Nitriding Potential Research Articles

Sensor system for controlled carbonitriding

Carbonitriding is mainly used to enhance the hardenability and wear resistance of unalloyed steels. Last year investigations have shown that improved component properties can efficiently be obtained by carbonitriding also low alloy and even higher alloy steels. The importance of carbonitriding rises. In the past, carbonitriding was done with constant ammonia additions, e.g. 2–5 vol% are added to the carburizing atmosphere without controlling or measuring the nitriding potential of the atmosphere. The results scatter in a wide rage depending on furnace, batch size and load and many other influencing factors. The need for a control system is obvious. The presented sensor system allows carbonitriding processes, where carbon and nitrogen potentials of the atmosphere are controlled. This allows adjusting surface carbon and nitrogen contents to desired values independently and guarantees constant product quality. The sensor system consists of a combination of an ammonia and an oxygen sensor and simulation software. By this way online diffusion profile calculation for carbon and nitrogen are possible even for alloyed steels taking alloy factors for both into account. These alloy factors, measured for many steel grades and phase boundaries, were calculated with Thermocalc.

Theoretical Investigation of Antioxidant Activity of Hydroxy-Quinoline Derivatives and their Delivery Via Boron Nitride Nanocage in Gas Phase and Solvent

The antioxidant activity of hydroxy-quinoline derivatives was studied in gas phase and solvent. Results indicate that substituents in hydroxy-quinoline decrease the bond dissociation enthalpy and ionization potential values and thus increase the antioxidant activity of hydroxy-quinoline. Results also show that NHMe hydroxy-quinoline has the highest antioxidant activity. The ability and potential of boron nitride (B 36 N 36 ) nanocage in the delivery of hydroxy-quinoline derivatives via DFT method was studied. Results show that adsorption of hydroxy-quinoline derivatives on the surface of B 36 N 36 nanocage was exothermic. There were linear dependencies between antioxidant parameters and adsorption energy (E ad ) values of hydroxy-quinoline derivatives. We thus propose to synthesize novel hydroxy-quinoline derivatives with higher anti-oxidant activity.

Microstructure and wear resistance of gas-nitrided steel after laser modification

Purpose: The aim of this work was to study the microstructure and wear resistance of hybrid surface layers, produced by a controlled gas nitriding and laser modification. Design/methodology/approach: Nitriding is well-known method of thermo-chemical treatment, applied in order to produce surface layers of improved hardness and wear resistance. The phase composition and growth kinetics of the diffusion layer can be controlled using a gas nitriding with changeable nitriding potential. In this study, gas nitriding was carried out on 42CrMo4 steel at 570°C (843 K) for 4 hours using changeable nitriding potential in order to limit the thickness of porous e zone. Next, the nitrided layer was laser-modified using TRUMPF TLF 2600 Turbo CO2 laser. Laser tracks were arranged as the multiple tracks with scanning rate vl=2.88 m/min and overlapping of about 86% using the two laser beam powers (P): 0.21 kW and 0.26 kW. Microstructure was observed by an optical microscope. Phase composition was studied using XRD. Hardness profiles in the produced hybrid layers was determined using a Vickers method. Wera resistance tests were performed using MBT-01 tester. Findings: Gas nitriding resulted in formation of compound zone, consisting of e nitrides close to the surface and a zone, composed of e + g' nitrides. Below the white compound zone, the diffusion zone occurred with nitric sorbite and precipitates of g' nitrides. In the microstructure after laser heat treatment (LHT) of nitrided layer, the zones were observed as follows: the re-melted zone (MZ) with e nitrides, nitric martensite and non-equilibrium FeN0.056 phase, the heat-affected zone (HAZ) with nitric martensite and precipitates of g' phase and the diffusion zone (DZ) without visible effect of laser treatment. Laser beam power influenced the depth of MZ and HAZ, so the thickness of hardened zone. The hardness of MZ was slightly decreased compared to the hardness of compound zone after gas nitriding. However, the significant increase in hardness was observed in HAZ. The formation of hybrid layers advantageously influenced the tribological properties. The laser-heat treated nitrided layers were characterized by improved wear resistance compared to the only gas-nitrided layer. Research limitations/implications: The effect of LHT on the microstructure and properties of gas-nitrided layer was limited to the two laser beam powers. In the future research, this range should be exceeded, especially, taking into account the lower values of laser beam power. It will result in laser modification without re-melting. Practical implications: The selection of suitable LHT parameters could provide the hybrid layers of modified microstructure and improved wear resistance. Originality/value: This work was related to the new concept of modification of nitrided layer by laser heat treatment.

