The jet characteristics of supersonic plasma jet spraying (SPJS) system were studied. Comparison of jet property was made between conventional plasma spray system and SPJS system. The results showed that the characteristics of the SPJS system are superior to the latter system. The particles velocities in the range of 400~800 m/s are obtained for supersonic plasma jet guns with 4.5 mm diameter nozzles and 60 l /min total gas flow rates, SPJS operate about 36 KW. The particle velocity is more than two times as much as conventional plasma jet spraying. The supersonic plasma jet is much longer than that of the conventional torch. It can bring about improvement for flying powder heated and accelerated and also prolong spray distance.

The effect of argon carrier gas flow, ethanol- or water injection on the plasma-composition, -enthalpy and – temperature as well as on the entrainment from the ambient was investigated in comparison to the pure plasma condition of an Ar-H 2 -plasma. Additionally, the plasma gas flow rate and power levels were varied. The enthalpy, and thus the plasma temperature, as well as the composition and speed are determined by means of an enthalpy probe system. Spatial resolved data could be obtained by translating the torch via a robot so that a temperature and speed map shows the evolution of plasma features with increasing stand-off distance.

Despite the fact that plasma spraying has been a widely used technology over the past three decades, industries using this technology still need higher quality products. Presently, only a small degree of process control is used in most plasma spraying systems. Improved process control should lead to more consistent results and higher quality products. We discuss a relatively simple control scheme consisting of a microphone as a primary sensor and a fuzzy logic look-up model indicating the condition of the anode. Selected frequency peaks in the power spectrum of the microphone signal are analyzed online, and the results are correlated with an average jet length obtained from a series of high speed images. The jet length, in turn, is correlated with coating characteristics. A simple feedback control system is proposed which will counteract the negative effects of an eroded anode on coating quality.

The aim of this work is to better understand the build-up of thermal barrier coatings (TBC) on microtextured substrates, particularly the influence of geometry on the behavior of plasma jets in substrate boundary layers. Coatings produced by suspension plasma spraying served as an experimental reference for numerical analysis, which involved advanced turbulent flow and volumetric heat source modeling along with the use of commercial fluid flow software. Geometric and numerical models were used to simulate the generation of plasma inside the torch and the resulting plasma flow with its highly nonlinear thermophysical characteristics. This work opens the possibility of predicting feedstock particle movement and deposition, which is essential in understanding coating build-up mechanisms in general and the flow of fine particles on substrate surfaces in particular.

Conventional DC plasma torch designs lead to a circular cross-section of the emanating plasma jet. Consequently in surface treatment applications the plasma jet hits the substrate within a limited circular working area. Large scale workpieces therefore have to be scanned resulting in a time-consuming procedure. The innovative DC plasma torch system LARGE is characterized by the arrangement of the anode and the cathode opposite to each other on a common axis with a variable distance. The central body of the torch between the electrodes is divided into electrically insulated cascade plates. The plasma gas is injected perpendicular to the torch axis. Passing through the arc, the gas is transferred to the plasma state and leaves the torch laterally through a slit as a plasma jet with extended stripe width. The plasma torch LARGE is investigated by electrical, optical and enthalpy probe diagnostics. Shrouding the electrodes with an inert gas and feeding reactive gas mixtures as main plasma gas allow the torch to be used for plasma chemical reactions, too. Preliminary applications focus on preheating, surface modification of paper and plastic materials as well as on sterilization of nutrition packaging. The capability of plasma enhanced CVD is examined experimentally.

Mathematical and computer models of movement and heating of particles in low pressure conditions are developed. The mathematical models are based on the molecular-kinetics theory of gases. A program complex for computer realization of models is developed. It contains a built-in data base of temperature dependent properties of substances, system of processing and graphic visualization of simulation results. For verification of the developed models, computer simulation and experimental measurements of Al2O3 particle temperature and velocity are conducted. These materials were sprayed with Plasma-Technik equipment at pressure 60 mBar in argon. Particle velocity was measured with a special optical device, particle temperature was defined by intensity radiation method. It was established that the developed models are adequate to real process (error of 5-8 %) and may be used for study and improvement of VPS processes.

In this paper, spectroscopic and electrostatic probe measurements are made to examine the characteristics of a supersonic dc plasma jet near the surface of titanium plate during a nitriding treatment. The low-pressure nitriding process is done using a mixture of ammonia, nitrogen, and hydrogen gasses. Heating effects from the plasma are evaluated with nickel slug and thermocouple attached to the plate. The authors present the results of their study along with observations, insights, and suggestions on how to improve plasma nitriding processes. Paper includes a German-language abstract.

