Tin coatings have been successfully applied to polymeric substrates by means of cold spraying. In this work, three low melting point powders, including Sn, Sn-Zn, and Sn-Bi, are cold sprayed onto various polymeric substrates and different combinations of gas temperature and pressure are assessed. Based on the results, the effect of melting points on the cold sprayability of feedstock powders is discussed.

In this work, metallic powders are applied to carbon fiber reinforced polymer (CFRP) substrates by low-pressure cold spraying. The coatings as well as the coating-substrate interfaces are characterized and the deposition mechanism is determined. It is shown that gas temperatures above 300°C are required for the continuous deposition of tin. These temperatures bring about partially melting, which facilitates adhesion. Accordingly, a “crack filling” mechanism is proposed to explain the deposition.

This study employs a combination of numerical analysis and experimental testing to obtain a better understanding of the changes that occur in hollow spherical metal-oxide powders during detonation spraying and how they affect coating quality. The heating and melting characteristics of hollow spheres are initially calculated for the general case then refined based on a simple detonation spraying model. The estimates are compared with experimental results obtained from detonation-sprayed Al 2 O 3 coatings produced using fused and crushed, dense spherical, and hollow spherical powders. The coatings as well as the powders are characterized based on morphology, particle size distribution, splat formation, cross-sectional microstructure, porosity, and hardness. Important findings, observations, and correlations are identified and discussed in the paper.

It is well known that the inlet temperature of the spray gas influences the impact velocity of particles which, in turn, affects the mechanical and chemical properties of the final coating. From cold spray of high- and-low-melting-point feedstock such as Cu-Sn, it was found that those effects can vary with changes in particle shape and size. Copper powder feedstocks with different shapes, such as and dendritic (under 25 μm), were selected for analysis. For spherical (under 10 μm) powders of Cu 6 Sn 5 , an intermetallic compound (IMC) of Cu-Sn was formed in the as-coated state at and above gas inlet temperatures of 100 °C. for A gas inlet temperature of at least 300 °C was needed for the dendritic Cu powders. As temperatures increase, another IMC, Cu3Sn, was also formed. The onset temperature for the formation of the additional IMC was 450 °C for both shapes. Below 300 °C, both Cu and Sn were in solid state and thermodynamic driving forces were drawn from impact energy. Therefore, the spherical particles had more stored energy (strains) than the dendritic particles to initiate IMC formation.

Laser Based Particle Visualization instruments such as SprayCam provide a unique picture into the radial injection of powders in APS processes. Traditional injection optimization methods utilizing these instruments involve optimization of particle temperature and velocity while measuring the particle plume position in the plasma. The goal of these optimization techniques is to ensure maximum energy transfer to materials with a high melting point and a low thermal conductivity, such as is typical for materials applied as thermal barrier coatings. Conversely, optimizing energy transfer of composite powders with a low melting point and a high thermal conductivity, such as Al-8Si-20BN, has very little effect, thus it is difficult to optimize the injection process of this material in the traditional fashion. In addition, these materials have a tendency to bounce off the plasma rather than penetrate it due to their low inertia, resulting in low deposition efficiencies. A new method of injection optimization of these powders is proposed utilizing Laser Based Particle Visualization Techniques to view the injection from above in order to maximize powder injection into the plasma. A real-time examination of particle plume width inside the plasma will be conducted, varying an array of torch conditions while deposition efficiency is monitored.

Metallization of plastics by thermal spraying is studied. The possibility to obtain high adhesion of metal particles to the surface of a wide range of plastic materials is shown. Powders are sprayed with a new generation detonation gun “Dragon” designed at Lavrentyev Institute of Hydrodynamics SB RAS. The apparatus is characterized by a high-precision gas supply system and a dosed localized powder feeding system. Computer control provides a flexible programmed readjustment of the detonation gases energy impact on powder particles which is a key factor in precision control of spraying parameters for low-melting point powder materials. It is found that under certain spraying conditions molten particles of a low-melting point material not only do not provoke erosion of plastic material at their high velocity impact on the substrate but strong-bond fusion, sufficient to further form a thick coating, occurs. Aluminium, zinc and tin powders are sprayed on substrates from fibreglass, polyester, fluoroplastic and some other plastics. Load capacity of the obtained coatings reaches 100 kg/cm 2 . It is shown that on top of a thin layer from a low-melting point powder material high-melting point metals and even ceramics can be deposited.

