High Nitrogen Gas Pressure Research Articles

Laser texturing of Inconel 718 alloy surface: Influence of environmental dust in humid air ambient

Laser texturing of Inconel 718 alloy surface under high nitrogen gas pressure is considered and the resulting surface morphology and wetting state are examined. Analytical tools are used to characterize the laser textured surface. Environmental dust particles and liquid solution formed from the water condensate on the dust particles in humid air ambient are analyzed. The tangential force required to remove the dried liquid solution from the laser textured and as received surfaces are measured incorporating the micro-tribomoter. It is found that laser treatment results in micro/nano size pillars on the textured surface and forms nitride compounds on the surface. This, in turn, modifies the wetting state of the workpiece surface from hydrophilic to hydrophobic. A liquid solution is formed due to the dissolution of alkaline and alkaline earth metals of the dust particles into the water condensate in humid air ambient. The liquid solution has high pH and forms different sizes of crystals on the surface upon drying. The liquid solution spreads on the textured surface while forming a film. It adheres strongly to the surface upon drying; in which case, the tangential force required removing the dried liquid from the surface remains high, which is more pronounced for the as receive surfaces.

Solid Solution (AlN) x (SiC)1–x (x ≈ 0.7) by SHS under High Pressure of Nitrogen Gas

Solid solution (AlN) x (SiC)1–x (x = 0.7) was prepared from Al–SiC mixtures by SHS under high pressure of nitrogen gas (50, 70 MPa) and characterized by XRD and SEM. Combustion product was found to have a wurtzite 2H structure with lattice parameters a = 3.10889 ± 0.00022 A and c = 5.00741 ± 0.00080 A.

Aluminum oxynitride by SHS under high pressure of nitrogen gas

Aluminum oxynitride (γ-AlON) powders were prepared from low-caloric Al–Al2O3 mixtures by SHS under high pressure of nitrogen gas in the presence of heat-generating agent, Mg(ClO4)2, as a booster. The preparation procedure was characterized and optimized with respect to Al/Al2O3 ratio, amount of heatgenerating additive, and nitrogen gas pressure. The morphology of synthesized γ-AlON powders was found to depend on Al powder brand. Compared to γ-AlON powders obtained in chemical furnace, we managed to prepare less sintered arenaceous cakes that could be easily disintegrated into target γ-AlON powder. SHSproduced powders may find their application in production of optical ceramics.

β-SiAlON-TiN/TiB2-BN composites by infiltration-mediated SHS under high pressure of nitrogen gas

β-SiAlON-TiN/TiB2-BN composites by infiltration-mediated SHS under high pressure of nitrogen gas

β-SiAlON–BN composites by infiltration-mediated SHS under high pressure of nitrogen gas

Infiltration-mediated SHS of β-Si6–zAlzOzN8–z–TiN/TiB2–BN composites was explored upon variation in applied nitrogen pressure, amount of combustible and inert components in green mixture, sample size, and BN content of resultant composites. Synthesized ceramics of different density and phase composition were characterized by their strength parameters, tribological behavior, electrical resistance, and thermal shock resistance.

Aluminum oxynitride by SHS in chemical furnace

AlON powders of varied composition were produced from Al–Al2O3 mixtures by SHS without and with B/BN chemical furnace under high pressure of nitrogen gas as a third reactant and characterized by XRD, SEM/EDS, and chemical analysis. The products obtained without chemical furnace were found to contain Al5O6N, Al7O3N5, AlN, as well as unreacted Al and Al2O3. The powders produced by SHS with chemical furnace contained largely the Al5O6N phase with an admixture of Al7O3N5 and AlN. After etching with KOH solution, the Al5O6N powders became single-phased. The etching also leads to marked changes in the microstructure of synthesized powders. Due to their unique microstructure, the synthesized Al5O6N powders can be expected to exhibit unusual electrophysical and optical properties.

SHS under high pressure of nitrogen gas: Feasibility of nitrides melting

Under some certain conditions, SHS reactions yielding AlN, BN, and Si3N4 under high pressure of nitrogen gas can be accompanied by fusion of reaction products. Upon appropriate choice of filler, compact materials with a porosity of around 10% can be readily synthesized by SHS nitridation under pressure.

