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6369 |
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Wednesday, June 10, 2020, Hall G1 11:10 AM New Processes |
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Aerosol deposition of Ti3SiC2-MAX-Phase coatings |
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Andreas Elsenberg* / Helmut Schmidt University of the Federal Armed Forces, Germany Frank Gärtner / Helmut Schmidt University/ University of the Federal Armed Forces Hamburg, Germany Thomas Klassen/ Helmut Schmidt University/ University of the Federal Armed Forces Hamburg, Germany |
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The rather new material class of MAX-phases combines properties of covalent bonded, brittle ceramics with those of metals. The metallic properties as machinability and electrical conductivity are due to atomic metal layers in the crystallographic structure. The general formula Mn+1AXn describes the composition with M as an early transition metal (Ti, Zr, Cr,&), A as an A-group element (Si, Al,&) and X as carbon or nitrogen. For possible applications, particularly Al-, or Cr-based MAX-phases are claimed to guarantee good oxidation protection up to temperatures of more than 1100°C. Operating with liquid phase deposition, usual thermal spray processes result in oxidation of the MAX-phase material and the decomposition into less protective compounds. In contrast, kinetic spray methods as cold spraying (CS) or aerosol deposition (AD) have the potential to retain the original MAX-phase structure in the coating without oxidation. For the present study on aerosol deposition, the Ti3SiC2 MAX-phase was chosen as model system due to the availability of commercial powder and property data. The as received powder was milled to different nominal sizes. For revealing details on coating formation and possible bonding mechanisms, aerosol deposition experiments were performed for different particle size batches and varied process gas pressures. Microstructural analyses reveal, that coating formation preferably occurs for particle sizes smaller two microns. Using small particle sizes, crack-free, dense layers can be obtained. The individual deposition efficiencies for the particle different sizes, particularly the critical size below which deposition gets prominent, vary with process gas pressure. Detailed microstructural analyses of coatings and single impact phenomena by high resolution scanning electron microscopy reveal plastic deformation and fracture, both attributing to shape adaption to previous spray layers and probably bonding. In correlation to coating thickness or deposition efficiencies, respective results are used to discuss possible bonding mechanisms. |