Nitrided Samples Research Articles

Thermophysical behavior of boron nitride and boron trioxide ceramics compounds with high energy electron fluence and swift heavy ion irradiated

We report differential scanning calorimetry (DSC) studies of boron nitride and boron trioxide compounds under different irradiation conditions. In the present work, boron nitride (h-BN) (purity of 99.8% and density of 2.29 g/cm3) and boron trioxide (B2O3) (purity of 99.5% and density of 3.10 g/cm3) samples were irradiated by using high intense electron beam and swift heavy ions irradiation. Electron beam irradiation of the samples was carried out at the different electron fluence of 4.16 × 1016, 1.20 × 1017 and 1.03 × 1018 cm−2 with energy of 2.5 MeV. Whereas the swift heavy ion irradiation of the samples was carried out using 132Xe ions with energy of 167 MeV/u at the different fluence of 5 × 1012, 5 × 1013 and 3.83 × 1014 ion/cm2. The thermal parameter changes with a differential mechanism under different irradiation conditions were investigated. In the DSC curves at the low temperature for initial and irradiation samples do not undergo phase transitions. However, at the 100 ≤ T ≤ 300 K temperature range widely changed the mechanism of the heat flow rate, specific heat capacity and thermodynamic functions in the boron nitride and boron trioxide samples is a more completed. In addition, for each of irradiation fluences, the calculated thermodynamic functions and specific heat capacity was found to increase from 0.002 J/g‧K to 0.08 J/g‧K as the irradiation electron fluence increased. For swift heavy ion irradiation, the specific heat capacity was found to increase from 0.005 J/g‧K to 0.06 J/g‧K. The results have revealed that there was a thermodynamic change.

Thermal Fatigue Testing of SiMoCr Compacted Graphite Cast Iron for HPDC Tooling Application

SiMoCr CGI (compacted graphite iron) has the potential to be a cost-effective replacement for some hot working tool steel parts like shot sleeve in HPDC (High-Pressure Die Casting) applications. Thermal fatigue testing of SiMoCr CGI cast alloy was performed on Gleeble 1500D machine. Cracks were evaluated on non-nitrided and nitrided samples at test temperatures of 400 and 600 °C, after 1000, 2000 and 4000 thermal cycles. Samples were heated to prescribed test temperature and afterward cooled in computer-guided cycles. After the test, all the samples were axially and radially sectioned and cracks on cross sections were evaluated. Length of all cracks which occurred was measured and statistically evaluated, i.e., the average length of cracks and distribution of crack lengths were determined. At nitrided samples, higher values for average crack lengths were obtained while density of cracks was lower in comparison with non-nitrided samples.

Influence of sintering process and interfacial bonding mechanism on the mechanical properties of MgO–C refractories

Two kinds of MgO–C refractories were separately prepared by carbon-embedded method and high-temperature nitridation. The phase compositions, microstructures and physical properties of heat-treated samples were investigated. Specially, the relationship between interface bonding and physical properties was mainly studied. Compared with the carbon-embeded burnt samples, the nitrided samples showed higher porosity, but exhibited better mechanical properties. And a direct chemical bonding interface was formed between Si3N4 and flake graphite in the nitrided samples, which enhanced the driving force between the molecules. Based on the fact, the molecular dynamics simulation of the interface between Si3N4 and flake graphite was carried out by the Material Studio software, and the interface phase relationship was β-Si3N4 (1 1 0)//graphite (1 0 0).

