alloy were investigated. The as-spun ribbon was annealed at various temperatures for different time in nitrogen atmosphere. It indicates that both of annealing temperatures and time have an important influence on the formation of nanocrystalline structure. Through a series of heat treatments, it found that the rapid thermal processing could effectively prevent the precipitation of Fe-(B, P) compounds and reduce the Hc of alloy. Before the precipitation of secondary phases, the increase of annealing time is effective for the precipitation of a large number of α-Fe phases, which contributes to the increase of saturation magnetization (Ms) of the alloy. The Fe85Si1.4B9Cu0.5P4C0.1 nanocrystalline alloy annealed at 420 °C for 1 min exhibits lowest Hc of 5.5 A/m and higher Ms. of 204.5 emu/g (Bs ≈ 1.92 T). The Fe85Si1.4B9Cu0.5P4C0.1 nanocrystalline alloy annealed at 420 °C for 30 min exhibits highest Ms. of 207.9 emu/g (Bs ≈ 1.95 T) and lower Hc of 6.7 A/m.

Structural, morphological and magneto-optical properties of CuMoO4 electrochemical nanocatalyst as supercapacitor electrode

Copper molybdate (CuMoO4) nanoparticles (NPs) were synthesized by microwave combustion method and urea act as the fuel. The formation of nanocrystalline structure was confirmed by X-ray powder diffraction (XRD). The chemical composition of the CuMoO4 NPs was investigated by Fourier transform infrared (FT-IR) spectroscopy. Scanning electron microscope (SEM) associated with energy dispersive X-ray (EDX) was used to investigate morphological and elemental composition of the prepared sample. The morphology and particle size of sample were investigated by high-resolution transmission electron microscope (HR-TEM) analysis. The optical and electronic defects were confirmed by the UV-Vis absorption and photoluminescence (PL) spectroscopy at room temperature (RT). The magnetic behavior was analyzed by vibrating sample magnetometer (VSM) analysis recorded at RT. The X-ray Photoelectron spectroscopy (XPS) was used to analyze the chemical state of the elements in the prepared sample. The electrochemical behavior was examined by cyclic voltammetry (CV), galvanostatic charge and discharge analysis (GCD) and electrochemical impedance spectroscopy (EIS). The presence of redox pairs is showed in CV curves and along with the EIS data showed the supercapacitor nature. The GCD analysis displayed discharge curves and a high specific capacitance of ~ 127 F/g was acquired at a stable discharge current density (1 mA/cm2). The cyclic stability analysis showed capacitance retention of about 82.5% after 1000 cycles, proposing the potential application of CuMoO4 in energy storage devices.

Electrochemical and magneto-optical properties of cobalt molybdate nano-catalyst as high-performance supercapacitor

Nanorod shaped cobalt molybdate (CoMoO4) electro-catalysts synthesized by microwave combustion route using urea as the fuel. The formation of monoclinic nanocrystalline structure, metal-oxygen (M–O) and chemical bonding was confirmed by X-ray powder diffractometry (XRD), Fourier transform infrared (FT-IR) and Raman spectroscopy, respectively. Scanning electron microscope (SEM) associated with energy dispersive X-ray (EDX) and high-resolution transmission electron microscope (HR-TEM) were used to confirm the morphology, elemental composition and particle size of the samples, respectively. The optical and defects were confirmed by the UV–vis. absorption and photoluminescence (PL) spectroscopy at room temperature (RT). The room temperature magnetic behaviors of product were investigated by vibrating sample magnetometer (VSM). Surface binding energy and element confirmation were examined by X-ray Photoelectron spectroscopy (XPS). The electrochemical (EC) performance was studied by cyclic voltammetry (CV), galvanostatic charge-discharge analysis (GCD) and electrochemical impedance spectroscopy (EIS) analysis. The CV curve proved the existence of redox pairs and the supercapacitor nature exhibited by the EIS (Nyquist plots). The GCD studies provided the non-symmetrical discharge curves and the highest specific capacitance (Csp) of ~ 133 F/g were acquired at a constant discharge current density (1 mA/cm−2). The cyclic stability investigations revealed capacitance retention of about 100% after 1000 cycles, proposing the prospective usage of CoMoO4 in energy-storage devices.

