Pulsed ion extraction from a hybrid plasma using a shunting arc discharge

A hybrid plasma is generated by combining a burst methane rf (195 kHz) plasma with a carbon shunting arc discharge. The shunting arc discharge triggers the rf methane plasma. As a result, the rf plasma is initiated over a wide range of ambient gas pressure from 0.045 Pa as a base pressure to a methane pressure of 1.26 Pa, at which the rf plasma is not self-ignited. When a target is immersed in the rf- and shunting arc-hybrid plasma, and a negative pulse voltage is applied to the target, carbon ions are extracted from the hybrid plasma. When the carbon shunting arc ionizes the methane gas, an rf plasma is initiated and the ionization of methane is significantly enhanced in the rf plasma. The plasma density in the hybrid plasma increases by a factor of approximately 5-9 compared to that of the shunting arc discharge.     

Ion extraction from magnetically driven shunting arc and estimation of ion density at sheath boundary

Ion density of a magnetically driven shunting arc discharge is estimated from the target voltage characteristics of the pulse modulator circuit in plasma-based ion implantation (PBII). The voltage recovery time constant directly reflects the ion sheath characteristics, and the sheath resistance is related to the ion density inside the transient sheath. The measured characteristics are analyzed using an equivalent circuit of the pulse modulator in PBII. The estimated ion density decreases from 3 × 10⁸ to 4 × 10⁷ cm^− 3 with time after the arc ignition from 100 to 400 μs. This characteristic almost agrees with that of an ion current extracted from the arc plasma by applying a negative pulse voltage to the target.     

Gas contamination during plasma welding in Al–Li alloy 2195

Abstract

Keyhole and cover pass variable polarity plasma arc welds were made on aluminium alloy 2195 with measured contamination levels of nitrogen, oxygen, and hydrogen. Contamination levels ranged from less than 10 to 500 ppm in both the argon plasma gas and the helium shield gas. It was found that nitrogen leads to more severe porosity than either hydrogen or oxygen, and that rear shielding is required for keyhole welding of Al–Li 2195 alloy to protect the weld from nitrogen in the atmosphere. Both nitrogen and oxygen contamination produced a dark surface on the weld bead, which comprised metallic aluminium particles, nucleated in the melt, that had aggregated at the surface of the weld pool.     

On the Plasma （ion） Carburized Layer of High Nitrogen Austenitic Stainless Steel

The manganese concentration of austenltic stainless steel decreases from the inner layer towards the surface of the plasma (ion) carburized layer due to the evaporation of manganese from the specimen surface. The carbon concentration in the carburized layer is influenced by alloyed elements such as Cr, Ni, Si, and Mo, as well as Nitrogen. This study examined the effects of nitrogen on the properties of the carburized layer of high nitrogen stainless steel. Plasma (ion) carburizing was carried out for 14.4 ks at 1303 K in an atmosphere of CH4 H2 gas mixtures under a pressure of 350 Pa. The plasma carburized layer of the high nitrogen stainless steel was thinner than that of an austentric stainless steel containing no nitrogen. This suggested that the nitrogen raised the activity of carbon in the plasma carburized layer, GDOES measurement indicated that the nitrogen level in the layer did not vary after plasma (ion) carburizing.     

氮氧元素联合过渡对气体熔池耦合活性TIG焊电弧的影响

针对外层引入氮氧混合气体的气体熔池耦合活性TIG焊电弧,采用Boltzmann作图法分析在不同耦合度下电弧等离子体的温度分布和电弧电压的变化规律,并与传统TIG焊及外层只引入氧气的气体熔池耦合活性TIG焊进行比较. 结果表明,氮氧联合过渡时气体熔池耦合活性TIG焊电弧的中心区域温度和电弧电压均高于传统TIG焊与外层只引入氧气时的气体熔池耦合活性TIG焊的数值;当耦合度由0变为+2时,电弧中心区域温度与电弧电压均略有升高.     