Effect of Low-Temperature Plasma Nitriding on Corrosion and Surface Properties of Duplex Stainless Steel UNS S32205

The duplex stainless steel UNS S32205 was plasma nitrided at 380 °C for 10 h using a gas mixture of 25% N2-75% H2. The thickness of the nitrided layer was 4.5 ± 0.5 μm, composed mainly of nitrogen-expanded austenite and iron nitrides precipitates. There was an increase in surface hardness around 2.6 and 3.8 times in the nitrided layer formed on the austenite and the ferrite phases, respectively, in relation to the untreated samples. The surface texture parameters skewness (Ssk), maximum peak height (Sp) and texture aspect ratio (Str) were the most appropriate parameters for studying the topography changes after treatment. An improvement in the localized corrosion properties after the nitriding treatment was revealed by the cyclic polarization curves. The nitrided samples showed higher pitting corrosion and repassivation potentials compared to the untreated material. The ferritic phases and grain boundaries were more susceptible to corrosion in the nitrided samples. The potentiodynamic curves of the nitrided samples exhibited a hillside on the passive-to-transpassive transition. This feature was already observed by other researchers, but it has not been well investigated. Potentiostatic studies demonstrated that metastable pitting took place on this transition.

Ti+ and Mg+ Ion Beam Extraction from the Modified Bernas Ion Source

The korea multi-purpose accelerator complex (KOMAC) has a metal-ion-beam irradiation facility (150 keV/1 mA) equipped with a Bernas ion source. Metal-ion beams such as Cr+, Fe+, Co+, and Cu+ have been successfully extracted from our facility. Recently, some research groups have requested us to irradiate Ti+ and Mg+ ions into materials. These two kinds of ions have never been provided before. In response to these requests, we carried out the extraction of Ti+ and Mg+ beams at our facility. The vaporization temperatures of TiCl(III) and MgCl(II) under a pressure of 10−4 Torr were less than 300 °C and more than 600 °C, respectively. In this study, optimal extraction conditions for Ti+ and Mg+ ion beams were acquired successfully. To confirm the fluences of the Ti+ and the Mg+ beams, we prepared a silicon wafer sample and a gallium nitride (GaN) sample. Ti+ ions were irradiated with a current density of ∼6 μA/cm2 onto a silicon wafer sample for 90 min, and the dose was 1.68 × 1016 ions/cm2, we measured by using Rutherford backscattering spectrometry (RBS) analysis. Mg+ ions implanted in GaN were confirmed by using secondary ion mass spectroscopy (SIMS). The depth and the concentration of Mg+ ions at the peak were found to be 130 nm and 7.4 × 1019 ions/cm3, respectively. We would expect the newly extracted Ti+ and Mg+ ions to be helpful for research in the fields of material science and condensed matter physics.

Formation of a protective TiN layer by liquid phase plasma electrolytic nitridation on Ti–6Al–4V bipolar plates for PEMFC

The current work mainly investigates the corrosion resistance and conductivity of TiN layer on Ti–6Al–4V with liquid phase plasma electrolytic nitridation for PEMFC bipolar plate (BP). The X-ray diffraction (XRD) results show that TiN phase presents in the nitriding samples. The surface morphology analysis indicates that higher CH4NO2 concentration tends to form more compact structure. The potentiodynamic polarization test indicates that sample N-600 prepared by 600 g/L CH4NO2 concentration possesses the lowest corrosion current density of 0.57 μA cm−2 in the simulated PEMFC cathode potential (+0.6 VSCE), which completely satisfies the DOE 2020 technical targets. Meanwhile, sample N-600 also exhibits the highest corrosion resistance and stability in the potentiostatic polarization, electrochemical impedance spectroscopy (EIS) and high potential (+1.6 VSCE) polarization test. Interfacial contact resistance (ICR) results show that sample N-600 possesses the lowest ICR value of 6 ± 0.4 mΩ cm2, which fully meets the DOE 2020 requirements.

The effect of plasma nitriding on the synergism between wear and corrosion of SAF 2205 duplex stainless steel

