Nitriding of VT1-0 titanium in low-pressure non-self-maintained glow discharge with the use of different gas mixtures

The results of nitriding of VT1-0 titanium in the plasma of non-self-maintained glow discharge with a hollow cathode are presented. A nitriding process has been implemented in different gas mixtures at low pressure and temperatures less than 650°C. It is shown that two-hour nitriding in a helium-nitrogen mixture leads to formation of a nitrided layer on the specimen’s surface. The obtained layer hardness of 14.5 GPa exceeds the hardness corresponding to pure nitrogen and argon-nitrogen nitriding by a factor of 2 and 1.5, respectively.     

Microstructure and corrosion resistance of the layers formed on the surface of precipitation hardenable plastic mold steel by plasma-nitriding

Plasma-nitriding is used to improve the wear resistance and corrosion resistance of plastic mold steels by modifying the surface layers of these steels. In this study, a precipitation hardenable plastic mold steel (NAK80) was plasma-nitrided at 470, 500, and 530 °C for 4, 8, and 12 h under 25% N₂ + 75% H₂ atmosphere in an industrial nitriding facility. The microstructures of the base material and nitrided layers as well as the core hardness were examined, and various phases present were determined by X-ray diffraction. The corrosion behaviors were evaluated using anodic polarization tests and salt fog spray tests in 3.5% NaCl solution.The results had shown that plasma-nitriding does not cause the core to soften by overaging. Nitriding and aging could be achieved simultaneously in the same treatment cycle. Plasma-nitriding of NAK80 mold steel produced a nitrided layer composed of an outer compound layer constituting a mixture of ?-nitride and γ′-nitride and an adjacent nitrogen diffusion layer on the steel surface. The amount of ?-nitride and total nitrides increased with an increase in nitriding temperature and nitriding time. Corrosion study revealed that plasma-nitriding significantly improved the corrosion resistance in terms of corrosion potential, corrosion and pitting current density, and corrosion rate. This improvement was found to be directly related to the increase in the amount of ?-nitride at the surface, indicating the amount of ?-nitride controlling the corrosion resistance.     

Influence of the composition of a plasma-forming gas on nitriding in a non-self-maintained glow discharge with a large hollow cathode

The article presents the results of an investigation into the influence of the composition of a plasma-forming gas (N₂, Ar, He) on nitriding of VT1-0 grade titanium (0.25%-Fe; 0.1%-Si; 0.2%-O) and commercial 40X steel (0.4%-C; 1.0%-Cr) in the plasma of a non-self-maintained glow discharge with a large hollow cathode. It is shown that the efficiency of nitriding of 40X steel weakly depends on the composition of the plasma-forming gas mixture, whereas nitriding of VT1-0 titanium in a helium-nitrogen mixture leads to a noticeable increase in the microhardness of the specimen’s surface in comparison with nitriding in an argon-nitrogen gas mixture.     

Average velocity of electrons in the cathode fall region during glow-discharge nitriding

The problem about the average velocity of electrons in the cathode fall region of a glow discharge during nitriding has been solved theoretically and verified experimentally. The technique and analytical apparatus for practical calculations of the average electron velocity have been presented.     

Defect-dependent nitride surface layer development upon nitriding of Fe–1 at.% Mo alloy

Upon nitriding of binary Fe–1 at.% Mo alloy in a NH₃/H₂ gas mixture under conditions (thermodynamically) allowing γ′-Fe₄N_{1– x} compound layer growth (nitriding potential: 0.7?atm^?1/2 at 753?K (480?°C) – 823?K (550?°C)), a strong dependency of the morphology of the formed compound layer on the defect density of the specimen was observed. Nitriding of cold-rolled Fe–1 at.% Mo specimens leads to the formation of a closed compound layer of approximately constant thickness, comparable to nitriding of pure iron. Within the compound layer, that is, in the near-surface region, Mo nitrides are present. The growth of the compound layer could be described by a modified parabolic growth law leading to an activation energy comparable to literature data for the activation energy of growth of a γ′-Fe₄N_{1? x} layer on pure iron. Upon low temperature nitriding (i.e. ?793?K (520?°C)) of recrystallized Fe–1 at.% Mo specimens, an irregular, ‘needle-like’ morphology of γ′-Fe₄N_{1? x} nucleated at the surface occurs. This γ′ iron nitride has an orientation relationship (OR) with the matrix close to the Nishiyama–Wassermann OR. The different morphologies of the formed compound layer can be interpreted as consequences of the ease or difficulty of precipitation of Mo as nitride as function of the defect density.     

Synthesis of Nano-Crystalline Graphite Films in Hollow Cathode Discharge

The results of experiments on the production of nano-crystalline graphite films in the hollow cathode discharge on Ni(111)/sapphire substrate are presented. The characteristics of the discharge for different gases and pressures are given. The emission spectra of the plasma have been measured. The layers of the deposited graphite have been characterized by the methods of Raman scattering and atomic force microscopy. The field emission of nano-crystalline graphite was also measured. The produced layers have good homogeneity and high value of the electron field emission. The presence of vertically growing graphene is revealed.     

