Thermal behavior of B_4 Cparticles under plasma arc powder surfacing condition

The effect of plasma arc powder surfacing process on the amount of B4C particles in the coating and the thermal behavior of B4C particles in different surfacing stages has been investigated.The results showed that the feeding rate of B4C partiles is the most important factor affecting the amount of B4C particles in the surfacing coating among all the surfacing parameters,and the most part of B4C Particles in the coating is nto the remainders of original solid B4C particles,but the consolidation products of the unmelted liquid B4C globules in the pool.The results also showed that the B4C particles would not be melted in the plasma arc column, their melting process mainly takes place in the anode spot region on the surface of the pool when surfacing current is less than 200A.

Synthesis and Characterization of Nano-sized Boron Powder Prepared by Plasma Torch

Hydrogen thermal plasma jet was employed to prepare nano-sized boron powder with hydrogen reduction of BCI3. The maximum yield of nano-sized boron powders was about 50% with the operational conditions of H2/BCl3 of 4.5：1, total feed of 4.9 m3/h, and plasma power of 25 kW. The samples were analyzed by X-ray diffraction （XRD）, field emission scanning electron microscopy （FE-SEM）, and inductively coupled plasma - mass spectrometry （ICP-MS）, inductively coupled plasma - atomic emission spectrometry （ICP-AES）, inductive combustion infrared absorption （ICIA） and infrared thermal conductivity of oxygen and nitrogen analyzer （ITCA）. The results show that the boron powders have different crystal structures with higher dispersion and purity. The average diameter is about 50 nm, and the purity is 90.29% or so. This new technology can use simple process to produce high quality boron powders, and is feasible for industrial production.

Spheroidization of molybdenum powder by radio frequency thermal plasma

To control the morphology and particle size of dense spherical molybdenum powder prepared by radio frequency（RF） plasma from irregular molybdenum powder as a precursor, plasma process parameters were optimized in this paper. The effects of the carrier gas flow rate and molybdenum powder feeding rate on the shape and size of the final products were studied. The molybdenum powder morphology was examined using high-resolution scanning electron microscopy. The powder phases were analyzed by X-ray diffraction. The tap density and apparent density of the molybdenum powder were investigated using a Hall flow meter and a Scott volumeter. The optimal process parameters for the spherical molybdenum powder preparation are 50 g/min powder feeding rate and 0.6 m^3/h carrier gas rate. In addition, pure spherical molybdenum powder can be obtained from irregular powder, and the tap density is enhanced after plasma processing. The average size is reduced from 72 to 62 μm, and the tap density is increased from 2.7 to 6.2 g/cm^3. Therefore, RF plasma is a promising method for the preparation of high-density and high-purity spherical powders.

Research of precise pulse plasma arc powder welding technology of thin-walled inner hole parts

The inner hole parts played an oriented or supporting role in engineering machinery and equipment,which are prone to appear surface damages such as wear,strain and corrosion. The precise pulse plasma arc powder welding method is used for surface damage repairing of inner hole parts in this paper. The working principle and process of the technology are illustrated,and the microstructure and property of repairing layer by precise pulse plasma powder welding and CO2 gas shielded welding are tested and observed by microscope,micro hardness tester and X-ray residual stress tester etc. Results showed that the substrate deformation of thin-walled inner hole parts samples by precise pulse plasma powder welding is relatively small. The repair layer and substrate is metallurgical bonding,the transition zones( including fusion zone and heat affected zone) are relatively narrow and the welding quality is good. It showed that the thin-walled inner hole parts can be repaired by this technology and equipment.

Surface Treatment of Polypropylene Powders Using a Plasma Reactor with a Stirrer

A radio frequency argon plasma reactor with a stirrer was employed for the surface treatment of polypropylene （PP） powders. The changes in the superficial contact angle and the superficial composition of the un-treated and treated PP powders were analyzed by means of water contact angle （WCA） measurement, X-ray photoelectron spectroscopy （XPS） and attenuated total reflection Fourier transform infrared spectroscopy （ATR-FTIR）. The water contact angle changed from the original value of 130.2° before plasma treatment to the value of 73.6° after treatment for 5 minutes. With the increase in plasma treating time, there were a decrease in the water contact angle and an increase in the content of oxygen containing polar functional groups （i.e., C-O, C=O and O-C=O）. Both XPS and ATR-FTIR results indicated that the plasma treatment led to the formation of oxygen containing polar functional groups due to oxidation on the surface of the PP powders, and the trend of variation of the water contact angle with plasma treating time was related to the concentration of oxygen atom on the treated PP powders surface. Furthermore, the aging of the plasma-treated PP powders was investigated.

