Growth Kinetics Of Layers Research Articles

Influence of the chemical potential of carbon on the microstructural and compositional evolution of the compound layer developing upon nitrocarburizing of α-iron*

Abstract Controlled nitrocarburizing experiments were performed at 823 K and 853 K in order to systematically investigate the influence of the chemical potentials of carbon and nitrogen imposed by NH3/H2/CO/CO2/H2O-containing gas mixtures on the microstructural and compositional evolution of the compound layer formed on pure α-Fe substrates. The morphological evolution of the compound layer was investigated by optical microscopy. The nitrogen and carbon concentration-depth profiles in the layer were determined by electron-probe microanalysis (EPMA). Layer-growth kinetics was analysed on the basis of compound layer-thickness measurements. For a fixed chemical potential of nitrogen it was found that the microstructure and the layer-growth kinetics are strongly dependent on the chemical potential of carbon.

Dependence of the growth rate of an AlN layer on nitrogen pressure in a reactor for sublimation growth of AlN crystals

The dependence of the layer growth rate on nitrogen pressure in a reactor has been examined in order to analyze the conditions of growth of AlN thick layers and bulk crystals by the sublimation sandwich method. It is shown that the layer growth rate steadily increases as the pressure in the reactor is lowered within the range 1–0.02 bar. This suggests that a key role in the layer growth kinetics is played by the source-to-substrate transfer of the components (Al, N), rather than by their adsorption (desorption) on the substrate surface.

Low temperature pulsed gas-phase deposition of thin layers of metallic ruthenium for micro- and nanoelectronics: Part 2. Kinetics of the growth of ruthenium layers

Experimental data of growth kinetics of layers of ruthenium in a temperature range of 110–350°C by pulsed deposition from the gas phase with the participation of the carbonyl-diene precursor complex Ru(CO)3(C6H8), as well as NH3 and N2O as the second reagent are generalized.

The Kinetics of Gas Nitrided Layer Growth on Austenitic Stainless Steel

This paper presents the results of investigations on gas nitrided austenitic stainless steel. The treatment was conducted at various temperatures (400-515°C), gas compositions of atmospheres used (20-100% NH3) and times (0.5-12h). The layers were investigated by X-ray diffraction, Light and Electron Microscopy and Glow Discharge Optical Spectrometry. The kinetics of layer growth has been analysed in terms of the process parameters and compared with the data presented for plasma treated steel. The specific nitrogen profiles of nitrided layers are discussed in the context of the layers’ microstructure and phase composition.

Dependence between the Boron Surface Concentration and the Growth Kinetics of Boride Layers in AISI 4140 Steels

The present work estimated the growth kinetics of Fe2B layers formed at the surface of AISI 4140 steels. The thermochemical treatment was applied in order to produce the Fe2B phase, considering temperatures of 1123, 1173, 1223 and 1273 K with five exposure times (2, 4, 5, 6, and 8 h), using a 4 mm thick layer of boron carbide paste over the material surface. The growth of boride layers was described by the mass balance equation between phases in thermodynamic equilibrium, assuming that the growth of boride layers obeys the parabolic growth equation and the boron concentration at the interfaces remains constant. Also, the boron diffusion coefficient at the Fe2B ( ) was established as a function of boriding temperature. Likewise, the parabolic growth constant (k), the instantaneous velocity (v) of the Fe2B/substrate interface and the weight-gain of borided steels were established as a function of the parameters and , which are related to the boride incubation time ( ) and boron surface concentration ( ), respectively.

A model for studying the kinetics of the formation of Fe 2B boride layers at the surface of a gray cast iron

The present work estimates, using a kinetic model, the growth kinetics of Fe 2B boride layers generated at the surface of a gray cast iron via the powder-pack boriding considering three different temperatures (1173, 1223 and 1273 K) and four treatment times (2, 4, 6 and 8 h). By the use of the mass balance equation at the (Fe 2B/substrate) interface under certain assumptions and considering the effect of the boride incubation time, it was possible to estimate the corresponding parabolic growth constant in terms of two parameters α C up F e 2 B and β( T) depending on the boron content in the Fe 2B phase and on the process temperature, respectively. The mass gain at the material surface and the instantaneous velocity of the (Fe 2B/substrate) interface were also estimated. A fairly good agreement was observed between the experimental parabolic growth constants taken from a reference work (Campos-Silva et al., Characterization of boride layers formed at the surface of gray cast irons, Kovove Mater. 47 (2009) 1–7.) and the simulated values of the parabolic growth constants. Furthermore, the boride layer thicknesses were predicted and experimentally verified for three process temperatures and four treatment times.

