Abstract Pulsed plasma transferred arc surfacing is presently used in many industrial applications to make protective layers against corrosion, temperature exposition, and excessive wear. Increasing wear resistance is especially important in areas of industry where titanium alloys are used, such as aviation and cosmonautics, because the wear resistance of titanium alloys is often weak. One way to increase the wear resistance is to deposit or form a cermet with a titanium matrix (TMC) on the surface of the part. The present study deals with the fabrication and characterization of TMC based on B4C. TMC with B4C was formed by cofeeding Ti6Al4V and B4C powder into a melting pool. It has been found that the deposited, relatively thick layers have homogeneously dispersed B4C grains in the matrix. The deposits are metallurgically connected to the substrate - Ti6Al4V. The TMCs were investigated in terms of microstructure and chemical composition. Wear resistance was determined using the linear pin test.

Abstract Wire atomization processes used to make refractory and high temperature alloy powders are relatively expensive due to the cost of feedstock, energy, and gas. A new process based on Transferred Arc Wire Atomization technology, however, has the potential to overcome these problems. This paper introduces the innovative process which, in combination with hydrogen generation, presents new opportunities for several alloys that can be more easily processed by plasma wire atomization. The new approach shows promise to reduce both fixed and variable costs for certain refractory and high temperature materials.

Abstract In this paper, investigations into the improved wear behavior are carried out on Plasma Transferred Arc-coated sleeves and bushings from electroplating. Basically, Stellite 6 and Tribaloy 800 with WC, WC-Co, TiC, NbC, and chromium carbide are analyzed using X-ray diffractometry, SEM, and micro-hardness measurements. Changes in the microstructure during the respective solidification processes are discussed. Using pin-and-disk tests in Zn-0.18Al baths at 470 deg C, conclusions are drawn about the wear behavior and correlated with microstructure analyzes and hardness measurements. Paper includes a German-language abstract.

Abstract Plasma spraying with a transferred arc (PTAW process) in conjunction with the use of materials containing tungsten carbide is very economical because it helps to increase the service life of production equipment. This paper deals with applications in which a reduction in wear and tear could be successfully achieved under ambient conditions containing oil sands. An overview of the material testing and development of the layers used is given. The requirements for equipment for the extraction and processing of oil sands require continuous testing and constant further development of new materials and PTAW processing techniques. In the current competitive environment, these results are of critical importance to all industries that have severe abrasion and erosion problems and where downtime and maintenance costs are critical. Paper includes a German-language abstract.

Abstract The high velocity oxygen fuel process is a powerful tool to produce WC-based coatings with minimum carbide degradation through a limited temperature and a reduced time of interaction between the powder and the flame. WC-10Co-4Cr cermets have been modified by adding carbon-based materials to protect the WC phase from decarburization during the spraying process. The novel powders were made by ball milling and spray drying. The layers were characterized by means of SEM, X-ray diffractometer, microhardness, and wear tests. Structural properties were correlated with the wear behavior and the microhardness. In order to protect the WC-10Co-4Cr powder, this paper evaluates the effectiveness of the addition of a carbon-based material (graphite and amorphous carbon), as attempted by Moreau et Dallaire to protect TiC powders produced by plasma spraying. It discusses the effects resulting from the agglomeration process. Paper includes a German-language abstract.

Abstract Spectroscopic and electrostatic probe measurements were carried out to understand the plasma feature inside and outside a 10-kW-class direct-current arc plasma jet generator with a supersonic expansion nozzle. Ammonia and a mixture of nitrogen and hydrogen were used as the working gas. The NH3 and N2+3H2 plasmas in the throat were expected to be nearly in a temperature-equilibrium condition, although the plasmas in the expansion nozzle and in the downstream plume without substrate plates were in thermodynamical nonequilibrium states. As a result, the H-atom excitation temperature and the N2 rotational excitation temperature decreased from 7000-11000 K in the throat to about 4000 K and to 1000-1500 K, respectively, on the nozzle exit at 0.1-0.2 g/s, although the NH rotational temperature did not show an axial decrease even in the nozzle. On the other hand, each temperature was almost kept a small range in the downstream plume without substrate plates under an ambient pressure of 130 Pa except for the NH rotational temperature for NH, working gas, although in the case with a titanium plate the nonequilibrium plasma came to a temperature-equilibrium one as approaching the plate.