Surface Zeta Potential and Diamond Seeding on Gallium Nitride Films.

The measurement of ζ potential of Ga-face and N-face gallium nitride has been carried out as a function of pH. Both of the faces show negative ζ potential in the pH range 5.5–9. The Ga-face has an isoelectric point at pH 5.5. The N-face shows a more negative ζ potential due to larger concentration of adsorbed oxygen. The ζ potential data clearly showed that H-terminated diamond seed solution at pH 8 will be optimal for the self-assembly of a monolayer of diamond nanoparticles on the GaN surface. The subsequent growth of thin diamond films on GaN seeded with H-terminated diamond seeds produced fully coalesced films, confirming a seeding density in excess of 1011 cm–2. This technique removes the requirement for a low thermal conduction seeding layer like silicon nitride on GaN.

Elastocaloric effect on the piezoelectric potential of boron nitride nanotubes

In this paper, molecular dynamics (MD) simulations and analytical calculations are performed to study the influence of the elastocaloric effect (ECE) on the piezoelectric potential of hexagonal boron nitride (BN) nanotubes. To take into account the ECE in the simulations and calculations, the adiabatic condition is required. To reach this goal, the heat transfer between the BN nanotubes and their environment is excluded in the present study. In MD simulations, we find a large ECE in BN nanotubes, which will make the temperature of the BN nanotubes greatly change after external loads are applied on them. Moreover, the piezoelectric and dielectric properties of BN nanotubes calculated from MD simulations are found to be strongly dependent on the temperature. The temperature-dependent piezoelectric and dielectric properties together with the ECE are thus considered in the analytical calculations of the piezoelectric potential of BN nanotubes. The obtained analytical results reveal that the large ECE in BN nanotubes will make the piezoelectric potential of BN nanotubes strongly depend on the loading path of external loads. Specifically, stretching a BN nanotube is found to be more efficient than compressing the nanotube to generate the piezoelectric potential. These results are expected to significantly expand the knowledge of the electromechanical behaviours of piezoelectric nanomaterials and provide important guidelines for the optimum design of piezotronics nanodevices.

Integrating AlN with GdN Thin Films in an in Situ CVD Process: Influence on the Oxidation and Crystallinity of GdN.

The application potential of rare earth nitride (REN) materials has been limited due to their high sensitivity to air and moisture leading to facile oxidation upon exposure to ambient conditions. For the growth of device quality films, physical vapor deposition methods, such as molecular beam epitaxy, have been established in the past. In this regard, aluminum nitride (AlN) has been employed as a capping layer to protect the functional gadolinium nitride (GdN) from interaction with the atmosphere. In addition, an AlN buffer was employed between a silicon substrate and GdN serving as a seeding layer for epitaxial growth. In pursuit to grow high-quality GdN thin films by chemical vapor deposition (CVD), this successful concept is transferred to an in situ CVD process. Thereby, AlN thin films are included step-wise in the stack starting with Si/GdN/AlN structures to realize long-term stability of the oxophilic GdN layer. As a second strategy, a Si/AlN/GdN/AlN stacked structure was grown, where the additional buffer layer serves as the seeding layer to promote crystalline GdN growth. In addition, chemical interaction between GdN and the Si substrate can be prevented by spatial segregation. The stacked structures grown for the first time with a continuous CVD process were subjected to a detailed investigation in terms of structure, morphology, and composition, revealing an improved GdN purity with respect to earlier grown CVD thin films. Employing thin AlN buffer layers, the crystallinity of the GdN films on Si(100) could additionally be significantly enhanced. Finally, the magnetic properties of the fabricated stacks were evaluated by performing superconducting quantum interference device measurements, both of the as-deposited films and after exposure to ambient conditions, suggesting superparamagnetism of ferromagnetic GdN grains. The consistency of the magnetic properties precludes oxidation of the REN material due to the amorphous AlN capping layer.

Heteroatoms doped C3N4 as high performance catalysts for the oxygen reduction reaction

Different kinds of carbon nitride were successfully synthesized through pyrolyzing the precursors. Their physical properties were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. While the electrochemical properties were measured by cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The results showed that the sulfur-doped carbon nitride exhibited better electrochemical catalytic properties towards oxygen reduction reaction. Most importantly, the onset potential of sulfur-doped carbon nitride was 0.77 V (vs. RHE), which positively shifted 40 mV than that of the carbon nitride. The calculation of kinetics parameters showed that it occurred through an approximately four electron pathway with a lower Tafel slope (115 mV/decade). Furthermore, the sulfur-doped carbon nitride also presented excellent stability and methanol tolerance.