Enhanced dissolution of nitrogen during gas tungsten arc welding of steels

Abstract

Although nitrogen concentrations at levels much higher than Sieverts' Law predictions during the arc welding of iron and steel are well established, there is currently no commonly accepted methodology to determine this concentration quantitatively. The nature and concentrations of various species in the plasma phase above the weld pool surface are therefore investigated in the present work using both theoretical and experimental techniques. A comprehensive thermodynamic analysis of the nitrogen containing plasma phase of a gas tungsten welding arc shows that ionised species dominate close to the electrode, whereas neutral monatomic and diatomic nitrogen are the primary species near the metal surface at plasma temperatures as low as 5000 K. When oxygen is added to a nitrogen containing plasma, the resulting nitrogen concentration in the weld metal is further enhanced. Definitive proof is provided for a mechanism in which nitrogen and oxygen species interact in the plasma phase at temperatures below 6000 K, resulting in a significant increase in the concentration of monatomic nitrogen. Furthermore, at plasma temperatures as low as 5000 K, the equilibrium monatomic nitrogen partial pressure is sufficiently high to cause nitrogen saturation in the weld metal. Emission spectroscopy of glow discharge plasmas validates both the species density calculations and the presence of NO in the nitrogen and oxygen containing plasmas.     

Ar/O2 gas pressure dependences of a pulsed zirconium arc and extracted ion characteristics

A pulsed dc zirconium arc discharge is generated in an argon diluted oxygen gas by separating a pin electrode as an anode from the cathode. The arc is transiently generated, and its life time is approximately 3 ms for a series resistance of 1 Ω and a dc output of 33 V. The life is prolonged and the plasma becomes stable with increasing the arc current. A target with a diameter of 100 mm is set at 150 mm from the arc source, and is immersed in the plasma. A pulse voltage is applied to the target to extract ions from the plasma. The ion current is not detected after approximately 8 ms since the plasma initiation. When the plasma is generated in oxygen without argon, the plasma generation time is scattered, and the plasma is unstable. An ion density is estimated from the temporal behavior of the target voltage in the recovery region after the pulse voltage. The ion density at the target is approximately 2.5 × 10¹⁵ m^− 3 at a mixed gas pressure of 1.9 Pa, which corresponds to the plasma density of 1.1 × 10¹⁷ m^− 3 under an assumption of electron temperature of 1 eV.     

Nitrogen absorption phenomenon of GTA welding with nitrogen-mixed shielding gases: effect of plasma characteristics on nitrogen content in GTA welded metal

In order to clarify the nitrogen absorption mechanism in gas tungsten arc welding, the measurement of the weld metal nitrogen content under nitrogen mixture shielding gases, and the numerical analysis of plasma heat source characteristics in nitrogen dissociation phenomenon were conducted. The nitrogen content of weld metal produced by He arc reduces to approximately a half relative to that by Ar arc in the shielding gas condition of less than about 1% mixture ratio. Additionally, it is assumed that a decline in the plasma temperature in the vicinity of the molten pools due to the generation of metal vapour, accompanied by a reduction in atom-like nitrogen content, cause intense impact on the reduction mechanism of weld metal nitrogen content in a He arc.     

Arc plasma nitriding of graphite surface towards production of a hard carbon nitride case

Electrode grade graphite substrates were exposed in a nitrogen plasma produced in a pot type 35 kW dc extended arc furnace/reactor operating in non-transferred mode. Different gas (Ar, N₂, H₂) configurations were employed to nitride graphite for 15-20 min in the thermal plasma. Characterization of the plasma-nitrided graphite surface made by XRD revealed the presence of carbon nitride in a mixed form consisting of different phases. The 120-160 μm thick nitrided case exhibited enhanced microhardness values by more than 7 times. XPS studies confirmed the carbon and nitrogen bonding in the nitrided layer/case grown on surface. A comparison of morphologies between the un-nitrided and nitrided graphite surface showed a significant difference in the microstructure. Micro Raman spectra of the nitrided graphite surface showed further evidence of nitrogen incorporation and corroborate the XPS and SEM results. The new compound, carbon nitride, which was recently predicted from theoretical studies, is found to have been formed by the interaction between carbon (graphite) and nitrogen plasma due to a favourable free energy condition available in the high temperature plasma ambient.     

9Cr18轴承钢的金属离子加氮离子复合注入处理新工艺

简单地叙述了金属等离子体浸没离子注入与沉积（ＭｅＰⅢＤ）表面处理新工艺的发展,以及ＭｅＰⅢＤ工艺对于脉冲阴极弧金属等离子体源的要求。详细报导了９Ｃｒ１８轴承钢样品的氮离子注入表面处理工艺及金属离子加氮离子复合注入处理新工艺,对被处理和未被处理试样进行了显微硬度、磨痕、摩擦因数及腐蚀特性测试后表明：用金属离子加氮离子复合注入处理的９Ｃｒ１８钢试样的表面特性改善明显优于只有氮离子处理的试样,证明脉冲阴     

Plasma channel formation for triggering arc welding

Abstract

A method of starting arc welding using a plasma channel formed between electrodes in a tungsten inert gas arc welding system was demonstrated. The plasma channel was generated by gas breakdown in the laser beam path. In a previous study by the present authors, the arc welding could be started using a laser produced plume. Results in the present study indicated that the laser energy required to start the process using the plasma channel was lower than that using the plume.     