PurposeThis study aims to assess the performance of SAF 2205 duplex stainless steel against pure wear, tribo-corrosion, corrosion and the synergism between wear and corrosion. The effect of plasma nitriding conducted at low temperature (380°C) on SAF 2205 steel was analyzed.Design/methodology/approachThree systems were used for assessing the synergism between wear and corrosion: tribo-corrosion – wear tests conducted using the micro-scale abrasion test, performed under a slurry of alumina particles containing 3.5% NaCl; pure wear – tests conducted using the previous system but isolated in a glovebox with a 99% N2 atmosphere; and cyclic polarization under 3.5% NaCl solution. A hard nitrided layer of 3 µm thickness was characterized using X-ray diffraction, presenting expanded austenite.FindingsThe wear mode after micro-scale abrasion tests changed in the absence of an oxygen atmosphere. During pure wear, a mixed mode was identified (rolling + grooving), with the grooving mode more intense for the untreated steel. For tribo-corrosion tests, only rolling wear was identified. For all cases, the nitrided samples presented less wear. The corrosion results indicated a higher repassivation potential for the nitrided condition.Practical implicationsThe synergism was more positive for the nitrided sample than for the untreated one, which can be considered for surface treatments of duplex stainless steels in practical applications.Originality/valueA detailed description of wear mechanisms showed a significant change in the presence of oxygen atmosphere, a new approach for isolating pure wear.

Ion-Stimulated Chemisorption of Nitrogen on the Si(111) Surface

Nitriding of a silicon surface with a beam of low-energy (100–700 eV) nitrogen ions from a source with electronic excitation was studied. The density of the N+ flux on the nitrided sample was up to 4.0 μA/cm2. After the treatment, a silicon nitride monolayer film formed on the silicon surface, as evidenced by the results of profiling, calculation of the surface concentration, and energy shift of the Auger peak of silicon by 6.1 eV.

Synthesis and testing of defected g-C3N4 with improved photocatalytic activity

Graphitic carbon nitride samples with defected structure but larger surface areas were synthesized by adding urea as additive to the thermal decomposition (pyrolysis) of melamine. The pyrolysis was carried out at 600°C in ope-air conditions for 2 hours. The as-prepared samples were compared through detailed characterizations such as SEM, BET, XRD, XPS, FTIR and DRS. It was found out that the addition of urea functioned against the perfection of polymerization, and led to defected structure, which were suggested to be g-C3N4 segments in small crystalline domains. As a result, the formation of the defected structure led to blue-shifts in the optical transitions in the UV-Vis spectral range, as well as larger surface areas. In addition, the photocatalytic activities of the samples were measured by degrading Rhodamine B (RhB) with a concentration of 10 mg/L. It was found out that the samples with defected structure exhibited improved photocatalytic activity.

Duplex plasma treatment of AISI D2 tool steel by combining plasma nitriding (with and without white layer) and post-oxidation

AISI D2 tool steels are widely applicable in dies or tools manufacturing. Unfortunately, their use is drastically reduced due to short lifetime. Plasma nitriding without formation of white layer is an effective technique to improve the lifetime of tool steel by improving tribological features. Usually, white layer formation is unavoidable, thus its detrimental effects (its brittle nature causes severe abrasive wear) must be removed or reduced by some alternative treatment. Here, in this study, we attempted to investigate the effect of post-oxidation of nitrided tool steel with and without presence of white layer on its wear performance and its dynamic mechanical response. The micro-hardness and nano-hardness are enhanced by plasma nitriding, but a slight decrease with post-oxidation treatment. The post-oxidized samples show the formation of hematite and magnetite phases, which changes the wear mechanism of nitrided samples from abrasive to adhesive wear. This study suggests that the removal or avoidance of white layer formation is not compulsory, and its unfavorable effects on tribological performance of tool steel can be escaped by post-oxidation for a short time of 1 h. Analysis of contact stiffness and storage and loss moduli shows that the post-oxidation can result in surfaces less prone to cracking under cyclic loads. Duplex treatment by combining plasma nitriding and plasma oxidation is carried out in the same processing reactor by changing processing gasses admixture, thus it is favorable and economical for large scale industrial applications.

