Plasma Ion Nitriding Research Articles

Functionality of a hinge joint in endoprostheses with titanium and chirulen components

The article deals with a study of functional characteristics of the “nitrided pure titanium-chirulen” friction pair and determination of the contact pressure. Pure titanium was examined. In order to increase its tribotechnical characteristics, ion-plasma thermocyclic nitriding (IPTN) and thermodiffusion nitriding (TDN) were used. Tests of the “nitrided pure titanium-chirulen” friction pair were carried out on an end friction machine with fresh frozen human blood plasma of 0 ( І ), А ( ІІ ) and В ( ІІІ ) groups as working fluid. It was found out that by its rub resistance and antifriction properties the “nitrided pure titanium-chirulen” friction pair significantly surpassed the “CoCrMo-chirulen” pair. It was revealed that titanium samples, hardened by TDN technology, had better results than after IPTN. Tests in blood plasma, unlike those in Ringer’s solution, reproduced operation conditions of an artificial joint, implanted into the human body, more correctly. The wear rate of a component with chirulen within the contact pressure range of 3.54-6.5 MPa actually did not change, while at pressure over 6.5 MPa the wear assumed a catastrophic character. Therefore when an endoprosthesis is chosen it is necessary to consider the patient’s body weight.

Mechanomaking of nanostructure in nitrided Fe–Cr alloys by cyclic “dissolution–precipitation” deformation-induced transformations

Structural-phase transformations in surface layers of iron and Fe‒ Cr‒ (Ni) alloys subjected to ion-plasma nitriding and subsequent cold plastic compression shear deformation in Bridgman anvils have been investigated by the methods of Mössbauer spectroscopy, transmission electron microscopy and X-ray analysis. It has been shown that the deformation-induced cyclic phase “dissolution–precipitation” transformations of nitrides in alloys lead to the formation of nitrogen oversaturated solid solutions, precipitation of secondary nitrides and nanostructurization of the metal matrix.

Parameter Prediction through Soft PIN System in a Plasma Ion Nitriding Steel Hardening Unit

This paper introduces an excellent merge of Soft computing techniques from Computer Science Engineering, Plasma Technology and Material Surface Engineering. The paper is mainly focused on the Case Based Reasoning (CBR) approach for plasma nitriding process in the prediction of the values of the process parameters for different alloyed steels based on the actual data available from number of high-cost processing experiments. For different grade alloying steel-materials a number of process parameters have to be adjusted to get requisite surface hardness and case depth in the plasma nitriding process, which includes sample temperature, process time, working gas pressure, gas composition etc needed to be maintained in the optimal conditions. In practice, in the laboratory, it is usually achieved through hit-and-trial method and intuition, which becomes difficult for large-volume and large-scale plasma nitriding experiments to bear the cost. It is demonstrated that the CBR based computational reasoning can minimize the monitory losses and physical efforts in identifying the process parameters for those steel-materials for which such parameters are not currently available. The utility and implementation of CBR for the surface hardening of steel in a Plasma Nitriding process is justified. It is expected that the suggested methodology would prove a successful achievement in the plasma nitriding technology and also on the other emerging trends and technologies of industrial relevance.

Deformation-induced cyclic phase transitions of dissolution-precipitation of nitrides in surface layers of Fe-Cr-(Ni)-N alloys

Methods of Mossbauer spectroscopy, transmission electron microscopy, and X-ray diffraction have been used to study structural and phase transformations in surface layers of iron and Fe-Cr-(Ni) alloys subjected to ion-plasma nitriding and subsequent severe cold plastic deformation by shear under pressure in Bridgman anvils. It has been shown that the cyclic phase transformations of dissolution-precipitation of nitrides in the alloys result in the formation of nitrogen-supersaturated solid solutions, precipitation of secondary nitrides, and the nanostructurization of the metallic matrix. It has been established that the introduction of chromium into iron alloys accelerates the formation of nitrides upon nitriding and makes it possible to obtain solid solutions strongly supersaturated with nitrogen (more than 10 at % N in the fcc lattice) during subsequent deformation.

