Nitride Compound Layer Research Articles

Degradation Processes of Two Compound Layers on Nitrided Surfaces During the Wear Test by “Block on Hot Al Cylinder”

The results obtained in the study help to explain the degradation process of the nitrided steel compound layer. Compound layers with different properties on gas-nitrided H10 tool steel blocks were tested for wear with “block on hot Al cylinder”. Degradation processes were observed on both compound layers with different properties and at three contact pressures. In order to observe the degradation processes in the compound layers, the wear tests were interrupted at various fixed time intervals and the resulting changes were closely monitored. The comprehensive analysis highlighted the complexity of the degradation process in the compound layers and emphasized the existence of complex relationships between the above-mentioned parameters. The reaction of the nitrided steel surface with hot Al is more pronounced in areas with lower contact pressure, while adhesive removal and furrow formation are pronounced in areas with low and medium contact pressure. This process begins with a sufficient density of the areas where islands of adhesive removal are located, their enlargement during the test, the breaking up of the walls between them, and finally the removal of the compound layer in the sliding direction, which appears as furrowing in the final phase of wear.

Surface Photovoltage Method for Photovoltaic Quality Control of GaAs-Based Solar Cells

In this paper, we demonstrate the potential of the contactless surface photovoltage (SPV) method for fast and reliable control of GaAs-based solar cells directly on epitaxial heterostructures before metallization and photolithography processes. The magnitude of the SPV corresponds to the generated photovoltage in the photoactive region, which is related to the open circuit voltage of the cell. The focus of this investigation is the potential of dilute nitride compounds grown by low-temperature liquid-phase epitaxy (LPE) for application as intermediate cells in multijunction solar cells. First, SPV spectroscopy is used to determine the photosensitivity spectral range and bandgap of the grown dilute nitride compound layers. Further, the photovoltaic quality of the grown solar cell heterostructures is evaluated by comparing the magnitude of their SPV signals with that of a reference GaAs solar cell. A drastic reduction in the measured SPV is observed for nitrogen-containing solar cell structures, which correlates with the lowering of solar cell open-circuit voltage values measured under standard test conditions. Finally, solar cell structures based on nitrogen-free GaAsSb compounds with the same long-wavelength photosensitivity limit as GaAsSbN are grown by LPE. They show one order of magnitude higher SPV signal and, therefore, have a great potential for solar cell application.

Surface preparation for characterization of nitride compound layers using hardness indentation and the Palmqvist method

The Palmqvist method is usually used as a measure to evaluate the toughness of ceramics and thin coatings, as these cannot be determined with classic test methods such as the tensile test or the Charpy impact test due to their brittleness or the small proportion of the coating in the specimen volume. Nitride compound layers, formed during nitriding and nitrocarburizing, are also brittle and only have a thickness of a few micrometers, so determining their toughness is also challenging. In this work, compound layers with different phase compositions and thicknesses were investigated on EN31CrMoV9 and EN42CrMo4 steels using the Palmqvist method. Barrel finishing and polishing were used for specimen preparation, for which a significant effect on the formation of Palmqvist cracks was found. Barrel finishing reduced the length of the Palmqvist cracks with increasing barrel finishing time until a constant level was reached. The surface condition caused by the porosity near the surface of the compound layer was identified as another influencing factor, thus the pore seam was removed for the further investigations. Various specimen variants were prepared and their phase compositions and compound layer thicknesses evaluated in relation to the crack lengths of the Palmqvist cracks. A correlation was found between the length of the Palmqvist cracks and the extent of the compound layer thickness.

Comparison of Friction Behaviour of Titanium Grade 2 after Non-Contact Boriding in Oxygen-Containing Medium with Gas Nitriding

The surface characteristics and friction behaviour of titanium Grade 2 with modified nitride (TiN, Ti2N) and boride (TiB) compound layers were investigated. It was shown that during non-contact boriding in oxygen-containing medium of titanium, the diffusion processes take place mainly by the interscale mechanism; however, during nitriding, besides the traditional interscale diffusion mechanism, the grain boundary mechanism of diffusion of nitrogen atoms is also realized. The optimal set of surface roughness parameters (height and step parameters, a combination of kurtosis and asymmetry, and profile reference curve parameters) was obtained after boriding. It was determined that the intensity of the adhesive wear of the tribo-pairs with stainless steel and ultrahigh molecular weight polyethylene under dry sliding conditions was influenced not only by the hardness but also roughness of the modified surface layer. The lowest friction coefficient was fixed for the TiB compound layer in both tribo-pairs.

