Microstructural characterization of creep in the single crystal superalloy CMSX–4

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.

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Monokrystaliczne odlewy nadstopu niklu CMSX–4 stosuje się na najbardziej wytężone elementy silnika odrzutowego, takie jak łopatki turbiny wysokiego ciśnienia. Musza one charakteryzować się dużą żarowytrzymałością oraz żaroodpornością. Dlatego jest ważne precyzyjne określenie wpływu zjawiska pełzania na strukturę tego materiału w zależności od warunków jego wytwarzania. Celem pracy było scharakteryzowanie zmian strukturalnych oraz określenie wytrzymałości na pełzanie monokrystalicznych odlewów otrzymanych z prędkościami wyciągania formy wynoszącymi 3 oraz 5 mm/min.

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Opracowanie ze środków MNiSW w ramach umowy 812/P-DUN/2016 na działalność upowszechniającą naukę (zadania 2017).