Phenomena in GTA and GHTA welding in Mars-like atmosphere

NASA is advancing the project of manned Mars exploration. In the future, Martian outposts and structures will be constructed. To realize this, welding technology is expected to be applied. The main atmospheric component of Mars is carbon dioxide, and the atmospheric pressure is approximately 700 Pa. In this study, welding experiments were carried out in a simulated Mars atmosphere of 99.5% carbon dioxide and a pressure of 700 Pa. Conventional gas tungsten arc (GTA) welding and gas hollow tungsten arc (GHTA) welding, in which arc operating gas is allowed only to flow out from the electrode tip of a hollow tungsten electrode, were investigated. The arc discharge behaviour and the melting characteristics in the simulated Mars atmosphere were studied. As a result, it was shown that GTA welding and GHTA welding might be applicable even in the Mars atmosphere.     

铝合金Plasma-GMAW-P复合焊接电弧特性及熔滴过渡行为

研究了Plasma-GMAW复合焊接过程中的电弧特性以及熔滴过渡行为。结果表明,不同电流的等离子弧通过改变GMAW电弧的导电以及受力状态来影响GMAW电弧形态以及熔滴过渡行为。等离子弧电流较小时,GMAW电弧的等离子流效应对GMAW电弧形态影响显著,基值时期的GMAW电弧基本沿焊丝轴线燃弧,峰值时期由于在焊接方向上同时受到方向相反的2个力而被压缩,熔滴所受的等离子流力以及等离子流力垂直向下的分力因此增加,对熔滴过渡的促进作用增强,熔滴更易从焊丝脱落。等离子弧电流增加,氛围中金属蒸气增多,电荷流效应对GMAW电弧的影响增强,基值时期GMAW电弧偏向等离子弧方向燃弧,由于焊接电弧存在热惯性,MIG电弧在峰值时仍偏向等离子弧,熔滴所受等离子流力垂直向下的分力因此减小,熔滴脱离焊丝的时间增加。     

加氮对直流电弧等离子体喷射金刚石膜显微组织和断裂强度的影响

利用DcArcP1asmaJetcVD法制备搀杂氮的金刚石厚膜。研究了在反应气体cH。／Ar／H：中加入N!对金刚石膜显微组织和力学性能的影响。在固定H2、Ar、CH4流量的情况下改变N2的流量，即反应气体中氮原子和碳原子的变化比例(N／C比，范围从0．06～0．68)，同时在固定的腔体压力(4kPa)和衬底温度(800℃)下进行金刚石膜生长。用扫描电镜(SEM)观察金刚石膜形貌、用X射线衍射表征晶体取向，用三点弯曲的方法来测量金刚石膜的断裂强度。结果表明，氮气在反应气体中的大量加入，对直流等离子体喷射制备金刚石膜的显微组织和力学性能有显著的影响。     

不同电场环境对镀料脱靶方式及TiN镀层微观结构的影响

当前主流的镀层沉积技术中,电弧离子镀因镀料熔融喷溅脱靶致镀料中夹杂微米尺度高温颗粒,易使镀层表面粗糙和基体高温损伤;直流磁控溅射因镀料碰撞溅射脱靶致离化率低,易使镀层厚度不均和组织疏松。为解决以上技术缺点,依据气体放电等离子体物理学知识,采用新型阶梯式双级脉冲电场诱发阴极靶材与阳极腔体间气体微弧放电,依靠微弧放电后产生的高密度等离子体,增强Ar+对靶面的轰击动能和靶面产生的焦耳热,实现镀料由碰撞溅射脱靶向热发射脱靶的转变,并以此提高镀料的离化率,达到改善镀层结构的目的。实验结果表明：双级脉冲电场诱发的气体微弧放电呈现出耀眼白光,而靶面形貌则表现出高低起伏的凹坑和水流波纹,其靶面形貌不同于镀料碰撞溅射脱靶后的多边形凹坑,说明靶面局部区域的镀料以热发射方式脱靶。同时,在双级脉冲电场下制备的TiN镀层具有较为致密的组织结构,沉积速率可达51nm/min。     

