Iron Nitride Layers Research Articles

Evaluation of wear and corrosion resistance in acidic and chloride solutions of Cathodic Arc PVD chromium nitride coatings on untreated and plasma nitrided AISI 4140 steel

Chromium nitride ceramic like coatings are well known for their hardness and wear resistance, especially under severe conditions. When deposited on mild steel, nitriding is required for such applications to create a gradient hardness profile and improve the coating adhesion and the system's mechanical properties. Corrosion resistance is also necessary since these chromium coatings are recommended for applications in the plastic mould and injection industry. Therefore, in this work, the combination of a nitriding without white layer pretreatment and CrN coating was studied in a chloride and an acidic electrolyte, to asses if the diffusion layer also plays an important role as a corrosion protection treatment. Coating microstructure, adhesion to both nitrided and non-nitrided steel, wear resistance, and corrosion resistance in chloride and acidic media were evaluated. For comparison, bare and nitrided steel were also examined. Results indicated an improvement in the adhesion for the duplex treatment (nitriding + CrN). The CrN coating demonstrated a considerably lower coefficient of friction and wear rate compared to both non-nitrided and nitrided steel. Regarding corrosion, the iron nitride layer provides some protection in chloride environments; however, in acidic media, only the CrN coating plays a protective role. In both media, localized attack occurred at sites where the coating had defects, such as pores or pinholes through which the electrolyte comes into contact with the substrate. The duplex treatment proved to be the most effective surface treatment for AISI 4140, achieving excellent tribological properties, good adhesion, and high corrosion resistance in both neutral chloride and acidic solutions.

Kinetics of Iron Nitride Layer Growth during the Nitriding of AISI 1085 Non-Alloy Steel and AISI 52100 Alloy Steel.

This paper presents a comparison of two-component ammonia-based inlet atmospheres diluted with either hydrogen (NH3/H2) or nitrogen (NH3/N2). Taking advantage of the features of inlet atmospheres diluted with nitrogen and hydrogen, four two-stage processes were designed and carried out, which were juxtaposed with two single-stage processes carried out only in an NH3 atmosphere. A common parameter of the processes carried out was the same value of nitrogen availability in each process stage. The gas nitriding process was carried out on ASIS 1085 non-alloy steel and ASIS 52100 alloy steel. It was found that the chemical composition of the steels studied, for the adopted nitriding process parameters, did not affect the kinetics of the growth in the mass of nitrided samples as a function of the nitriding time. However, the additions of alloying elements present in the steels studied significantly affected the nitrogen distribution between the resulting iron nitride layer and the diffusion zone in the nitrided substrate. Because of the presence of chromium in AISI 52100 steel, a larger mass of nitrogen accumulated in the nitriding zone in the solution compared with unalloyed AISI 1085 steel. As a result, with the same increase in the mass of nitrided steel, a thicker layer of iron nitrides formed on AISI 1085 steel than on AISI 52100 steel.

Phase Transformations of Iron Nitrides during Annealing in Nitrogen and Hydrogen Atmosphere

The aim of the research discussed in the manuscript was to check the availability of control of nitrogen decomposition processes on nitrided AISI 52100 and AISI 1010 steels during annealing at 520 °C in N2 and at 600 °C in H2. The tests have shown that when annealing AISI 1010 steel at a temperature of 520 °C in N2 under a pressure of 200 Pa for 2 h, an ε → γ’ + N2↑ phase transformation occurs. Over the next 3 h, the ε phase disappears and the γ’ phase gradually transforms into Feα(N). When annealing AISI 52100 steel, the denitrification process is faster; after 2 h there is a complete transformation of ε → γ’ + N2↑, and in the next 3 h, there is a complete transformation of γ’-Feα(N). During annealing in H2 at a temperature of 600 °C, the denitrification processes are most intense; the complete transformation of γ’ → Feα(N) + N2 occurs after 45 min of the process. When annealing nitrided AISI 1010 steel in nitrogen at atmospheric pressure, phase transformation (ε → γ’ + N2↑) and weight loss of the sample are observed only in the first 20 min of the process, then the sample weight increases. This was the result of the formation of iron oxide, which also inhibited the denitrification process of the iron nitride layer.