플라즈마 이온질화에 의한 Fe 나노분말소결체의 표면경화 가능성 연구

This study has been performed on the full density sintering of Fe nanopowder and the surface hardening by plasma ion nitriding. The Fe sintered part was fabricated by pressureless sintering of the Fe nanopowder at <TEX>$700^{\circ}C$</TEX> in which the nanopowder agglomerates were controlled to have 0.5-5 <TEX>${\mu}m$</TEX> sized agglomerates with 150 nm Fe nanopowders. The green compact with 46% theoretical density(T.D.) showed a homogeneous microstructure with fine pores below 1 <TEX>${\mu}m$</TEX>. After sintering, the powder compact underwent full densification process with above 98%T.D. and uniform nanoscale microstructure. This enhanced sintering is thought to be basically due to the homogeneous microstructure in the green compact in which the large pores are removed by wet-milling. Plasma ion nitriding of the sintered part resulted in the formation of <TEX>${\gamma}$</TEX>'-<TEX>$Fe_4N$</TEX> equilibrium phase with about 12 <TEX>${\mu}m$</TEX> thickness, leading to the surface hardening of the sintered Fe part. The surface hardness was remarkably increased from 176 <TEX>$H_v$</TEX> for the matrix to 365 <TEX>$H_v$</TEX>.

Investigation of properties of ion‐nitrided AISI 304 austenitic‐stainless steel

PurposeThe aim is to provide detailed mechanical and metallurgical examinations of ion‐nitrided austenitic‐stainless steels.Design/methodology/approachAustenitic‐stainless steel was the material chosen for the present study. Ion nitriding process was applied to fatigue and tensile samples prepared by machining. Process temperature was 550°C and treatment time period 24 and 60 h. Then, tensile, fatigue, notch‐impact, hardness tests were applied and metallographic examinations were performed.FindingsHigh temperature and longer treatment by ion nitriding decreased fatigue and tensile strengths together with notch‐impact toughness. Scanning electron microscopy and energy dispersive X‐ray spectroscopy analysis revealed formation of nitrides on the sample surfaces. Surface hardness increased with an increase in process time due to diffusion of nitrogen during ion nitriding.Research limitations/implicationsIt would be interesting to search the different temperature and time intervals of the ion nitriding. It could be a good idea if future work could be concentrated on ion nitriding on welded stainless steels.Practical implicationsSurfaces of mechanical parts are exposed to higher stress and abrasive forces compared to inside mechanical parts during the time period that mechanical components carry out their expected functions. When stresses and forces exceed the surface strength limit of the material, cracks begin to form at the material surface leading to abrasion and corrosion. Therefore, surface strength of materials needs to be increased to provide a longer service life. Ion (plasma) nitriding is a possible remedy for surface wear.Originality/valueThe main value of this paper is to contribute and fulfil the detailed mechanical and metallurgical examinations of ion‐nitrided austenitic‐stainless steels that are being studied so far in the literature.

A review of the corrosion of laser nitrided Ti‐6Al‐4V

PurposeThe purpose of this paper is to consider the corrosion properties of laser nitrided Ti‐6Al‐4V alloys that have been reported previously by several researchers.Design/methodology/approachDifferent kinds of surface nitriding methods of titanium alloys, such as plasma nitriding, ion nitriding, gas and laser nitriding, are introduced. Microstructure changes, such as phase formation and the influence of laser processing parameters in laser nitriding layers of Ti‐6Al‐4V alloys, were investigated using scanning electron microscope, transmission electron microscope, X‐ray photo‐electron spectroscopy, and X‐ray diffraction. Based on investigations presented in the literature, the effect of laser nitriding on the corrosion behavior of Ti‐6Al‐4V alloy was reviewed.FindingsBy regulating the laser processing parameter, the microstructure of the nitrided layer can be controlled to optimize corrosion properties. This layer improves corrosion behavior in most environments, due to the formation of a continuous TiNxOy passive film, which can retard the ingress of corrosive ions into the substrate and can maintain a constant value of a current density. Therefore, the laser gas nitrided specimens have a relatively noble corrosion potential and a very small corrosion current, as compared to untreated specimens.Originality/valueThis paper comprises a critical review, and its collection of references is useful. It summarizes current knowledge in laser surface treatment research.

Corrosion process in NaCl/Na2SO4 solutions of AISI 316L stainless steel treated by ionic nitriding

This work is a corrosion study of an AISI 316L austenitic stainless steel after different plasma ion nitriding conditions. The properties of the coated AISI 316L were measured. The corrosion resistance was evaluated by cyclic voltammetry and salt spray testing. Sample surfaces were characterised by SEM and the phase determination with XRD analysis. Nanohardness was determined by using a Vickers indenter. The nitrided samples treated at 400°C, in a gaseous mixture of 5%N2 and 95%H2 for 4 and 5 h, had the best corrosion resistance. For the salt spray test, where the potential range is near the equilibrium potential, the nitrided material presented a reduced corrosion resistance. Through the control of the process parameters it is possible to improve the stainless steel surface hardness, combined with a good corrosion resistance. The highest value of temperature and N2 proportion increased the surface roughness and hardness, though it caused a decrease in corrosion resistance.