Advancement of an intelligent system based on ANFIS for predicting machining performance parameters of Inconel 690 – A perspective of metaheuristic approach

The convincing potential of sophisticated milling tools exploited for machining of Inconel alloys in CNC milling machine offers minimal surface roughness-cutting force-cutting temperature trade-off footprint as compared to the conventional machining operation, which afforded a strong motivation to accomplish an in-depth discovery of the parametric design of CNC milling operation. In this study, the synergistic potential of contemporary Cubic boron nitride coated tool is used for machining of Inconel 690 in CNC milling machine, which has been scrutinized in order to build up a correlation among the objective function and the control variables by a metamodel called Adaptive Neuro-fuzzy inference system (ANFIS). The developed ANFIS model was capable of predicting the performance parameters with commendable accuracy as observed from correlation coefficients within the range of 0.946542–0.988996, Mean absolute percentage error (MAPE) in the range of 3.879652–7.456275% along with noticeably low root mean square errors (RMSE). Moreover, the ANFIS acquired results were compared with an Artificial Neural Network (ANN) model, developed on the identical parametric ranges. The comparison of the obtained results indicated that the ANFIS overtakes the ANN model in predicting the preferred response variables, which suggests the modesty of the ANFIS model.

The potential of manganese nitride based materials as nitrogen transfer reagents for nitrogen chemical looping

A systematic study was carried out to investigate the potential of manganese nitride related materials for ammonia production. A-Mn-N (A=Fe, Co, K, Li) materials were synthesised by nitriding their oxide counterparts at low temperature using NaNH2 as a source of reactive nitrogen. The reactivity of lattice nitrogen was assessed using ammonia synthesis as a model reaction. In the case of Mn3N2, limited reactivity was observed and only 3.1% of the available lattice nitrogen was found to be reactive towards hydrogen to yield ammonia while most of the lattice nitrogen was lost as N2. However, the presence of a co-metal played a key role in shaping the nitrogen transfer properties of manganese nitride and impacted strongly upon its reactivity. In particular, doping manganese nitride with low levels of lithium resulted in enhanced reactivity at low temperature. In the case of the Li-Mn-N system, the fraction of ammonia formed at 400°C corresponded to the reaction of 15% of the total available lattice nitrogen towards hydrogen. Li-Mn-N presented high thermochemical stability after reduction with hydrogen which limited the regeneration step using N2 from the gas phase. However, the results presented herein demonstrate the Li-Mn-N system to be worthy of further attention.

Study of the Iron Catalyst for Ammonia Synthesis by Chemical Potential Programmed Reaction Method

A new method, entitled chemical potential programmed reaction, for determining the physicochemical properties of iron ammonia synthesis catalyst has been proposed. Two model reactions were applied: nitriding of the iron catalyst and reduction of the obtained nitrides. Measurements of the rates of those reactions were carried out at 350 °C in a differential tubular reactor. The reactor is equipped with a system that allows us to perform simultaneous thermogravimetric measurements and a catharometric system to determine hydrogen concentration in the gas phase. The reactor was fed with a mixture of ammonia and hydrogen of varying composition, which was changing in a controlled way. Different accelerations of the nitriding potential change were applied. During the processes of nitriding of nanocrystalline iron and reduction of the obtained nanocrystalline iron nitrides rates of these processes were measured. The minimum nitriding potential, at which the phase transformation of nanocrystallites of a certain si...

Improvement in interfacial characteristics of low-voltage carbon nanotube thin-film transistors with solution-processed boron nitride thin films

In this article, we demonstrate the potential of solution-processed boron nitride (BN) thin films for high performance single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) with low-voltage operation. The use of BN thin films between solution-processed high-k dielectric layers improved the interfacial characteristics of metal-insulator-metal devices, thereby reducing the current density by three orders of magnitude. We also investigated the origin of improved device performance in SWCNT-TFTs by employing solution-processed BN thin films as an encapsulation layer. The BN encapsulation layer improves the electrical characteristics of SWCNT-TFTs, which includes the device key metrics of linear field-effect mobility, sub-threshold swing, and threshold voltage as well as the long-term stability against the aging effect in air. Such improvements can be achieved by reduced interaction of interfacial localized states with charge carriers. We believe that this work can open up a promising route to demonstrate the potential of solution-processed BN thin films on nanoelectronics.