Development of Room-Temperature Ferromagnetism in Nanocomposite CdO Codoped with Al and Gd: Treatment in Hydrogen Atmosphere

Cadmium oxide codoped with Al and Gd ion powders was synthesised by thermal codecomposition of a mixture of complexes of cadmium acetate dihydrate, gadolinium acetate hydrate, and aluminum nitrate nonahydrate. The mass ratio of Al/Cd was fixed while the mass ratio of Gd/Cd varied systematically. The purpose of the present study is to synthesise and study the transparent conducting oxide (TCO) CdO powder having room-temperature ferromagnetic (RT-FM) properties. To realize that purpose, the synthesised Al/Gd-codoped CdO powder was annealed under hydrogen gas with certain conditions. The X-ray diffraction (XRD) method confirmed the formation of a single nanocrystalline structure; thus, both Al/Gd ions were incorporated into CdO lattice forming solid solutions. Magnetic measurements revealed that some of the doped CdO powders gained paramagnetic (PM) properties where the susceptibility increases with increasing dopant Gd content; the measured effective magnetic moment of dopant Gd3+ was around 8 μB. Furthermore, the magnetic energy of the created RT-FM of the codoped CdO samples by hydrogenation was found to be dependent on the Gd% doping level. For hydrogenated CdO powder doped with 3% Gd, the coercivity (Hc) was 195.9 Oe, the remanence (Mr) was 0.77 memu/g, the saturation magnetisation (Ms) was 5.05 memu/g, and the energy product (Um) was 150.6 merg/g. Thus, the possibility of production of TCO CdO with RT-FM, where magnetic characteristics can be tailored by doping and post treatment under H2 gas, was proven. Thus, a new potential candidate to be used as a dilute magnetic semiconductor (DMS) was successfully synthesised.

Formation of Nanocrystalline Structures under Germanium and Indium Electrodeposition

The processes of electrodeposition of Ge and Ge–In from ammonia-tartrate solutions have been studied. The nature of interactions in thin-film systems obtained by germanium and indium codeposition has been investigated by means of potentiodynamic voltammetry in the inversion mode. The role of electrodesurface modification has been emphasized for deposition of a germanium film of a preset thickness from aqueous solutions. As was shown by the atomic force microscopy study, glossy films with a nanocrystalline structure had been formed. It has been established that, to develop silicon–germanium technologies, deposition of thin films must be performed from ionic liquids.

Fabrication of a Gradient Nano-/Micro-structured Surface Layer on an Al–Si Casting Alloy by Means of Ultrasonic–Electropulsing Coupling Rolling Process

By using a novel surface modification technique named ultrasonic–electropulsing coupling rolling (UECR) process on an Al–Si casting alloy rod, the surface of material was smoothened significantly. Meanwhile, a strengthened layer with a gradient change in hardness was obtained in the outer surface, corresponding to a homogeneous gradient nano-/micro-structure. The thickness of nanometer-thick laminated structures was at least 40 μm, which was much thicker than conventional ultrasonic rolling process. During UECR, the formation of the well-defined nanocrystalline structure was attributed to the high strain rate and simultaneous annealing process realized by ultrasonic impact and electropulsing treatment.

Effect of (Cd, Al) Co-doping and hydrogenation on the long-range ferromagnetic ordering of ZnO: Experimental and DFT studies

Nanopowders of ZnO codoped with Al and Cd ions (ZnO:Al:Cd) were synthesised by thermal co-decomposition of a mixture of Zn and metals complexes. X-ray diffraction analysis using the Rietveld method confirmed the formation of single nanocrystalline structure, thus, both Al and Cd ions are incorporated into ZnO host lattice forming solid solutions (SSs). Optical properties measured by diffuse reflectance spectroscopy (DRS) revealed a redshift associated with the creation of point defects and that the energy band gap is slightly affected by doping; i.e. 3.23–3.12 eV. Annealing of the as-synthesised SSs in H2-atmosphere (hydrogenation) was conducted in order to clarify the reinforcement and/or the creation of ferromagnetic order. Magnetic measurements showed that ZnO doped with 1.2 at% Al and 0.6 at%Cd became ferromagnetic with a coercivity ∼100 Oe, remanence ∼1.4 memu/g and saturation magnetization of ∼6.5 memu/g. Moreover, hydrogenation of undoped diamagnetic (DM) ZnO transformed into ferromagnetic. To elucidate the changes on the optical properties due to presence of dopants (Al, Cd) and the vacancies, we have employed first principle calculations based on density functional theory to calculate the optical properties and the change operated in the band gap due to structural changes. The observed RT-FM was associated to the doping and vacancies created by the hydrogenation.