Mechanical and Magnetic Investigations of Balls Made of AISI 1010 and AISI 1085 Steels after Nitriding and Annealing

This paper discusses the changes in the phase composition and magnetic properties of the AISI 1010 and AISI 1085 steels that were nitrided at 570 °C in an ammonia atmosphere for 5 h and that were then annealed at 520 °C in a N2/Ar atmosphere for 4 h. The test samples were made in the form of balls with diameters of less than 5 mm. The thickness of the obtained iron nitride layers was assessed through metallographic tests, while the phase composition was verified through X-ray tests. The magnetic properties were determined using ferromagnetic resonance (FMR) and superconducting quantum interference device (SQUID) techniques. Our research shows that, during the annealing of iron nitrides with a structure of ε + γ′, the ε phase decomposes first. As a result of this process, an increase in the content of the γ′ phase of the iron nitride is observed. When the ε phase is completely decomposed, the γ′ phase begins to decompose. The observed FMR signals did not come from isolated ions but from more magnetically complex systems, e.g., Fe–Fe pairs or iron clusters. Studies have shown that nitriding and annealing can be used to modify the magnetic properties of the tested steels.

Measurement of coating thickness with X-ray diffraction

X-ray fluorescence (XRF) is frequently used to measure layer thickness in the micrometer range. But also X-ray diffraction (XRD) can be used in a comparable way and offers the benefit to differentiate coating layers by their crystal structure. Thus, the thickness of different oxide layers of the same element can be determined, e.g., FeO, Fe3O4, and Fe2O3 on Fe-substrate. An approach for such measurement is discussed. Furthermore, with a suitable sample stage, a spatially resolved coating thickness map can be measured in a nondestructive way. Applications and validations of the presented XRD method for the measurement of the thickness of zinc coatings on steel are given and compared with results from XRF, glow-discharge optical emission spectroscopy, and optical micrographs. In addition, the methodology was tested and validated using XRF reference standards and iron nitride and iron oxide layers.

The Stability of the Layer Nitrided in Low-Pressure Nitriding Process

The kinetics of the nitrided layer thickness growth and its structure depend on the nitrogen flux from the atmosphere to the nitrided surface. A nitrogen flux to the surface is more significant than a diffusion flux into the substrate, during forming surface iron nitrides and the internal nitriding zone. For pure iron, nitrided under low pressure, cutting off the nitriding atmosphere creates a flux from the subsurface layer of nitrides to the surface. The purpose of this paper is to determine the direction of the nitrogen flux in a similar situation for steels containing nitride-forming elements, thus answering the question of the stability of the layer nitrided under such conditions. The surface of X37CrMoV5-1 steel was nitrided under low pressure (of 24 hPa) and annealed in a vacuum or nitrogen. The microstructure, thickness of the nitride layers nitrided layers, the thickness of the internal nitriding zone, surface hardness and stresses were examined. The highest values of the nitrided layer properties were observed for the samples saturated only with nitrogen obtained from ammonia dissociation or additionally heated in nitrogen. It has been shown that using a pure vacuum during the annealing stage leads to unfavourable changes in the structure of the nitrided layer formed and, in particular, to the decomposition of the iron nitride layer formed at the saturation stage and occurrence of the tensile stresses—what excludes practical application of such layer. Ultimately, it has been shown that in the low-pressure nitriding process, the stability of the nitride layer of the nitrided surface strongly depends on the annealing atmosphere during the annealing stage, while the stability of the internal nitriding zone remains mainly at the same level.