Nanostructure formation and phase transformations in nitrided stainless steel Kh18N8 during severe cold deformation

The phase transformations and nanostructure formation in metastable stainless steel Kh18N8 are studied during nitriding and subsequent severe cold plastic deformation by high-pressure torsion in Bridgman anvils. Ion-plasma nitriding of the steel leads to the nitrogen saturation of austenite, CrN nitride formation, and the destabilization of the structure with respect to the γ-α transformation. Subsequent deformation is accompanied by the reverse α-γ phase transformation, the dissolution of nitrides, and the formation of nitrogen-supersaturated solid solutions and secondary nanonitrides. These fine particles restrict the grain growth in the matrix and stabilize the nanostructure formed.

Treatment of Surface Properties of Titanium with Plasma (Ion) Nitriding

In order to improve the poor surface hardness and the wear resistance, titanium has been nitrided with plasma (ion) nitriding which is one of the methods to treat surface properties of titanium alloys. The increment at surface hardness and so the wear resistance of nitrided titanium alloys has been provided by means of compound layer (ε-Ti2N+δ-TiN) and diffusion zone (α-Ti) occurred by plasma ion nitriding. The goal of the present paper is to investigate effects of nitriding temperature and nitriding time on the microstructure and hardness value of nitrided surface layers. A systematic study was undertaken with specimens of commercial pure Ti and Ti-6Al-4V alloy. As treatment parameters, we have used; nitriding time (from 2 to 9 hour), nitriding atmosphere (H2-80%N2), total pressure (1 kPa) and cathode temperature (from 600 to 800 oC). The Vickers indenter was used for analysis of the micro hardness measurements. The thin hardened layer at the nitrided surface was characterized by glancing-angle X-ray difractometer. X-ray diffraction analysis has confirmed the formation of ε-Ti2N and δ-TiN phases on the nitrided specimens. Experimental details and characterization of plasma (ion) nitrided titanium have reported and discussed.

High Intensity Plasma Ion Nitriding of AerMet 100 Martensitic Steel

Fully hardened martensitic steel AerMet alloy 100 was nitrided using a newly developed technique known as high intensity plasma ion nitriding (HIPIN). A systematic study, using the experimental techniques of optical and scanning electron microscopy, microhardness measurement, and Rockwell C-scale (150 kg load) indentation was executed to determine the resulting case depth and hardness profile as affected by the processing parameters of ion energy, current density, process temperature and duration. It was observed that nitrogen diffused rapidly at the temperature range from 427 to 480 °C and a case depth up to 200 µm was obtained. The surface hardness after nitriding increased to HK200g = 800–900 from 600–700. However, the bulk hardness reduced slightly from Rc56 for the unnitrided to Rc55 upon nitriding even for a short duration of about 1 h. When the nitriding temperature was not too high (≤454 °C) and the duration was not too long (≤15 h), the bulk hardness remained within the range of Rc53–55. Further increase in temperature and duration resulted in significant reduction in the bulk hardness. Using simulated gear samples in the form of V-notch bars, the nitrided case depth was determined to be quite uniform around the entirety of the notch geometry. Considering the bulk hardness, surface sputtering, and nitride case depth, it appeared that nitriding at 454 °C for up to 15 h that produced a case depth of about 120 µm may be the optimal condition. From the experimental data, the diffusion coefficient and activation energy for nitrogen in AerMet 100 were determined to be D0 = 4.33 × 10−6 cm2 · s−1 and Ea = 0.488 eV, respectively. Based on the results of this study, the viability of the HIPIN technique has been demonstrated for the thermochemical processing of prototype components composed of AerMet 100 alloy steel.

The Characteristics of Surface Layers Produced on SKD 61 Steel by Plasma Radical Nitriding Compared with Conventional Plasma Ion Nitriding

Plasma radical nitriding has been performed to harden the surface of SKD 61 steel for 1- 10 hours at temperature range of 450-550°C. A NH radical, which has played a key role to produce a nitrogen diffusion layer without the formation of the brittle compound layer, has been generated in a gas mixture of NH3 and H2 . One of the main advantages of the plasma radical nitriding is to improve the surface hardness by maintaining the roughness of the initial polished surface. The microstructures and material properties of the radical nitrided layer have been characterized in order to investigate the effects of various radical nitriding processing parameters. The hardness and surface roughness of the hardened layer were compared between two processes. In addition, PVD CrN coating has been deposited on both the radical nitrided substrates and conventional nitrided substrates by an arc ion plating (AIP) technique. The effect of two different of plasma nitriding treatments on the adhesive strength of the coating layer on the substrates was also investigated.