Electrodeposition of nanocrystalline zinc‑tin alloy from aqueous electrolyte containing gluconate in the presence of polyethylene glycol and hexadecyltrimethylammonium bromide

Electrodeposition of nanocrystalline Zn-Sn alloy was investigated in aqueous acidic electrolyte containing gluconate in the absence and presence of additives. Distribution diagrams of Zn (II) and Sn (II) species in acidic gluconate electrolyte showed that ZnSO4 and Sn(GH4)+ were the main species over the pH range of 2 to 5. The surface morphology of the Zn-Sn alloy deposited under various plating conditions showed that the production of nanocrystalline structure was not possible in the absence of additives. Additions of hexadecyltrimethylammonium bromide (CTAB) and polyethylene glycol (PEG) with various molecular weight (M¯n = 400 and 2050 g mole−1) were found to assist the formation of nanocrystalline structure. In the presence of CTAB and equal concentrations of PEG, the surface morphology of deposits exhibited a finer and more uniform structure with PEG 2050 than PEG 400. Nanocrystalline Zn-Sn alloy coating was produced from the bath containing 1 mM of CTAB and 1 g/L of PEG 2050. All zinc‑tin alloy deposits exhibited a low tin content (<35 wt%) as identified by EDS. X-ray diffraction patterns of deposits showed peaks of hexagonal zinc and tetragonal tin and confirmed the production of a co-deposited alloy coating, akin to a mechanical type zinc‑tin plating.

Special Features of Strain Localization and Nanodipoles of Partial Disclinations in the Region of Elastic Distortions

In the zones of strain localization in the region of elastic distortions and nanodipoles of partial disclinations representing the defects of elastically deformed medium, a theoretical analysis of the elastically stressed state and the energy of these defects, including the cases of their transformation into more complex ensembles of interrelated disclinations, is performed. Using the analytical results, the mechanisms of strain localization are discussed in the stages of nucleation and propagation of the bands of elastic and plastic strain localization formed in these zones (including the cases of nanocrystalline structure formation).

Improved hydrogen storage kinetics of nanocrystalline and amorphous Ce-Mg-Ni-based CeMg12-type alloys synthesized by mechanical milling.

In this paper, ball milling was used to prepare CeMg11Ni + x wt% Ni (x = 100, 200) alloys having nanocrystalline and amorphous structures. The structures of the alloys and their electrochemical and gaseous kinetic performances were systematically investigated. It was shown that the increase in Ni content was beneficial to the formation of nanocrystalline and amorphous structures, and it significantly enhanced the electrochemical and gaseous hydrogen storage performances of as-milled alloys. In addition, the hydrogen storage capacities of the alloys fluctuated greatly with variation in milling duration. The maximum values of hydrogen capacity detected by varying the milling durations were 5.949 wt% and 6.157 wt% for x = 100 and 200 alloys, respectively. Similar results were observed for the hydriding rates and high-rate discharge abilities (HRD) of the as-milled alloys. The dehydriding rate increased with the increase in milling duration. The reduction in hydrogen desorption activation was the reason for enhanced gaseous hydrogen storage kinetics.

The formation of friction-induced nanocrystalline structure in submicrocrystalline Cu–Cr–Zr alloy рrocessed by DCAP

The effect of high strain-rate (100000 s-1) deformation by the method of dynamic channel-angular pressing (DCAP), annealing and quasi-static severe plastic deformation (SPD) by sliding friction on the evolution of structure and properties of a low-alloyed dispersion-hardened Cu–Cr–Zr alloys have been investigated. It is shown that the alloying of copper with chromium (0.09–0.14%) and zirconium (0.04–0.08%) microadditions changes the mechanisms of submicrocrystalline (SMC) structure formation and elastic energy relaxation during DCAP: a cyclic character of structure formation due to alternation high-rate processes of fragmentation and dynamic recrystallization, is changed by the processes of fragmentation and partial strain aging with the precipitation of second-phase nanosized particles. The temperature-time annealing (aging) conditions of Cu-Cr-Zr SMC alloys obtained by DCAP for improvement of mechanical properties and electrical conductivity was established. In particular, for the Cu-0.14Cr-0.04Zr SMC alloy, it has been shown that the optimal combination of microhardness (HV=1880 MPa), electrical conductivity (80% IACS) and strength (σ0.2=464 MPa, σu =542 MPa) at retaining satisfactory plasticity was obtained by treatment: DCAP+400°C, 1 h. The increased level of mechanical properties of alloys, compared to copper, is associated with additional strengthening due to precipitation of nanoparticles (5-10 nm) of the Cu5Zr and Cr during DCAP and aging. It has been shown that the low-alloyed Cu–Cr-Zr alloys possess a high ability to strengthen via the methods of DCAP and SPD by sliding friction. It has been determined based on the example of Cu–0.09Cr–0.08Zr alloy that the wear rate of samples with the SMC structure obtained by the DCAP method decreases by a factor of 1.4 compared to coarse-grained state. It was established that the combined treatment DCAP + 400°С + SPD by friction of the alloy gives rise to the friction-induced NC structure with grains 15– 60 nm in size in the surface-layer material, which provides a high level of the microhardness (3350 MPa) and satisfactory tribological properties.

