Thermal behavior of B_4 Cparticles under plasma arc powder surfacing condition

ＴｈｅｒｍａｌｂｅｈａｖｉｏｒｏｆＢ_４Ｃｐａｒｔｉｃｌｅｓｕｎｄｅｒｐｌａｓｍａａｒｃｐｏｗｄｅｒｓｕｒｆａｃｉｎｇｃｏｎｄｉｔｉｏｎ￥ＷＡＮＧＸｉｂａｏ；ＺＨＡＮＧＷｅｎｙｕｅ；ＬＵＴｏｎｇｌｉａｎｄＰＥＮＧＪｉｅ（ＨｅｂｅｉＵｎｉｖｅｒｓｉｔｙ...     

Thermal behavior of B_4C particles under plasma arc powder surfacing condition

0InstructionCarbides.asavariesofadvancedcoatingmaterialsfortheirsuperhardnessandexcellentthenllalstabilizer,havebeenwidelyusedinplasmaspra}illgandlasercladdingprocess.andattractedmuchattentionl"ZI.Especially.theresearchpapersaboutmetalcarbidessuchasTiC.WC…     

The theoretical evaluation of powders transportation in plasma transferred-arc space under coaxial powder feeding condition

0ＩｎｔｒｏｄｕｃｔｉｏｎＧｅｎｅｒａｌｌｙ ,ｔｈｅｐｏｗｄｅｒｉｓｕｓｕａｌｌｙｃｏａｘｉａｌｌｙｆｅｄｉｎｔｏｔｈｅｍｅｌｔｉｎｇｐｏｏｌｂｙａｓｐｅｃｉａｌ ｄｅｓｉｇｎｅｄｐｏｗｄｅｒｆｅｅｄｅｒｄｕｒｉｎｇｔｈｅ ｐｌａｓｍａｔｒａｎｓｆｅｒｒｅｄ ａｒｃ (ＰＴＡ ) ｐｏｗｄｅｒｓｕｒｆａｃｅｄｅｐｏｓｉｔｉｎｇ ｐｒｏｃｅｓｓ.Ｔｈｅｐａｒｔｉｃｌｅｓ’ｔｈｅｒｍａｌｂｅｈａｖｉｏｒｓｕｃｈａｓｍｅｌｔｉｎｇ ,ｖａｐｏｒｉｚｉｎｇａｎｄｄｅｃｏｍｐｏｓｉｎｇｗｉｌｌａｆｆｅｃｔｔｈｅｓｕｒ…     

Study on behaviors of tungsten powders in radio frequency thermal plasma

This paper describes an investigational study of the spheroidization of refractory metal tungsten powders by radio frequency thermal plasma, with emphasis on the melting, solidification and growth behavior of the tungsten powder particles during the spheroidization process. The flight time and melting time of tungsten powder particles in the plasma were estimated, and the growth behavior of the tungsten powder particles was analyzed in detail by investigating the change in the average particle size before and after plasma spheroidization. The morphology and spheroidization rate were analyzed using field emission scanning electron microscopy. The flight time and melting time for tungsten powder particles with radius of 7.8 μm were calculated to be 9.3 ms and 2.9 ms, respectively. The change in powder particle size during the process showed that the growth of tungsten powder particles was mainly caused by the coalescence of droplets in the thermal plasma system. The experimental results demonstrated that the spheroidization rate can reach up to 95% under the operating conditions used in this work.     

Investigation on the deposition rate and the dilution ratio of plasma surface welding

A new kind of plasma technology with both high deposition rate and low dilution ratio was developed under the calculation and analysis of the arc flame characteristics of plasma arc, the kinematics behavior of powder and powder‘ s heating in the arc. Compared with normal plasma surfacing method, the idea using constricting nozzle with small orifice diameter, long plasma arc and increasing the distance from meeting point of the two beams of powder to workpiece , to achieve the goals of high deposition rate and low dilution ratio, was put forward here. In order to prove this idea, a set of experimental system was built up and obtained satisfied results including high deposition rate( more than 25kg/h)and low dilution ratio(less than 5% ). The success of this study offers a promising prospect for developing the powder plasma surface welding in China and may open a way to improve this technology further in efftciency and quality.     

