Creep characteristics of directionally solidified turbine blades based on the difference in original casting characteristics

Highlights: • The study of the creep properties and the differences in different parts of unused turbine blades can obtain first-hand information. • To ensure the maximum utilization rate of turbine blades, we developed a set of sampling fixtures, five parts of the turbine blades can be obtained. • The mechanism of microstructure evolution and the creep fracture behavior were proposed in this condition. • The difference in the creep characteristics caused by the complex geometric factors produced by the DS process is studied. • An improved two-parameter creep constitutive model is adopted. -- Abstract: Due to the difference between original material and the processed material for use in turbine blades, research that solely focuses on the original materials may not fully explain the performance of operational turbine blades. In order to ensure the maximum utilization rate of turbine blades, the study examines the creep properties and differences of different parts of the directional solidification of original casting turbine blades. In this article, a set of sampling fixtures from different parts of a turbine blade were proposed to quantitatively measure the difference in creep properties caused by the complex geometric factors created during the DS process. The special fixtures would cut the blades into five different parts, which were to be further processed into small samples. Creep tests under two different conditions (980 °C/245 MPa, 980 °C/267 MPa) were carried out. Round rod specimens (standard parts) were used for creep tests under the same conditions for comparison. By employing scanning electron microscopic (SEM) and creep tests on different parts of original casting turbine blades, the mechanism of microstructure evolution and the creep fracture behavior were proposed in this condition. In addition, the original microstructure of different parts of a blade was observed by scanning electron microscopy (SEM), and the characteristics of the different parts were simulated based on an improved two-parameter creep constitutive model. The results suggest that the creep life of the different parts of the original casting blade is different, which caused by the differences in microstructure and morphology of the different parts of the original casting blade. The creep property of standard parts is better than that of original casting blades. The creep life of original casting blades from small to large is as follows: CVS, DP, LE, CCS, TT. An improved two-parameter creep constitutive model was adopted to simulate the difference in creep properties (including creep life) resulted from different parts in a turbine blade. This difference needs to be considered in designing the structure and service life of turbine blades formed by directional solidification. The research results are of great significance for improving the design of directionally solidified turbine blades and for improving the directional solidification forming process.