The present study is conducted to simulate the multi-component chemical reactions of a turbulent argon-hydrogen plasma jet flowing into the surrounding atmosphere under typical operating conditions. Based on the initial spraying process parameters, the temperature, velocity profiles and the basic chemical species at the nozzle exit are calculated, and then used for the boundary conditions of the next step, where the chemical reactions in the multicomponent plasma jet are calculated by employing the Eddy-Dissipation model and the Realizable k-ε turbulence model. As the result of the calculation, the distribution of the mole fractions of the products as well as the temperature and velocity distributions is discussed. The approach presented in this paper will be theoretically helpful to perform further analysis of the interaction between the plasma and the particles.

This work deals with a 3-D transient simulation of the air plasma spraying of ceramic powders using a C.F.D. commercial code ESTET v3.4 that has been adapted to thermal plasma conditions. The mathematical model computes the distribution of particle velocity, temperature, molten state and size at impact and predicts the heat transfer to the substrate by plasma jet and particles. It incorporates the conversion from electrical to thermal energy in the torch nozzle as well as coating formation on the substrate. It makes it possible to predict the shape of the coating footprint when the torch and the substrate are fixed. The projections of the model are compared with experimental results that involve flow characteristics, time-dependant particle behavior in the flow and heat flux to the substrate.

Plasma spraying using liquid feedstock makes it possible to produce thin coatings (< 100 µm) with more refined microstructures than in conventional plasma spraying. However, the low density of the feedstock droplets makes them very sensitive to the instantaneous characteristics of the fluctuating plasma jet at the location where they are injected. In this study the interactions between the fluctuating plasma jet and droplets are explored by using numerical simulations. The computations are based on a three-dimensional and time-dependent model of the plasma jet that couples the dynamic behavior of the arc inside the torch and the plasma jet issuing from the plasma torch. The turbulence that develops in the jet flow issuing in air is modeled by a Large Eddy Simulation model that computes the largest structures of the flow which carry most of the energy and momentum.

We present the results of an investigation of the effects of a travelling magnetic field (TMF) on the plasma flow using a commercial program package. The argon plasma generation in the electric arc and the Lorentz force induced by the TMF are simulated with specific equations, which are derived from the magnetofluiddynamic equations using appropriate simplifications. First calculations confirm the predicted effects.

In the Plasma Spray-Physical Vapor Deposition (PS-PVD) process, the vapor atom of feedstock material is one deposition unit of the columnar structure coating. It is reported that the gas phase may be transformed into cluster when the powder feeding rate increases from small to large or the sedimentation distance increases from a certain distance to another distance. In order to understanding the variation of vaporized coating material in free plasma jet, the gaseous material capacity of plasma jet must be fundamentally understood. In this work, the thermal characteristics of plasma were firstly measured by optical emission spectrometry (OES). The results show that the free plasma jet is in the local thermal equilibrium due to a typical electron number density from 2.1×1015 to 3.1×1015 cm -3 . In this condition, the temperature of gaseous zirconia can be equal to the plasma temperature. A model was developed to obtain the vapor pressure of gaseous ZrO 2 molecules as a two dimensional map of jet axis and radial position corresponding to different average plasma temperatures. The overall gaseous material capacity of free plasma jet was further established. At a position of plasma jet, clusters may form when the gaseous material exceeds local maximum gaseous material capacity.

The conditions of particle injection into the side of plasma jets play an important role in determining the microstructure and properties of sprayed deposits. However, few investigations have been carried out on this topic. The current work presents the results of an experimental and computational study of the influence of injector geometry and gas mass flow rate on particle dynamics at injector exit and in the plasma jet. Two injector geometries were tested: a straight tube and a curved tube with various radii of curvature. Zirconia powders with different particle size range and morphology were used. A possible size segregation effect in the injector was analyzed from the space distribution of particles collected on a stick tape. The spray pattern in the plasma jet was monitored from the thermal radiation emitted by particles. An analysis of the particle behavior in the injector and mixing of the carrier-gas flow with the plasma jet was carried out using a 3-D computational fluids dynamics code.