Study on the RF inductively coupled plasma spheroidization of refractory W and W-Ta alloy powders

Spherical powders with good flowability and high stacking density are mandatory for powder bed additive manufacturing. Nevertheless, the preparation of spherical refractory tungsten and tungsten alloy powders is a formidable task. In this paper, spherical refractory metal powders processed by high-energy stir ball milling and RF inductively coupled plasma were investigated. By utilizing the technical route, pure spherical tungsten powders were prepared successfully, the flowability increased from 10.7 s/50 g to 5.5 s/50 g and apparent density increased from 6.916 g cm-3 to 11.041 g cm-3. Alloying element tantalum can reduce the tendency to micro- crack during tungsten laser melting and rapid solidification process. Spherical W-6Ta （%wt） powders were prepared in this way, homogeneous dispersion of tantalum in a tungsten matrix occurred but a small amount of flake-like shape particles appeared after high-energy stir ball milling. The flake-like shape particles can hardly be spheroidized in subsequent RF inductively coupled plasma process, might result from the unique suspended state of flaky particles under complex electric and magnetic fields as well as plasma-particle heat exchange was different under various turbulence models. As a result, the flake-like shape particles cannot pass through the high-temperature area of thermal plasma torch and cannot be spheroidized properly.

Fabrication of Ti_2AlC by Spark Plasma Sintering from Elemental Powders and Thermodynamics Analysis of Ti-Al-C System

A ternary-layered carbide Ti2AlC material could be synthesized by spark plasma sintering（SPS） technology using elemental powder mixture of Ti, Al and active carbon. By means of XRD and SEM, phases were identified and microscopically evaluated. The experimental results show that the main phase in the product was fully crystallized Ti2AlC with small particle size when sintered at 1200℃. The synthesis temperature of SPS was 200-400℃ lower than that of hot pressing （HP） or hot isostatic pressing （HIP）. Through thermodynamics calculations, the mechanism of Ti2AlC was studied by calculating changes of Gibbs free energy of reactions.

SILICON NITRIDE POWDER SYNTHESIZED BY THERMAL PLASMA METHOD

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Estimation of plasma parameters in the process of micro-scale powder plastic and characteristics of its products

The temperature and density of plasma jets were estimated with a Boltzmann plot and Stark broadening of Ar I(696.54 nm) lines by optical emission spectroscopy(OES) in the process of plasma plastic, and the morphology and microstructure of tungsten(W) powders were investigated by scanning electron microscope(SEM) and x-ray Diffraction(XRD), respectively.The results show that the assumption of local thermodynamic equilibrium(LTE) was invalid at the end of the plasma jets, and earlier than this after the injection of tungsten powder. The temperature and electron density of the plasma jets were up to about T?=?6797 K with Qc?=?50 slpm and ne?=?1.05?×?1016 cm-3 with Qs?=?115 slpm at Z?=?60 mm, respectively, and both dropped rapidly with the injected tungsten powders of 20 μm. After the plasma plastic process,the spherical tungsten powders were prepared and there were some satellite particles on the surface of the spherical products. The tungsten powders were both composed of a single equilibrium α-W phase with a body centered cubic(bbc) crystal structure before and after plasma treatment.

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

The powders transportation in the plasma transferred-arc space during the coaxial powder-feeding surface depositing process was theoretical evaluated. The axial acceleration and velocity of various particles in the arc column were described. According to the results from theoretical calculations, it was found that: (1) The powder’s transporting velocity is much lower than the plasma fluid’s; (2) The powders axial transporting velocity presents “valley-shape distribution” along plasma arc column traverse section when surfacing current is greater than 100 A . When the arc current exceeding 100 A , the powders coming through the center field of arc column will transport slower than the powder through the outer-around field of arc column. It is in the field where the temperature is in the range of 9 000 K ～11 000 K that the particles can achieve its maximum axial acceleration in the argon plasma space. (3) For the given powder mass density, the smaller its size is, the greater its acceleration and the greater its averaged transporting velocity will be in the arc space; (4) For the given powder size, the greater its mass density is, the smaller its acceleration and averaged velocity will be in the arc space.

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

In this paper, the influence of plasma arc powder surfacing technical parameters on the property of layer is defined using the orthogonal design. By the orthogonal polynomial regression, when plasma arc powder surfacing is used on the surface of the X65 steel plate with the Fe-07 alloy powder, the optimum technical parameters are the following: I=180～190 A , G=41.5 g/min , v=102 mm/min , T_0=350 ℃ , Q_l=280 L/h , Q_s=400 L/h . Further, analysis of the cracking test data showed that the cracking preheat temperature is 350 ℃ .