Laser controlled melting of Hastelloy X alloy with presence of B4C particles at surface

Laser controlled melting of pre-prepared Hastelloy X alloy surface is carried out at high nitrogen gas pressure environment. The pre-prepared workpiece surface consists of 40 μm carbon film with uniformly distributed 5%B4C particles. The carbon film enhances the absorption of the incident laser irradiation and holds B4C particles at the workpiece surface prior to the laser treatment process. The morphological and metallurgical changes in the treated layer are characterised using scanning electron microscope, energy dispersive spectroscopy, and X-ray diffraction. The microhardness at the treated surface and the residual stress formed in the surface vicinity are measured. It is found that dense layer consists of fine grains are formed at the surface because of the high cooling rates. Locally distributed undissolved B4C particles are observed at the surface due to high melting temperature of B4C. Although thermal expansion coefficients of B4C and the base material are different, no microcracks are took place in the close neighbourhood of the particles. The microhardness of the surface increased almost 2·2 times of the base material hardness and the residual stress formed at the surface is on the order of −1·4 GPa, which is compressive.

Nitriding of high speed steel by bipolar PBII for improvement in adhesion strength of DLC films

In the present study, bipolar plasma based ion implantation and deposition (bipolar PBII) was used for plasma nitriding of high speed steel (SKH2), and the effects of the treatment parameters (positive pulse voltage, negative pulse voltage, treatment pressure, treatment time, and precursor gases) on the nitriding process were investigated. The hardness, roughness, and depth of nitride layer were also measured. The adhesion strength of diamond-like carbon (DLC) films coated on the nitride substrate was evaluated by carrying out Rockwell indentation and microscratch tests. Nitriding by bipolar PBII was achieved in the combining of two effects: nitrogen ion implantation by applying a high negative pulse voltage and thermal diffusion of nitrogen atoms under the application of a high positive pulse voltage. However, a very high voltage negative pulse caused surface roughening of the nitride layer. Application of a high positive pulse voltage during nitriding was found to be effective in promoting the thermal diffusion of the implanted nitrogen atoms. Effective nitriding could be achieved under the following conditions: high positive pulse voltage, low negative pulse voltage, high nitrogen gas pressure, and addition of hydrogen to the precursor gas. The adhesion strength of the DLC films on the SKH2 substrate was well improved after nitriding.

Combustion synthesis and tribological properties of SiALON-based ceramic composites

β-Sialon-based composite ceramics with varied BN, TiN, TiB2, SiC, and ZrO2 contents were fabricated by infiltration-mediated combustion under high pressure of nitrogen gas. Friction and wear behavior of synthesized composites were explored as a function of their microstructure, phase/elemental composition, density, and pore size distribution.

Femtosecond optical spectroscopy studies of high-pressure-grown (Al,Ga)N single crystals

We present our time-resolved studies of the carrier dynamics in high quality Al0.86Ga0.14N single crystals, grown using a solution technique in a high nitrogen gas pressure autoclave. Our optical measurements were performed using a femtosecond, pump-probe spectroscopy, by invoking the two-photon-absorption-type process and scanning the normalized transient differential transmissivity signal (ΔT/T) of the probe beam. Our time-resolved ΔT/T photoresponse consisted of a Gaussian-shape correlation signal with the pulse width of ~300 fs, which in two-color experiments was followed by a bi-exponential hot-electron relaxation transient. By plotting the autocorrelation signal amplitude versus the total energy of the absorbed pump and probe photons, we were able to very accurately determine the optical bandap of Al0.86Ga0.14N, as equal to 5.81±0.01 eV.

Effect of Nitrogen on Crevice Corrosion and Repassivation Behavior of Austenitic Stainless Steel

Austenitic stainless steels were produced based on a Fe-23 mass%Cr-4 mass%Ni alloy with varying nitrogen (0.7–1 mass%) and molybdenum contents (0–1 mass%), through electro-slag remelting (ESR) under high nitrogen gas pressure. The effects of nitrogen on crevice corrosion behavior in an acidic chloride solution were investigated, and the passive film of the crevice corrosion area after corrosion tests was analyzed using X-ray photoelectron spectroscopy (XPS). At the same time, the effects of nitrogen on the passivation behaviors after scratching were also investigated. During crevice corrosion at a noble potential of 0.7 V (SCE), the nitrogen in solid solution in the steel dissolves into the solution as NO3−, and its concentration increases with the nitrogen content in the steel. It was also established that the number of corrosion spots, the corrosion loss, and the maximum depth of corrosion all decrease with the increase in the nitrogen content present in the steel and the applied potential. Such results can be attributed to the presence of NO3− dissolved into the aqueous solution. On the other hand, results from scratch tests show that the increase in the amount of added nitrogen decreases the peak value of passivation current as well as the amount of electricity during repassivation, suggesting that nitrogen stimulates the passivation process and suppresses the occurrence of crevice corrosion. XPS analysis shows the presence of nitrogen as nitrides and NH3 in the surface layer of crevice corrosion and the internal layer of passivation films.