Abstract This paper compares two types of hydroxyapatite (HA) composite coatings, HA/Ti-6Al-4V and HA/Y-ZrO2. The powders used in the study were prepared using a slurry process then deposited by plasma spraying. The resulting coatings were characterized based on their microstructure, mechanical properties, and biocompatibility. Both composite coatings performed better than pure HA coatings in tensile adhesion and indentation tests. Testing also revealed that the HA/Y-ZrO2 coatings had favorable strength and fracture toughness and that the HA/Ti-6Al-4V coatings had good affinity to living tissue and sufficient mechanical strength.

Abstract A brief feasibility study was performed to produce thermal spray coatings using gas atomized powders of Cu47Ti34-xZr11Ni8Six, where x=0 and 1. These alloys have previously been shown to be capable of forming metallic glasses having thick (1-2 cm) cross sections because they can be cooled from the melt at relatively low cooling rates (e.g., 100-102Ks-1). The properties of these metallic glasses include high strength, high elasticity and high fracture toughness. Amorphous plasma arc sprayed coatings were produced which were close in composition to the starting powders, and exhibited comparable glass transition and crystallization behavior. The amorphous structure of the as-sprayed coatings was used as a source for forming a range of partially devitrified and fully crystallized structures. The average hardness of the coatings increased from around 6 GPa to near 10 GPa as the degree of crystallization increased.

Abstract Three actual applications of spray plume sensors for industrial coating operations are presented. Two of these are in the aeronautic industry and one in the automotive industry. Depending on the application, different types of sensors were used ranging from plume shape monitoring (particle trajectories) to full plume characterization including in-flight measurement of individual particle properties. In each case, the process monitoring scheme developed depended on the manufacturer's requirements as well as the nature of the information provided by the sensor. The significant differences in usage and working conditions compared to an R&D environment are examined. Advantages and drawbacks in each of the three situations are detailed. A tentative forecast of coming developments in this field is also given.

Abstract Impact performance of plasma spray coatings is usually evaluated by means of surface observation after impact action. As a matter of fact, the dynamic response characteristics of coatings in the course of impact action are also very important. In this paper, a method of response frequency spectrum analysis is developed for the impact evaluation of plasma spray coatings. An impact test machine, in which the impact load is generated by a pivot-rod-lever system, is specially designed, allowing both single impact test and repeated impact test. The frequency spectra of Cr2O3 ceramic coating and WC-Co17% alloy coating under single and repeated impact action are analyzed. The results show that there is an obvious relationship between the impact performance and the impact response frequency spectrum. Abrupt changes in the coating, such as appearance of surface cracks and surface damage, correspond the sudden changes of the response frequency spectrum.

Abstract Physical properties of coatings based on Fe-B, Fe-Ni-B, Fe-Cr-P-C, Fe-Ni-Si-B, Ni-P, Ni-Nb and Co-Fe-B-Si, deposited by the methods of flame, plasma-arc, and detonation spraying were investigated. The coatings have mostly the amorphous structure with the volume content of the amorphous phase equal to 75-95 %. Values of the distribution and temperature coefficients of electric resistance of the coatings, depending upon a method and conditions of spraying, as well as upon their treatment parameters, were determined. Comparative studies of these coatings and thin amorphous strips produced by the melt spinning method were conducted. The amorphous coatings of ferromagnetic iron and cobalt alloys are shown to be magnetically soft materials and are characterized by a high magnetic induction combined with a high magnetic permeability. As compared with the amorphous strips, Curie temperature of the amorphous ferromagnetic coatings is by 50-140 K higher and their anisotropy of magnetic properties is lower.

Abstract Electrodes play an important role in the plasma-spraying process and must be frequently replaced to ensure good coating properties. The purpose of this work was to assess the effect of different plasma gases and oxygen and humidity levels on electrode lifetime. The change in arc voltage over time was recorded during spraying, and the elapsed time for a 5V drop was taken as the electrode lifetime. It was found that variations in oxygen and humidity in Ar-H2 gas mixtures have a major effect on lifetime and that the use of SPRAL22 gas could extend electrode life by a factor of three to four. These and other results are discussed in the paper.