Layer Growth, Thermal Stability, and Desorption Behavior of Hexaaza-triphenylene-hexacarbonitrile on Ag(111)

The layer growth, thermal stability, and desorption kinetics of ultrahigh vacuum (UHV)-grown organic discoid molecules (hexaaza-triphenylene-hexacarbonitrile (HATCN)) on Ag(111) have been studied by atomic force microscopy (AFM), thermal desorption spectroscopy (TDS), low-energy electron diffraction (LEED), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In the initial growth stage (≤0.24 nm mean film thickness) a strongly bonded monolayer of face-on oriented molecules is formed which does not desorb upon heating to 900 K, probably due to the formation of paracyanogen. With increasing film thickness the monolayer of face-on oriented molecules transforms at room temperature into a monolayer built up of edge-on oriented molecules, which saturates at a mean film thickness of around 0.8 nm. This layer partially decomposes during heating, and C2N2 fragments desorb between 650 and 900 K. On the monolayer of standing molecules a second, metastable, layer forms, which saturates at 1.36 nm. Wi...

A kinetic model for analyzing the growth kinetics of Fe2B layers in AISI 4140 steel

A kinetic model for analyzing the growth kinetics of Fe2B layers in AISI 4140 steel

Microstructural transformations and kinetics of high-temperature heterogeneous gasless reactions by high-speed x-ray phase-contrast imaging

Heterogeneous gasless reactive systems, including high-energy density metal-nonmetal compositions, have seen increasing study due to their various applications. However, owing to their high reaction temperature, short reaction time, and small scale of heterogeneity, investigation of their reaction mechanisms and kinetics is very difficult. In this study, microstructural changes and the kinetics of product layer growth in the W-Si system was investigated using a high-speed x-ray phase-contrast imaging technique. Using the Advanced Photon Source of Argonne National Laboratory, this method allowed direct imaging of irreversible reactions in the W-Si reactive system at frame rates up to $36\text{ }000$ frames per second with $4\text{ }\ensuremath{\mu}\text{s}$ exposure and spatial resolution of $10\text{ }\ensuremath{\mu}\text{m}$. Details of the Si melt and reactions between W and Si, that are unable to be viewed with visible-light imaging, were revealed. These include processes such as the initiation of nucleated melting and other physical phenomena that provide insight into the mixing of reactants and subsequent reaction. Through the use of this imaging technique and future optimization in the imaging process, a model for accurately identifying kinetics of chemical reactions, both spatially and temporally, is also proposed.

Optimized monolayer grafting of 3-aminopropyltriethoxysilane onto amorphous, anatase and rutile TiO2

Abstract Experimental conditions were studied for optimized attachment of 3-aminopropyltriethoxysilane (APTES) onto amorphous, anatase and rutile titanium dioxide (TiO2) surfaces. The attachment process and extent was characterized using X-ray photoelectron spectroscopy (XPS). In particular, the effect of attachment time, silane concentration, reaction temperature and the TiO2 crystalline structure on the growth kinetics of the silane layers was studied. The measurements reveal that typically monolayers are more dense on amorphous than on crystalline TiO2. The results show that critical experimental conditions exist where APTES attachment to the TiO2 surface changes from a monolayer to a multilayer growth mode. The obtained results and parameters to produce optimized APTES layers are of a high practical relevance as APTES attachment often constitutes the initial step for organic modification of TiO2 surface with biorelevant molecules such as proteins, enzymes or growth factors.

Growth kinetics of the compound layers: Effect of the nitriding potential

The aim of this work is to study the effect of the nitriding potential on development of the compound layers during the gas nitriding of Armco Fe and XC38 carbon steel. The gas nitriding experiments were realized in an atmosphere of partially dissociated gas ammonia (NH3) at 520∘C under a variable nitriding potential (from 0.25 to 3.5atm−0.5) for 2 h.Using XRD analysis and SEM observations of the cross-sections of the treated samples, it was shown that the compound layer was composed of γ′ iron nitride after exceeding a critical value of the nitriding potential that depends on the substrate’s nature. A linear semi-logarithmic relationship relating the nitriding potential to the experimentally measured layer thickness for the γ′ phase was used to evaluate the critical nitriding potential giving rise to its formation on the material substrate. It was found that the required value of the critical nitriding potential for XC steel is greater than that of Armco iron.

