Growth Behaviour Of Layers Research Articles

Modelling and experimental study of surface morphology evolution during layer growth on nanograting structures

Coating nano/micro-structured elements with a single or multi-layered film can greatly enhance their functionality. The experimental enhancement, however, is significantly limited by the smoothing and distortion of the structural profile after coating. This requires a comprehensive understanding of the layer growth behavior on nanoscale non-isotropic surface with a proper model to analyze and predict the structure evolution. Here, a simplified linear growth model with single free parameter was successfully used for analysis of the smoothening of grating grooves. The model enables a quantitative description of the evolution of surface morphology from substrate to the top surface with sub-nanometer accuracy. Based on this, the smoothing behavior of single-Si layer and W/Si multilayer growth on nanoscale gratings (period ∼ 40 nm) and flat substrates were studied experimentally, for applications in X-ray optics. The smoothing effect of the W/Si multilayer coating is more pronounced than that of the single Si layer for both substrate types. The corrugated nanogratings suppressed the smoothing effect as compared to the flat isotropic surface. These works provide new guidance to predict and control the growth of layers on nanostructures.

Interfacial structure and formation mechanism of 90 W-7Ni-3Fe/steel using co-sintering method

In this study, we proposed a powder metallurgy method to develop an interlocking interface in tungsten heavy alloy/steel composites, which is achieved by co-sintering technology using tungsten heavy alloy and steel powders with a large difference in particle size. The interfacial microstructure evolution and mechanical properties of the co-sintered joint as a function of co-sintering temperature were investigated systematically. Results showed that a well-bonded interlocking interface was formed along the steel particles as a result of the tungsten heavy alloy particles filling in the gaps between two neighboring steel particles. The co-sintered joint contains four regions: the W alloy matrix, the Fe3W3C layer, the Ni-affected layer, and the steel matrix. Based on the microstructural characterization, the interface formation mechanism and reaction layer growth behavior are discussed in depth. Benefitting from the interlocking structure, the highest tensile strength of the co-sintered specimen is 265 MPa, which is 66% higher than that of the non-interlayer joint obtained by diffusion bonding method. Moreover, its performance is better than that of some W alloy/steel with an interlayer. This technique offers a potential method for the efficient preparation of a W alloy/steel composite structure with outstanding properties.

Analysis of frost layer growth behavior on cryogenic surfaces in ultralow dew point environments by experimental tests and numerical simulations

Maintaining an ultralow dew point is essential for the operation of transonic cryogenic wind tunnels, as it significantly influences aerodynamic characteristics. Even in extremely dry conditions, minute quantities of frost can form on cryogenic surfaces, which compromises data quality. Conducting experiments on frost desublimation in such ultralow dew point environments poses significant challenges due to the demanding experimental conditions. Therefore, this study aimed to explore the desublimation characteristics of cryogenic surfaces in ultralow dew point environments and to address the challenges of experimental investigations under such extreme conditions. Initially, the study experimentally investigated frost formation by assessing the impact of various factors, such as temperature and water vapor content. It was observed that the type of frost formed depended on the water vapor content, and altering the surface temperature influenced the growth region of the frost crystals. The irregular growth of the frost layer on low-temperature surfaces was evident, as temperature markedly affected both the growth rate and the diffusion direction of frost formation. Moreover, the process of trace water frost formation was simulated using a dispersive multiphase model, predicting the frost layer's thickness. The numerical results suggest that the frost layer is micrometers thick, with a minimum thickness of 20 μm. A nonlinear relationship was identified between frost growth and dew point level. This research lays the groundwork for a deeper understanding of desublimation characteristics in ultralow dew point environments and for further investigation of low-temperature heat and mass transfer phenomena.

