Effect of Processing Parameters and Shape of Blade on the Solidification of Single-Crystal CMSX-4 Ni-Based Superalloy

Dariusz Szeliga

doi:10.1007/s11663-018-1347-z

Abstract

The effect of mold withdrawal velocity, heater and pouring temperatures and the thickness of blade root on the solidification parameters and shape of the liquidus isotherm as well as microstructure of single-crystal CMSX-4 nickel-based superalloy, manufactured by the Bridgman method, has been analyzed in the article. The temperature gradient G, solidification rate v and location of the liquidus isotherm were determined in relation to the radiation baffle on the basis of temperature measurements conducted in nine test points along the height of castings (140 mm) with different thicknesses of root (27, 15 and 7 mm) and withdrawal velocities of 3 and 5 mm/min. The increase of root thickness, relative to the airfoil, resulted in the rise of inhomogeneity of solidification parameters as well as the primary dendrite arm spacing and unsteady state solidification along the whole blade height. However, in the case of blade with constant thickness, the steady-state solidification was created at the distance of 65 to 130 mm from its base. The increase of mold withdrawal velocity caused the decrease of temperature gradient. However, the solidification rate was different from the mold withdrawal velocity, especially in the root and middle part of the airfoil. The increase of heater temperature resulted in a rise of temperature gradient and reduction of the curvature of the liquidus isotherm, whereas the pouring temperature did not affect the solidification parameters in the blade. Particularly unfavorable conditions of the solidification process could occur in the middle part of the airfoil and root because of the lowest value of G/v and the largest primary dendrite arm spacing.

Highlights

THE development of turbine aircraft engines is focused on the improvement of their efficiency, which mainly depends on the temperature of exhaust gases before the turbine
Cooling the ceramic shell mold with liquid metal (LMC) makes increasing the withdrawal velocity and temperature gradient possible compared with the Bridgman method in which the cooling technique is performed by radiation in vacuum.[4]
Based on the analysis of research results, the following conclusions were drawn: 1. The solidification parameters were established along the blade height with variable thicknesses of the root and platforms

Summary

Introduction

THE development of turbine aircraft engines is focused on the improvement of their efficiency, which mainly depends on the temperature of exhaust gases before the turbine. Kubiak et al.[2] described Bridgman and liquid metal cooling (LMC) methods for the directional solidification of single-crystal turbine blades made of nickel superalloy, applied in the aircraft engines and industrial gas Manuscript submitted April 29, 2017. The manufacturing technique and value of the withdrawal velocity of the ceramic shell mold influence the parameters of the solidification process, i.e., the temperature gradient and solidification rates of casting, to a large extent.[3] Cooling the ceramic shell mold with liquid metal (LMC) makes increasing the withdrawal velocity and temperature gradient possible compared with the Bridgman method in which the cooling technique is performed by radiation in vacuum.[4] The temperature gradient, solidification and cooling rates determine the shape of the solid/liquid interface and microstructure of single-crystal castings.[5] An increase of the cooling rate leads to the favorable refinement of primary dendrite arm spacing and the decrease of eutectic islands (c+c’) and c’ precipitation as well as microsegregation, which result in the reduction of the duration and cost of the heat treatment process.[6]

Methods

Results

Conclusion