Arc Plasma Spraying Research Articles

A new design of a re-entrant cavity ionisation chamber for use in brachytherapy

A theoretical model has been developed for evaluating the response of re-entrant cavity ion chambers to various gamma energies from simple geometry considerations. The method involves evaluating the charge generated in a differential volume of the chamber and integrating this over the entire volume of the detector. The theory has been applied to two chambers (one having SS cavity wall and the other having Al cavity wall) developed earlier. The calculated and experimental sensitivities of the SS cavity chamber are 12.78 and 12.41±0.76 pA/MBq for 60Co. For the Al cavity chamber the sensitivity values for 125I are, respectively, 0.047 and 0.049±0.003 pA/MBq. The technique described above has been used to design and develop re-entrant cavity ionisation chambers for the assay of brachytherapy sources. The design provides adequate sensitivity to assay 37 MBq of 192Ir and good saturation at 150 V for 37 GBq of 60Co. The design ensures that the change in the chamber current remains within ±2.5% over a 120 mm long ‘sweet spot’. Since the outer housing of the chambers carries high voltage a special alumina–titania coating by plasma arc spray has been given to prevent electrical shock hazard to users. Two detectors have been developed: one with SS construction is filled with argon while the other one with aluminium construction is filled open to atmosphere. The two detectors have calculated sensitivity of 3.22 and 1.46 pA/MBq for 60Co. The corresponding experimental sensitivities are 3.3±0.2 and 1.42±0.085 pA/MBq, respectively.

On the ‘rocket’ effect during plasma arc spraying

A particle's surface is not heated uniformly during plasma arc spraying: the side of the surface that faces the torch is hotter than the opposite side. If the particle temperature is high enough for substantial evaporation to occur, the imbalance of the vapour pressure gives rise to a net recoil force accelerating the particle toward the substrate. Estimations show that if particle loss of mass due to evaporation , the suggested effect is as important for particle dynamics as aerodynamic drag. (M is the particle mass, Ud is the particle speed and is the speed of the evaporating atom, m is its mass, and T is the particle surface temperature.)

Research on Surface Quality Control of Moulds Formed by Plasma Arc Spraying

Rapid manufacturing moulds by plasma arc spraying is a new kind of plasma arc machining technology. This technology has many advantages. An experimental apparatus has been set up. The influence of some special factors on the surface quality of work moulds formed by plasma arc spraying have been analyzed and experimentally researched. The micro structure of the interface between master moulds and work moulds shows that work moulds copy geometrically master moulds very well after optimizing processing parameters. Some experimental samples by plasma arc spraying have been obtained. They show that the surface patterns of work moulds match with the ones of master molds very well.

Oxygen effects on glass formation of plasma arc sprayed Cu47Ti33Zr11Ni8Si1 surface coatings

Abstract A series of thermal spray experiments were performed to produce Cu 47 Ti 33 Zr 11 Ni 8 Si 1 coatings from gas atomized powders synthesized with oxygen contents ranging from 0.125 to 0.79 wt.%. The amount of oxygen increased with decreasing particle size, which suggests the oxide is present as a surface film. Surface coatings were deposited using plasma arc spraying (PAS) in air and in an argon environment within an environmental chamber. The amount of amorphous phase was estimated for the gas atomized powders and plasma arc sprayed coatings. Despite the rapid solidification occurring during these two processing methods, substantial devitrification occurs in the high oxygen content powders and their associated coatings. Coatings deposited in air exhibit significantly more devitrification than their counterparts produced in the controlled environment chamber.

Fluctuation Phenomenon Analysis of an Arc Plasma Spraying Jet

The effects of three factors, including the power supply, the arc behaviourin the arc channel and the fluid dynamic process of the jet, on a plasmaspraying jet have been experimentally detected by means of spectroscopicdiagnostic techniques. The fast Fourier transform method has been applied tothe analysis of the arc voltage and spectral line intensity of the jet. The threefactors have been studied and distinguished from each other.