CRUD deposition induced multi-physics effects analysis in PWR

In PWR, the deposition of corrosion products from the steam generator leads to the formation of Chalk River Unidentified Deposits (CRUD) on the surface of fuel rods. CRUD deposition can cause issues such as CRUD induced localized corrosion, axial power anomaly and deterioration of cladding heat transfer. A new multi-physics program named CIFF (CRUD Induced eFFects analysis) is developed to analyze the effects caused by CRUD deposits. CIFF is a 1.5D model and can be used to simulate the variations in surface temperature, cladding corrosion and fuel deformation caused by CRUD deposition. A three-node CRUD deposition model is developed based on mass transfer theory and chemical equilibrium. The calculations of heat transfer, mechanical deformation, oxide layer growth, CRUD deposition and fission gas behavior are fully coupled based on finite element analysis and numerical solution technology. Axisymmetric element is used to solve the deformation of fuel rod under thermal expansion, gas pressure, creep and radiation swelling. The performance of CIFF is validated through IFA-513, ANO-2, Oconee and PCCL cases. The DBN-1 case is used to explore the influence of CRUD. The results indicate that CRUD deposition and CRUD induced local corrosion deteriorate the heat transfer of cladding, resulting in a three-stage increase of cladding temperature and accelerated growth of the oxide layer. CRUD deposition also leads to a relative increase in the gap pressure exceeding the coolant pressure by 8.4 %, a relative increase in the fuel rod strain by 10 % and a relative decrease in the gap size by 11 %, which indirectly leads a premature pellet-cladding mechanical interaction by 90 days.

Linear growth behaviour of intermetallic compound layer in electronic interconnections

We observed a linear behaviour of intermetallic compound (IMC) layer growth in electronic metallurgical interconnections, although the time required was twice that of commercial reliability standards for electronic packaging. This finding contradicts the classical parabolic growth law, which is widely reported to represent growth behaviour. We suggest that the parabolic growth law may be inadequate to thoroughly explain the IMC layer's growth by considering (a) one-directional growth and (b) reactions between elements for formation and growth. Further analysis has been carried out to analyse the logical judgment of the parabolic growth law and support our finding over linear IMC layer growth behavior.

Off-critical wetting layer divergence at the liquid/vapor interface of binary liquid mixtures.

Surface wetting phenomena impact chemistry, physics, biology, and engineering. The wetting behaviors of partially miscible binary liquid systems are especially complex. Here, we report evidence of universal behavior in the divergence of wetting layer growth at liquid-vapor interfaces of the cyclohexane + aniline, hexane + o-toluidine, and methanol + carbon disulfide systems. Layer growth on the micron scale was followed using visible light scattering from stirred samples. The layer thicknesses were found to diverge with decreasing temperature when coexistence was approached from the one-phase region, but only for solutions richer in the higher density/higher surface tension component. The onset of divergence was <1K above the bulk coexistence temperature; nearer the critical composition, the onset temperature was the critical temperature itself. All three systems showed identical divergent wetting properties after variable normalization. In contrast, no divergent wetting layer formation was seen in the benzene + 1,2-propanediol or water + phenol systems. The mathematical signof the Hamaker constant correlates with the contrasting behaviors. Collectively, these results have implications for theoretical descriptions of adsorption layer growth and crossover behavior, for measurements of complete wetting temperatures, and for practical applications.

Kinetics of the UNS S32750 Super Duplex Stainless Steel Low-Temperature Plasma Nitriding

This work reports an experimental investigation on the thermodynamic and kinetic view-point of the nitrided layer growth behavior, carried out separately at ferrite and austenite phase grains, for the UNS S32750 super duplex stainless steel (SDSS). For this purpose, and motivated by the DSSs distinct behavior showing formation of two- or single-phase nitrided layers, which apparently depend on the steel substrate chemical composition, two series of treatment were studied here, one varying the nitriding temperature on the 300-450 °C range for 4 h time, and other one varying the time on the 2-8 h range at 350 °C. Microstructural characterization of studied layers by means of SEM and EDS analysis, XRD and microhardness measurements showed precipitation-free nitrogen-expanded austenite layer formation on both steel phases for all samples treated up to 400 °C. The nitriding kinetics study showed that the layer thickness on both steel phases is proportional to the square root of the treatment time and follows an Arrhenius law for the studied treatment temperatures. The nitrogen diffusion activation energy, separately determined from the layer growth on each steel phase, was 115±3.2 and 120±5.4 kJmol-1, for austenite and ferrite grains, respectively.