Modeling of high pressure discharge lamps including electrodes

Electrode behavior in high pressure discharge lamps (HID), although understood qualitatively, is still not well understood quantitatively. Traditional models using different layers in front of the cathode are based on the assumption that the electrons gain substantial kinetic energy in the cathode fall to ionize the gas. For many HID lamps (e.g., p>1 MPa) this assumption may not be fulfilled. This paper uses a different model first proposed by Fischer (1987). We present modeling results for a Xe lamp with special emphasis on the cathode region     

Investigation of parameters of inductively coupled plasma and its use in steel nitriding

Parameters of inductively coupled plasma (ICP) discharges in a mixture of gases N₂, H₂, and Ar at a total pressure of 1.5 × 10^–3 mbar and a partial pressure ratio N₂: H₂: Ar = 2: 12: 1 are discussed. The plasma properties are analyzed using Langmuir probes and optical emission spectroscopy. The ICP discharge is used for the nitriding of specimens made of Russian grade 30ChGSA structural steel. The nitriding experiments are performed at different bias voltages V_b in the range of–200 V to +100 V with respect to the walls of the discharge chamber. The surface hardness of the treated specimens depends substantially on the bias voltage, being much higher than the initial value in all cases. The obtained results demonstrate the possibility of increasing the surface hardness up to 1000 HV (4–5 times the initial values) at the bias voltage equal to the floating potential.     

Calculation of geometrical changes in cylindrical copper hollow cathodes due to sputtering

To fine the reasons for the distortion of a cylindrical hollow cathode into a row of hollow spheres, the system of diffusion equations for the three most important types of particles in the hollow cathode discharge is solved, taking into consideration the essential source terms. In qualitative agreement with the experiments, the results show inhomogeneities of the cathode erosion at the cathode edges and at the boundary between hollow cathode discharge and normal glow discharge areas.     

假火花开关初始放电过程的理论计算

假火花开关具有耐压高、放电电流大及电流上升速率快的优点。本文利用流体模型及当地场近似，对其放电过程进行了理论计算。结果表明，在放电初始阶段，空心阴极效应起关键作用。同时，对不同初始条件（初始电子、离子密度不同）及不同边界条件（开关结构尺寸不同）的放电过程进行了计算。给出了放电时间、放电电流、最佳阴阳极距离和阴极孔尺寸大小。     

小型空心阴极等离子体电子枪实验

基于空心阴极效应和低压辉光放电原理,设计了一种小型空心阴极等离子体电子枪并进行了实验研究,在低气压下获得了稳定的空心阴极辉光放电,测量电子枪放电结果表明:在空心阴极中加入灯丝热子可明显降低放电气压;电子束电流的大小随放电电压增大而增大,受气体气压影响较小;在气压2Pa,放电电压10kV,脉宽4μs脉冲下放电,可得到脉宽为2μs,电流为600mA的电子束。     

Intense emission from a grid-stabilized plasma cathode

Intense emission from a grid-stabilized plasma cathode based on a glow discharge with an expanded anode area is studied. In the electrode system of the ion source, the potential difference between a large-mesh grid electrode (a hole diameter of 4–6 mm) and cathode and anode plasma reaches 200 V and the glow discharge current is up to 1 A. The current distribution over the electrodes of the plasma cathode is taken, and the dependences of the electron extraction efficiency and electron-emitting-plasma potential on the gas pressure and discharge parameters are obtained. A relationship between the geometric parameters of the grid, cathode plasma potential, and efficiency of electron extraction from the plasma is derived. It is shown that stable intense emission from the plasma cathode can be provided in wide ranges of gas pressure and discharge current by varying the geometry and mesh size of the plasma cathode grid. Discharge contraction in the grid plane at elevated gas pressures is explained. It is assumed that the emitting plasma becomes inhomogeneous due to variation in the thickness of near-electrode layers in the holes of the grid, which makes the distribution of the emission current from the plasma more nonuniform.     

小型空心阴极等离子体电子枪实验

基于空心阴极效应和低压辉光放电原理,设计了一种小型空心阴极等离子体电子枪并进行了实验研究,在低气压下获得了稳定的空心阴极辉光放电,测量电子枪放电结果表明：在空心阴极中加入灯丝热子可明显降低放电气压;电子束电流的大小随放电电压增大而增大,受气体气压影响较小;在气压2 Pa,放电电压10 kV,脉宽4 μs脉冲下放电,可得到脉宽为2 μs,电流为600 mA的电子束。     

Penetration of a low-pressure reflex-discharge plasma into a hollow electrode

It is shown experimentally that the plasma of a hollow-cathode reflex discharge is characterized by a nonequilibrium electron velocity distribution. The parameters of the electron distribution, which is approximated by a superposition of two Maxwellian distributions with different temperatures, are estimated. The penetration of the discharge plasma into the hollow cathode at various cathode potentials and a gas pressure of ∼10^{\t− 2} Pa is studied. It is shown that the plasma parameters in the hollow electrode depend not only on the parameters of the reflex-discharge plasma, but also on the magnitude and configuration of the magnetic and electric fields in the plasma expansion region. It is shown that the plasma penetration can be accompanied by quasineutrality violation and the formation of space-charge double layers. Experiments confirm that the ion current from the nonequilibrium plasma exceeds the Bohm current.     