プラズマ溶射Ｎｉ‐５０Ｃｒ皮膜の組織，物性および溶射条件の相関性

The Ni-50Cr coatings are prepared under different plasma spray conditions which are arranged according to the orthogonal experimental design method using three typical parameters of plasma arc current, Ar flow and spray distance in order to obtain the quantitative regression correlations between spray parameter and coating mechanical properties, and examine the relationship between the mechanical properties and microstructure features. The mechanical properties of sprayed Ni-Cr coatings are characterized by hardness, abrasive wear weight loss and erosion rates. The microstructure of the coatings is examined by optical and electron scanning microscopes. The porosity in the coating is quantitatively estimated from by the increase in Cr content of the coating after the impregnation of Cr2O3 into pores of the coating. The effects of spray parameters on the mechanical properties of the coating are discussed according to regression formulas systematically.The results evidently show that three typical parameters have significant inter-effects on the microstructure and properties of the Ni-Cr coatings. There are evident correlations among the hardness and abrasive wear resistance, and porosity for plasma sprayed Ni-Cr coatings. With the decrease in the porosity of the coating, the hardness and abrasive wear resistance of the Ni-Cr coating are increased. On the other hand, there are no correlations between erosion resistance and hardness, and porosity as well. It has been found that the abrasive wear occurs mainly by micro-cutting of abrasives while the erosion occurs mainly by the successive separation of flattened particles exposed to the surface which are subjected to the direct impact of erosive particles. Therefore, the abrasive wear resistance is primarily dependent on the density and hardness of the coating, while the erosion wear is mainly dependent on the condition of the cohesion between flattened particles. The results also revealed that the deposition of partially melted particles into the coating deteriorates the erosion resistance of the coating, especially at low impact angle.

Caracterización de recubrimientos de hidroxiapatita depositadas sobre la aleación Ti6Al7Nb a través de aspersión térmica a plasma

Hydroxyapatite (HA) coated onto titanium alloys by atmospheric plasma-arc spraying is a promising
 technique for improving biocompatibility of materials. The tissue adherence to the HA coating
 increases when compared to the provided by the natural environment of the human body.
 Hidroxyapatite coating applied to a Ti-6Al-7Nb alloy substrate by plasma spray was characterized
 morphologically via Scanning Electron Microscopy (SEM) and X-Ray diffraction. X-Ray diffraction
 results of the HA layer indicated the presence of crystalline HA, amorphous phase and another
 constituents, like tricalcium phosphate (TCP) and calcium oxide. However, after annealing at a
 temperature of 600oC there was recristalisation of the amorphous phase and transformation of some
 of the TCP to HA. SEM results revealed a lamellar morphology which is typical of plasma sprayed
 surfaces. The HA/alloy interface exhibited some irregularities, however these are not present in the
 majority of the interfacial area.

Active electronic devices fabricated by DC plasma arc spray process

Polycrystalline silicon of 300–400 Å average grain size has been deposited onto various substrate materials by DC plasma arc spraying. Both self-supporting sheets and adherent coatings have been made. These films have had their electronic properties partially characterized and have been found to retain, to a degree, the physical and electronic properties of the silicon source material. Rectifying barriers have been fabricated and photoconductivity modulation observed for M–S structures prepared on plasma-deposited silicon films using metallurgical grade starting material. In structures with layers of silicon deposited sequentially, using p- and n-type silicon source material, photocurrent response was observed. Laser scanning was used to study the photo-response.

Catalytic behavior of plasma-sprayed Al–Al2O3 coatings doped with metal oxides

Reactive plasma spraying of aluminum and Al(OH)3 powders with oxide additives, CuO and Cr2O3, was investigated. An arc-plasma spray gun was constructed with the injection of powders into the plasma torch both internally and externally. The spraying was done at atmospheric pressure in a working gas comprising an argon/air mixture. The resulting oxide-doped Al–Al2O3 coatings, which were 30–50μm thick, were investigated by X-ray diffraction and scanning electron microscopy. Their catalytic behavior was identified observing by the combustion effect of propane in a tube furnace.

Deposition of Al65Cu23Fe12 and Composite Quasicrystalline Pvd Thin Film Coatings

AbstractThin film coatings of Al-based quasicrystals were deposited by magnetron sputtering. Sputtering targets of Al65Cu23Fe12 and Al65Cu23Fe12+5v/o Fe-Al were prepared with plasma arc spraying by forming thick (∼5mm) coatings onto Cu substrates. By incorporating a controlled fraction of porosity and micro-cracks within the plasma sprayed target, cracking or delamination of the target during magnetron sputtering could be avoided. Compositions of the as-deposited PVD films were close to the sputtering target composition when the bias voltage was kept around –40V; higher bias voltages (e.g., -100 to -200V) lead to coatings that were deficient in Al. As-deposited coatings prepared with the lower bias voltage could be subsequently annealed at 700°C for two hours to yield a nearly single-phase icosahedral structure. After annealing, composite coatings indicate the presence of an Fe-Al phase along with the icosahedral phase.