Plasma spraying process modeling is useful to understand physical phenomena and to decrease the number of experiments. In this paper, a study of the external plasma jet is proposed: the PHOENICS™ CFD code was used with a 2D axisymmetrical geometry and a standard K-ε turbulence model. In a first step, thermodynamic and transport properties were calculated from chemical equilibrium composition, thermodynamic derivatives and kinetic theory of gases. Local Thermodynamic Equilibrium (LTE) was assumed for both plasma and surrounding gases. The proposed numerical results were computed for comparison with temperature measurements realized by Brossa and Pfender in the case of an argon plasma jet discharging into air, using enthalpy probes. The predictions were found reasonably accurate. The influence of the surrounding gas nature was also verified as the validity of the parabolic assumption.

The preheating of metallic substrates before powder deposition in air plasma spraying improves the adhesion of oxide coatings, provided heating is performed with an optimal procedure to avoid a too high oxidation state of the surface. It means that the temperature level and heating time have to be monitored carefully. In these conditions a thin layer (<100 nm) of oxides is formed on the substrate surface, the resulting contact of the molten droplets impinging the hot substrate is excellent (R th <10 -7 m 2 .K/W) and the adhesion properties of coatings are enhanced. This paper is devoted to the study of the metallic surface. The substrate heating and thus oxidation are obtained with a d.c. Ar-H 2 plasma jet flowing in air of which the stand off distance is maintained at 100 mm. The parameters investigated are macroscopic surface temperature and heating time. The characterization of the oxide layers is achieved by Mossbauer spectroscopy, near grazing X-ray diffraction, near UV-Visible-near IR spectroscopy and specular reflection infrared spectroscopy. At the end of this paper an attempt will be made to correlate these characterizations to the splats microstructure and coatings adhesion.

A mathematical model of the impingement of a plasma jet on a flat structure is proposed. This model can be used to predict temperature and velocity fields in the jet and in the near substrate region, but also to estimate thermal exchanges at the surface of this substrate. Different options were tested concerning the modeling of the near wall region and results indicate that a boundary layer calculation is necessary to predict the energy flux transferred to the substrate with a good accuracy. Nevertheless, the influence of the presence of the substrate on temperature and velocity fields was found to be important only in the near substrate region, indicating that the flow fields calculated from free jet modeling are accurate over the major part of the domain.

The present study is conducted to clarify the magnetic control characteristics of a particle-laden plasma jet impinging on a substrate for the improvement of a low pressure plasma spraying process and its controllable optimization. The plasma jet is described by Eulerian approach and each injected particle is described by Lagrangian approach respectively taking into account the compressible effect, variable transport properties and plasma-particle interactions, coupled with the Maxwell's equations. The effects of the location of the applied radio-frequency electromagnetic field, and of the injected particle size on the particle trajectory, particle velocity and its phase change are clarified by numerical simulation. It is concluded that the particle trajectory is influenced effectively and the injected particle temperature can be controlled strongly by applying the radio-frequency electromagnetic field to the nozzle. The reasonable agreement of particle velocity between calculation and experiment is observed.

On the base of gases molecular and kinetic theory a mathematical model of interaction between powder particles and plasma jet is developed. Three-dimensional description of plasma forming gas density distribution as well as particle motion in the plasma jet are a characteristic property of the model. A software for practical realization of the mathematical model is created. Said software provides the possibility to investigate an effect of low-pressure plasma spraying parameters on particle velocity and coordinates in the plasma jet. Computer simulation of particle velocity for powders from aluminium and tungsten oxides in argon plasma under 60 Mbar is conducted. A "Plasma-Technik" VPS unit is used for testing the developed model. Particle velocity measurement is made by a specially developed optical-electronic unit.

A diameter of 30 mm polycrystalline diamond film has been deposited by magnet-enhanced DC plasma jet CVD. The diamond film was characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and surface profilograph. Results reveal that under the same depositing parameters, magnetic field can increase purity of diamond film, improve thickness uniformity of diamond film, but no influence on crystal perfection and size of microcrystal of diamond film. A discussion on magnetic effect is presented.

The covering of titanium implants by means gas-thermal spraying of hydroxyapatite powders is an actual scientific, technical and medical problem. Application of hydroxyapatite for these purposes is more preferable. However, the problem of its structural and cyclic strength under conditions of bioenvironment response determines of application areas of such coatings and reliability of them usage. Structure and phase composition of hydroxyapatite coating under plasma spraying on titanium substrates and their changing, caused as conditions of forming coating on its increasing, so and conditions of spraying an laminar and turbulent plasma streem were studied. Exact belief about the crystalline structure and phase composition of coating is obtained by methods electronic microscopy and X-ray analysis. Changing of coating structure after sintering in the vacuum and electron beam melting in the vacuum is discussed.