Gas Nitriding Research Articles

CORROSION RESISTANCE OF BRAKE DISCS AFTER NITRIDING

The article presents the work carried out to create a surface layer, ultimately on cast iron brake discs, by theZeroFlow method using regulated gas nitriding. The presented research is aimed at creating a nitrided layerwith corrosive wear resistance maintained at the stage of brake disc manufacture, waiting for sale of a newvehicle, and even during further exploitation. Examples of nitriding parameters enabling such treatment ofbrake discs made of flake cast iron are presented. The research also includes measurements of the roughnessof the working areas of brake discs before and after nitriding. The properties of the nitrided layers producedare assessed following microscopic observations and microhardness measurements using the Vickers method.The impact of nitrided layers on corrosive wear is also analyzed by observing the behavior of the surfaces ofthe tested discs in a corrosive environment in the so-called “corrosion experiment.”

Effect of stage gas nitriding on corrosion and wear resistance of Ti6Al4V alloy in physiological environment

The wear and corrosion resistance of the Ti6Al4V alloy after gas nitriding combined with stage heat treatment was studied in the physiological environment. It was shown that nitriding temperature at the first stage of the heat treatment mainly effects on the surface quality and microhardness of the treated alloy. The corrosion behaviour of the nitrided Ti6Al4V alloy was studied in Ringer's solution, which simulates the physiological environment of human body. It was shown that the corrosion resistance of the alloy is enhanced by increasing thickness and TiN content in the nitride layer, and improving surface quality. The tribological characteristics of the nitrided Ti6Al4V alloy in a tribo-pair with PE-UHMW were evaluated in a 10 % aqueous solution of chondroitin sulfate, which simulates the synovial fluid. It was established that reducing nitriding temperature at the first stage of the heat treatment improved the wear resistance of the treated alloy due to decrease of the surface roughness and microhardness.

Fabrication of a new core–shell structured magnetic abrasive particles with good performance

The traditional Fe-based magnetic abrasive powders (MAPs) are prone to degrade by corrosion and oxidation. The extremely low stability to some extent limits the development of magnetic finishing. In this study, a new kind of 410 stainless steel-based spherical MAPs with core–shell structure was synthesized by gas nitriding. The nitride layer shows the dendrite structure containing (Fe, Cr)4N phase and lath-like CrN phase. The Zirconium tube roughness can be reduced from 0.280 to 0.153 μm. The origin of the good finishing performance was investigated through the Vickers hardness and nanoindentation tests.

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.

Two-dimensional code marking and coloration mechanism on titanium alloy surfaces via laser gas nitriding

In this study, a nanosecond laser marking machine was employed to nitride the surface of a Ti-6Al-4V alloy in a nitrogen-rich environment. Consequently, a crack-free and uniform nitriding layer was successfully achieved. Furthermore, a 2D code with enhanced contrast was imprinted on the sample, and subsequently, a durability test was conducted to assess its performance. The impacts of laser power (ranging from 9 to 11 W), scanning speed (17 to 23 mm/s), and line spacing (20 to 40 µm) on the surface morphology, thickness, and color alteration of the nitride layer were systematically investigated through experimental analysis. Utilizing a spectrophotometer, scanning electron microscope, optical microscope, energy dispersive spectroscopy instrument, and other advanced equipment, we further delved into the underlying mechanism of surface color change during laser gas nitriding of a Ti-6Al-4V alloy. Results indicate that an increase in laser power and a decrease in line spacing and scanning speed lead to the generation of higher energy densities on the material surface, intensifying ablation and causing the formation of more molten material. Consequently, this results in the development of more complex surface structures, thicker nitride layers, and lower reflectance. The surface microstructure of the nitride layer exhibits similarities and variations, and the thickness of the nitride layer differs, leading to distinct light absorption and reflection properties on its surface. Consequently, the nitride-layer surfaces prepared under varying laser parameters exhibit diverse contrasts.