Porous defective carbon nitride obtained by a universal method for photocatalytic hydrogen production from water splitting

For the first time, herein this work, we have developed an effective and adaptable method to introduce defects onto the polymeric carbon nitride by simply grinding urea with urea nitrate which resulting new carbon nitride composite (UNU-C3N4) and melamine with urea nitrate which resulting new carbon nitride composite (UNM-C3N4). The UNU-C3N4 reveals high performance towards photocatalytic hydrogen production and as well as photocatalytic removal of contaminants. The results confirm that the defects enhanced the specific surface area, and improved performance of adsorbed oxygen which beneficial to generate more active radicals and more conducive sties to improve d the overall photocatalytic performance. The high N, H, and O content-enhanced electron polarization effects, by introducing the additional N, H, and O atoms into the g-C3N4 matrix, which will increase the charge transfer rate and charge separation efficiency. At the same time, the results of ESR also expression that the new type of as-prepared carbon nitride samples exhibit abundant of hydrogen radical (H) formation, which is also assist to improve the photocatalytic hydrogen production performance. As expected, the H2 evolution rate of UNU-C3N4(or UNM-C3N4) underneath simulated solar light irradiation is 9.93 times (13.76 times) than that of U-C3N4 (urea as raw material) (or M-C3N4 (melamine as raw material)). The high hydrogen evolution rates of UNU-C3N4 and UNM-C3N4 are 830.94 and 556.79 μmol g−1 h−1 under the visible-light irradiation, respectively. Meanwhile, the synthesized UNU-C3N4 and UNM-C3N4 material are demonstrated an efficient ability to degrade pollutants. In general, this work provides a viable way to introduce defects and hydrogen bands into the structure of carbon nitride.

Surface modification of M2 steel by combination of cathodic cage plasma deposition and magnetron sputtered MoS2-TiN multilayer coatings

Titanium nitride (TiN) is a good choice for the improvement in surface hardness of high-speed steel. Unfortunately, it has low adhesion with substrate and exhibits high friction coefficient; as a result it does not provide sufficient protection against sliding wear in metal-to-metal contact. The adhesion problem can be removed by nitriding process, whereas friction coefficient can be reduced by solid lubrication coating. In this study, an attempt is made to synthesize TiN hard coating as well as solid lubrication coating of molybdenum disulfide (MoS2) using magnetron sputtering, along with substrate pre-treatment by cathodic cage plasma deposition using titanium cathodic cage. The cathodic cage plasma nitrided sample exhibits significantly higher surface hardness, which reduced by solid lubrication coating. The nitrided sample depicts the presence of iron nitrides, TiN and nitrogen diffused martensite phases, whereas coated samples shows the presence of MoS2 and TiN phases. The friction coefficient and machining temperature are dramatically reduced by lubrication coating. This study recommends that the use of cathodic cage plasma nitriding using titanium cathodic cage is beneficial for improved surface hardness, and addition of solid lubrication coating is beneficial for reducing the coefficient of friction and machining temperature by scarifying hardness. As, both the systems are already proven to be appropriate for industrial-scale uses, thus results from this study can be applied for industrial-scale application.

Stability of expanded austenite by gas nitriding process on austenitic stainless steel material under low temperature conditions

Austenitic stainless-steel grade AISI310 are utilized in various applications like heaters, house apparatuses, turbine parts, blower parts. This task researches on the wear conduct of AISI 310 steel treated with gas nitriding treated to various time parameters to 6 h, 12 h and 18 h respectively. Wear test is led by utilizing pin on disc wear testing apparatus contraption for the both nitriding samples and untreated samples to check wear resistance of the material. The wear tests were conducted by applying a constant load of 30 N, constant speed of 500 rpm for a time period of 5 Minutes. Scanning electron microscope perceptions were made for the adjustments in surface and at naturally visible level. Hardness test is performed by utilizing Vickers hardness test and it was found to be improvement in hardness level in treated samples whereas no hardness in untreated samples. The microstructure results demonstrated that a white layer namely expanded austenite that was seen in nitrided samples. Subsequent to nitriding time was expanded, white layer disintegrated to chromium nitride (CrN) stage. From wear results it was noted that huge wear loss was obtained in untreated specimen that leads to expand wear increments. It was seen that hardness increments with the nitriding time. With the wear test and metallographic test outcomes, the best of gas nitrided samples were compared with untreated samples and were contrasted all together with decided to be sample with better wear resistance.

