Al+Y codeposition using EB-PVD method for improvement of high-temperature oxidation resistance of TiAl

An "Al + Y codeposition" on TiAl by the single EB-PVD method has been devel oped to improve the oxidation resistance of TiAl. To determine the optimum codeposition condition, the Al + Y codepositions with various ratios of Al and Y are evaluated through the isothermal and cyclic oxidation tests. The oxidation resistance of TiAl can be improved extensively by the AIS Y codep osition due to the formation of a gradient coating of Al and Y. The Al + Y codeposition with the ratio of Al:2Y for evaporation source material is pro ved to be the best. With a proper ratio of Al:Y, the Al + Y codeposition fo rms two distinctive layers of the oxides during high-temperature oxidation; Al2O3 in the inner layer and (Y, Al)O type oxide in the outer layer. In ad dition to the inner Al2O3 layer, the formation of the outer (Y, Al)O type o xide layer further improves the stability of the coatings. The stability of the Al + Y codeposition greatly depends upon the alloying element of TiAl substrate or oxidation resistance of the TiAl substrate alloy. The non-allo yed TiAl shows a poor coating stability, whereas TiAl-2.8Nb and Alloy K5 sh ow a good coating stability under severe thermal stresses during cyclic oxi dation since a stable Al2O3 can form on the surface of these alloys. (C) 19 99 Elsevier Science S.A. All rights reserved.