Improving the surface characteristics of metallic glass thin ribbons by laser gas nitriding

The single-roll cooling method excels in producing metallic glass ribbons (MGRs), offering rapid cooling rates and exceptional thickness consistency. Nevertheless, a large number of defects including micro-pits and micro-gaps usually appear on the surface of MGRs after the roll forming process, significantly impacting their service life and performance. Laser gas nitriding is a cutting-edge surface modification technology that has been extensively used to improve the comprehensive performance of various metal components. Herein, an attempt was made to simultaneously improve the surface quality and mechanical properties of Zr41.2Ti13.8Cu12.5Ni10Be22.5 MGRs by nanosecond pulsed laser irradiation in a flowing nitrogen atmosphere. The effects of laser irradiation parameters on the surface characteristics of the laser gas nitrided regions were systematically investigated. The experimental results showed that the surface quality of MGRs after laser gas nitriding was enhanced, accompanied by a simultaneous improvement in hardness and scratch resistance. This study underscores laser gas nitriding as a potent strategy to augment the comprehensive surface characteristics of MGRs. This enhancement is poised to significantly extend their service life and reinforce their reliability when utilized as structural and functional materials in sectors such as machinery, national defense, and aerospace.

Effects of rare earth on nitriding microstructure and properties of a La-Ce micro-alloyed Q235RE steel

Accelerating nitriding is an interesting topic in chemical heat treatment of ferrous parts. In order to have a deeper understanding of the catalysis principles of rare earth in nitriding, a Q235 carbon steel and a Q235RE steel micro-alloyed with rare earth elements La and Ce were nitrided respectively by plasma nitriding and gas nitriding. The microstructure, phase constitution, and composition of the nitrided specimens were analyzed. The hardness profile of nitriding layer and the brittleness of surface compound layer were measured. The results demonstrate that the Q235RE specimens obtained a higher hardness and deeper effective hardening layer than the Q235 specimens without rare earth microalloying. The rare earth catalysis effects were presented as the acceleration of nitrogen diffusion and the inhibition of nitride precipitation in the diffusion layer of the Q235RE specimens. In addition, the surface compound layer of the Q235RE specimens showed higher toughness and better adhesion to the matrix than that of the Q235 specimens, which is considered to be strongly related to the rare earth elements diffused into the compound and the enhanced residual compressive stress in the layer.

EFFECT OF GAS NITRIDING PARAMETERS ON THE MICRO-HARDNESS OF HIGH-SPEED STEEL-CUTTING TOOLS

In this study, the nitriding parameters, such as nitriding time, nitrogen flow, and cooling type, were regularly modified to assess the effects of each on the microhardness of tools constructed of high-speed steel designed for commercial usage. The nitriding temperature was maintained at 670 °С for all of the tools. The tools were designed to measure microhardness. With a maximum value of 2000 HV at a time of 42 hours, direct nitriding with a nitrogen flow of 20 l/h and air cooling exhibits an apparent relationship between nitriding time and microhardness. The maximum microhardness value (1555.44 HV) was achieved by quenching after nitriding for 72 hours with a nitrogen flow rate of 20 l/h. The relationship between nitrogen flow and microhardness is semi-direct for direct nitriding at a nitriding duration of 30 hours and furnace cooling, with a maximum value of 1566.65 HV at a nitrogen flow of 110 l/h. The maximum microhardness was 2000 HV, with a 1.63% increase. The microstructure of the tools was improved by increasing the concentration of iron nitride in the ferrite cell, which means that the gas nitriding process increases the efficiency of cutting operations and reduces workpiece material surface roughness, based on the results of this study, it is advised to use high-purity nitrogen rather than ammonia. high-purity nitrogen gives better results than traditional nitriding using ammonia gas.