Influence of plasma nitriding treatment on the micro-scale abrasive wear behavior of AISI 4140 steel

• Nitriding treatment leads to a reduction in the volume of wear and the specific wear coefficient. • Nano nitrides phases formed on the surface of the material. • Microstructural parameters and the number of phases influence the micro-abrasive wear behavior. • The hard layer of nitrides increased the AISI 4140 steel hardness more than 2.5 twice. Plasma nitriding was performed on AISI 4140 steel for various times. Untreated and plasma nitrided AISI 4140 steel were microstructurally, mechanically and tribologically characterized. The nitrided compound layer, consisting of ε-Fe 2-3 N and λ-Fe 4 N phases, was approximately of 5.0 μm thick. Microhardness of treated steel for 3 h was significantly higher than that of the untreated. The ball cratering test revealed that abrasivity of the treated samples decreased with the nitriding time due to an increasing in micro-strain values, quantify of nitrided phases, and the formation of nanocrystalline size of nitrides.

The influence of the plasma-nitriding temperature on the microstructure evolution and surface properties of additive-manufactured 18Ni300 maraging steel

Maraging steel grade18Ni300 produced by powder bed fusion (PBF) in its as built condition was plasma nitrided at three different temperatures. The aim of the work was to investigate the impact of the nitriding temperature on the microstructural changes as well as on the surface properties such as hardness, wear and corrosion resistance. The microstructural features in the bulk as well as in the nitride layer were investigated using electron-backscatter diffraction (EBSD), transmission electron microscopy (TEM) and X-Ray diffraction (XRD) analysis. The bulk microstructure consists of martensite with a small amount of retained austenite, the amount of which increases with a higher nitriding temperature. The nitriding process also causes the formation of precipitates and can therefore also act as an aging treatment. A specific lamellar structure occurs on the surface during the nitriding process, which in the majority of cases consists of the Fe4N phase. The retained austenite also transforms during nitriding to the nitride phase Fe4N. It was found that nitriding at higher temperatures leads to the formation of cracks in the nitride layer. The crack formation is related to nano and micro segregation during the LPBF. These segregations lead to austenite formation, which also takes place along the grain boundaries and transforms during nitriding to Fe4N. Higher nitriding temperatures lead to a thicker nitride compound layer and to better wear resistance. The impact of the cracks on the static mechanical properties is negligible. However, the corrosion resistance is governed by the formation of cracks at higher nitriding temperatures.

Micromechanical tensile test investigation to identify elastic and toughness properties of thin nitride compound layers

The measurement of thin-layer mechanical properties, like compounds generated by thermo-chemical nitriding process, is a key issue to optimize and predict the endurance of surface treatment against contact fatigue and wear. An original FIB micro-tensile test strategy involving plain and micro-notched tensile specimens is proposed. These specimens were FIB machined in a thin ε(50%)- γ’(50%) compound layer resulting from a common low pressure gaseous nitriding process (Allnit ©) and tested using a dedicated micro-testing system. Combined with DIC analysis, such micro-tensile test strategy allows extracting both the elastic modulus and the Poisson's ratio. Additionally, testing micro-notched specimens underlines the necessity to include FE simulations in order to take into account the radius of the micro-notch tip as well as the surface roughness induced by the FIB machining process. The investigation of this ε - γ’ compound layer suggests a Young's modulus E = 200 GPa, a Poisson's ratio ν =0.31 and a rather low fracture toughness KIC = 0.55 MPam. This methodology involving FIB machining, DIC analysis, test procedures and FE post processing simulations is fully detailed and the given results are discussed regarding literature.