强流离子源新型LaMo阴极实验研究

对从美国购进的强流离子源新型LaMo阴极的发射特性以及用于强流离子源阴极的放电性能进行了测试.实验结果表明了LaMo阴极是一种有效的热阴极发射体,且该阴极用于强流离子源时,离子源工作稳定,放电起弧正常,使用寿命大大延长(相对于LaB₆阴极).从实际应用来看,LaMo阴极确是强流离子源的一种有效的新型阴极.     

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开发了氮空心阴极放电PIC/MC二维自洽模型。研究了N2传统空心阴极向微空心阴极放电转变过程中电势和电场的变化。结果表明,不同尺寸的空心阴极放电的电势及电场分布规律几乎类似,但空心阴极孔径减小且气压增加时,电场近似线性增加;典型微空心阴极电场比传统空心阴极放电电场约大3个量级;微空心阴极放电产生的电子,氮分子离子和氮原子离子的密度比传统空心阴极放电约大3个量级,且微空心阴极放电中,N2+密度比N+密度大8倍以上。     

Transition of Discharge Mode of a Local Hollow Cathode Discharge

The discharge characteristics of hollow cathode discharge in argon in a cylindrical cavity are investigated experi- mentally. The voltage-current （V - I） characteristics and the light emission are measured. It is found that the discharge plasma is localized inside the hollow cavity, with an extensive Faraday dark space between the cathode and the anode. The discharge develops from predischarge to abnormal glow discharge, the hollow cathode effect （HCE） and a hybrid mode as the discharge current increases. The onset of the HCE is found for the first time by the transition from abnormal glow discharge together with a significant decrease in the slope of the V - I curve which shows a positive differential resistivity. The voltage increases proportionally with the current when the HCE is reached.     

Investigations of the Cathode Spot Dynamics in a Vacuum Arc Coating Process

Influence of cathode materials (Ti, Al, Cu, TiN), ambient gases (Ar, N₂, p = 0.1-1 Pa) and the arc current itself on the motion and the velocity of cathode spots in an arc coating process have been investigated with the help of a new high speed framing camera. It was found, that the cathode material causes different spot currents but in general the spot arrangement and the motion on the surface are similar. Surface contaminations due to ambient gases affect this dynamics in several ways. Insulating layers like AIN can drastically increase the instantaneous spot velocity, for example from <5 m/s on Al up to 170 m/s on AIN contaminated areas. TiN layers with a high conductivity increase the spot mobility at first. But at nearly completely contaminated surfaces (simulated by a TiN cathode), the mobility is strongly decreased. The values change from an average velocity of 6.3 m/s with a diffusion constant of 54 cm²/s (Ti, 0.01 Pa) to 2 m/s and 6.4 cm²/s at TiN. The course of the instantaneous spot velocity during the spot splitting phase was investigated too. The instantaneous spot velocity of each of the two new spots originated from the starting spot is relatively high (30–40 m/s) within the first 50 μs. The cathode material and the ambient gases are of slight influence in this phase. The movement is directed. In the further development the instantaneous spot velocity is decreasing to values under 5–10 m/s. The motion is now more and more random. Additionally it could be proved, that the lower stability limit for a stable discharge is strongly connected with the spot current, which depends on discharge conditions.     

空心阴极光源在原子发射光谱分析中的应用

本文介绍了空心阴极光源发射光谱分析中用地测定痕量元素的特点,供电电源的种类,阴极灯及电极,载气的选择等。并介绍了空心阴极光源在痕量分析上的应用。     

The Radio Frequency Hollow Cathode Discharge Induced by the RF Discharge in the Plasma‐Jet Chemical Reactor

In the recent decade an RF driven, low‐pressure plasma reactor with supersonic plasma jet was developed (RPJ). This reactor was successfully used for deposition of thin films of various materials. The deposition of thin films indicates that the properties of the deposited films are dependent on the sputtering or reactive sputtering processes appearing inside the nozzle (hollow athode). The nozzle (hollow athode) fabricated of different kinds of materials and alloys works both as a cathode of the radio frequency (RF) hollow cathode discharge and as a nozzle for plasma jet channel generation as well. The RF hollow cathode discharge is a secondary discharge, which is induced by the primary RF plasma generated in the reactor chamber. The present paper deals with the experimental study of this RF hollow cathode discharge. The stress is laid on the investigation of the axial distribution of discharge parameters and sputtering processes inside the nozzle. On the base of experiments, the simple model of the axial distribution of the investigated RF hollow cathode discharge has been developed.