Abstract In dc plasma spray guns, the properties of the plasma forming gas largely control the characteristics of the plasma jet and the momentum and heat of the particles injected into the flow. This paper examines the effect of Ar-He-H2 mixtures on the dynamic and static behavior of plasma jets expressed in terms of arc voltage and gas velocity. Correlations between these parameters and operating variables (arc current, gas flow rate, volume composition) were established from a dimensional analysis and supported by the calculation of the thermodynamic and transport properties of the gas mixtures used in the study.

Abstract This paper presents a method for optimizing plasma spraying parameters based on statistical analysis and related models. The models presented account for particle velocity and plasma mass enthalpy and make it possible to study the influence of plasma properties on the deposition process.

Abstract 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.

Abstract The development of nuclear fusion reactors is presently considered to be the only possible answer to the world's increasing demand for energy, while respecting the environment. Nuclear fusion devices may be broadly divided into two main groups with distinctively different characteristics: magnetic confinement fusion (MCF) and inertial confinement fusion (ICF) reactors. Although the two nuclear fusion technologies show similarities in energy levels (as high as 3 J/cm2) and type of environment (high temperature plasmas) to be contained, the materials of choice for the protective shields (first wall in the ICF and deflectors in the MCF) differ significantly. In ICF reactors, multiple laser beams are used to ignite the fuel in single pulses. This process exposes the first wall to microshrapnel, unconverted light, x-rays, and neutrons. B4C is a low Z material that offers high depth x-ray absorption to minimize surface heating, is not activated by neutrons (will not become radioactive), and offers high hardness and vapour temperature. The long term operation envisioned within MCF reactors, where a continuous nuclear fusion of the fuel is sustained within the confinement of a magnetic field, favours the use of high Z materials, such as W, to protect the plasma exposed deflectors. The reason is a lower erosion rate and a shorter ionization distance in the plasma, which favours the redeposition of the sputtered atoms, both resulting in a lower contamination of the plasma. The production of the first wall and the deflector shields using solid B4C and W materials respectively, is obviously unthinkable. However, ProTeC has developed high density coatings for both ICF and MCF nuclear fusion reactors. W coatings with less than 2% porosity have been produced for both, the Tokamac MCF reactor and its Toroid Fueler. The toroid fueler is a plasma generating device designed to accelerate particles and inject them into the centre of the operating fusion reactor in order to refuel. For the application in an ICF reactor, B4C coatings exhibiting porosity levels below 3% with a hardness above 2500 HV have been deposited directly onto Al substrate. Properties such as outgassing, resistance to erosion and shrapnel, and the influence of x-rays have been studied and showed exceptional results.

Abstract Plasma transferred arc (PTA) welding is widely used in the petroleum and chemical industry to deposit nickel and cobalt-based materials on key parts for the purpose of surface modification. As test results show, the process improves corrosion, wear, and high-temperature resistance, prolonging the service life of components and equipment and reducing production costs.

Abstract A new family of spherical powders produced by the spray drying route has been developed. This paper describes as an example the manufacturing method of an Y2O3-coated aluminum powder. Atmospheric Plasma Spraying (APS) was used to test the corresponding coatings. Morphology and phases of powders and coatings were investigated by optical and scanning electron microscopy while the level of porosity was evaluated using image analysis. Results show that homogenous composite coatings can be obtained from cladded spray dried powders.

Abstract Dc plasma torches typically use a mixture of inert and molecular gases when spraying high melting powders. The addition of molecular gases increases the enthalpy of plasma jets, but it also produces arc root fluctuations that can cause variations in injected powders. This paper describes an innovative plasma torch system characterized by a long nozzle and three parallel cathodes. The nozzle consists of several electrically insulated rings and a ring-shaped anode. By adding more rings, the arc gap and voltage can be increased along with the enthalpy of the plasma jet. The results of various tests, comparing the spray rates and deposition efficiencies of new and conventional torches, are presented in the paper.

Abstract A composite was obtained by spraying ferromagnetic powder with a plasma arc torch onto an aluminum substrate. The influences of spraying conditions (substrate temperature, plasma gas composition, powder granulometry) on the efficiency of the induction heating by the composite are investigated.