等离子喷涂的电弧伏安特性

等离子弧的伏安特性决定电弧功率的大小,从而影响喷涂粒子的熔融状态,进而影响了涂层的质量。等离子喷涂过程电弧伏安特性受多种因素的影响。通过改变气体的种类和流量、喷嘴几何尺寸（孔径和压缩角）来研究这些因素对电弧伏安特性的影响。结果表明,电弧电压在一定范围内随着主气流量的增加而增加;氢气流量对电弧电压影响显著;氮气对电弧电压的影响比氩气大;在喷嘴总长度相同的情况下,电弧电压随着压缩角的增大而减小,随着孔径的减小而减小。     

Pulsed flash welding strips of nickel alloys

Summary

Type 329J1 duplex stainless steel was welded by gas tungsten arc welding in argon‐nitrogen mixed gas atmospheres. The tensile properties and microstructures of the weld metals were examined. The nitrogen content increases and the ferrite content decreases with increasing nitrogen partial pressure of the atmosphere. The ferrite content linearly decreases with an increasing nitrogen content. The tensile strength and elongation of the weld metal produced in the argon atmosphere are much lower than those of the base metal, but they increase with an increasing nitrogen content and approximate those of the base metal at around 0.4 mass% nitrogen content. The fractographs suggest that only the base metal and high‐nitrogen weld metal clearly show dimple patterns. The tensile‐tested base metal and high‐nitrogen weld metal have complex crack paths, whereas the other weld metals have relatively straight paths. The tensile properties of the weld metal are affected by the ferrite content and chromium nitride.     

Plasma Spraying of Copper by Hybrid Water-Gas DC Arc Plasma Torch

Water-stabilized DC arc plasma torches offer a good alternative to common plasma sources used for plasma spraying applications. Unique properties of the generated plasma are determined by a specific plasma torch construction. This article is focused on a study of the plasma spraying process performed by a hybrid torch WSP500^®-H, which combines two principles of arc stabilization—water vortex and gas flow. Spraying tests with copper powder have been carried out in a wide range of plasma torch parameters. First, analyses of particle in-flight behavior for various spraying conditions were done. After, particles were collected in liquid nitrogen, which enabled analyses of the particle in-flight oxidation. A series of spraying tests were carried out and coatings were analyzed for their microstructure, porosity, oxide content, mechanical, and thermal properties.     

小孔型等离子弧焊接条形气孔形成机理

等离子弧焊接中厚钢板时,常存在焊接工艺窗口窄问题. 在中厚不锈钢板小孔型等离子弧焊(keyhole plasma arc welding,K-PAW )中发现,离子气体流量较弱而使匙孔未打开,形成盲孔时,会在焊缝内产生平行于焊接方向的长条形气孔,形成条形气孔时,等离子弧形态发生明显变化,电弧面积增加且波动更为剧烈,出现向后的反射. 使用高速摄影装置研究了条形气孔的形成过程.结果表明,中厚板等离子弧焊中,条形气孔是在一定的焊接速度和较低的电弧能量下,熔池前壁倾角较大,等离子弧受熔池前壁反射作用冲击熔池后壁,使熔池后壁发生弯曲,并在一定的凝固条件下保留,产生平行长气孔. 对条形气孔的研究有助于为匙孔等离子弧焊接中匙孔形成条件及机制提供新认识.     

Effects of pressure on metal atom transport and plasma properties during arc ion plating of TiAlN

Arc ion plating is used to deposit titanium and aluminum nitrides as wear and corrosion resistant layers on the surface of steel tools. In this study, the deposition efficiency for the evaporated metal atoms in arc ion plating was obtained by a view factor solution for the collisionless transport and a diffusion solution for the continuum transport. In the diffusion solution, the deposition efficiency decreases rapidly with pressure. A global nitrogen plasma model with a set of simplified plasma chemistry was used to investigate the plasma properties at pressures ranging from several mTorr up to 50 mTorr. The results indicate that the electron temperature, the ratio of electric field to gas density, and the nitrogen atom density all decrease with increasing pressure, while the plasma density increases. Based on the combined considerations of deposition efficiency and effective ion bombardment of the films on the substrate, an operating pressure range from 20 to 30 mTorr is recommended for highly efficient (Ti, Al)N coating during film deposition.