Plasma-Chemical Synthesis of Oxide Powders Using Transformer-Coupled Discharge

An experimental investigation of transformer-coupled discharge in an Ar-O2 mixture with the addition of SICl4, TiCl4 and ZrCl4 has been carried out under the atmospheric pressure of plasma-forming gases. Discharge power and discharge heat losses have been determined, and the dispersion and phase composition of reaction products （oxide powders） has been analyzed with SEM and X-ray diffraction analysis. Investigations reveal the formation of ultrafine oxide powders in the case of vaporized chloride （SiCl4 and TiCl4） injecting into the transformer coupled discharge. In the case of fine powder （ZrCl4） injection, full oxidation was not observed and reaction products consisted of a mixture of ZrO2 and ZrOCl2. A conclusion has been made regarding the perspectives of using transformer-coupled discharge to produce ultrafine oxide powders.

Plasma preparation and low-temperature sintering of spherical TiC –Fe composite powder

A spherical Fe matrix composite powder containing a high volume fraction （82vo1%） of fine TiC reinforcement was produced using a novel process combining in situ synthesis and plasma techniques. The composite powder exhibited good sphericity and a dense structure, and the fine sub-micron TiC particles were homogeneously distributed in the α-Fe matrix. A TiC-Fe cermet was prepared from the as-prepared spherical composite powder using powder metallurgy at a low sintering temperature; the product exhibited a hardness of HRA 88.5 and a flexural strength of 1360 MPa. The grain size of the fine-grained TiC and special surface structure of the spherical powder played the key roles in the fabrication process.

Plasma-Chemical Synthesis of Nanosized Powders-Nitrides,Carbides,Oxides,Carbon Nanotubes and Fullerenes

In this article the plasma-chemical synthesis of nanosized powders （nitrides, car- bides, oxides, carbon nanotubes and fullerenes） is reviewed. Nanosized powders - nitrides, carbides, oxides, carbon nanotubes and fullerenes have been successfully produced using different techniques, technological apparatuses and conditions for their plasma-chemical synthesis.

Spark plasma sintering on mechanically activated W-Cu powders

Mechanically activated W-Cu powders were sintered by a spark plasma sinteringsystem (SPS) in order to develop a new process and improve the properties of the alloy. Propertiessuch as density and hardness were measured. The microstructures of the sintered W-Cu alloy sampleswere observed by SEM (scanning electron microscope). The results show that spark plasma sinteringcan obviously lower the sintering temperature and increase the density of the alloy. This processcan also improve the hardness of the alloy. SPS is an effective method to obtain W-Cu powders withhigh density and superior physical properties.

Plasma-induced Styrene Grafting onto the Surface of Polytetrafluoroethylene Powder for Proton Exchange Membrane Application

Low-temperature plasma treatment was adopted to graft styrene onto polytetrafluo- roethylene （PTFE） powder, which is widely used in the fabrication of proton exchange membrane （PEM）. The grafted PTFE powder was sulfonated in chlorosulfonic acid and fabricated into a membrane, which was used as inexpensive PEM material for a proton exchange membrane fuel cell （PEMFC）. Fourier transform infrared spectroscopy attenuated total reflection spectroscopy （FTIR-ATR） and X-ray photoelectron spectroscopy （XPS） analysis were used to characterize the structure of the sulfonated PTFE powder. The results showed that all the PTFE powders were successfully grafted by nitrogen plasma and then sulfonated under such experimental conditions. A scanning electron microscopy （SEM） image indicated that the fabricated membrane exhibits flat morphology and homogenous structure. The ion exchange capacity （IEC） of this kind of PEM was also investigated.

An investigation on plasma spraying with artificial bone powder and bonding characteristics of coating

Artificial bone powder is satisfactorily deposited onto the surface of synthetic metal arthrosis(Co-Cr-Mo) with plasma spraying process. Factors influencing the quality of coating are investigated. Bond of artificial bone powder coating sprayed with different parameters is measured. and the coatings are anlyzed with metallographic examination and electron probe analysis. Experiments show that artificial bone powder coating sprayed onto synthetic metal arthrosis with satisfactory bond strength can be obtained by manipulating plasma spraying.

Characterization of functionally graded ZrO_2 thermal barrier coatings sprayed by supersonic plasma spray with dual powder feed ports

The functionally graded thermal barrier coatings （FG-TBCs） with 80%ZrO2-13%CeO2-7%Y2O3 （C-YSZ）/NiCoCrAlY were prepared using a recently developed supersonic plasma spraying（S-PS） with dual powder feed ports system. The thermal shock experiment of FG-TBCs specimens was carried out by means of the automatic thermal cycle device, in which the samples were heated to 1200℃ by oxygen-acetylene flame jet then water-quenched to ambient temperature. The temperature—time curves of specimens and photographs can be watched on-line and recorded by a computer during the test. The results show that the totally 1mm-thick FG-TBCs have excellent thermal shock resistance due to the fact that the coatings have no any peeling-off after 200 thermal cycles. The microstructures and morphologies of FG-TBCs were characterized and analyzed by SEM.