Environmental degradation of thermal barrier coatings (TBC) by molten deposits such as calcium magnesium alumino-silicates (CMAS) is one of the most vital factors resulting in the failure of thermal barrier coatings, while turbine engine inlet temperatures are kept increasing for higher fuel efficiency. A new phase composite ceramic had been developed and evaluated for the topcoat of a durable thermal barrier coating (TBC) system with low thermal conductivity property and improved erosion resistance. The present work is to continue the effort to exploring the behavior of CMAS resistance of the phase composite TBC at high temperatures. The effects of CMAS attack and thermal exposure on the TBC degradation were investigated in experimental runs. In addition, a YAG-modified layer over the top of the TBC was applied with the attempt to improve CMAS resistance of the TBC system. The evaluation of CMAS resistance was focused on the most important characteristics of coating microstructure, CMAS penetration, and failure mode and test condition factors. The mechanisms for the CMAS infiltration and the TBC damages were discussed based on the analyses of the CMAS corroded samples in details.

Casting molds in the aluminium industry show a short lifespan due to the high corrosiveness of aluminium melts and alternating thermal and mechanical loads. By using new materials, in example pseudoalloys containing tungsten, the lifetime of casting molds can be elongated up to hundredfold. Today, casting molds made of steel are state of the art. In spite of the advantages of pseudoalloys, high manufacturing cost and the increasing commodity price of tungsten prohibit the use of molds consisting of these progressive materials. By coating the standard steel molds with a FeNiW-layer, the excellent thermal and corrosive resistance of the pseudoalloy surface can be combined with minimal manufacturing costs. For present work steel substrates had been coated with FeNiW-pseudoalloys. Therefore, arc spraying and different deposit-welding methods (Laser, Plasma, TIG) had been compared. By modifying the machine parameter set, a smooth transition between substrate and coating was realized. Thermal and chemical resistance of the samples will be tested. In this paper first results are presented.

Thermoplastic Polyamide-11 powder coatings serve many industries – such as water handling, automotive, and appliances. This utility is based on the ability to simultaneously provide exceptional resistance to: corrosion, impact/abrasion, and numerous chemicals. Typically application is by traditional methods – electrostatic spray or fluidized bed dipping. The present work demonstrates for the first time that the flame spray method can produce Polyamide- 11 powder coatings very close in performance to those produced by traditional methods. The keys are proper substrate pre-heating, and flame conditions that minimize polymer degradation. Coatings performance, impact resistance, and molecular weight data are presented.

Plasma-sprayed ceramic coatings were deposited on refractory substrates to improve their chemical resistance to molten glass. Mullite, coarse and fine alumina powders were employed. Different layers with step-wise varying compositions were deposited in order to avoid dilatometric incompatibility troubles. In all the samples, the top coating consisted of plasma-sprayed fine alumina powders, to achieve low porosity and confer adequate chemical resistance, while mullite was used to match the low thermal expansion coefficient of the porous refractory substrates. The coatings were characterized by SEM, XRD, fracture toughness, abrasion resistance, thermal shock resistance and resistance to chemical attack. Since the overall thermo-mechanical and chemical behaviour is greatly affected by microstructural features, such as porosity amount, stacking sequence of layers and their composition, a FEM simulation of the thermo-mechanical properties (with particular regard to thermal stresses-induced cracking) has been conducted and compared to the experimental results.

A novel material has been used for plasma spraying by WSP. The material is composed of three main phases, namely corundum (aluminum oxide), baddeleyite (zirconium oxide), and glassy phase (silicon oxide). The material is a refractory and exhibits very high hardness, extremely high abrasion resistance, and chemical resistance. Conventionally, the material is fabricated by melt casting and machining. Cast tiles of the material were ground and sieved to obtain the right powder cut size for plasma spraying by water stabilized plasma torch (WSP). Both dense coatings and free standing parts were achieved with the new material, which sprays very well with WSP. Spraying parameters were varied and molten particles were monitored in flight by DPV 2000. The coatings exhibit very low porosity and high hardness. The as-sprayed material is mostly amorphous with some nanocrystalline grains of aluminum and zirconium oxide present. The phase composition of the as-sprayed material is thus different from that of the feedstock material, which is mostly crystalline with a small fraction of amorphous silica glass. The microstructure of the newly sprayed material was studied by electron microscopy (SEM, TEM) and is very complex. Upon annealing, the as-sprayed material crystallizes around 950ºC. This result and other thermal properties were measured by TMA and DTA. The ease of plasma spraying and the coating properties make this material a suitable candidate for many industrial applications.

Over the last years, interest in thermally sprayed polymer coatings has increased. They have excellent corrosion and chemical resistance properties. Unfortunately, they have some limited properties like scratch and wear resistance. Fillers can be a good solution to improve these properties. In the Thermal Spray Centre of Barcelona, blends of polyamide powder with different contents of boron and silicon nitride have been flame-sprayed and studied. Microstructural characterisation of the composite coatings has been done using Optic and Scanning Electron Microscopies. Wear resistance has been evaluated by means of Ball on Disk (ASTM G99-90) and Rubber Wheel (ASTM G65-91) tests. Salt Spray Fog tests (ASTM B117-90) have been performed in order to evaluate their corrosion resistance.

The system B-C-N contains the hardest known materials like diamond, cubic boron nitride and boron carbide, which also show excellent chemical resistance. The oxidation resistance is shifted to higher temperatures in comparison to pure diamond. But pure BCN coatings cannot be produced by conventional thermal spray processes, as the materials lack both a liquid phase and sufficient ductility to permit deposition. Conventional VPS equipment is successfully applied in Thermal Plasmajet CVD processes for high deposition rate synthesis of diamond coatings. The feasibility of SiCN or boron carbide synthesis by this method has also been proven. The use of liquid precursors results in outstanding deposition rates and improved operational safety. Methylized borazine is applied for synthesis of BCN coatings in thermal plasma jets. The use of single source precursors is advantageous with concern to the homogeneity of the coating forming species stoichiometry. For long-term storage cooling is necessary, but also under ambient conditions the precursor shows sufficient stability. Plasma gun nozzles with different diameter and design are applied and evaluated with concern to the resulting coating properties. Deposition rates of up to 1,500 µm/h have been achieved with homogeneous coating thickness and morphology on areas with 50 mm diameter. No porosity is detected in SEM investigations on cross sections and fracture surfaces show a fine columnar coating morphology. XRD investigations point at an amorphous structure. Only for very high substrate temperatures the formation of crystalline boron carbide B8C and h-BN or graphite phases is detected. Oxygen contamination results in boric acid formation and therefore has to be avoided carefully. During coating deposition on mild steel substrates the formation of boride and nitride reaction zones is observed. VPS sprayed nickel or molybdenum interlayers permit to inhibit the evolution of reaction zones. Thereby BCN coatings with thicknesses of up to 10 µm are deposited without local delamination. Space resolved emission spectroscopic analyses are carried out in order to detect coating forming and intermediate species. As Thermal Plasmajet CVD is a pure gas phase deposition process, the control of the space resolved emission permits easy process control.