Characterization of AISI 4140 borided steels

The present study characterizes the surface of AISI 4140 steels exposed to the paste-boriding process. The formation of Fe 2 B hard coatings was obtained in the temperature range 1123–1273 K with different exposure times, using a 4 mm thick layer of boron carbide paste over the material surface. First, the growth kinetics of boride layers at the surface of AISI 4140 steels was evaluated. Second, the presence and distribution of alloying elements on the Fe 2 B phase was measured using the Glow Discharge Optical Emission Spectrometry (GDOES) technique. Further, thermal residual stresses produced on the borided phase were evaluated by X-ray diffraction (XRD) analysis. The fracture toughness of the iron boride layer of the AISI 4140 borided steels was estimated using a Vickers microindentation induced-fracture testing at a constant distance of 25 μm from the surface. The force criterion of fracture toughness was determined from the extent of brittle cracks, both parallel and perpendicular to the surface, originating at the tips of an indenter impression. The fracture toughness values obtained by the Palmqvist crack model are expressed in the form K C ( π /2) > K C > K C (0) for the different applied loads and experimental parameters of the boriding process.

Formation and growth kinetics of intermediate phases in Ni-Al diffusion couples

Formation and growth of the intermediate phases in the Ni-Al diffusion couples prepared by pouring technique were investigated. Electron probe microanalysis, scanning electron microscopy and X-ray diffraction were used to characterize the product phases in the joints. The results show that two intermediate phases form in the sequence of NiAl3 and Ni2Al3 during solidification. After annealed, Ni2Al3 and NiAl3 still exist in the joints of the couples. The reasons for the formation of Ni2Al3 and NiAl3, as well as the absence of NiAl, Ni5Al3 and Ni3Al were discussed, respectively. The growth kinetics of both product phase layers indicates that their growth obeys the parabolic rate law. The activation energies and frequency factors for NiAl3 and Ni2Al3 phases were also calculated according to the Arrhenius equation.

Growth kinetics of intermetallic compounds between Sn–9Zn solder and electroplated Fe–42Ni metallization

Interfacial reactions and growth kinetics of intermetallic compound layers formed between Sn–9Zn solder and electroplated Fe–42Ni metallization were investigated after ageing at 120, 150 and 170 °C for up to 360 h. Experimental results show that the intermetallic compound formed at the interface was mainly δ-FeZn 8.87 phase, rather than the FeSn 2 phase. The reason is that the attraction between Zn and Fe is stronger than that of Sn and Fe. The growth exponent n for δ-FeZn 8.87 phase was found to be about 0.5, indicating that it grew by a diffusion-controlled process. The activation energy for the growth of δ-FeZn 8.87 phase was determined to be 42 kJ/mol, which is in good agreement with the reported data.

Features of molecular beam epitaxy of the GaN (0001) and GaN (000 % MathType!MTEF!2!1!+- % feaagaart1ev2aaatCvAUfKttLearuqr1ngBPrgarmWu51MyVXguY9 % gCGievaerbd9wDYLwzYbWexLMBbXgBcf2CPn2qVrwzqf2zLnharyav % P1wzZbItLDhis9wBH5garqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC % 0xbbL8F4rqqrFfpeea0xe9Lq-Jc9vqaqpepm0xbba9pwe9Q8fs0-yq % aqpepae9pg0FirpepeKkFr0xfr-xfr-xb9adbaqaaeGaciGaaiaabe % qaamaaeaqbaaGcbaGafGymaeJbaebaaaa!3CDF! $$ \bar 1 $$ ) layers with the use of different methods of activation of nitrogen

The results of comparative studies of the growth kinetics of the GaN layers of different polarity during ammonia molecular beam epitaxy and plasma-assisted molecular beam epitaxy (PA MBE) of nitrogen with the use of sapphire substrates and GaN(000\( \bar 1 \))/c-Al2O3 templates grown by gas-phase epitaxy from metalorganic compounds are presented. The possibility is shown of obtaining the GaN layers with an atomically smooth surface during molecular beam epitaxy with plasma activation of nitrogen. For this purpose, it is suggested to carry out the growth in conditions enriched with metal near the mode of formation of the Ga drops at a temperature close to the decomposition temperature of GaN (TS ≈ 760°C). The conclusion is made that an increase in the growth temperature positively affects the structural, optical, and electrical properties of the GaN (000\( \bar 1 \)) layers. A high quality of the GaN (0001) films grown by the PA MBE method at a low temperature of ∼700°C on the GaN/c-Al2O3 templates is shown.