Phase transformations in the nitrided layer during annealing under reduced pressure

The article presents studies of phase transformations taking place in surface layers of nitrided steels as a result of their annealing at 520 °C for 5 and 10 h. Two steel grades were tested, the unalloyed AISI 1085 and the low-alloy AISI 52100. As a result of glow discharge nitriding, at 570 °C/5 h and 540 °C/12 h, respectively, nitrided layers were produced on the steels, consisting of a surface layer of iron nitrides with the structure of e + γ′ and γ′ and of similar thickness 25. The study showed that during 5 h of annealing at 520 °C, the iron nitride layer already decomposed, which was documented by the analysis of chemical composition and X-ray analysis of the surface layers of steel. Comparative studies on the hardness distribution of surface layers of nitrided as well as nitrided and subsequently annealed AISI 52100 steels showed that after both 5 and 10 h of annealing, the hardness depth profiles were very similar and the effective thickness of the diffusion layer did not change. The results obtained enabled the demonstration that the emission of nitrogen into the atmosphere during annealing of nitrided steels is not accompanied by diffusion of nitrogen into the base layer. This proves that the iron nitride layer is not a source of nitrogen for the diffusion layer during annealing at reduced pressure.

Tribological response of MoS2 coated and oxy-nitrided samples with alternative extreme pressure and anti-wear additives

Oxy-nitriding and MoS2 coatings are widely used surface modification techniques in industry to improve the friction and wear characteristics of components and interacting surfaces. To ensure optimum performance of components within tribological environments, it is crucial to ensure compatibility between surfaces and lubricants, as the break-down of the lubricating film could lead to seizure between interacting components. This study analyses the interaction of extreme pressure and anti-wear additives with two modified surfaces. The friction and tribofilm formation behaviour were investigated using a Mini Traction Machine fitted with a 3D Spacer Layer Imaging Method. The chemical composition of the species formed after testing was analysed using X-ray photoelectron spectroscopy. This study found that the properties of the modified surfaces and their interaction with the various lubricant additives impact their tribological performance. With the oxy-nitrided samples, no real effect on friction was observed when using the sulphurised olefin or tricresyl phosphate additives, mostly due to lack of interaction with the less reactive iron nitride layer and their roles as anti-wear additives. However, when using the sulphurised olefin additive with the MoS2-coated sample, a significant reduction in friction was observed with time. This was mostly likely due to the combined effect with the formation of FeS and MoS2 within the tribofilm.

Effects of Using Alternative Extreme Pressure (EP) and Anti-Wear (AW) Additives with Oxy-Nitrided Samples

Oxy-nitriding is a widely used industrial process aiming to improve the tribological properties and performance of components. Previous studies have shown the effectiveness of the treatment with friction and wear performance, but very few have focussed on optimising this behaviour. The lubrication properties of several EP and AW additives were examined to investigate their effectiveness in improving the tribological properties of the layers formed after treatment. Previous studies showed the presence of an oxide layer on the sample could improve the effectiveness of the sulphurised olefin (SO) and tricresyl phosphate (TCP) additives. The friction and wear behaviour of oxy-nitrided samples were analysed using a tribometer and surface profiler. Scanning electron microscope, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were employed to identify the morphologies and chemical compositions of the treated surface before and after testing. No real effect on friction was observed when using the SO or TCP additives, mostly due to lack of interaction with the less reactive iron nitride layer and their roles as anti-wear additives. However, when the zinc dialkyldithiophosphate-containing lubricant was used, a higher friction coefficient was observed. Greater improvements in anti-wear properties with the presence of additives in comparison with only using base oil were reported, with the TCP additive producing the lowest wear rates. The study effectively demonstrated that the additive package type used could impact the tribological and tribochemical properties of oxy-nitrided surfaces.