Electrochemical Methods for Characterisation of Thermal Spray Corrosion Resistant Stainless Steel Coatings

The use of thermal spray stainless steel coatings for protection of low alloyed steels against different types of corrosion is limited due to high porosity levels and oxide inclusions. In this paper electrochemical methods like corrosion potential monitoring and cyclic voltammetry are reported to monitor the corrosion resistance of thermal spray coatings. The studied stainless steel AISI 316 coatings are deposited by arc spraying, plasma spraying or high velocity oxygen fuel (HVOF) spraying. The electrochemical tests are performed in a 0.5 M H2SO4 solution. It is found that none of the tested coatings had an electrochemical response equal to that of stainless steel alloy AISI 316. The results indicate that the HVOF coating has the highest corrosion resistance and the corrosion resistance of arc spray coatings can be improved by spraying in an inert argon atmosphere. The electrochemical response of the studied arc spray coatings is independent of substrate type (including the case of no substrate), indicating that the underlying alloy does not contribute to the corrosion process and only the coating itself is attacked. The HVOF coatings age rapidly in a 0.5 M H2SO4 solution. It is proposed that this is due to pore opening and pore widening.

Phase stability of MoSi2 in the C11b and C40 structures at high temperatures

Abstract The phase equilibrium of molybdenum disilicide in arc melt and plasma spray processed samples has been investigated in order to define the phase relationship between α -MoSi 2 (C11 b structure) and β -MoSi 2 (C40 structure) phases. The analysis of solidification microstructures and X-ray diffraction patterns of arc melt processed MoSi 2 -based alloys indicates solidification takes place by primary α -MoSi 2 . Retained β -MoSi 2 phase in plasma spray processed powders exhibits an irreversible transformation to α -MoSi 2 , at T ≈1110 K, with an exothermic enthalpy of transformation of Δ H β – α =0.9±0.1 kJ g-atom −1 atom during heating from room temperature at 0.5 K s −1 . The Mo–Si and MoSi 2 –TiSi 2 equilibria phase diagrams have been used to derive the upper bound of the metastable melting point of the β -MoSi 2 phase T β m ≈2299 K, which is below the experimentally measured melting point of MoSi 2 ( T m =2303 K). The phase stability analysis indicates that the β -MoSi 2 phase is a metastable phase relative to α -MoSi 2 at temperatures below the congruent melting point.

Domain structure of the arc-plasma sprayed Nd-Fe-B anisotropic permanent magnet

Magnets with anisotropic magnetic properties were prepared by the process of arc-plasma spraying of Nd-Fe-B powders onto copper substrates heated in the temperature range 500–800°C. Optimal magnetic properties were obtained in magnets with a domain structure consisting of a network of small islets of size less than 1 μm.

プラズマ溶射法によるＡｌ基複合材料の接合

Aluminum metal matrix composite welds have been produced by non-transferred plasma arc spraying of aluminum alloy powder containing SiC (Osprey powder). Almost no Al4C3 phase was observed in the sprayed deposit. However, the deposit contained excess soluble silicon because of pyrolysis of some SiC particulates. Heat treatment after spraying tends to improve the strength significantly, possibly by enhancing the bond between the substrate and the deposit and/or by improving the bonding between the particulates and the aluminum matrix, as well as by improving the deposit matrix itself. Hot isostatic pressing of the samples to eliminate porosity had only a small effect on the final strength of the joint.

Microstructure of plasma-sprayed YBa2Cu3Ox high-temperature superconductors

The arc plasma spraying process has been applied to deposit YBaCuO superconductors on to steel substrates. Detached, as-sprayed coatings were heat treated at 950 °C in air in order to restore superconductivity. Oxygen annealing at temperatures 400–500 °C has been used as the final stage in material preparation. The changes in the microstructure of the material during heat treatment have been followed with the aid of scanning electron and optical microscopy. The phase transformations resulting from heat treatment have been studied by differential thermal analysis and X-ray diffraction.

Plasma Arc Spraying of Ti-6Al-4V with Cu-Ni-In

The influence of atmosphere, current, voltage, and powder feed rate on the microstructure of air plasma sprayed Cu-Ni-In coatings has been investigated. The effect of substrate pretreatment by blasting with alumina grit on substrate-coating bonding was also studied. Air blasting with alumina at appropriate pressures produced surface roughness that enhanced bonding by allowing particles of Cu-Ni-In powder contacting the substrate surface to bond by a combination of mechanical interlocking, solidification forces, diffusion, and micro welding. Blasting also caused alumina particles to become embedded in the surface, causing local contamination. A logarithmic relationship was found between the kinetic energy of microthe alumina particles and substrate weight loss during blasting. Substrate-coating lap shear bond strength was found to increase with increasing alumina particle size in the range studied (24-220 mesh) and to reach a maximum at the air pressure corresponding to maximal surface roughness. Spraying parameters found to give optimal microstructural properties and microstructures are given.