Kinetics of the formation of Fe 2B layers in gray cast iron: Effects of boron concentration and boride incubation time

The growth kinetics of Fe 2B layers formed at the surface of gray cast iron were evaluated in this study. The pack-boriding process was applied to produce the Fe 2B phase at the material surface, and the variables included three temperatures (1173, 1223 and 1273 K) and four exposure times (2, 4, 6 and 8 h). Taking into account the growth fronts obtained at the surface of the material and the mass balance equation at the Fe 2B/substrate interface, the boron diffusion coefficient on the borided phase was estimated for the range of treatment temperatures. Likewise the parabolic growth constant, the instantaneous velocity of the Fe 2B/substrate interface, and the weight gain in the borided samples were established as a function of the parameters τ( t) and α( C), which are related to the boride incubation time ( t 0( T)) and boron concentration at the Fe 2B phase, respectively. Observation of the growth kinetics of the Fe 2B layers in gray cast irons suggest an optimum value of boron concentration that is in good agreement with the set of boriding experimental conditions used in this work.

Surface Hardening of AISI H13 Steel Using Pulsed Plasma Electrolytic Carburizing (PPEC)

AbstractIn this work, the feasibility of a plasma electrolytic carburizing (PEC) treatment on AISI H13 steel using an aqueous solution of C3H5(OH)3, and NaOH was investigated. The substrate samples were biased cathodically to a 20 kW pulsed DC power supply with a variable voltage. The formation of hard carbon‐rich layer on the surface of the treated samples was confirmed by XRD analysis. Metallographic and SEM studies revealed that a uniform and compact nanocrystalline carbon‐rich layer was firmly stuck to the surface of the samples, and no cracks were observed between the carburized layer and the substrate. The coating mechanical performances were evaluated using microhardness tests. The microhardness of the carbon‐rich layer on the substrate was 866 HV, while the hardness of the substrate was 210 HV. Pin‐on‐disk abrasion tests were conducted to evaluate the surface wear resistance. Although all treated samples manifested a magnificent increase in wear resistance, the results showed different resistance in the differently treated samples. The microscopical investigation of the surfaces also showed that the wear mechanism of the tested samples varied by different treatment parameters, especially by the applied frequency. The results also showed that the current pulse frequency significantly influenced both the layer growth kinetics and the coating morphologies.

A simulation study of the mixing, atomic flow and velocity profiles of crystalline materials during sliding

Self-contained Non-Equilibrium Molecular Dynamics (NEMD) simulations using Lennard–Jones potentials were performed to identify the origin and mechanisms of atomic scale interfacial behavior between sliding metals. The mixing sequence and velocity profiles were compared via MD simulations for three cases, viz.: self-mated, similar and hard–soft crystal pairs. The results showed shear instability, atomic scale mixing, and generation of eddies at the sliding interface. Vorticity at the interface suggests that atomic flow during sliding is similar to fluid flow under Kelvin–Helmholtz instability and this is supported by velocity profiles from the simulations. The initial step-function velocity profile spreads during sliding. However the velocity profile does not change much at later stages of the simulation and it eventually stops spreading. The steady state friction coefficient during simulation was monitored as a function of sliding velocity. Frictional behavior can be explained on the basis of plastic deformation and adiabatic effects. The mixing layer growth kinetics was also investigated.

Layer growth and desorption kinetics of a discoid molecular acceptor on Au(1 1 1)

The layer growth and desorption kinetics of discoid organic acceptor molecules hexaazatriphenylene-hexacarbonitrile (HAT-CN) on Au(1 1 1) have been studied by thermal desorption spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and X-ray diffraction (XRD). The molecules form two wetting layers of flat lying molecules when evaporated at or below room temperature. Increasing the coverage beyond two monolayers and upon heating of the sample a destabilization of the 2nd layer and subsequently of the 1st layer takes place and 3D islands are formed. A quite unusual desorption behavior is observed for the individual layers, which is discussed in detail.

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.