Hot Tensile Behavior and Fracture Characteristics of a Plasma Nitrided Maraging 300 Steel

The influence of plasma nitriding of a maraging 300 steel on mechanical properties at high temperature has been studied. Samples were tensile tested at 600°C in four conditions: solution treated (MAR-S), solution treated and aged (MAR-SA), solution treated and plasma nitrited (MAR-SP) and solution treated, aged and plasma nitrited (MAR-SAP). In the same sequence, the yield strength and ultimate tensile strength increased slightly respectively from 1073 to 1189 MPa and 1174 to 1301 MPa, an increase of about 10% due to plasma nitriding. All the samples presented similar values of elongation, around 18%, but the cross section area reduction decreased significantly by plasma nitriding from ~70% for MAR-S and MAR-SA to ~45% for MAR-SP and MAR-SAP, that is an decrease of 36% in average. This decrease is attributed to brittle fracture nucleated at 50 μm thick iron nitride layer. The inner fracture surface of the tensile tested specimens was predominantly ductile presenting characteristic microcavities.

Incubation time for iron-nitride layer formation upon gaseous nitriding of iron-based alloys

A model was developed to predict quantitatively the influence of alloying element (Me) dissolved in the ferrite (α) matrix on the incubation time for iron-nitride layer formation upon gaseous nitriding of iron-based alloys. The model incorporates the coupled, concurrent processes of inward diffusion of nitrogen and the depth dependency of the time dependency of the precipitation of alloying-element nitride particles in the α matrix. Experimental results were obtained by gaseous nitriding of an Fe-2.23 at.% V alloy. The incubation time for iron-nitride formation on Fe–Me alloy is generally much larger than that for iron-nitride formation on pure iron due to a pronouncedly lesser rate of increase of dissolved N content at the surface of Fe–Me alloy. The extent of segregation of N at the MeN/α-Fe interfaces has distinct influence on the incubation time.

Effect of Hydrogen on Formation of Fe-Al Nanoparticles by Mechanical Milling

Nanocrystalline powders of iron aluminum alloy of the Fe82Al18 nominal composition were prepared under air, hydrogen and nitrogen atmospheres from the Fe and Al elemental powders by mechanical alloying and also from the conventionally cast Fe82Al18 alloy by the high-energy ball milling. The intensive plastic deformation during high-energy mechanical treatment has introduced high concentrations of open volume defects and contributed to a rapid decrease in the crystallite size down to a nanoscopic range.The hydrogen atmosphere was found to be the most efficient for the Fe-Al mechanical alloying since it has resulted into the fully alloyed Fe82Al18 after 30 h of milling. On the other hand, the nitrogen and air atmosphere have slightly prevented mechanical alloying and after the same milling time the pure iron particles were still detected in the powder mixtures. This partial suppression of the mechanical alloying process is explained by a formation of thin iron nitride and/or oxide layers on the surface of Fe particles preventing mutual inter-diffusion of Fe and Al atoms.

Ion-induced modification of contact surfaces

Iron-nickel contact surfaces subjected to ion-induced modification are studied by AES, XPS and AFM. The corrosion and erosion resistance of the modified contacts is associated with features of the surface topography, and with the formation of iron and nickel nitride layers. The fine energy structure of the atomic state is revealed. Ion irradiation of the contact surfaces yields the formation of pores and cones.

Formation dynamics of FeN thin films on Cu(100)

To investigate the structural and magnetic properties of thin films of FeN we have performed ab initio molecular dynamics simulations of their formation on Cu(100) substrates. The iron nitride layers exhibit a p4gm(2×2) reconstruction and order ferromagnetically in agreement with experiment. We establish the dynamics and time scale of the film formation as a function of the film thickness. The process is split in two phases: formation of almost flat FeN layers and optimization of the distance to the substrate. Our calculated magnetic moments are 1.67μB, 2.14μB, and 2.21μB for one, two, and three monolayers of iron nitride.