Plasma nitrided compound layers in sintered parts: Microstructures and wear mechanisms

The shape and dimensions of the component play an essential role in plasma nitriding processes, a surface treatment crucial for the powder metallurgy industry since salt bath and gas nitriding poorly interact with porous structures. When the geometry of the components contains cavities, holes, or even parallel flat surfaces, the hollow cathode effect (HCE) can be activated, and, as a consequence, microstructural transformations that develop columnar nitride compound layers and the formation of a N-rich eutectoid, the braunite, may occur. The tribological properties of nitride compound layers with microstructural characteristics induced by the hollow cathode effect were evaluated in this work. Hollow cylinders of sintered iron were plasma nitrided and the tribological behaviour was assessed via reciprocating dry sliding tests. Unlike the friction coefficient, which is high (~0.4) regardless of the surface treatment, the wear rate is strongly increased by the presence of columnar morphology (2.4x) and braunite layer (2.1x), which are at the origin of brittle mechanisms such as crack propagation and interaction, resulting in the detachment of the compound layer.

Influence of elevated temperature and reduced pressure on the degradation of iron nitride compound layer formed by plasma nitriding in AISI D2 tool steels

AbstractThe stability of an iron nitride compound layer prepared by plasma nitriding of AISI D2 tool steel is investigated using in situ high‐temperature X‐ray diffraction at rising temperature up to 470°C and for an isothermal treatment at 450°C. Both kinds of experiment were carried out in vacuum. For all treatments, the iron nitride compound layer, which consists mainly of ε‐Fe3N, decomposes and forms an α‐Fe ‘black’ layer. The stability of the iron nitride compound layer is discussed in terms of the phase composition, the relative change of the lattice parameter, the nitrogen content and the decomposition kinetic. The decomposition takes place via a phase transition in two steps: (i) the out‐diffusion of nitrogen from ε‐Fe3N above an annealing temperature of 300°C and (ii) the transformation of ε‐Fe3Ny into α‐Fe when the nitrogen content (y) declines below 0.66. The second step is accompanied by the formation of Fe3C precipitates at about 450°C.

Effect of Nitriding Potential KN on the Formation and Growth of a \u201cWhite Layer\u201d on Iron Aluminide Alloy

This paper investigates the effect of nitriding potential under well-defined gas nitriding conditions on the formation and growth of a compound layer called “white layer” on a FeAl40 (with the composition of 40 at. pct Al) iron aluminide alloy. The nitriding potential was systematically varied in the range of 0.1 to 1.75 bar−1/2 at 590 °C for 5 hour nitriding time with an ammonia-hydrogen-nitrogen atmosphere. Characterization of the microstructure and phases formed within the white layer was performed using optical and scanning electron microscopy, X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and glow discharge optical emission spectroscopy (GDOES). Experimental results indicated that the nitriding potential strongly influences morphology and crystal structure of the white layer. The nitride compound layer consists of the phases γ′-Fe4N, ε-Fe2-3N, and AlN. A mechanism is proposed for the formation and growth of the white layer, depending on the effect of the nitriding potential.

On the kinetics of nitride and diffusion layer growth in niobium plasma nitriding

This work reports results of a study on niobium plasma nitriding kinetics, conducted at relatively low temperatures, regarding the N-Nb system (1523 K) eutectoid temperature, and short times (on the 1253–1453 K and 1–4 h ranges). Results confirm that the niobium plasma nitriding is diffusion-controlled. The obtained nitride (compound) layer is multiphase, mainly constituted of ε-NbN, γ-Nb4N3 and β-Nb2N nitrides. The estimated compound and diffusion layer growth activation energy was 97.11 and 120.11 kJ mol−1, respectively. Considering the hardness distribution all over the nitrided layer, the transition between the compound and diffusion layers is very sharp. As example, it can vary from 18.5 GPa (⁓1850 HV) at the surface compound layer to decreasing values from ⁓480 to 100 HV, along the diffusion layer, depending on the studied condition. All results obtained from the Sa and Sz roughness characterization indicated increasing measured values for longer treatment times and higher temperatures, for atom clusters islands-like surface morphology. Finally, apparently crack-free compound layers were yielded, highlighting the importance of the use of relatively low treatment temperatures, below the N-Nb system (1523 K) eutectoid temperature, and relatively short treatment times for the plasma nitriding treatment studied here.

