Investment casting of nozzle guide vanes from nickel-based superalloys: part I – thermal calibration and porosity prediction

Efrain Carreño-Morelli,Laura Maestro,Srdjan Milenkovic,Ole Koeser,Ilchat Sabirov,Agustín Jose Torroba,Javier Llorca,Loic Calba,Mehdi Rahimian

doi:10.1186/s40192-014-0025-5

Abstract

AbstractInvestment casting is the only commercially used technique for fabrication of nozzle guide vanes (NGVs), which are one of the most important structural parts of gas turbines. Manufacturing of NGVs has always been a challenging task due to their complex shape. This work focuses on development of a simulation tool for investment casting of a new generation NGV from MAR-M247 Ni-based superalloy. A thermal model is developed to predict thermal history during investment casting. Experimental casting trials of the NGV are carried out and the thermal history of metal, mold, and insulation wrap is recorded. Inverse modeling of the casting trials is used to define accurately some thermophysical parameters and boundary conditions of the thermal model. Based on the validated thermal model, another model is developed to predict porosity in the as-cast NGVs. The porosity predictions are in good agreement with the experimental results in the as-cast NGVs. The advantages and shortcomings of the developed modeling tool are discussed.

Highlights

Nozzle guide vanes (NGVs) are important structural parts of gas turbines [1]
The analysis of these results shows a good agreement between simulation predictions and experimental results in all zones
The highest level of porosity (≤2.91%) is predicted for the middle part of the solid vane and it is in quantitative agreement with the experimental shrinkage porosity of 3.07% in this area (Figure 8b and Table 3)

Summary

Introduction

Nozzle guide vanes (NGVs) are important structural parts of gas turbines [1]. NGVs are typically made from Ni-based superalloys because they have to withstand very high temperatures and aggressive environments [2]. Large improvements in turbine efficiency can be achieved with improved designs of the NGVs that normally lead to more complex shapes and thinner geometries These innovations are hindered by the complexity of the manufacturing process, which leads to an increasing number of defects (mainly porosity) during investment casting of parts with complex shapes and very thin elements. The development of investment casting routes for the new generation of NGVs is carried out via a ‘trial and error’ approach or, in other words, via experimental casting trials. This strategy is very expensive and time consuming and dramatically limits the rate of innovation

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Results

Conclusion