A new experimental/numerical method is proposed to measure the surface tension coefficient of high-melting-point materials. Regular surface tension measurement methods are basically limited by proper heating procedure and more importantly by materials used for containers. In the proposed method, radio frequency - Inductively Coupled Plasma (rf-ICP) is employed to melt materials. Dynamics of melting is photographed. The surface tension dominant phenomenon of melting is then numerically modeled. Interfacial tension, as the major parameters governing the dynamics of melt, is estimated by comparison between the theory and observation. The results for copper generally agree with those obtained in previous studies. Preliminary findings suggest promising application of the method for ceramics.

The suspension plasma spraying (SPS) technique implemented on DC plasma spray guns is a complex thermal spraying process. In order to gain a better understanding of this deposition technique a systematic “splat” study using a shutter mechanism and the line-scan test was conducted varying liquid feedstock properties (viscosity and surface tension) and injection parameters (stream velocity and mass-loading). Splat morphology revealed the degree of particle agglomeration within the droplet formed from the liquid/plasma interaction, as well as their impacting velocity and heating history. The droplet formation was correlated to the liquid feedstock injection velocity and its viscosity. A simple model was developed to explain the experimental results correlating suspension properties to suspension droplet fragmentation mechanism.

The very singular pore network architecture of thermal spray coating results from the combination of several phenomena occurring during the coating buildup process. Close pores, usually of large dimensions, result from stacking defaults when impinging particles spread onto previously deposited layers. Intra-lamellar cracks, perpendicular to the substrate surface, develop mostly in ceramic lamellae during solidification. Inter-lamellar cracks, parallel to the substrate surface, depend significantly from the surface tension characteristics during the particle spreading stage. One way or another, these characteristics are related to the processing parameters implemented to manufacture the coating and they significantly modify the coating characteristics, their cohesion, their compliance and their impermeability, among the most significant. Al 2 O 3 -TiO 2 (13% wt.) coatings were atmospheric plasma sprayed implementing several sets of processing parameters, among which power parameters (i.e., arc current intensity, plasmas gas flow rates, etc.), feedstock injection parameters (i.e., carrier gas flow rate, injector internal diameter, etc.) and environment parameters (i.e., spray angle, etc.) were varied. Pore contents were analyzed implementing image analysis. Pore network connectivity was analyzed implementing an electrochemical test: the higher the passivation potential of the substrate, the higher the coating pore network connectivity.

Aerosol Flame Spraying (A.F.S) combines the atomization of a colloidal suspension with the lateral injection of the aerosol in a flame. The aerosol droplets are partially dried when crossing the flame and deposited as a coating onto a substrate. The coating is then consolidated by a heat treatment. In this paper, a modeling of the trajectories, acceleration and vaporization of the droplets is presented. This model supposes that the droplets dry at a constant rate until they impact onto the substrate. It predicts the size and water content of droplets at impact. From these data and hydrodynamic properties (viscosity, surface tension, contact angle) of the suspensions, the morphology and size of the lamella deposited on the substrate can be determined by using classical impact models. A colloidal monoclinic zirconia suspension with a 60-nm particle diameter is used in this study. In spite of the complexity of the mixing of suspension spray and flame, and the diversity of the thermal histories of the droplets, the observation of the latter after impact shows that the results of the model are quite consistent with measurements.

Wetting between the spreading droplet and the substrate plays an important role in the droplet flattening because it affects not only the surface effects but also the contact thermal resistance at the splat-substrate interface which is an important parameter for the development of the coating structure. In this paper, analytical formulas are determined which show the influence of wetting phenomena on the thickness or the radius of the splash, on the pressure developed upon drop impact and on the splash porosity. An effect of surface tension on the flattening parameters is investigated. The results obtained show good agreement with the experimental data. Paper includes a German-language abstract.

This paper aims to measure the residual stresses of plasma sprayed oxide ceramic deposits using the X-ray diffraction method and measure the Young’s Modulus in specially designed four-point bend test device. Aluminum oxide and chromium oxide coatings are made with a water stabilized plasma spray gun. The paper analyzes the microstructure and the phase composition. The X-ray diffraction method is used to determine residual stresses on the layer surfaces. The same method is used for the local measurement of surface tensions in a four-point bending device built into an X-ray diffractometer. This device also enables the force applied and the specimen deflection to be measured. Effective modules of elasticity are determined from the gradient from load to deflection during bending. The results of the tension measurements and the values calculated from the applied force are compared. Paper includes a German-language abstract.