新型大气长层流等离子体喷涂方法和研究进展

介绍了一种新型大气等离子喷涂方法,该方法采用特殊内通道结构的直流非转移电弧等离子发生器,可以直接在大气条件下获得长度100～1000 mm之间变化的等离子射流。在大气条件下,等离子射流的流动特性具有"长、直、准"的层流或类层流状态,工作时噪音小于80 dB。在工作参数范围内,等离子射流的长度在固定总气流量条件下可以随输出功率的增加而增长;射流的长度在固定输出功率的条件下随总气流量的增加而减小。当使用在大气等离子喷涂技术中时,会为飞行粉末颗粒带来超长的加热和加速过程。文中详细介绍了大气层流等离子喷涂技术的研究历史和研究现状,以及研究团队利用该新型技术制备的6种涂层的显微结构、颗粒的飞行和加热特点,并对比了目前其他大气等离子喷涂技术的结果。结果表明,文中介绍的方法在最低的输出功率和气流量条件下,为金属和陶瓷颗粒提供了超长的飞行和加热条件,表现为较低的颗粒飞行速度和超高的颗粒表面温度。可以在不同的射流长度或喷涂距离下,获得不同的颗粒熔化状态或涂层结构,并发现可以直接在大气条件下获得大规模气液共沉积的涂层。     

The performances of TiB2-contained iron-based coatings at high temperature

The TiB₂-contained composite Fe-B-C coatings are deposited by the plasma transferred-arc (PTA) powder surfacing process. The coating's thermal ability, arc ablation resistance and wear resistance at high temperature were analyzed. It is concluded that TiB₂-contained composite Fe-B-C coating having excellent wear resistance at 600 °C and tempering resistance at 900 °C. Furthermore, this coating can effectively resist the arc ablation (120 A arc currents) within 7 s.     

In-Flight Particle Measurement of Alkali-Free Glass Raw Materials in 12-Phase AC Arc Plasma

In-flight particle measurements of the surface temperature and velocity are important for understanding of melting behavior of glass particles during in-flight melting by multi-phase AC arc plasma. However, the use of optical pyrometry for particle surface temperature has inevitable uncertainties due to non-thermal emissions signals from the plasma plume. This work presents spectroscopic measurements of the non-thermal signals which were found to be caused mainly by the plasma emissions scattered by the particles and the radiation emitted by vapor. After that, the accuracy of thermal radiation measurement was estimated and surface temperature of in-flight glass particle was corrected.     

Mathematical modelling of Inconel 718 particles in HVOF thermal spraying

High velocity oxygen fuel (HVOF) thermal spray technology is able to produce very dense coating without over-heating powder particles. The quality of coating is directly related to the particle parameters such as velocity, temperature and state of melting or solidification. In order to obtain this particle data, mathematical models are developed to predict particle dynamic behaviour in a liquid fuelled high velocity oxy-fuel thermal spray gun. The particle transport equations are solved in a Lagrangian manner and coupled with the three-dimensional, chemically reacting, turbulent gas flow. The melting and solidification within particles as a result of heat exchange with the surrounding gas flow is solved numerically. The in-flight particle characteristics of Inconel 718 are studied and the effects of injection parameters on particle behavior are examined. The computational results show that the particles smaller than 10 μm undergo melting and solidification prior to impact while the particle larger than 20 μm never reach liquid state during the process.     

Thermo-physical processes in cerium nitrate precursor droplets injected into high temperature plasma

The thermo-physical phenomena inside a droplet during its flight in a thermal plasma flow have been modeled for SPPS processes using cerium nitrate precursor. The different thermo-physical stages encountered during droplets' flight include aerodynamic breakup, rapid vaporization of solvent and precipitation, internal pressurization with shell rupture and rapid heating of volumetrically precipitated ceramic particle. The effects of injection type (transverse versus axial) and initial size of the droplets on the final deposit layer microstructure have been studied. The results show that for axial injection the heating process is very rapid and smaller droplets (< 10 µm) undergo full pyrolization resulting in favorable microstructure. On the contrary for transverse injection the heating process is slower as the droplets are injected in the outer shear layer of plasma where the temperature and velocity both are much lower than the core of the plasma. The larger droplets (> 20 µm) have better chances of getting pyrolized in the case of transverse injection. It was also observed that the angle of trajectory of the droplets after primary (first) precipitation does not have much effect on the final microstructure.     

