MANUFACTURING AND TESTING OF A NOVEL ADVANCED NiAl-BASE ALLOY FOR GAS TURBINE APPLICATIONS

摘要

A novel NiAl-base alloy has been developed for gas turbine applications. The alloy with nominal composition 45Ni, 45Al, 2.5Ta and 7.5Cr (in at.%, IP75 for short) has a NiAl matrix with precipitates of Laves phase and α-Cr. By different methods of processing, e.g. powder metallurgical processing, investment casting or hot forging, the distribution of these precipitates can be controlled, thus varying the mechanical properties of IP75 within a wide range. Compared to conventional Ni-based superalloys the alloy has lower density, higher thermal conductivity, higher melting point and excellent oxidation and corrosion resistance at least up to 1300°C. The coefficients of thermal expansion, the heat capacity and Young's modulus are comparable or slightly superior to those of the superalloys, and in contrast to Ni-base alloys IP75 exhibits excellent microstructural stability without marked coarsening or dissolution of second phases at temperatures up to 1400°C. The alloy has a higher strength and creep resistance above 1100°C than that of the superalloys, which is correlated with a poor ductility at room temperature. Methods have been established to produce the alloy by investment casting and powder metallurgy on an industrial scale. Various components have been produced and the material has been tested up to 1300°C including thermo-shock behaviour, long-time static and cyclic oxidation resistance, hot gas corrosion and creep properties. Possible applications are discussed.