Plasma-arc spray gun for surfacing parts of complex form

A plasma-arc spray gun (Fig. i) has been developed for surfacing of parts of complex configuration and also small diameter shafts with corrosion resistant materials. The gun is designed for axial delivery to the plasma arc of solid or powder wire up to 1.6 mm in diameter. The gun uses certain parts of a standard torch for argon-arc welding, which is made up of a UDG 501-1 unit (the nozzle holder i, coupling nut 2, and insulator 3). The copper plasma-forming nozzle is screwed into the nozzle holder using the thread on it. The nonconsumable copper electrode for welding with reverse polarity has a water cooling channel covered with a ring. The insulator 7 provides centering of the assembly for advance of the consumable electrode relative to the nonconsumable. The consumable electrode is advanced through the tip along the axis of the channel of the nonconsumable electrode and the nozzle. The water and argon are supplied through connections. The shaft is intended for fastening of the plasma gun to the delivery mechanism of the PDG 307 semiautomatic welding machine.

Low contact-resistivity junctions to ceramic superconductors

A report is presented on the development of a plasma-arc spray process for the application of low-resistivity silver contact junctions onto YBa/sub 2/Cu/sub 3/O/sub 7/ sintered ceramic materials. The contact resistances decrease montonically with decreasing temperature and are typically approximately 10/sup -8/ Omega -cm/sup 2/ at 75 K. I-V characteristics are linear up to a critical current density that agrees with that of the underlying superconducting material. Advantages over other contact methods include ease of application, absence of any postprocessing treatment, and applicability to large areas and arbitrary shapes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Plasma Spray Deposition Processes

The concept of plasma is central to many scientific and engineering disciplines—from the design of neon advertisement lights to fusion physics. Plasmas vary from low density, slight states of ionization (outer space) to dense, thermal plasmas (for extractive metallurgy). And plasmas are prominent in a wide range of deposition processes — from nonthermal plasma-activated processes to thermal plasmas, which have features of flames and which can spray-deposit an enormous variety of materials. The latter technique, arc plasma spraying (or simply, plasma spraying) is evolving rapidly as a way to deposit thick films (&gt;30 μm) and also freestanding forms.This article will review the technology of plasma spraying and how various scientific disciplines are contributing to both an understanding and improvement of this complex process.The plasma gun dates back to the 1950s, when it was introduced for the deposition of alloys and ceramics. Due to its high temperature flame it was quickly discovered that plasmas could be used for depositing refractory oxides as rocket nozzle liners or to fabricate missile nose cones. In the latter technique, the oxide (e.g., zirconia-based ceramics, spinel) was sprayed onto a mandrel and the deposited material was later removed as a free-standing form.The technique's versatility has attracted considerable industrial attention. Modern high performance machinery is commonly subjected to extremes of temperature and mechanical stress, to levels beyond the capabilities of present-day materials. It is becoming increasingly common to form coatings on such material surfaces to protect against high temperature corrosive media and to enhance mechanical wear and erosion resistance. Several thousand parts within an aircraft gas turbine engine have protective coatings, many of them plasma sprayed. In fact, plasma spraying has emerged as a major means to apply a wide range of materials on diverse substrates. The process can be readily carried out in air or in environmental chambers and requires very little substrate surface preparation. The rate of deposit buildup is rapid and the costs are sufficiently low to enable widening applications for an ever increasing variety of industries.

Catastrophic loss of superconductivity in ion-irradiated films of YBa2Cu3O7−δ

We have investigated the effects of low fluence (&amp;lt;1014 cm−2 ) 63 MeV H+ and 65 MeV He2+ irradiation of prototype thin films of YBa2Cu3O7−δ produced by a plasma-arc spray technique. The observed changes in the resistance versus temperature behavior are much more dramatic than that observed for films produced by other techniques and resembles qualitatively a bond percolation threshold. The radiation sensitivity of these plasma-arc spray films is concluded to be due to poor intergranular characteristics. This information is being used to modify the processing steps to improve the properties of films produced by this technique.