Diffusion joining of Si3N4 ceramics by hot pressing under high nitrogen gas pressure

Diffusion joining of Si3N4 ceramics by hot pressing under high nitrogen gas pressure

ＡｌＮ膜のＸ線的残留応力測定（第四報） 交替式スパッタリング法によるＡｌＮ膜の残留応力測定

Crystal orientation and residual stress development in AlN films deposited on BLC glass (Borosilicate glass; the termal stress expansion coefficient of which is nearly equal to that of AlN) substrate were investigated by the X-ray diffraction method. The AlN films were prepsred by an alternating planar magnetron sputtering system under the condition of constant substrate temperature, various nitrogen gas pressure between 0.17Pa and 1.1Pa and various switching time to alternate the anodic and catholic polarity of two target electrodes between 30sec and 600sec.The measurement of intensity from 00·2-diffraction showed that the c-axis orientation of AlN film was improved when the film was deposited at low nitrogen gas pressure below 0.5Pa and large switching time over 300sec. The tensile residual stresses wrer found in the films deposited at low nitrogen gas pressure below 0.3Pa or high nitrogen gas pressure over 0.8Pa and short switching time below 120sec.

Effect of a plasma protection net on residual stress in AlN films deposited by a magnetron sputtering system

Crystal orientation and residual stress development in AlN films deposited on borosilicate glass (the thermal expansion coefficient of which is nearly equal to that of AlN) substrates were investigated by X-ray diffraction method. The AlN films were prepared by a conventional planar magnetron sputtering system with a plasma protection net under the condition of constant substrate temperature and various nitrogen gas pressures between 0.8 Pa and 13 Pa. We found that the residual stresses show the same qualitative tendency against the nitrogen gas pressure independent of the use of the plasma protection net. Large tensile residual stress was observed at high nitrogen gas pressure and large compressive residual stress was observed at low gas pressure. When the plasma protection net was used, residual stresses in the AlN film were shifted to the compressive side.

ｃ軸配向した窒化アルミニウム膜のＸ線的残留応力解析

Crystal structure and residual stresses in AlN films deposited on BLC glass substrates by a magnetron sputtering method were measured by X-ray diffraction method. Deposited AlN films had a columnar structure with its ‹00·1› orientation being perpendicular to the glass substrate. From this structure, the intensity of hk·l diffraction could be measured just only at a particular ψ-angle and, therefore, the so-called sin2ψ method could not be applied for measuring their residual stresses. A new stress analyzing method was proposed in the present investigation instead of the sin2ψ method.Compressive residual stresses were found in the AlN films deposited under the condition of fairly high nitrogen gas pressure, while tensile residual stresses were found under the condition of low gas pressure.

Nitrogen solubility and nitride formation in FeCrNi alloys

A series of FeCrMnNi alloys was melted under high nitrogen gas pressure. The nitrogen concentration in the solidified metal was found to be experimentally related to the melt pressures that ranged from 0.1 to 200 MPa, to the alloy composition, and to alloy concentration. The nitrogen solubility followed Sievert's law. The activity coefficients determined at these higher pressures for the alloying elements Cr, Mn and Ni were similar to those previously obtained at lower pressures. At the higher nitrogen melt-pressures, the nitrogen concentration exceeded the interstitial nitrogen solubility resulting in the formation of metal-nitrides.

Ｓｍ２Ｆｅ１７Ｎｘ系化合物における窒化と磁気的特性

Effects of crystallization and nitrogenation on permanent magnetic properties have been investigated in the Sm2Fe17 alloy. It has been shown that the high nitrogen gas pressure of several 100kgf/cm2 is effective for nitrogenation of Sm2Fe17 powder which has an appropriate particle size. The nitrogenated compound Sm2Fe17Nx, under condition of several 100kgf/cm2 in N2 atmosphere has a saturation magnetization of 145emu/g. This value is smaller than that of literature one (160emu/gr) because of impurities of O2 and Fe.

Effect of water on the thermal characteristic of silk fibroin under high pressure of nitrogen gas

Effect of water on the thermal characteristic of silk fibroin under high pressure of nitrogen gas