Friction in near-surface regions of plasma-nitrided and post-oxidized plain steel at various hydrogen contents

We investigated the low load friction behavior of plasma post-oxidized, plasma- nitrided AISI 1045 plain steel, using unidirectional sliding tests. The hydrogen content in the post-oxidation plasma was varied between 0 and 25%. The nitrided or oxidized layer thicknesses ranged from approximately 340–380 μm or 0.7–1.1 μm, respectively. The outermost iron oxide layer decreases the friction, whereas the underneath iron nitride layer increases the mechanical strength. The incorporation of hydrogen in the oxidative plasma mixture allows to control the type of iron oxide phase. It is observed that the presence of a superficial magnetite layer leads to a decrease of the friction coefficient with respect to the non-oxidized nitrided steel. The results are interpreted on the lights of crystal chemistry and with a model to explain the in-depth effects of hydrogen in the oxidative plasma.

Structural Properties of Iron Nitride on Cu(100): an Ab-initio Molecular Dynamics study

ABSTRACTDue to their potential applications in magnetic storage devices, iron nitrides have been a subject of numerous experimental and theoretical investigations. Thin films of iron nitride have been successfully grown on different substrates. To study the structural properties of a single monolayer film of FeN we have performed an ab-initio molecular dynamics simulation of its formation on a Cu(100) substrate. The iron nitride layer formed in our simulation shows a p4gm(2x2) reconstructed surface, in agreement with experimental results. In addition to its structural properties, we are also able to determine the magnetization of this thin film. Our results show that one monolayer of iron nitride on Cu(100) is ferromagnetic with a magnetic moment of 1.67μB.

Formation of a non-magnetic metallic iron nitride layer on bcc Fe(100)

We report the formation of a stable iron nitride thin film following the exposition of an Fe(001) single crystal to atomic N plasma produced by means of a radio-frequency (rf) discharge source. The obtained phase, enabled by N-atomic diffusion into the iron matrix, has been characterized using spectroscopical and structural techniques. The comparison of the experimental results with first-principles calculations sheds light on the formed structure stability. The result is the formation of a metallic non-magnetic protective coating film on the iron substrate with a zinc blende (ZB) structure (γ″-FeN). The formed film has high oxidation resistance, metallic character, non-magnetic ground state and good epitaxial growth. Thermal treatment of the iron nitride film shows that, at around 700 K, the FeN is decomposed, resulting in bcc Fe as a consequence of the high diffusivity of N in Fe.

Numerical simulation of the growth of theγ’-iron nitride in NH3-H2-N2gas mixture (570°C and 1 atm) (Part II)

The aim of this study is the control of the growth of the γ ’-iron nitride layer during gas nitriding. We simultaneously simulated both the gaseous and solid phases as well as the development of the γ ’-iron nitride layer on the α -iron nitride layer. The theoretical atomic nitrogen flux at constant superficial concentration was used as the boundary limit at the sample’s surface. Only using the input data, we obtained, as a function of the time, the atomic nitrogen profiles in the sample and the evolution of the γ ’-iron nitride layer thickness. The numerical results favorably compare with the experimental ones.

Method of implementation of the positive gradient of mechanical properties of triboengineering materials

Modern methods of implementation of the rule of positive gradient of mechanical properties are considered; this rule was formulated by I.V. Kragelskii and its application serves to minimize the friction and wear of solids. The given methods include the application of coatings with the method of finishing antifricton abrasion-free treatment; application of new metal-cladding lubricating materials; and creation of a nanostructural state of the surface iron nitride layer by nitriding steel with a positive gradient of hardness normal to the surface.

Molecular beam epitaxial growth of zinc-blende FeN(111) on wurtzite GaN(0001)

We report a study of the growth of iron nitride on gallium nitride using molecular beam epitaxy with Fe e-beam evaporation and rf N-plasma growth. Thin iron nitride layers of thickness about 16 nm were grown and monitored in situ using reflection high energy electron diffraction. The samples following growth were analyzed ex situ using a variety of techniques including X-ray diffraction, Rutherford Backscattering, and atomic force microscopy. By monitoring the structure, morphology, and lattice constant evolution of the iron nitride film, the crystal phase and orientation with respect to the GaN substrate are deduced; and from RBS data, the stoichiometry is obtained. The growth is discussed in terms of a 2-D to 3-D growth mode transition, and a critical thickness is estimated.