Diffusion‐Triggered Synthesis of Mg2Si Based on Infiltrated Silicon Structures in Molten Mg

Magnesium silicide (Mg2Si) has many good properties and therefore shows a high application potential as thermoelectric material. Herein, the intermetallic layer growth behavior in the Mg–Si system is investigated. A process for synthesizing Mg2Si on the surface of open‐pore cellular Si structures is developed. The structure is fabricated by investment casting and followed by infiltration of magnesium. Subsequently, magnesium silicide is obtained by a two‐step heat treatment. Complete synthesis of Si to Mg2Si is achieved using a liquid–solid reaction between the liquid Mg and solid Si. The optimal heat treatment for the first step is at the eutectic temperature of 950 °C and for a duration of 120 min. The second treatment is at 1150 °C, slightly above the melting point of Mg2Si, and the remaining Si is synthesized. The resulting microstructures are analyzed using a scanning electron microscope (SEM) and energy‐dispersive spectroscopy (EDS).

Frost layer growth behavior on ultra-low temperature surface with a superhydrophobic coating

Experimental research was conducted to study the frost formation on superhydrophobic surfaces at ultra-low temperatures, which might broaden the insight into frost growth behavior on the heat exchangers. The frost properties were examined over time, and the frost retardation according to the frosting factor was identified using the frost reduction ratios. The ablimation-dominant (desublimation) mechanism was observed at ultra-low temperatures in which almost no water droplets were generated. Consequently, the influence of the superhydrophobic surface on frost retardation was insignificant within −5% owing to the frosting mechanism. It is difficult to expect an increase in thermal performance of heat exchangers by applying superhydrophobic surfaces; using superhydrophobic surfaces for the purpose of frost retardation at ultra-low temperatures is not recommended.

Quantitative analysis of frosting characteristics at ultra-low temperatures under forced convection conditions

The quantitative analysis of frosting characteristics was conducted at ultra-low temperatures under forced convection conditions, which may deepen the understanding of frosting mechanism on air source heat pump (ASHP). The frosting experiments were performed under various experimental conditions. The correlations for the frost thickness and density were proposed as functions of Reynolds and Fourier number, absolute humidity, and non-dimensional temperature. The frost layer growth behavior was predicted within 6% of the maximum error when the predicted data of the correlation and the testing data were compared. A parametric study was performed, and the effect of the frosting parameters on the frost layer growth was identified. Consequently, the frosting behavior on the devices that operate at ultra-low temperatures and forced convection conditions can be identified using the correlations proposed in this study.

Microstructure evolution and hard x-ray reflectance of ultrathin Ru/C multilayer mirrors with different layer thicknesses

Nanoscale Ru/C multilayers are essential reflective optics in the hard x-ray region of 7–20 keV. To understand the layer growth behavior and develop ultrathin Ru/C multilayer mirrors with periods smaller than 3.0 nm, multilayers with different periods of 6.2–1.5 nm were fabricated and studied. It is found that the average interface width started to increase obviously when the period became smaller than 2.5 nm while the surface roughness of different multilayers remained almost the same. The intrinsic stress of the multilayer gradually decreased with decreasing period and reached a very low value of −82 MPa at d = 2.3 nm. High reflectance of 54% and 65% (at E = 8.04 keV) were demonstrated for the multilayers with periods of 2.5 nm and 3.0 nm, respectively, whereas that for 1.9 nm period was significantly lower. To further analyze the layer microstructure, x-ray diffraction and transmission electron microscopy were used. The polycrystallized structure of Ru remained similar for the multilayers with period less than 2.5 nm, while a non-continuous layer growth and severe intermixing between Ru and C were observed for the multilayer with period of 1.9 nm. The increased intermixing between Ru and C was found to be the main reason for the larger interface width and lower reflectance of the multilayers with period smaller than 2.5 nm. It also indicated that the layer thickness threshold for a Ru/C multilayer growing with good layer quality is 1.0–1.2 nm.

Frost layer growth behavior under cryogenic conditions

This study aims to achieve an in-depth understanding of frost layer growth behavior on cryogenic surfaces (below −100 °C) under forced convection conditions. Carrying out frosting experiments using liquid nitrogen led to observations of the characteristic phenomenon in the frost layer growth behavior. Particularly, frost layers were growing separately in the leading edge and downstream of the cooling surface under the unique frosting mechanism. Irregularly sized shrub-shaped frost crystals, which were not observed in the previous studies, appeared at the initial frosting stage. The effect of operating conditions on the average frost thickness was investigated. As the cooling surface temperature decreased, the average frost thickness decreased. The increase in air velocity yielded an increased frost layer thickness.

