ON THE RELATION BETWEEN DENDRITE MICROHETEROGENEITY INDEX AND EFFECTIVE PARTITION COEFFICIENT OF ELEMENTS IN CREEP-RESISTING Ni-ALLOY BLADES

ON THE RELATION BETWEEN DENDRITE MICROHETEROGENEITY INDEX AND EFFECTIVE PARTITION COEFFICIENT OF ELEMENTS IN CREEP-RESISTING Ni-ALLOY BLADES

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The chemical microheterogeneity of elements in two cast blades of the first stage of a gas turbine was measured. The first blade was measured in as-cast state, the second one after operation. By means of an original method, the microheterogeneity indíces IH and the effective partition coefficients kef were established. Using a metallographic method, the interdendritic distances, 2L = 32,8 mikro m, of the creep-resisting nickel-alloy blades were measured. By means of the Brody-Flemings (BF) heterogeneity model and with the help of mathematical and statistical methods, a relation between the parameters IH and kef and parameter a = D /L2 of the BF model has been derived. Then the numerical values of parameter alfa from measured heterogeneity data (IH and kef) were calculated and a comparíson was made with literature data. By means of numerical values of parameter alfa it was possible: - to evaluate the relations among diffusion coefftcients D of element of nickel-based alloy (these elements can segregate eitlier in the liquid or in the solid state); - to appreciate the local solidification time 9~, - and to compare the parameters of as-cast and operated blades.

The chemical microheterogeneity of elements in two cast blades of the first stage of a gas turbine was measured. The first blade was measured in as-cast state, the second one after operation. By means of an original method, the microheterogeneity indíces IH and the effective partition coefficients kef were established. Using a metallographic method, the interdendritic distances, 2L = 32,8 mikro m, of the creep-resisting nickel-alloy blades were measured. By means of the Brody-Flemings (BF) heterogeneity model and with the help of mathematical and statistical methods, a relation between the parameters IH and kef and parameter a = D /L2 of the BF model has been derived. Then the numerical values of parameter alfa from measured heterogeneity data (IH and kef) were calculated and a comparíson was made with literature data. By means of numerical values of parameter alfa it was possible: - to evaluate the relations among diffusion coefftcients D of element of nickel-based alloy (these elements can segregate eitlier in the liquid or in the solid state); - to appreciate the local solidification time 9~, - and to compare the parameters of as-cast and operated blades.

microheterogeneity, partition coefficient, Ni-based alloy

DOBROVSKÁ, V., DOBROVSKÁ, J., PODRÁBSKÝ, T., STRÁNSKÝ, K.

01.04.2001

1335-1532

Acta Metallurgica Slovaca

7

1/2001

Slovenská republika

56

5