Modification of Structure and Tribological Properties of the Surface Layer of Metal-Ceramic Composite under Electron Irradiation in the Plasmas of Inert Gases

Metal-ceramic composites are the main materials for high-load parts in tribomechanical systems. Modern approaches to extend the operation life of tribomechanical systems are based on increasing the strength and tribological properties of the surface layer having 100 to 200 microns in depth. The essential improvement of the properties occurs when high dispersed structure is formed in the surface layer using high-energy processing. As a result of the dispersed structure formation the more uniform distribution of elastic stresses takes place under mechanical or thermal action, the energy of stress concentrators emergence significantly increases and the probability of internal defects formation reduces. The promising method to form the dispersed structure in the surface layer is pulse electron irradiation in the plasmas of inert gases combining electron irradiation and ion bombardment in one process. The present work reports upon the effect of pulse electron irradiation in plasmas of different inert gases with different atomic mass and ionization energy on the structure and tribological properties of the surface layer of TiC/(Ni-Cr) metal-ceramic composite with the volume ratio of the component being 50:50. It is experimentally shown that high-dispersed heterophase structure with a fraction of nanosized particles is formed during the irradiation. Electron microscopy study reveals that refining of the initial coarse TiC particles occurs via their dissolution in the molten metal binder followed by the precipitation of secondary fine particles in the interparticle layers of the binder. The depth of modified layer and the fraction of nanosized particles increase when the atomic number of the plasma gas increases and ionization energy decreases. The wear resistance of metal-ceramic composite improves in accordance to the formation of nanocrystalline structure in the surface layer.

Effect of the Conditions of the Nanostructuring Frictional Treatment Process on the Structural and Phase States and the Strengthening of Metastable Austenitic Steel

The effect of the multiplicity of frictional loading with a sliding synthetic diamond indenter at room temperature in an argon medium and the temperature of loading in the range of −196 to +250°C on the phase composition, fine structure, and micromechanical properties of the surface layer of metastable austenitic chromium-nickel steel has been studied. It has been established that the completeness of the strain-induced martensitic γ → α′ transformation in the surface layer of steel is determined by the loading multiplicity and temperature, as well as the level of strengthening grows with an increase in the frictional loading multiplicity, but weakly depends on the frictional treatment temperature. According to the microindentation data, the characteristics of the surface layer strength and resistance to elastic and plastic deformation are improved with an increase in the frictional loading multiplicity. Frictional treatment by scanning with a synthetic diamond indenter at room and negative temperatures provides high quality for the treated surface with a low roughness parameter (Ra = 80.115 nm), and an increase in the frictional loading temperature to 150–250°C leads to the development of a seizure and growth in Ra to 195–255 nm. Using transmission electron microscopy (TEM), it has been shown that frictional treatment results in the formation of nanocrystalline and fragmented submicrocrystalline structures of strain-induced α′-martensite (at a loading temperature of −196°C) and austenite (at a loading temperature of +250°C) in the surface layer of steel alongside with two-phase martensitic-austenitic structures (at a loading temperature of +20°C).

Structure and Mechanical and Corrosion Properties of a Magnesium Mg–Y–Nd–Zr Alloy after High Pressure Torsion

The structure and the properties of an Mg–Y–Nd–Zr alloy (WE43) are studied after high pressure torsion (HPT) in the temperature range 20–300°C. Structure refinement proceeds mainly by deformation twinning with the formation of a partial nanocrystalline structure with a grain size of 30–100 nm inside deformation twins. The WE43 alloy is shown to be aged during heating after HPT due to the decomposition of a magnesium solid solution. HPT at room temperature and subsequent aging causes maximum hardening. It is shown that HPT significantly accelerates the decomposition of a magnesium solid solution. HPT at all temperatures considerably increases the tensile strength and the yield strength upon tensile tests and significantly decreases plasticity. Subsequent aging additionally hardens the WE43 alloy. A potentiodynamic study shows that the corrosion resistance of this alloy after HPT increases. However, subsequent aging degrades the corrosion properties of the alloy.