Influence of Crystal Structure of Nitride Compound Layer on Torsion Fatigue Strength of Alloy Steel

The demand for high-strength components for commercial vehicles has recently increased. Conventional gas nitrocarburizing has been used to increase strength and productivity of the crankshaft. A potential-controlled nitriding process was recently developed to control the crystal structure of the nitride compound layer. It has been found that this treatment improves the bending fatigue strength compared with conventional treatment, and has the potential to cope with the increase in crankshaft strength. However, the effect of torsional fatigue strength has not been studied. Therefore, in this study, the influence of the crystal structure of the nitride compound layer on torsional fatigue strength was investigated. Two kinds of test specimens with different crystal structures of the compound layer were prepared using gas nitriding treatment with controlled nitriding potential for an alloy steel bar (JIS-SCM435). Torsional fatigue tests were carried out using these test specimens. Although the compound layer of these test specimens had different crystal structures, the hardness distribution and residual stress distribution on the diffusion layer were almost the same. The relationship between stress amplitude and number of cycles to failure (S-N curve) showed that the torsional fatigue limits of the specimens were almost the same. This indicates that the crystal structure of the nitride compound layer did not affect the torsional fatigue limits, because the origin of the torsional fatigue failure is inside the specimen.

Gradient Microstructure in a Gear Steel Produced by Pressurized Gas Nitriding.

A tempered martensitic gear steel (18CrNiMo7-6) sample was nitrided on two sides using a 5 atm pressurized gas at 530 °C for five hours. The nitrided sample was characterized by means of microhardness, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. A microhardness gradient was identified over a distance of 1000 µm with hardness values from 900 HV0.1 at the surface to 300 HV0.1 in the center matrix. The gradient microstructure was mainly divided into three zones: (i) a nitride compound layer at the top surface (~20 µm thick), (ii) a diffusion zone with containing precipitates (~350 µm thick), and (iii) the center matrix of the tempered martensite. Compared with carburized sample, the harder surface of the nitrided one ensures a better performance of the present pressured gas nitrided gears.

Thermal fatigue evaluation of AISI H13 steels surface modified by gas nitriding with pre- and post-shot peening

In this work, the H13 hot work die steels were surface modified and experimentally evaluated in a homemade thermal fatigue simulation tester. Two types of nitrided compound layers, and compound-free layers with and without surface deformation were prepared by a selection of surface modifications including traditional gas nitriding, controlled gas nitriding, gas nitriding with pre-shot peening, and controlled gas nitriding with post-shot peening. Thermal cracks formed in the nitrided compound layer propagated faster on surface but slower along the depth direction as compared to those in the compound-free layer. Thermal crack advancing along the depth direction in the sample nitrided with pre-shot peening had a tendency to be suppressed by the higher cross-sectional hardness distribution. The deformed compound-free nitrided layer showed the excellent thermal fatigue cracking resistance in both surface and cross-section, which was attributed to the good combination of hardness and toughness, as well as the underlying enhanced compressive residual stress.

Microstructure, mechanical and adhesive properties of CrN/CrTiAlSiN/WCrTiAlN multilayer coatings deposited on nitrided AISI 4140 steel

A duplex treatment of plasma nitriding (PN), followed by the deposition of a CrN/CrTiAlSiN/WCrTiAlN multilayer coating, was performed on AISI 4140 steel. Untreated, plasma-nitrided, only-coated (just the coating) and duplex-treated (PN + coating) AISI 4140 steel were microstructurally and mechanically characterized. The nitrided compound layer, consisting of mainly ε-Fe2-3N and γ′-Fe4N phases, was approximately 8.0 μm thick. The total thickness of the multilayer coating, which consisted of a top W-Cr-Ti-Al-N multilayer, a periodic Cr-Ti-Al-Si-N interlayer, and a CrN bottom layer, was 2.3 μm. The CrN/CrTiAlSiN/WCrTiAlN multilayered coatings possessed a super-hardness of 47.9 GPa and the highest elastic modulus of 424.8 GPa in the all samples. The microhardness (2200 HV0.05) of the duplex-treated sample was significantly higher than that of the only-coated (740 HV0.05) and nitrided (900 HV0.05) samples. The scratch tests revealed that the adhesion strength of the duplex-treated sample increased significantly due to a gradient-hardness support of the coating-nitrided layer interface.