等离子堆焊Q235电解打壳锤头的组织和性能

采用等离子堆焊技术在Q235铝电解打壳锤头表面堆焊F40合金粉末熔覆层。利用扫描电镜、能谱仪和显微硬度计等分析等离子堆焊层的微观组织、微区成分和硬度分布。利用磨擦磨损仪对试样进行耐磨性测试,通过恒电位法评估堆焊层和基体的耐蚀性能。结果表明,堆焊层与基体形成了良好的冶金结合,堆焊层为典型的柱状晶组织。等离子堆焊层平均显微硬度为444HV0.1,为基体的2倍;耐磨性为基体的1.6倍;腐蚀速率Rcorr为3.524×10-4 mm/a,为基体的1/(4.2×104)。等离子堆焊后Q235钢材料的耐磨性、硬度和耐腐蚀性均有显著提高,有望提高电解铝打壳锤头的耐磨耐蚀性能。     

等离子弧粉末堆焊过程中粉末颗粒的输运行为

利用电弧物理和流体力学理论分析了等离子弧粉末堆焊过程中粉末材料在转移型等离子弧中的输运行为及其主要影响因素,并以铁基合金粉末和碳化硼粉末为例,具体计算了不同特征的粉末在不同堆焊参数下的弧柱中的输运速度分布及沿弧柱横截面上的粉通量分布.计算结果表明,堆焊粉末颗粒在等离子弧空间的流动速度要比等离子流速低得多;对于同一种粉末材料来说,粒径越小,其在等离子弧柱中越容易被加速,在弧柱中的平均流速也越大;粉末的质量密度对其流速的影响与粒径颇为相似,密度越小,粉末在弧柱中的加速度和平均速度就越大.理论计算结果还表明,在电流大于150A的转移型等离子弧柱中,粉末颗粒的轴向输运速度在弧横截面上呈"山峦形分布",电流越大,中心山谷就越深越大.     

Investigation of laser consolidation process for metal powder by two-color pyrometer and high-speed video camera

This paper deals with the measurement of surface temperature on metal powder during the laser consolidation process with two-color pyrometer. Additionally, the aspect of selective laser sintering (SLS) and selective laser melting (SLM) of metal powder is visualized with high speed video camera. As a result, the surface temperature during the laser irradiation was ranged 1520–1810 °C and the consolidation phenomena was classified according to the melting point of metal powder. The metal powder at the heating process cohered intermittently to the melt pool although the laser beam was continuously irradiated to the powder surface.     

Fe-Al金属间化合物对钢表面增强工艺参数的影响

进行了Q235钢表面的预制粉末覆层的等离子熔覆,研究了等离子熔覆工艺对熔覆层表面成形的影响,在此基础上得到了合适的熔覆工艺参数.进行了熔覆层组织的金相分析及熔覆层显微硬度测量与分析.结果表明,熔覆电流、焊枪摆动频率、熔覆速度的改变均能引起热输入的明显变化,影响熔覆层组织形态,基体熔化程度,以及界面的结合状态,进而影响熔覆层的耐磨性及耐腐蚀性.试验条件下的最佳熔覆工艺参数为熔覆电流130 A,熔覆速度5 cm/m in,焊枪摆动幅度4 mm,摆动频率0.4 Hz.     

Comparisons of particles thermal behavior between Fe-base alloy and boron carbide during plasma transferred-arc powder surfacing

0　IntroductionThepowder’sthermalbehaviorwhileittransferthroughplasmatransferred arc (PTA)spacemaybeoneofthemostinterestingquestionstothesurfacingpow der’smanufacturersandsurfacingengineersinthefieldofplasmatransferred arcparticlesurfacing .Theparti cle’sthermalbehaviorinPTAspacewillgreatlyaffectthedepositedlayers’structureandproperties,especialinthecaseofpowdermixture (metal ceramic)surfacingcondition[1] .Generally ,thepowderisusuallycoaxialfedintothemeltingpoolbyaspecial designedpartic…     

激光快速成形过程中粉末与熔池交互作用的数值模拟

建立了描述激光快速成形过程中气/粉两相流送粉、粉末与熔池交互作用及激光熔覆成形温度场的联合模型.采用有限单元生死技术模拟了熔池形成和自由界面形状演化及熔覆层的沉积过程:根据界面温度与粉末粒子动量损失状况模拟了熔池对粒子的捕捉以及工件对粉末的反射,并采用Lagrangian粒子追踪模型实现了对粉末颗粒的跟踪.在此基础上,模拟了激光快速成形过程中316L不锈钢粉末、激光与熔池的交互作用过程.计算结果与实验结果吻合.     