The application of plasma nitrocarburizing and plasma post oxidation technology to the automobile engine parts shafts

Plasma nitrocarburising and plasma post oxidation were performed to improve the wear and corrosion resistance of S45C and SCM440 steel by a plasma ion nitriding system. Plasma nitrocarburizing was conducted for 3h at <TEX>$570^{\circ}C$</TEX> in the nitrogen, hydrogen and methane atmosphere to produce the <TEX>${\varepsilon}-Fe_{2-3}$</TEX>(N, C) phase. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at constant temperature of <TEX>$500^{\circ}C$</TEX> for 1 hour. The very thin magnetite (<TEX>$Fe_3O_4$</TEX>) layer <TEX>$1-2{\mu}m$</TEX> in thickness on top of the <TEX>$15{\sim}25{\mu}m$</TEX> <TEX>${\varepsilon}-Fe_{2-3}$</TEX>(N, C) compound layer was obtained by plasma post oxidation. A salt spray test and electrochemical testing revealed that in the tested 5% NaCl solution, the corrosion characteristics of the nitrocarburized compound layer could be further improved by the application of the superficial magnetite layer. Throttle valve shafts were treated under optimum plasma processing conditions. Accelerated life time test results, using throttle body assembled with shaft treated by plasma nitrocarburising and post oxidation, showed that plasma nitrocarburizing and plasma post oxidation processes could be a viable technology in the very near future which can replace <TEX>$Cr^{6+}$</TEX> plating.

Plasma-ion nitriding of alloy steel with the use of a low-pressure arc plasma generator

The microhardness and structure of coatings deposited by ion nitriding in low-pressure (on the order of 10−1 Pa) arc discharge plasma on steels with different alloying systems (37G2S, 25Kh5M, and R6M5) are considered. The characteristics of steels nitrided in arc discharge and by the traditional method (in a furnace) are compared.

Self-propagating high-temperature synthesis of complex nitrides of intermetallics

In our previous papers, the Self-Propagating High-Temperature Synthesis (SHS) of aluminium and titanium nitrides was studied. In this paper the synthesis of the complex nitrides of intermetallics, based on titanium, aluminium and nickel, was carried out. The samples were produced by the direct SHS of nickel–aluminium and titanium–aluminium mixtures in a nitrogen atmosphere, as well as by the SHS synthesis of nickel–aluminium and titanium–aluminium intermetallics followed by pulsed plasma ion nitriding. Composition of products was studied by chemical analysis, as well as by X-ray diffraction and X-ray photoelectron spectroscopy. Experiments revealed that the highest extent of nitridation was achieved during direct one-stage SHS synthesis of the complex intermetallic nitrides.

Spectroscopic optimization of abnormal glow conditions for plasma ion nitriding

Optical emission spectroscopy is used to characterize the production of active species as a function of hydrogen concentration in the mixture under different operating conditions. A major concern is to enhance the concentration of the active species by hydrogen addition that carry several electron volts energy above their ground states, and thus affect the surface chemistry. The emission intensity of the selected optical transitions of molecular and atomic species is measured to determine the functional dependence of their radiative states. The relative ground state molecular ion density [N 2 + ] is measured from the emission intensity of the first negative band head ( λ = 391.4 nm, 0–0) by considering the fact that in low temperature plasma, ion with single charge is produced by the electron impact, and the ion density is proportional to the electron density. It is found that the concentration of the active species may be enhanced significantly by selecting an appropriate gas composition and operating parameters. The SS-304 samples are nitrided under the optimum conditions for 4, 8, 12 and 16 hours and hardness values are found to increase five times for 16 hours treatment time. The optimized discharge conditions are found favorable for plasma ion nitriding.

Enhancing the microstructure and properties of titanium alloys through nitriding and other surface engineering methods

Over the last 40 years, the commercial production of titanium and its alloys has increased steadily. Whilst these materials have some very attractive properties, enabling applications in many industries, they are seldom used in mechanical engineering applications because of their poor tribological properties. This paper starts with an introduction to the titanium material and a review of the different types of surface treatment. The processes of nitriding, oxidation and carburizing are among the most popular thermochemical treatments aiming at improving the surface properties of Ti-alloys. Different kinds of nitriding are investigated like plasma nitriding, ion nitriding, and laser and gas nitriding. The kinetics of nitriding and the conditions for the formation of nitrided layers are studied. The influence of the main processing parameters such as temperature, time on the microstructure and the formation of new phases during the processes of nitriding is discussed. Also based on investigations presented in the literature, the effects of nitriding on the microhardness and the corrosion resistance of titanium and titanium alloys are analyzed. The improved mechanical properties, which arise from these thermochemical treatments, are discussed in relation to the potential for applying these alloys to different industries.

