Simona Pospisilova, Tomas Podrabsky, Karel Stransky, Jana Dobrovska
2006 unpublished
The contribution deals with the chemical and structural heterogeneity of a creep resistant Ni-based alloy Inconel 713 LC and Inconel 738 LC. These materials belong to the cast poly-crystalline nickel super-alloys which are used for the production of circulating wheels of small combustion turbines for supplementary energetic units in aviation industry. In operational conditions of combustion turbines as part of turbo engines, blades of the circulating wheels are stressed in time, temperature and
more » ... stress variable cycles during the loading procedure. The blades are exposed to a series of degradation factors such as high-temperature corrosion, fatigue processes and creep during the operation. Measurement of the chemical microheterogeneity of elements was realized in as-cast state before and after exploitation. As microanalytical complex was applied JEOL JXA 8600/KEVEX Delta V Sesame and EDS. In the analysis of chemical microheterogeneity, the concentrations of Al, Ti, Cr, Ni, Zr, Nb, Mo were measured in 101 points of the structure. Then the indices of dentritic microheterogeneity I H were estimated. The redistribution of elements is discussed. Keywords: cast nickel alloy, chemical heterogeneity, mathematical-statistical analysis 1. INTRODUCTION Some materials, especially steels and nickel-based superalloys, solidify at the dendrits formation. Impurity segregation causes decrease of materials melting temperature. It sets up a negative thermal gradient. A tendency to balance the thermal gradient leads to the dendritic structure creation. Several elements segregate into dendritic zone and the rest to interdendritic zone. It causes a concentration heterogeneity. It also forms disequilibrium phases, enclosers or eutectic phases with low melting temperature. Interatomic bonds are weakened and it deteriorates mechanical and creep properties of mentioned alloys [1]. This paper aims to evaluate the dendritic heterogeneity and to measure the concentration sets of selected elements as found in the samples of INCONEL 713LC and 738LC. For details on the measurement methodology see literature [1-3]. To assess the dendritic heterogeneity and to determine the effective distribution coefficients of the elements, it was necessary to measure, in a defined manner, large concentration sets of the considered elements, in this case those encountered in the structurally suitable areas of the samples featuring the greatest possible measure of likeness [1-3, 6]. Data in following contribution were originally measured for another purpose for Inconel 713 LC and for Inconel 738 LC. Measurement methodology and expositions have a comparable features. And thus is possible trade off the mathematical-statistical results.