In this study, an experimental approach to investigate basic dependencies on impact and bonding of agglomerated ceramic particles in cold spraying is presented. Single impact morphologies of ceramic particles obtained from wipe tests are correlated with data obtained from powder compression experiments with a modified nanoindenter. Different feedstock powders of agglomerated TiO 2 -nanoparticles were used and also partially heat treated. The powder shapes and sizes prior and after the compression tests were analyzed by confocal microscopy. The single particle impacts were characterized by SEM. Besides the expected influence of substrate material, substrate temperature, and spray conditions, the deformation and bonding of ceramic particles to metal substrates critically depend on the powder properties. To which degree particles fracture or contribute to layer formation upon the high-energy impact is highly correlated to their individual deformation behaviour in quasi-static compression tests.

Recently, an advanced technique was developed to fabricate sandwich structures for high temperature applications by depositing alloy 625 skins on Ni alloy foam core by thermal spraying. This study tries to utilize an analytical model to estimate the mechanical performance of these structures based on the mechanical properties of the constituents. The mechanical behavior of the Ni alloy foam is assessed via compression testing, while tensile tests are used in the case of the alloy coating. The flexural rigidity of the sandwich structure is calculated using analytical models and experimentally obtained elastic moduli of the alloy 625 coating and Ni alloy foam. The model is also used to calculate the flexural rigidity of sandwich samples with different skin thicknesses to check the accuracy of the model and to understand the effect of skin thickness on the predicted mechanical performance of sandwich structures. The effect of heat treatment on the mechanical behavior of sandwich structures is investigated as well.

Various methods of making metallic foams and sponges have been studied, although the materials have not yet been put to commercial use. For foams produced using powder metallurgy, this is largely due to the poor surface quality and limited wear resistance. With thermal spray coatings, however, the foams can be upgraded to lightweight composites with defined surfaces, high wear resistance, and significantly increased strength. In this paper, commercial aluminum foams with closed cells and a closed foaming skin are coated with metal and ceramic layers by means of electric arc and plasma spraying. The coated foams are characterized based on their microstructure and the results of uniaxial compression testing. Paper includes a German-language abstract.

Near-net-shape spray forming reduces the cost and complexity of fabricating certain types of structures. Although such components perform adequately as-sprayed, improvements achieved through alloying, thermal treatments, and additional coating steps are often worth pursuing. In tungsten components, for example, additions of rhenium, nickel, or iron can significantly improve material strength and ductility; thermal treatments such as heat treating and hot isostatic pressing can change and densify microstructures; and coating exposed surfaces can improve environmental compatibility. Such improvements in plasma spray formed refractory metal components are presented in this paper.

Pure copper thick deposits were vacuum plasma sprayed in such a way that several porosity levels were obtained. Mechanical compressive tests permitted to assess the mechanical behavior of these materials and to study the associated pore microstructural changes. A linear porosity level decrease was observed during the first stages of the compressive squeezing, until the stress reached a specific value corresponding to a transition between pore contraction and copper splats deformation. Stereological measurements showed that the pore squeezing was isotropic.

Functionally gradient composites were spray formed via vacuum plasma spray deposition using tungsten cylindrical substrates. Materials deposited included tungsten-hafnium alloys and M-2 tool steel. Some deposits included micro-laminate layering with hafiiium alloys sprayed within the tungsten-hafnium matrix. Vacuum plasma deposition was shown to provide a viable means of producing functionally gradient composites from tungsten base materials. This was determined both by microstructural characterization of deposit structures and by measuring the compressive properties of the materials. Compression testing of the W-Hf matrix composites demonstrated compression strength of 1,552 MPa (225 ksi). Compression strengths of the tungsten/steel composite averaged 1,068 MPa (155 ksi). Failure of the W-Hf samples occurred via fracture of the tungsten/hafnium matrix whereas the tungsten/steel composites failed within the wrought tungsten core.