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Influence of manufacture conditions on the properties of CMSX-4 single crystal castings

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Single crystal turbine blades of the first turbine stages were casted of nickel and cobalt superalloys. Beginning of their production requires significant capital expenditure. It also causes many technological difficulties. Thus, it is essential to have suitable set of casting equipments, vacuum furnaces for the heat treatment and last but not least all the processing know-how. Therefore, only a few foundries are capable to manufacture such turbine blades. Mass production of these single crystal parts of an aircraft engines so far has not been implemented in Poland. The studies performed allow to realize a production technology for single crystal turbine blades casting in Research and Development Laboratory for Aerospace Materials of Rzeszów University of Technology. In practice, precise single crystal casts are obtained via directional crystallization with the use of a block starter and spiral grains selector in a ceramic mould. In the process of monocrystallization the ceramic mould is withdrawn from the heating zone of the furnace to grow the blade. The grains in the cast’s starter grow in a columnar way against their spiral selector. Only one grain survives during competitive growth in the spiral grain selector. The phenomenon of grains growth ‘competition’ is the basis for this process [1÷3]. A single crystal grain nucleus growing from the spiral selectors is the beginning of the single crystal crystallisation consisting in dendrites growth in three orthogonal crystallographic orientations [001]. The direction of [001] axis is parallel to single crystal’s growth axis [4÷10]. Intensive examinations of quality assessment methods were carried out in recent years for single crystal casts of a second generation[...]

Microstructural characterization of creep in the single crystal superalloy CMSX-4 DOI:10.15199/28.2017.1.3

  Blades and vanes structural components of turbine engines are processed to withstand high temperature during loading conditions of service, fulfilling high standards of quality control and safety for effective use. Therefore, characterization of mechanical properties, such as creep behaviour, are necessary for appropriate control procedures on prediction of exploitation lifetime. The materials mostly used in manufacturing of these components are single crystal nickel-base superalloys. Creep behaviour characterization, composed of creep-rupture tests, were performed on a single crystal rods made of CMSX-4 superalloy obtained at a withdrawal rate of 3 and 5 mm/min. Cylindrical rods were directly solidified in the [001] direction in an ALD Vacuum Technologies investment casting furnace (VIM-IC 2). Then, prepared specimens were tested in tensile creep under constant stress of 248 MPa at a temperature of 982°C. The longitudinal and cross sections from tested samples, were characterized by TEM and X-ray diffraction methods. It was found that all samples showed a similar rupture mechanism. The electron backscatter diffraction (EBSD) measurements showed that octahedral and cubic slip systems were present however, the critical stress was present on {111} planes. It was observed that the cubic slip has the highest calculated Schmid factor along the dendrite cores while the octahedral slip occurs through entire sample volume. Samples obtained at 5 mm/min possess a visible widening of coherent scattering regions as shown in inverse pole figures. The reason of these changes is the fact that higher rate has the greatest probability of creating small angle boundaries, often occurring in the interdendritic channels. Key words: CMSX-4, single crystal, superalloy, creep.1. INTRODUCTION Single crystal superalloys are widely used in the hot section of gas turbines due to their excellent resistant for creep, fatigue and oxidation at high temperature [1]. They ar[...]

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