感应等离子体球化热喷涂粉体材料研究进展

介绍了传统非等离子体法制备球形粉体方法--雾化法和喷雾造粒法,分析了其在热喷涂球形粉体制备过程中存在的优势和局限性。综述了等离子球化技术在热喷涂粉体材料领域中的应用现状,并深入讨论了感应等离子体球化过程中不同的工艺条件对粉体球化率和形貌的影响:原料粉体状态决定了球化后粉体的平均粒径,降低粉体原始粒径可以提高熔融程度,粒径分布较窄的原始粉体有利于得到高球形度粉体;适当增大输入功率和工作气体流量,可降低细小颗粒的粘附现象;工作气体的种类会影响等离子焰炬的热焓值;送粉速率需要结合粉体性质择优选取。这些关键影响因素对热喷涂粉体性能的调控机制,以及深入认识等离子体作用条件下的热喷涂粉体球化机理,提供了有力的理论支撑。总结和展望了感应等离子球化技术在热喷涂陶瓷粉体材料制备中存在的问题和发展方向,感应等离子体球化技术作为制备高纯度、无污染热喷涂球形粉体材料的一种新技术,具有广阔的应用前景。     

Systematic Investigation on the Influence of Spray Parameters on the Mechanical Properties of Atmospheric Plasma-Sprayed YSZ Coatings

In the atmospheric plasma spray (APS) process, micro-sized ceramic powder is injected into a thermal plasma where it is rapidly heated and propelled toward the substrate. The coating formation is characterized by the subsequent impingement of a large number of more or less molten particles forming the so-called splats and eventually the coating. In this study, a systematic investigation on the influence of selected spray parameters on the coating microstructure and the coating properties was conducted. The investigation thereby comprised the coating porosity, the elastic modulus, and the residual stress evolution within the coating. The melting status of the particles at the impingement on the substrate in combination with the substrate surface condition is crucial for the coating formation. Single splats were collected on mirror-polished substrates for selected spray conditions and evaluated by identifying different types of splats (ideal, distorted, weakly bonded, and partially molten) and their relative fractions. In a previous study, these splat types were evaluated in terms of their effect on the above-mentioned coating properties. The particle melting status, which serves as a measure for the particle spreading behavior, was determined by in-flight particle temperature measurements and correlated to the coating properties. It was found that the gun power and the spray distance have a strong effect on the investigated coating properties, whereas the feed rate and the cooling show minor influence.     

等离子沉积直接成形传热传质与晶粒生长多尺度数值模拟

运用有限容积法(FVM)对等离子沉积直接成形(PDM)过程中的沉积层温度场、熔池液相流动场进行了数值模拟.采用水平集方法追踪液/气界面演变过程,采用焓孔隙率法处理固/液相变过程,并采用Monte Carlo(MC)方法模拟沉积温度载荷作用下成形件热影响区(HAZ)组织的晶粒长大过程.基于所提出的FVM-MC法耦合的宏/微观统一模型模拟了镍基高温合金K163薄壁零件PDM过程中沉积层HAZ晶粒的生长过程,预测了在重复热冲击作用下热影响区晶粒长大与转变过程.模拟结果表明,热冲击频率与温度幅值直接决定热成形件的组织形态;热扫描速度影响熔池液相流动与温度场分布,从而间接决定了成形件的最终晶粒尺寸与分布.随着热扫描速度的增加,成形件晶粒趋于细化.在保证粉末充分熔融条件下,提高热扫描速度可以细化HAZ的晶粒尺寸.     

Application of orthogonal design in the experiment of plasma arc powder surfacing technology

0　ＩｎｔｒｏｄｕｃｔｉｏｎＰｌａｓｍａａｒｃｐｏｗｄｅｒｓｕｒｆａｃｉｎｇｈａｓｔｈｅａｄｖａｎｔａｇｅｏｆｈｉｇｈｄｅｐｏｓｉｔｉｏｎｅｆｆｉｃｉｅｎｃｙ ,ｓｈａｌｌｏｗｆｕｓｉｏｎｄｅｐｔｈ ,ｃｏｎｃｅｎｔｒａｔｅｄｅｎｅｒｇｙａｎｄｈｉｇｈｐｒｏｄｕｃｔｉｖｉｔｙ ,ｓｏｉｔｈａｓｂｅｅｎａｐｐｌｉｅｄｓｕｃｃｅｓｓｆｕｌｌｙｉｎｍａｎｕｆａｃｔｕｒｉｎｇｉｎｄｕｓｔｒｙｓｕｃｈａｓｉｎｔｅｒｎａｌ ｃｏｍｂｕｓｔｉｏｎｅｎｇｉｎｅ ,ｖａｌｖｅ ,ｅｔｃ .,ａｎｄｈａｓｏｂｔａｉｎｅｄｇｏｏｄ…