Response of a DIN 18MnCrSiMo6-4 Continuous Cooling Bainitic Steel to Plasma Nitriding with a Nitrogen Rich Gas Composition

The use of continuous cooling bainitic steels can provide a more energy efficient manufacturing route. However, for their use in mechanical components like gears, it is necessary to improve their surface properties without impacting the core properties to guarantee reliable mechanical performance. The effect of temperature and time on the plasma nitriding response of a DIN 18MnCrSiMo6-4 steel was investigated. The plasma nitriding was performed for 3, 6 and 9 hours, at 400, 450, 500 and 550 °C, using a gas mixture composed of 76 vol.% nitrogen and 24 vol.% hydrogen. Samples were characterized before and after plasma nitriding concerning the microstructure, hardness and microhardness, fracture toughness, phase composition and residual stress states. Based on the results presented, layer growth constants (k) for different temperatures was determined. Moreover, it could be found that 500 °C gave the best results investigated here, as higher temperature took to core and surface hardness decrease. The nitrided samples with thicker compound layers presented a fracture behavior dominated by the formation of Palmqvist cracks. X-ray phase analysis indicated the formation of biphasic compound layer on the surface of all nitrided samples. The diffusion zone presented compressive residual stresses with highest values near the surface.

Structure and Properties of Nitrided Ferroalloys

The structure and the physicochemical properties of nitrided chromium- and manganese-based ferroalloys have been studied experimentally. Nitrogen in the alloys is shown to be mainly in the form of nitrides Mn2N, CrN, and Cr2N, the fractions of which are dependent on the nitrogen content and the methods of alloy manufacture. The liquidus temperature of the nitrided chromium-bearing ferroalloys is lower than that of analogous nitrogen-free ferroalloys, which positively influences the rate and degree of assimilation of elements by steel. The introduction of 8–16% nitrogen in the ferroalloy compositions decreases their real densities, which enables one to produce alloys with the optimal density. The apparent densities of the nitrided chromium and manganese ferroalloys are very low (3000–4200 kg/m3) due to their high porosity; as a result, they will be melted at the steel melt surface and will have a low degree of nitrogen assimilation. Higher degrees of nitrogen assimilation can be achieved as powdered alloys are injected in a gaseous nitrogen jet. The degree of transition of nitrogen to steel from the ferroalloys is 47–84%; it is mainly dependent on the holding time of a nitrided steel in liquid state, the physicochemical characteristics of nitrided ferroalloys, the composition of an alloyed metal, and the types and content of nitride-forming elements (Cr, Mn, Ti, etc.) in it. The highest degree of transition of nitrogen to steel (84%) was reached using an as-cast nitrided chromium sample with 8% N in the first minute of holding. Further holding up to 30 min of the liquid sample at 1500°C leads to a decrease in the degree of nitrogen assimilation to 52%.

Plasma nitriding Ti-6Al-4V with the aid non-transmitted plasma-arc using different protection atmosphere

Investigations on the atmospheric plasma nitriding of Ti-6Al-4V are presented. Different operating parameters were varied, e.g. nitriding time, sample temperature and plasma gas composition. The plasma process was realized by a protective argon gas flow as well as by the operation in an argon glove box to investigate the influence of the residual oxygen on the sample surface. The nitride layers were characterized by X-ray diffraction and scanning electron microscopy. Also microhardness measurements were performed on cross sections. The results show that the nitriding success strongly depends on the residual oxygen concentration in the process environment. The use of argon as a local protective gas in the process leads to a reduction of this involuntary oxidation, whereby the quality of the protective gas coverage correlates directly with the quality of the nitride layer formation. A surface hardening of more than 400% compared to the base material could be achieved.