Experimental investigation on microstructure, mechanical and optical properties of RB-SiC ablated by nanosecond pulsed laser in nitrogen atmosphere

Reaction-bonded silicon carbide (RB-SiC) has gained significant attention owing to its exceptional physical and chemical properties. Improving the photovoltaic efficiency and mechanical properties of RB-SiC is conducive to further enhancing its applicability. Laser gas nitriding is an effective strategy to simultaneously reduce the surface reflectivity and enhance the surface hardness of materials. Accordingly, the evolution of microstructure, mechanical and optical properties of RB-SiC composite ablated by nanosecond pulsed laser in nitrogen atmosphere was comprehensively investigated. After laser gas nitriding, the surface hardness of RB-SiC composite was increased by 10.6–44.6 %. The chemical composition analysis indicated that Si-based nitride was formed on the laser-ablated surface, which was mainly responsible for the hardness enhancement. Additionally, the reflectivity of the laser-ablated surface was reduced by up to 95.2 % compared to the original RB-SiC composite. This study provides a straightforward and effective method to simultaneously improve the mechanical and optical properties of RB-SiC composites.

Gas Nitriding of AISI 420 Martensitic Stainless Steel during the Incubation Period of CrN Precipitation

Gas Nitriding of AISI 420 Martensitic Stainless Steel during the Incubation Period of CrN Precipitation

Effect of atmospheric-pressure nitrogen plasma treatment at low temperature on fatigue properties of low-alloy steels

A device for parallel-plate-type atmospheric-pressure nitrogen plasma (APNP) treatment, which can generate plasma in a sealed environment with high-purity nitrogen gas, was developed. The objective of the present study was to use microstructural analyses to investigate the effect of APNP treatment at low temperatures on the fatigue properties of low-alloy steels. The APNP treatment was conducted at 473 K, which is lower than the common gas nitriding temperature. X-ray analyses revealed that a nitrogen–oxygen diffusion layer with high fatigue limit was formed on the steel by the APNP treatment at 473 K. Thus, the APNP treatment is an effective approach for increasing the fatigue limit of steels by increasing their surface hardness.

Increasing the Working Time of Forging Tools Used in the Industrial Process of Producing a Disk-Type Forging Assigned for a Gearbox through the Application of Hybrid Layers.

The article discusses the phenomena and destructive mechanisms occurring on the surface of 1.2344 steel dies used during the hot forging of disc-type forgings. Preliminary research has shown that gas nitriding alone, used so far, is insufficient due to the occurrence of destructive mechanisms other than abrasive wear, such as thermal and thermomechanical fatigue, which cause the average durability of such tools to be approximately 5000 forgings. Analyses were also carried out to assess the load on forging tools using numerical modeling (Forge 3.0NxT), which confirmed the occurrence of large and cyclically changing thermal and mechanical loads during the forging process. Therefore, in order to increase operational durability, it was decided to use two types of hybrid layers, differing in the PVD coating used: TiCrAlN and CrN, and then subjected to gas nitriding (GN). The obtained results showed that, depending on the area of the tool and the current working conditions, the applied PVD coatings protect the surface layer of the tool against the dominant destructive mechanisms. In both cases, the strength increased to the level of 7000 forgings, the tools could continue to work, and globally, slightly better results were obtained for the GN+TiCrAlN layer. The CrN-type layer protects the tool more against thermal fatigue, while the TiCrAlN layer is more resistant to abrasive wear. In areas where the hybrid layer was worn, a decrease in hardness was observed from 1300 HV to 600-700 HV, and in places of intense material flow (front-point 2 and tool bridge-point 9) the hardness dropped to below 400 HV, which may indicate local tempering of the material. Moreover, the research has shown that each process and tool should be analyzed individually, and the areas in the tool where particular destructive mechanisms dominate should be identified, so as to further protect the forging tool by using appropriate protective coatings in these areas.