Sliding wear of nitrided and duplex coated H13 steel against aluminium alloy

Abstract H13 steel was nitrided in a gas of 95%N2 and 5% CH2 with aid of hollow cathode plasma. Hard AlCrN coating was deposited onto H13 steel surface with various pretreatment, including a polishing treatment to remove the nitrided compound layer. Dry sliding wear test of these specimen against ADC12 alloy was made to clarify the influence of a nitride compound layer on the wear performance. It shows that the affinity to aluminum of various pretreatment H13 surface synchronously play important role during sliding against aluminum alloy, together with surface hardness, topography. The so called “affinity with Al” means the strength of an adhesive joint, which is formed by smeared Al film contacting H13 substrate directly. The adhesion strength of a hard AlCrN coating deposited onto the as nitrided (A-PN) surface still holds HF1, although it is a little less than that onto the surface with removing the nitrided compound layer (treatment B-PN). The affinity of different surface with Al can be ranked in the following order: H13 substrate > B-PN > A-PN > AlCrN. A-PN treatment is beneficial to lower the affinity with Al.

Effect of Pulse Repetition Time on Surface Properties of Pulsed Plasma Nitrided AISI 4340 Steel

Background/Objectives: Pulsed Plasma Nitriding (PPN) process is carried out on AISI 4340 steel at constant temperature and time. The key parameters which influence the nitrided compound layer properties in PPN are Pulse Duration (PD), Pulse Repetition (PR) time and Gas ratios of Hydrogen and Nitrogen. To obtain tailored properties of nitrided compound layer by varying the PR time and study the Microstructure, Crystalline phase formation and Wear properties and optimize the process parameters. Methods: In PPN process, PR time was varied from 100 μs to 500 μs and PD duration was fixed to 50μs. The nitrided samples were characterized by Optical Microscope, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Pin on Disc test. Findings: The decrease of PR time increases the formation of Iron Nitrides (Gamma nitride: γ-Fe4N and Epsilon Nitride: e-Fe3N) and it decreases when PR time is increased. Samples treated at PR-300 μs and PR-0 μs are observed with strong and weak intensities of Chromium Nitrides (Cr2N) respectively. The surface hardness is increased from 250±20 HV1 to 650±50 HV1, and the wear properties have increased by three times higher than base material. The nitrided properties are strongly influenced by PR time and the formation of Iron nitrides is inversely proportional to PR time. Novelty/Improvements: This investigation suggests that the PR time is a critical parameter for optimization of nitrided compound layer properties and the surface properties of AISI 4340 steel is improved by PPN process.

Gradient microstructure and microhardness in a nitrided 18CrNiMo7-6 gear steel

A commercial gear steel (18CrNiMo7-6) containing a tempered martensite structure was nitrided using a pressurized gas nitriding process under a pressure of 5 atm at 530 °C for 5 hours. The mechanical properties and microstructure of the nitrided sample were characterized by Vickers hardness measurements, X-ray diffraction, and backscatter electron imaging in a scanning electron microscope. A micro-hardness gradient was identified over a distance of 500 μm with hardness values of 900 HV at the top surface and 300 HV in the core. This micro-hardness gradient corresponds to a gradient in the microstructure that changes from a nitride compound layer at the top surface (∼ 20 μm thick) to a diffusion zone with a decreasing nitrogen concentration and precipitate density with distance from the surface, finally reaching the core matrix layer with a recovered martensite structure.

Investigation in the Influence of Surface Treatment on Mechanical and Electrochemical Corrosion Properties of Ti-6Al-4V Alloy

Potential difference between two phases in the Ti-6Al-4V alloy results in the galvanic cell reaction and corrosion. In order to improve the properties of Ti-6Al-4V, it was treated under different temperature with the atmosphere of 5vol. % oxygen and 95 vol. % nitrogen. The results showed that the titanium alloy surface is formed a layer of oxide and nitride compound layer. Sample treated at the temperature of 800°C had the most outstanding corrosion resistance and mechanical property.

Corrosion behaviour of triode plasma diffusion treated and PVD TiN-coated Ti–6Al–4V in acidified aqueous chloride environments

The corrosion resistance of triode plasma-nitrided and oxynitrided Ti–6Al–4V was investigated in a hydrochloric acid solution using potentiodynamic polarisation, cyclic voltammetry, and immersion testing at OCP. The untreated and the PVD TiN-coated alloy were used as benchmarks. When compared to the untreated alloy and a PVD-TiN coating, the diffusion treated alloys proved to be more durable due to the presence of a Ti2N compound layer. The corrosion barrier properties of the nitrided alloy depend on both thickness and integrity of the nitride compound layer; the thicker the layer, the better the performance in these tests.