New Insights of Wear Behavior Analysis on Low Temperature Treated AISI 253MA Stainless steel Material by Gas Nitriding Process

AISI 253MA Stainless steel samples were treat with the gas nitrating process at low heat around 450°C. It was seen that all-inclusive austenite stage exist when it is nitrade to 8 hours and post addition at time of nitrading to 16 hours the mix of ferrites and progressively substance of nitrogen was gathered in the following layers. Farther nitrading to 24 hour it has seen at Cr-N stage was discovered and turns the steel progressively firmer superficially. Erode tests were led by tribological wear testing machine to examine the tribological wear loss. Volume wear was found to be least in 18 hours test which demonstrated better improvement of wear improvement. High hardness were found in 24 hrs showing a hardness of 1080Hv. The sample nitrided to 24 hours exhibited better wear resistance, high hardness and low wear loss as well as low volume wear loss. Assessment examinations of nitrided test samples were investigated under scanning electron magnifying analysis.

Improving tribological properties of P91 steels through carburizing process

The wear conduct of P91 steel has been researched under a dry sliding contact at consistent load. It was discovered that Carburizing was successful in improving the wear conduct of P91 steel material. A low temperature carburizing was completed for three distinct examples at an hour, an hour and a half and 120 min. Unnitrided austenitic treated steel was utilized as a source of perspective material and experienced wear test for comparision with nitride examples. Wear tests were conducted at 1000 rpm with an applied load of 50 N to examine the wear loss and volume wear loss of the material. The nitrided samples uncovers that hard nitride layers are formed which improves the surface hardness. Miniaturized scale hardness estimations uncovered a huge increment in hardness after treatment. The layers were further by checking electron magnifying instrument investigation.

Influence of silicon, strontium and aluminum oxides on silicon nitride ceramics for bone replacements

Although silicon nitride ceramics have been shown very propitious to be used for bone replacements, some characteristics can be controlled to improve their osseointegrations process. One of them is the intergranular phase whose composition can be specified to stimulate mineralization and osteoblastic production. In this paper, the intergranular glassy phase was projected in order to contain silicon, strontium and aluminum oxides. Silicon nitride samples containing different contents of SiO2, SrO and Al2O3 were sintered at 1815oC for 1 hour and characterized by scanning electron microscopy and X-ray diffraction. Hardness and fracture toughness were determined by Vickers hardness test and compressive strength was evaluated using an universal material testing machine. The biological behavior was studied in regard to cytotoxicity and cell proliferation by means of in vitro experiments. The samples reached high densities (higher than 95 %TD), total →-Si3N4 transformation, fracture toughness higher than 6.5 MPa.m1/2, compressive strength up to 2500 MPa and Vickers hardness less than 9.8 GPa. All samples were non-cytotoxic and able to promote cell proliferation with great potential to be used as components for bone replacements. However, that sample with high content of strontium had the best results of cell proliferation, proving the importance of a careful choice of intergranular phase composition in silicon nitride ceramics. Keywords: silicon nitride, mechanical properties, osteoblasts.

Nanocrystalline Ga–Zn Oxynitride Materials: Minimized Defect Density for Improved Photocatalytic Activity?

Abstract We present an alternative synthesis strategy for developing nanocrystalline (Ga1−xZnx)(N1−xOx) semiconductors known to be very efficient photoabsorbers. In a first step we produce mixtures of highly crystalline β-Ga2O3 and wurtzite-type ZnO nanoparticles by chemical vapor synthesis. (Ga1−xZnx)(N1−xOx) nanoparticles of wurtzite structure are then formed by reaction of these precursor materials with ammonia. Microstructure as well as composition (zinc loss) changes with nitridation time: band gap energy, crystallite size and crystallinity increase, while defect density decreases with increasing nitridation time. Crystallite growth results in a corresponding decrease in specific surface area. In the UV regime photocatalytic activity for overall water splitting can be monitored for samples both before and after nitridation. We find a significantly lower photocatalytic activity in the nitrided samples, even though the crystallinity is significantly higher and the defect density is significantly lower after nitridation. Both properties should have led to a lower probability for charge carrier recombination, and, consequently, to a higher photocatalytic activity.