Effect of Pre-Annealing on Thermal and Optical Properties of ZnO and Al–ZnO Thin Films

Zinc oxide (ZnO) nanoparticles were synthesized by a simple solution route method using zinc acetate as the precursor and ethanol as the solvent. At a temperature of 60[Formula: see text]C, a clear homogenous solution is heated to 100[Formula: see text]C for ethanol evaporation. Then the obtained precursor powder is annealed at 600[Formula: see text]C for the formation of ZnO nanocrystalline structure. Doped ZnO particle is also prepared by using aluminum nitrate nonahydrate to produce aluminum (Al)-doped nanoparticles using the same solution route method followed by annealing. Thin film fabrication is done by air evaporation method using the polymer polyvinyl alcohol (PVA). To analyze the optical and thermal properties for undoped and doped ZnO nanocrystalline thin film by precursor annealing, characterizations such as UV, FTIR, AFM, TGA/DTA, XRD, EDAX and Photoluminescence (PL) were also taken. It was evident that precursor annealing had great influence on thermal and optical properties of thin films while ZnO and AZO film showed low crystallinity and intensity than in the powder form. TGA/DTA suggests pre-annealing effect improves the thermal stability, which ensures that Al ZnO nanoparticle can withstand at high temperature too which is the crucial advantage in the semiconductor devices. UV spectroscopy confirmed the presence of ZnO nanoparticles in the thin film by an absorbance peak observed at 359[Formula: see text]nm with an energy bandgap of 3.4[Formula: see text]eV. A peak obtained at 301[Formula: see text]nm with an energy bandgap of 4.12[Formula: see text]eV shows a blue shift due to the presence of Al-doped ZnO nanoparticles. Both ZnO and AZO bandgap increased due to precursor annealing. In this research, PL spectrum is also studied in order to determine the optical property of the nanoparticle embedded thin film. From PL spectrum, it is observed that the intensity of the doped ZnO is much more enhanced as the dopant concentration is increased to 1[Formula: see text]wt.% and 2[Formula: see text]wt.% of Al in ZnO.

Formation of nanocrystalline structure in pearlitic steels by dry sliding wear

Nanocrystalline grains, whose average size was approximately 35±5nm, were generated in the outermost layer of a pearlitic wheel steel by dry sliding wear. To explore the evolution of nanocrytalline grains, successive observations from the outermost layer of sliding wear to the undeformed matrix were done by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The investigations showed that the evolution process of nanometer-sized grains in pearlitic wheel steels included four steps: initially, pearlitic plastic deformation took place, lamellar spacing diminished, great amounts of dislocations occurred in ferrite, the thickness of ferrite lamellae decreased and some of ferrite lamellae fractured and dissolved; with increasing strains, considerable cementite started to dissolve into grains, and inside ferrite dislocations accumulated, tangled and formed dislocation walls, which cut ferrite into many short-rod shaped—and even equiaxed shaped dislocation cells; as strains continued to increase, dislocation cells gradually transformed into low-angle sub-boundaries. Accumulation and annihilation of dislocations and rotation of grains induced low-angle boundaries (LABs) to turn into high-angle boundaries (HABs), with the grains having random orientation. At this moment, cementite dissolution was relatively saturated and undissolved cementite particles scattered around the refined ferrite boundaries. Under higher strains and strain rates, refined ferrite grains repeatedly underwent plastic deformation, the formation of dislocation cells and the transformation from LABs to HABs, until finally the size of ferrite grains reached the stable minimum value and the refinement of grains ceased. Meanwhile, cementite continued to dissolve slightly due to dislocation accumulation. When dislocation accumulation rate and annihilation rate reached balanced, the dissolution of cementite ceased.

Presence of retained crystalline seed necessary for bicrystal-liquid-bicrystal phase transformation

Regaining of the original bicrystal structure during solidification after melting is found to be possible only if a fraction of crystalline seed is retained in the melt as per this molecular dynamics study. The effect of cooling rate on retaining the crystalline seed is also investigated. The bicrystal specimen is heated up to 1850K with a constant heating rate of 3.5Kps−1 and instantly cooled with different cooling rates i.e. 1Kps−1, 5Kps−1, 10Kps−1, 15Kps−1 and 20Kps−1. It has been observed through total energy analysis that specimen cooled with 1Kps−1 cooling rate dissipates the energy throughout the specimen causing randomization of atoms resulting into disappearance of the crystalline seed and formation of nanocrystalline structure. Whereas comparatively higher cooling rates does not allow complete dissipation of energy and retain the crystalline seed thus transform into bicrystal. It has been found through Voronoi polyhedra analysis that during slower cooling rate, icosahedral clusters are formed which play a vital role in formation of nanocrystalline structure.