Achieving in-situ Fe-based spherical particles for magnetic abrasive finishing process of Zirconium tube via gas nitriding method

The magnetic abrasive powders have great influence on the magnetic abrasive finishing accuracy and efficiency. A new kind of Fe-based spherical magnetic abrasive particles with Fe2N precipitates and Fe4N matrix was successfully synthesized by gas nitriding. The results show that the prepared Fe-based magnetic abrasive particles can reduce the roughness of the Zirconium tube from 0.325 to 0.154 μm by four MAF passes. The high hardness and wear resistance of the Fe-based magnetic abrasive particles are assessed based on the Vickers hardness and nanoindentation results. This study can provide theoretical and experimental support for fabricating high-performance magnetic abrasive particles.

Wear resistance and antibacterial properties of 3D-printed Ti6Al4V alloy after gas nitriding

This research focused on tribological and antibacterial studies of 3D-printed Ti6Al4V alloys based on the selective laser melting method vs conventional technology after gas nitriding for biomedical applications. Gas nitriding reduced friction and wear in the following order: 3D-printed AM Ti6Al4V > wrought CM Ti6Al4V > CP-Ti. The best tribological performance was demonstrated on nitrided Ti6Al4V alloy using 3D printing. The antibacterial activity of the samples was estimated for the Gram-positive Staphylococcus aureus and the Gram-negative bacteria Escherichia coli. AM Ti6Al4V showed a positive antibacterial effect of nitriding against S. aureus bacteria by up to 30 %. Gas nitriding of 3D-printed Ti6Al4V alloys suggests an effective strategy to improve the antibacterial activity and mechanical resistance of biomedical implants.

The Influence of Selected Process Parameters on the Efficiency of the Process of Gas Nitriding of AISI 1085 Steel.

The main aim of the manuscript was to investigate the impact of modifying the parameters of the gas nitriding process of samples made from AISI 1085 steel on the course and results of the process carried out in a chemical reactor allowing for thermogravimetric measurements. The tested steel was subjected in a chemical reactor to the process of gas nitriding in the temperature range of 490-580 °C, using different sample heating rates (in the range of 1-25 °C/min) and various mixtures of nitriding gases (pure NH3, or NH3 with the addition of H2 or N2). To assess the impact of the tested process parameters on its efficiency, the thickness of the nitrided layers produced, the change in sample mass, the structure of the phases produced, the phase composition and the microhardness were examined. For the research methodology used, it was found that reducing the amount of NH3 and/or using H2 or N2 admixtures adversely affects the thickness of the nitride layers produced. At the same time, the use of a lower maximum process temperature with the same gas mixture resulted in a significant difference in the thickness of the layers. It was also found that the use of pure NH3 or a gas mixture (NH3 + H2) with higher NH3 contents resulted in higher surface microhardnesses of the samples and that for these samples, the hardness increased to a greater depth.

Determination of boundary conditions from the solution of the inverse heat conduction problem in the gas nitriding process

Two non-linear unsteady methods for solving the inverse heat conduction problem are discussed and compared in this paper. The first method is based on the finite element method, uses the variational calculus and the BFGS (Broyden-Fletcher–Goldfarb–Shanno) optimization algorithm. The second is an analytical and numerical method based on the approximation of the solution in the form of a linear combination of Chebyshev polynomials. In numerical tests, the stability of the temperature, heat flux density, and heat transfer coefficient obtained from both methods was analyzed. On the basis of experimental data, oscillations of the measured gas temperature and temperature in the component were analyzed. Oscillations of the gas temperature obtained from the experiment were taken into consideration during tests. The first method to solve the inverse problem was used to determine the boundary conditions for the entire gas nitriding process. As a result, stable values of temperature, heat flux density, and the heat transfer coefficient on the surface of the component under treatment in a real gas nitriding process, so far unpublished, were obtained.

