Research On NiCoCrAlY Suface Modified Layers Of The TiAl Based Alloy By Double Glow Plasma Surface Alloying Technique

The TiAl based alloy offer attractive properties such as low density, high specific strength andhigh elastic modulus. Its working temperature is closely up to Ni based alloy，while the density ofTiAl is a half of Ni based alloy. Therefore the TiAl based alloy is recognized as one of the promisinghigh temperature structural materials and used for a wide applications for example the advancedaerospace and automotive engine components. However，the key problems in the practical use of theTiAl based alloy are its poor wear resistance and high-temperature oxidation resistance.In order to improve wear resistance and high-temperature oxidation resistance of the TiAl basedalloy, NiCoCrAlY surface alloyed layer was formed on the surface of TiAl based alloy by doubleglow plasma surface alloying technique. The alloying elements, which are feeded to the surface of thesubstrate by mutual diffusion mechanisms, were distributed gradedly. So the alloy layer ismetallurgically bonded to the substrate without spalling. The double glow plasma surface alloyingtechnique became a new surface modification technology of the TiAl based alloy. The microstructure，composition and phase structure of the surface modified layers will be analyzed by means of OM、GDS、XRD and SEM respectively and the hardness、wear resistance(at room and elevatedtemperatures) and high-temperature oxidation resistance will be tested too.The results shows that (1) the better modified layers can be acquired under specificallytechnological parameters， the composition of the surface modified layer presented gradientdistributing from the surface to interior of the TiAl substrate，the modified layer is metallurgicallybonded to the TiAl substrate;(2) The hardness of the TiAl based alloy was double that of the TiAlsubstrate, and the alloy layer are proved to be beneficial to the wear resistance, which improve thewear resistance of the TiAl substrate.(3) in the oxidation test, a dense oxidation film is formed on thesurface of NiCoCrAlY surface alloyed layer, which remarkably improved the high temperatureanti-oxidation ability of the TiAl based alloy.