Impact of Al2O3-40 wt.% TiO2 Feedstock Powder Characteristics on the Sprayability, Microstructure and Mechanical Properties of Plasma Sprayed Coatings

Atmospheric plasma sprayed (APS) Al2O3 TiO2 coatings have found a wide range of industrial application due to their favorable properties in combination with low costs and a high availability. However, the detailed effect of the phase composition and the element distribution of the feedstock powders on the coating properties and the spraying process has only crudely been investigated so far. Here the impact of aluminum titanate (Al2TiO5) on the microstructural features and mechanical properties of Al2O3 40 wt.% TiO2 APS coatings is demonstrated by investigating the detailed phase composition and the distribution of aluminum and titanium in three different fused and crushed feedstock powders and the respective coatings. Thereby, a direct influence of the Al2TiO5 on the deposition efficiency, the porosity, the elastic modulus, and the hardness of the coatings is revealed. In particular, the feedstock powder had a stronger effect on the coating properties than increasing the stand off distance from 150 to 350 mm. Furthermore, Al2TiO5 coatings were found to exhibit a strong texture. The obtained results emphasize the need for a more detailed specification of commercial Al2O3 TiO2 feedstock powders in terms of their phase composition and elemental homogeneity to ensure a high reliability of the coating process and ultimately the coating properties

Simulating permeabilities based on 3D image data of a layered nano-porous membrane

The macroscopic properties of materials are strongly influenced by their microstructure. Essential micro-structural information can be obtained from high-resolution 3D images, usually obtained by computed tomography. Here, a layered nano-porous ZrO2 Al2O3 membrane for fluid filtration is investigated, whose two finer layers can not be resolved properly by computed tomography. 3D image data of these structures are therefore obtained by the combination of focused ion beam sectioning and scanning electron microscopy. Reconstruction of porous structures from this type of image data and subsequent numerical simulation of flow properties within the reconstructed structure bear several sources of error. Using stochastic geometry models for the solid component, we examine more closely the error due to the typical anisotropic voxel setting as well as the error due to the also typical uneven sample shape

Aktivlöten von Kupfer mit Aluminiumnitrid- und Siliziumnitridkeramik. Tl.2

Copper-AlN- and copper-Si3N4-composites are used as substrates for semiconductor modules in power electronics. Silver-based active brazing alloys are used for the fabrication of composites from copper foils and nitride ceramics. In this study the mechanisms during active metal brazing (AMB) of aluminium nitride and silicon nitride in combination with copper foils were investigated. Therefore the melting process of the braze filler metal, the chemical interactions between the braze filler metal and the raw materials and the influence of the processing parameters were studied in detail using thermo analytic and microscopic methods. Additionally, the fabrication process was tested under close to production conditions and application like samples were fabricated. The combination of lab experiments with low volume productions in industrial relevant processing equipment ensures the transferability of the developed processing models from lab into production. An increase of the AMB process reliability and an associated quality improvement as well as a significant reduction of the rejection rate during fabrication was achieved by optimisation of the active brazing alloys and the processing conditions during the active metal brazing

Influence of Feedstock Powder Modification by Heat Treatments on the Properties of APS-Sprayed Al2O3-40% TiO2 Coatings27

The formation and decomposition of aluminum titanate (Al2TiO5, tialite) in feedstock powders and coatings of the binary Al2O3-TiO2 system are so far poorly understood. A commercial fused and crushed Al2O3-40%TiO2 powder was selected as the feedstock for the experimental series presented in this paper, as the composition is close to that of Al2TiO5. Part of that powder was heat-treated in air at 1150 and 1500 °C in order to modify the phase composition, while not influencing the particle size distribution and processability. The powders were analyzed by thermal analysis, XRD and FESEM including EDS of metallographically prepared cross sections. Only a maximum content of about 45 wt.% Al2TiO5 was possible to obtain with the heat treatment at 1500 °C due to inhomogeneous distribution of Al and Ti in the original powder. Coatings were prepared by plasma spraying using a TriplexPro-210 (Oerlikon Metco) with Ar-H2 and Ar-He plasma gas mixtures at plasma power levels of 41 and 48 kW. Coatings were studied by XRD, SEM including EDS linescans of metallographically prepared cross sections, and microhardness HV1. With the exception of the powder heat-treated at 1500 °C an Al2TiO5-Ti3O5 (tialite–anosovite) solid solution Al2−xTi1+xO5 instead of Al2TiO5 existed in the initial powder and the coatings