Diffusion Nitride Surface Layers on Aluminum Substrates Produced by Hybrid Method Using Gas Nitriding

While gas nitriding of steel is currently used in industry, nitriding of aluminum alloys remains an open challenge. The main obstacle is aluminum’s high susceptibility to passivation. The oxide film provides an effective barrier to nitrogen diffusion. Attempts to overcome this problem have mainly focused on glow discharge nitriding using cathode sputtering of an oxide layer. The produced AlN layers exhibit no diffusion zone and show limited performance properties. In this work, the effect of hybrid treatment aimed at producing diffusion layers of nitrides other than AlN on aluminum alloys was investigated on the model system of iron nitride–aluminum substrate. Hybrid treatment combines an electrochemical process involving the removal of the aluminum oxide layer from the substrate, its subsequent iron plating, and a further gas nitriding in high-purity ammonia. The obtained results prove that the hybrid treatment allows the production, at 530 °C/10 h, of diffusion layers of Fe3N iron nitrides on aluminum substrates with a nitrogen diffusion zone range in aluminum of ca. 12 µm. In alloys containing magnesium, its unfavorable effect on the nitrogen diffusion and the functional properties of the layers was observed. An interesting direction for further research is hybrid treatment of precipitation-hardened alloys without magnesium.

Synergetic effects of micro-shot peening and gas nitriding on the fatigue performance of AISI 4140 steel

Gas-nitriding was performed to enhance the surface hardness and fatigue performance of 4140 steel pre-treated with micro-shot peening (MSP). The 4140 steel was solutionized and tempered at 200 °C/1 h, named as the base metal (BM) with the hardness of 500 HV0.05. Some BM samples were subjected to MSP (i.e., SPBM), and subsequently gas-nitrided at 520 °C/6 h (i.e., NBM). A compound layer of about 10 μm thickness formed on the surface of the NBM sample consisted of nano-grained Fe3N and Fe4N. The NBM sample showed a decline in hardness from the nitrided surface (750 HV0.05) to the matrix (300 HV0.05). In the as-peened condition, the peak residual compressive stress (RCS) was close to −500 MPa, and a very shallow stress field was obtained. After gas-nitriding, the peak RCS decreased to less than −400 MPa, while the affected depth expended to 300 μm. Defects in the compound layer did not deteriorate the fatigue strength/life of the nitrided 4140 steel. The RCS field effectively suppressed fatigue crack initiation and propagation at the surface of the NBM and SPBM samples. By contrast, surface cracks resulted in the fatigue failure of the BM sample.

Failure Analysis of Cryogenically Treated and Gas Nitrided Die Steel in Rotating Bending Fatigue

<div>AISI H13 hot work tool steel is commonly used for applications such as hot forging and hot extrusion in mechanical working operations that face thermal and mechanical stress fluctuations, leading to premature failures. Cryogenic treatment was applied for AISI H13 steel to improve the surface hardness and thereby fatigue resistance. This work involves failure analysis of H13 steel specimens subjected to cryogenic treatment and gas nitriding. The specimens were heated to 1020°C, oil quenched followed by double tempering at 550°C for 2 h, and subsequently, deep cryogenically treated at −185°C in the cryochamber. Gas nitriding was carried out for 24 h at 500°C for 200 μm case depth in NH<sub>3</sub> surroundings. The specimens were subjected to rotating bending fatigue at constant amplitude loading at room temperature. Measurement of surface roughness, hardness, and microstructural analysis indicated improved fatigue life for cryogenically treated specimens as compared to gas nitride, which could be attributed to fine carbide precipitation accountable for the delayed crack initiation and propagation.</div>

Characterization of structural and mechanical properties of HfNbTaTiZr refractory high entropy alloy after gas nitriding

This study was initiated to improve surface hardness and wear resistance of a HfNbTaTiZr refractory high entropy alloy (RHEA) by gas nitriding at a medium temperature (600 °C) for 3 h. Structural characterizations conducted by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS) equipped scanning electron microscope (SEM) revealed that nitriding led to formation of a 1.5 μm thick surface layer containing precipitates of oxides and nitrides of the alloying elements. Detection of oxides within the surface layer was attributed to the presence residual oxygen in the nitriding atmosphere. Nevertheless, the employed gas nitriding provided remarkably higher scratch resistance compared to the untreated state, as the results of increment in the surface hardness and development of larger compressive residual stress.