Isothermal Oxidation Behavior of Gadolinium Zirconate (Gd2Zr2O7) Thermal Barrier Coatings (TBCs) produced by Electron Beam Physical Vapor Deposition (EB-PVD) technique

Abstract Thermal Barrier Coatings (TBCs) provide thermal insulation for gas turbine components operating at high temperatures. Generally, TBCs were produced on a MCrAlY bond coat with 7-8% Yttria Stabilized Zirconia (YSZ) using Atmospheric Plasma Spray (APS) technique. In this study, Inconel 718 substrate material was coated with CoNiCrAlY bond coat using high velocity oxygen fuel (HVOF) technique. Afterward, Gd2Zr2O7 was deposited on samples using Electron Beam Physical Vapor Deposition (EB-PVD) technique. Produced TBCs were exposed to isothermal oxidation tests at 1000°C for 8 h, 24 h, 50 h and 100 h in muffle furnace. Scanning electron microscopy-energy distribution X-ray (SEM-EDX) spectroscopy was used to investigate thermally grown oxide (TGO) layer and TGO growth behavior of TBCs. In addition, X-ray Diffractometer (XRD) analysis was performed to TBCs to understand whether phase transformation occurs or not before and after oxidation.

The behavior of frost layer growth under conditions favorable for desublimation

The purpose of this study is to understand the behavior of frost layer growth under conditions favorable for desublimation. The frosting experiments were conducted on a horizontal cooling surface. Condensation did not occur at the initial stage of frosting, and feather-shaped frost crystals were formed on the cooling surface. These frost crystals grew one-dimensionally while maintaining their shapes. In addition, the effects of operating conditions (air temperature, air velocity, air absolute humidity, cooling surface temperature) on frost layer growth under the conditions favorable for desublimation were investigated. As the cooling surface temperature decreased, the increase in the amount of frost was insignificant. Additionally, an increase in air velocity increased the frost density but not the thickness of the frost layer.

Size and temperature consideration in the liquid layer growth from nanovoids and the melting model construction

A new model for the solid melting point Tm(D) from nanovoids is proposed through considering the liquid layer growth behavior. This model, which does not have any adjustable parameter, introduces the classical thermodynamic treatment, i.e., the liquid nucleation and growth theory, for nanoparticle melting. With increased void diameter D, Tm(D) approaches to Tm0. Moreover, Tm(D) > Tm0 for a small void (Tm0 is the bulk melting point). In other words, the solid can be significantly superheated especially when D decreases, even if the difference of interface energy is larger than zero. This finding can be expected from the negatively curved surface of the void. The model predictions are consistent with the molecular dynamic (MD) simulation results for argon solids. Moreover, the growth of liquid layer from void surface relies on both size and temperature, which directly determine liquid layer thickness, and only when liquid layer thickness reaches to a critical value, can void become instable.

Crystal structure of oligothiophene thin films characterized by two-dimensional grazing incidence X-ray diffraction

Crystal structure in an highly oriented organic thin film was determined using two dimensional grazing incidence X-ray diffraction (2D-GIXD). α,ω-Hexyl-distyryl-bithiophene (DH-DS2T) was chosen as the material for the structural analysis, because it is a typical organic semiconductor showing a high crystallinity and an ordered layer-growth behavior. A 2D-GIXD pattern over large range of scattering angles was obtained by using high-brightness synchrotron radiation in SPring-8 and high-sensitive 2D X-ray detector (PILATUS 300 K). The analysis of the observed 2D-GIXD pattern was made to clarify that the crystal structure of highly oriented DH-DS2T thin films belongs to a monoclinic unit-cell with a = 0.58 nm, b = 0.78 nm, c = 3.43 nm, and β = 94.3°, and the space group is determined to be P21/a by considering the extinction rule. Furthermore, by fitting the simulated Bragg peak intensities to the experimental data, the molecular structure is determined. In this structure, two molecules are included in the unit cell and they tilt about 25° against substrate normal.