Wear and corrosion behavior of CrCN/CrN coatings deposited by cathodic arc evaporation on nitrided 42CrMo4 steel substrates

In the paper, the results of wear and corrosion tests of the CrCN/CrN multilayer coatings, formed by cathodic arc evaporation on 42CrMo4 (AISI 4140) steel substrates are presented. The substrates were subjected to thermo-chemical treatment–nitriding with various nitriding potential. The results of nitriding were determined by XRD and the hardness profile in the samples cross-section. The morphology of thin coatings was examined with SEM. A Vickers FV-700 and Fisherscope HM2000 hardness testers enabled to investigate hardness of steel substrates and CrCN/CrN coatings respectively. A pin-on-disc wear tests were used to determine the hardness and tribological parameters of the coatings: the coefficient of the friction and wear rate. The scratch test and Rockwell test were applied to assess the adhesion of the coatings to the substrates. The corrosion properties of coating–steel substrate systems were investigated using potentiodynamic polarisation tests. Corrosion potential, corrosion current density and polarization resistance were determined. It was found that that the nitriding of steel substrates improves properties of the coating–substrate system. The nitriding 42CrMo4 steel substrate with low nitriding potential enable to obtain substrates without surface “white layer” what favours good adhesion of the coating to the substrate. The CrCN/CrN multilayer coating–steel substrate systems show good mechanical and tribological properties and corrosion resistance.

Hard metal nitrides: Role in enhancing the abrasive wear resistance of UHMWPE

Enhancing the abrasive wear resistance (WR) of polymer composites is an extremely difficult task since the particles or fibers are easily dug out or broken leading to a deterioration of their wear resistance. Exploration of hard particles in the right amount, size and compatibility with the matrix may lead to the reduction in micro-cutting and micro-ploughing of the matrix. Very few successful efforts are reported in the literature. Nitrides of metals are known for their high hardness. However, their potential for enhancing wear resistance of polymers has not yet been explored. In this paper, the potential of nitrides of Aluminum, Silicon, and Titanium based on a constant amount (2wt%) was explored by preparing composites with Ultra high molecular weight polyethylene (UHMWPE) and investigating their abrasive wear performance using a pin on disc test with a single rotation and under various loads. Further efforts were focused on investigating the optimum amount of best-performing nitride particles (Si3N4) for highest possible wear resistance by developing a series with 2, 4, 6, 8, 10 and 12wt% Si3N4 particles. 10wt% of filler loading was found to be optimum for highest wear resistance and the improvement was ≈45%. The efforts were then focused on investigating the wear-property correlation and wear mechanisms.

2D time‐domain numerical Maxwell/transport modeling for THz distributed gallium nitride transferred electron device

AbstractThe potential of gallium nitride–distributed transferred electron device is theoretically investigated for the realization of terahertz radio frequency (RF) power sources. The device numerical physical modeling relies on a 2D time‐domain electromagnetism/transport simulator. It is based on the coupled solution of the Maxwell and energy‐momentum macroscopic transport equations. The study is focused on the analysis of the device complex internal RF operation. The device technological and geometrical structure is optimized for an RF operation at 1 THz. The time and space, local and functional quantities are analyzed following both electromagnetic and quasi‐electrostatic approaches. We finally conclude on the feasibility of such a device.

Microstructural Evolution of 31CrMoV9 Steel upon Controlled Gaseous Nitriding Treatment

Abstract The evolution of the microstructure and the surface residual stress upon controlled gaseous nitriding of quenched and tempered 31CrMoV9 steel was investigated by varying the nitriding potential and the nitriding time at the nitriding temperature of 550 °C. A graded microstructure developed as a function of depth: a surface adjacent decarburized-nitrided zone, in which all tempering induced carbides had trans-formed to nitrides, under loss of the released carbon through the surface, is followed by a nitrided zone in which the carbon released from the carbide-to-nitride transformation had diffused to grain boundaries and precipitated there as (new) carbides. The extent of decarburization showed a strong dependence on whether or not an outer iron-nitride compound layer was present, as well as on the type of iron nitride present at the specimen surface. The surface residual stresses varied as a function of nitriding time and nitriding potential which has been discussed in terms of the rates of the carbide-to-nitride transformation, the decarburization and/or the carbide pre-cipitation along the grain boundaries.