High-intensity plasma ion nitriding of orthopedic materials: Part I. Tribological study

In this paper, we describe a newly developed technique—high-intensity plasma ion nitriding (HIPIN), which takes the advantages of low energy beam ion implantation at elevated temperatures that generates thick nitrided layers compared to conventional plasma nitriding and ion implantation, but overcomes the inherent line-of-sight shortcoming of beam implantation. In this technique, a low-pressure nitrogen plasma (<1 mTorr) is used. With an electron source (filament) to emit electrons and by drawing them to the anode (vacuum chamber), the plasma is generated and maintained due to electron-neutral gas collisions. With the application of a low voltage on the parts that are immersed in the plasma, ions are drawn and implanted to the surface of the parts. At elevated temperatures, nitrogen diffusion occurs, thus forming deep nitride layers. Using this technique, we have processed orthopedic materials made of Ti-6Al-4V and CoCrMo at various temperatures. It has been observed that for Ti-6Al-4V, nitriding at higher temperatures generate deep nitrided layers that are quite hard and wear resistant. For forged CoCrMo, nitriding at both low and high temperatures show much better performance than at medium temperatures. For comparison purposes, nitrogen plasma immersion ion implantation has also been performed. However, nitrided samples using the HIPIN technique out perform the one using implantation. A reduction of wear over 30 times has been observed. In contrast to the forged CoCrMo, nearly no improvement has been observed on cast CoCrMo possibly due to the microstructure effect.

High intensity plasma ion nitriding of orthopedic materials: Part II. Microstructural analysis

Orthopedic materials (Ti-6Al-4V and CoCrMo) were nitrided at temperatures up to 850 °C using a newly developed technique—high intensity plasma ion nitriding (HIPIN)—in order to enhance lifetime wear properties. Near surface microstructure and phase formation of both nitrided Ti-6Al-4V and CoCrMo alloys were evaluated using cross-sectional SEM and X-ray diffraction techniques. Nitrogen was found to most readily incorporate into the Ti-6Al-4V structure at around 750 °C (slight expansion of the lattice) with additional formation of TiN and Ti 2N at higher temperatures. In the case of the CoCrMo alloys (forged and cast), a metastable, high nitrogen phase was also found to form at between 300 and 600 °C along with the formation of CrN/Cr 2N/σ phases above 700 °C. It was concluded that increased wear properties, as a result of HIPIN processing, can be related to both the formation of deep nitrided layers and the formation of specific microstructures at the surface (for both alloy types).

The Characteristics of the Oxide Layer Produced on the Plasma Nitrocarburized Compound Layer of SCM435 Steel by Plasma Oxidation

Plasma nitrocarburising and post oxidation were performed on SCM435 steel by a pulsed plasma ion nitriding system. Plasma oxidation resulted in the formation of a very thin ferritic oxide layer 1-2 <TEX>$\mu\textrm{m}$</TEX> thick on top of a 15～25 <TEX>$\mu\textrm{m}$</TEX> <TEX>$\varepsilon$</TEX>-F <TEX>$e_{2-3}$</TEX>(N,C) nitrocarburized compound layer. The growth rate of oxide layer increased with the treatment temperature and time. However, the oxide layer was easily spalled from the compound layer either for both oxidation temperatures above <TEX>$450^{\circ}C$</TEX>, or for oxidation time more than 2 hrs at oxidation temperature <TEX>$400^{\circ}C$</TEX>. It was confirmed that the relative amount of <TEX>$Fe_2$</TEX><TEX>$O_3$</TEX>, compared with <TEX>$e_3$</TEX><TEX>$O_4$</TEX>, increased rapidly with the oxidation temperature. The amounts of <TEX>${\gamma}$</TEX>'-<TEX>$Fe_4$</TEX>(N,C) and <TEX>$\theta$</TEX>-<TEX>$Fe_3$</TEX>C, generated from dissociation from <TEX>$\varepsilon$</TEX>-<TEX>$Fe_{2-3}$</TEX> /(N,C) phase during <TEX>$O_2$</TEX> plasma sputtering, were also increased with the oxidation temperature.e.