Intermetallic growth study on SnAgCu/Cu solder joint interface during thermal aging

The intermetallic compound (IMC) growth behavior at SnAgCu/Cu solder joint interface under different thermal aging conditions was investigated, in order to develop a framework for correlating IMC layer growth behavior between isothermal and thermomechanical cycling (TMC) effects. Based upon an analysis of displacements for actual flip-chip solder joint during temperature cycling, a special bimetallic loading frame with single joint-shear sample as well as TMC tests were designed and used to research the interfacial IMC growth behavior in SnAgCu/Cu solder joint, with a focus on the influence of stress–strain cycling on the growth kinetics. An equivalent model for IMC growth was derived to describe the interfacial Cu-Sn IMC growth behavior subjected to TMC aging as well as isothermal aging based on the proposed “equivalent aging time” and “effective aging time”. Isothermal aging, thermal cycling (TC) and TMC tests were conducted for parameter determination of the IMC growth model as well as the growth kinetic analysis. The SnAgCu/Cu solder joints were isothermally aged at 125, 150 and 175 °C, while the TC and TMC tests were performed within the temperature range from −40 to 125 °C. The statistical results of IMC layer thickness showed that the IMC growth for TMC was accelerated compared to that of isothermal aging based on the same “effective aging time”. The IMC growth model proposed here is fit for predicting the IMC layer thickness for SnAgCu/Cu solder joint after any isothermal aging time or thermomechanical cycles. In addition, the results of microstructure evolution observation of SnAgCu/Cu solder joint subjected to TMC revealed that the interfacial zone was the weak link of the solder joint, and the interfacial IMC growth had important influence on the thermomechanical fatigue fracture of the solder joint.

Research on Measurement Thickness and Growth Behaviors of Oxide Layers in Pre-Dressing Process of ELID

In order to measure thickness and Study on growth behaviors of oxide layers on grinding wheel surface in ELID, measurement system accuracy is verificated with laser and eddy current sensor for simulation measurement of oxide layers, Growth behaviour of oxide layers were measured in pre-dressing process, the results indicate inward growth speed of oxide layer is greater than outward growth speed along the radius of grinding wheel in the early , oxide layers keep linear growth and growth speed is the fastest; In the late ,inward growth speed of oxide layer slows, outward growth speed is slightly faster, but overall oxide layer growth slows down.

Recent developments in the study of ionic liquid interfaces using X-ray photoelectron spectroscopy and potential future directions

A perspective is given on the potential of X-ray photoelectron spectroscopy to investigate ionic liquid (IL) interfaces and related bulk properties. To allow for cross-correlation of different IL properties, the study is restricted to imidazolium-based systems. By systematic variation of alkyl chain lengths, by investigation of different anions, and by introduction of functional groups detailed information on surface orientation, enrichment effects, cation-anion interactions, and the correlation to macroscopic properties such as density and surface tension of ILs are derived. Furthermore, the molecular arrangement and growth behaviour of ultrathin ionic liquid layers on various substrates, in situ monitoring of chemical reactions, and the dissolution of transition metal complexes are addressed.

The growth behaviours of IMC layers in solid‐liquid interfacial reactions of Sn1.5Cu/Cu in high magnetic fields

PurposeThe aim of this paper is to investigate the growth behaviours of intermetallic compound (IMC) layers in solid‐liquid interfacial reactions of Sn1.5Cu/Cu in various intensities of high‐magnetic field.Design/methodology/approachSn1.5Cu solder was prepared and melted in a vacuum furnace at 873 K and cast into solder bars. Samples were mounted using resin and etched after being carefully polished. Then the IMC layers were observed by using scanning electron microscopy.FindingsThe results show that the growth of IMC layers has been accelerated by high‐magnetic field through the comparison of growth kinetics of IMC layers among 0‐2.5 T magnetic filed. IMC grains in high‐magnetic field are much bigger than that in 0 T. By the analyzing of X‐ray diffractometer patterns of IMC layers, it can be found that the orientations of IMC have been changed by magnetic field.Originality/valueThis paper investigates the growth behaviour of IMC layers during the solid‐liquid interfacial reactions of Sn1.5Cu/Cu in a high magnetic field.