Effect of Powder Mixture Composition on the Deposition Efficiency in Cold Spay: Modelling and Experimental Validation

In this paper, a new semiempirical probability model, allowing for prediction of the composition of multimaterial cold spray coating in dependence on the initial percentage of blend components, is developed and applied. The proposed modeling approach takes into account the deposition efficiencies and the particle sizes of each component of the spraying powder blend. The experimental validation using several Cu/Cr2C3NiCr mixtures with different percentages of copper and cermet powders showed that the simulation results were in a good agreement with the experimental data. It was demonstrated that the deposition efficiency of the Cr2C3NiCr cermet powder strongly decreased when its mass percentage in the Cu/Cr2C3NiCr mixture increased from 5% to 75%. It was also shown that the dependence of the Cr2C3NiCr content in the coating on the initial percentage in the blend was nonlinear and the standard rule of mixtures was not applicable for prediction of copper–cermet coating composition.

Comparison of Structure and Wear Properties of Fine-Structured WC-CoCr Coatings Deposited by HVOF and HVAF Spraying Processes

The aim of the work was to study the microstructure and wear properties of fine-structured HVOF and HVAF sprayed WC-10Co-4Cr coatings prepared from powder having submicron-sized tungsten carbides. The coatings were deposited by HVOF (High Velocity Oxygen Fuel) and HVAF (High Velocity Air Fuel) using propane as a fuel gas in both processes, and using oxygen or air as oxidizing gas for combustion, respectively. Nitrogen was used as carrier gas for the powder. Commercially available agglomerated and sintered cermet powder with main carbide sizes under 500 nm was used in this study. Scanning electron microscopy (SEM) and X-ray diffraction were performed in order to characterize the powder and the microstructures formed during the spraying processes. The microhardness HV0.3 of the coatings was investigated and the pin on disk test was used to determine the sliding wear behaviour. The rubber wheel abrasion test was performed in order to determine the abrasion wear resistance of the coatings.

New Integrated Cermet Powder Preparation and Consolidation Method–Ni-ZrO2 Case

A new integrated method for direct preparation of cermet materials is proposed consisting of a powder processing method allied to a special sintering step. The powder is obtained by mechanical alloying route where a specific morphologic design is searched to yield thin metal plated ceramic particles. These have the proper characteristics to engage the sintering by activated surface (SAS) consolidation method. The last is triggered by partial evaporation and reactive sintering of thin metal layers, therefore exposing high active surfaces with superior sinterability. Refractory sacrifice metal components are found to play an important role. The application of the integrated method to Ni-ZrO2 cermet with selected metal additives is investigated. Sintering temperatures can be reduced by more than 300°C for the same final density range. The resulted powders and pellets microstructures are analysed accordingly to the projected expected ones. The thermophysical and electrical properties measurements are performed for evaluate phases percolation.

YZrO2-Ni Cermet Processing by High Energy Milling

A new method for SOFC fuel cell anode preparation is proposed where the main difference lies over cermet powder processing by high energy milling. Yttria stabilized zirconia powder and metallic nickel undergo co-milling in a vibratory device employing zirconia bead media. Dispersed and homogeneous powders are therefore obtained. The material is pressed uniaxialy and sintered at 1350°C for 0,5 h in air and under argon and hydrogen. In the former case, partial nickel oxidation occurs before sintering leading to small shrinkage down to 2% and porosity about 38%. Linear shrinkages from 5 to 7% after sintering in both inert and reduced atmospheres were observed not demanding pore-former additives. Conventional YSZ, Ni and NiO powder mixtures were prepared for comparison purpose. The high energy milling process is able to reduce the starting sintering temperature by 130° C besides a higher densification compared to the simple mixtures YSZ+Ni. The excessive sintering and particle coalescence is absent in high energy milled material, where the metal is well dispersed and the microstructure is highly homogenous. The high energy milling process is a promising route to prepare with excellent performance anode materials for SOFC cells.