A method of determining nanoparticle size distribution in iron ammonia synthesis catalyst by measuring mass changes during the nitriding process

A new method for determination of nanoparticle size distribution, on the basis of measurements of nanomaterial conversion degree as a function of the chemical potential of gas reagent, was presented. The method was applied for determination of nanocrystallite size distribution in a pre-reduced iron catalyst for ammonia synthesis being an example of a nanomaterial. Samples were reduced with hydrogen at 500°C and then nitrided at 300°C in gaseous ammonia-hydrogen mixtures of different nitriding potentials. Conversion degree measurements, viz., measurements of mass changes of the catalyst were performed in a differential reactor equipped with systems that enable thermogravimetric measurements and analysis of gas phase chemical composition. Based on the performed measurements, a relationship binding the conversion degree with size distribution was proposed. The resulting size distribution of nanocrystallites was compared to distributions determined by known techniques based on XRD or on measurements of the nitriding reaction rate. The size distribution determined using the new method has a higher resolution, revealing more details of the sample morphology.

Size-Dependent Transformation of α-Fe into γ′-Fe4N in Nanocrystalline the Fe–NH3–H2 System

On the basis of the results of experiments concerning nanocrystalline iron nitriding with ammonia–hydrogen mixtures, it was found that α-iron crystallites transform to iron nitride γ′-Fe4N in their whole volume in the order of their size, from the largest to the smallest ones. During the phase transition, the saturated solid solution of nitrogen in α-iron, being in the chemical equilibrium state, changes into an unsaturated solid solution of nitrogen in γ-iron, being in the transition state, and then to γ′-nitride, being again in the chemical equilibrium state. The phase transition is an adiabatic and isothermal process, and thus the change in Gibbs energy of the system is zero. On that basis the energy balance of the system was performed in this paper. The Gibbs energy required for phase transition was supplied to the iron nanocrystallite by the nitriding potential of the ammonia–hydrogen mixture. This energy depends on the ratio of the nanocrystallite active surface to its volume ratio and is the lowest...

Generating duplex microstructures by nitriding; nitriding of iron based Fe–Mn alloy

Nitriding of Fe–2 at-%Mn alloy at 650°C employing a nitriding potential of 0·05 atm− 1/2 resulted in a highly complex microstructural development as a function of depth below the specimen surface: a surface adjacent layer exhibiting an austenite–martensite duplex microstructure, followed by an intermediate region showing a ferrite–austenite duplex microstructure, and at even larger depths a region where an austenite layer covers the grain boundaries of the ferrite matrix grains. Development of this complex microstructure is attributed to the strong austenite stabilising effects of Mn and N. This work demonstrates the power of a relatively simple nitriding treatment to realise a highly complex microstructure known to be associated with strongly enhanced mechanical properties.

FMR study of samples obtained by nitriding and nitrides reduction of nanocrystalline iron

Abstract Samples obtained by nitriding of promoted nanocrystalline iron and the nitrides reduction at various nitriding potential in terms of thermodynamic parameters were investigated by electron paramagnetic resonance/ferromagnetic resonance (EPR/FMR) method at room temperature. Experimental FMR spectra were fitted by the Dysonian-type resonance lines arising from the presence of different Fe–N phases. The obtained FMR parameters allowed us to identify the component phases and to determine their magnetic properties. In general, the proposed simple method of decomposition of the FMR spectra produced results on the phase content in investigated samples that were consistent with XRD measurements and additionally, magnetic characteristics of the studied nanomagnets.

Synthesis of micron particles with Fe–Fe4N core–shell structure at low-temperature gaseous nitriding of iron powder in a stream of ammonia

Synthesis of the single-phase γ′-Fe4N on the surface of the micron-sized particles of iron at low-temperature gaseous nitriding of carbonyl iron powder in a stream of ammonia is studied. It is shown that synthesis of particles with such structure is possible with simultaneous control of the number of process parameters: temperature, degree of dissociation of ammonia, and treatment time. It is found that, at temperature T = 400°C and nitriding potential of the atmosphere rN ≈ 1.3 atm−1/2, the shells with a thickness of about 1 μm are formed on the particles within ~15–20 min and the powder consists of the γ-Fe4N phase within ~60 min of treatment. The mechanisms of formation of microparticles with a core–shell structure are considered. A qualitative model for the thermochemical treatment of the micron iron powder with consideration of the diffusion processes of the transport of ammonia molecules in the pore space of the powder and atomic nitrogen diffusion inside the particles is developed. Geometric and dimensional effects at nitriding of iron powders are discussed.