Recently, the thermal spray community has focused considerable attention on Cold Spray and Warm Spray techniques, in which the temperatures of sprayed particles are kept under the melting points and adhesion occurs based on the impact phenomenon between a solid particle and a substrate. The mechanisms of adhesion are still unclear but the degree of the mechanical deformation at the interface is considered to be one key factor. However, it is very difficult to directly measure the strain at the interface. Instead, in this work, the strain fields on a substrate around an impacted particle were measured by applying Electron Moiré method, and corresponded to the spray conditions by a warm spray deposition.

When describing the cold spray process, one of the most widely used concepts is the critical velocity. Current models predicting critical velocities take the temperature of the sprayed particles explicitly into account but not the surface temperature (substrate or already deposited layers) on which the particle impact. This surface temperature is expected to play an important role since the deformation process leading to particle bonding and coating formation takes place both on the particle and the substrate side. The aim of this work is to investigate the effect of the substrate temperature on the coating formation process. Experiments were performed using aluminum, zinc and tin powders as coating materials. These materials have a rather large difference in critical velocities that gives the possibility to cover a broad range of deposition velocity to critical velocity ratio using commercial low pressure cold spray system. The sample surface was heated and the temperature was varied from room temperature to a high fraction of the melting point of the coating material for all three materials. The change in temperature of the substrate during the deposition process was measured by means of a high speed IR camera. The coating formation was investigated as a function of (1) the measured surface temperature of the substrate during deposition, (2) the gun transverse speed and (3) the particle velocity. Both single particle impact samples and thick coatings were produced and characterized. Both the particle-substrate and interparticle bondings were evaluated by SEM and confocal microscopy

This paper describes an arc spraying process developed for the production of metalized film capacitors. It discusses the role of metal spraying in capacitor manufacturing, the basics of thermal spraying, and the function of various components in a wire arc spraying system. It also reviews the production steps typically used for capacitor end spray. Paper includes a German-language abstract.

A large expansion of the applicability of thermally sprayed coatings will be achieved, if there is success in tailoring the coatings structure. This is particularly necessary for functional coatings with special electrochemical or electromechanical properties. The coating structure is determined by the solidification of the sprayed particles on the substrate respectively the earlier deposited particles. In addition to the particle parameters - particle size, velocity, degree of melting and temperature of the melt, the substrate surface conditions - roughness, temperature, activity - influence the spreading and subsequently the solidification of the particles and the formation of the coating. Theoretical parameter studies show the particular influence of the above mentioned parameters on the coatings microstructure. The influence of the remelting of deposited particles caused by the following particles is regarded. The amount of remelted volume depends on the particle feed rate, particle size distribution, heat content and substrate temperature. By controlling these parameters even directionally solidified coatings can be produced. The calculations are in good agreement with the experiments.

A numerical study was realized in order to simulate the plasma spraying of a Mo/NiCrBSi powder mixture under atmospheric conditions. The influence of the spray parameters on particles' in-flight characteristics was investigated numerically. The PHOENICS CFD code was used for the computation of the plasma jets and an in-house code was developed for the modeling of plasma/particles interactions. In view of the high melting temperature of Molybdenum and the presence of a self fluxing alloy like NiCrBSi, the state of the Mo particles prior to their impact on the substrate (velocity, temperature) was regarded as one of the major element influencing the quality of the produced coatings. Different spray parameters were considered: the plasma gas was an argon/hydrogen mixture with two different total flow rates and three different hydrogen fractions. Corresponding experiments are presented and appear to be consistent with numerical results.

Yttrium oxide-stabilized zirconium dioxide is mainly used in thermal barrier coatings. However, the desired higher gas inlet temperatures have initiated the search for novel materials. Low thermal conductivity and high melting points are important criteria for the selection of these materials. This paper investigates a zirconate material with a pyrochlore structure and a high melting point. In addition, it investigates the sintering behavior of the coatings at elevated temperatures. Dilatometer tests are carried out at 1200 deg C for at least 70 hours. For samples which had been annealed for 24 hours at 1250 deg C, the change in the porosity distribution is determined by means of mercury porosimetry. The paper presents the first results of thermal cycling tests on a plasma-sprayed coating. These first results are very promising. Paper includes a German-language abstract.