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JMEPEG (2018) 27:721–727 https://doi.org/10.1007/s11665-017-3084-x

Effects of Strain Rate on Tensile Deformation and Fracture Behavior of Directionally Solidified Superalloy DZ125L Taosha Liang, Lei Wang, Yang Liu, and Xiu Song (Submitted August 25, 2017; in revised form November 29, 2017; published online January 19, 2018) The tensile deformation and fracture behavior of directionally solidified superalloy DZ125L were studied with a strain rate ranging from 1023 to 7 3 102 s21 at room temperature. Results show that the strength of DZ125L alloy presents positive strain rate sensitivity in tested strain rate range which is mainly resulted from the increasing accumulation of dislocations in the matrix. The ductility of the alloy first increases and then it remains insensitive with the increase in strain rates. The enhancement of ductility is primarily due to the increasing amount of broken MC carbides and plastic deformation in the matrix at higher strain rates. The strain rates influence the amount of broken MC carbides and then affect the deformation behavior of the alloy. Based on observations and discussions of the lateral microstructures and dislocations, it is concluded that the MC carbides with sizes larger than 10 lm are easy broken in the early deformation stage and act as crack sources during the proceeding plastic deformation. The growth and connection of microcracks and the propagation of main crack lead to the fracture of the matrix. Keywords

MC carbides, strain rate sensitivity, superalloy, tensile deformation behavior

1. Introduction DZ125L alloy is a directionally solidified nickel-based superalloy used as land-based and aircraft turbine blades (Ref 1). It usually undergoes dynamic loading conditions (Ref 2), such as the impact loading from hot air impingement and the inhalation of birds and other damaged blades. These conditions can cause serious hazards to the safety of engines. Therefore, it is essential to study the deformation behavior of the alloy under different strain rates. Up to now, the studies for DZ125L alloy have mainly been focused on the microstructure, recrystallization, and mechanical properties under quasi-static conditions (Ref 1, 3). However, metals usually behave differently under dynamic loading (Ref 4, 5). Zhang et al. (Ref 6) found that the flow stress of nickel–iron-based alloy was independent of strain rate when the strain rate was less than 100 s 1 while it varied greatly at higher strain rates. Zhang et al. (Ref 7) and Chichili et al. (Ref 8) also confirmed the similar phenomenon in aluminum alloy. Nevertheless, no research on the deformation behavior of DZ125L under high strain rates can be found. Additionally, there are primary MC carbides in the final solidification areas (Ref 3, 9). Since these MC carbides are brittle and cannot deform coordinately with the matrix (Ref 10), they will disturb the continuity of the microstructure of DZ125L alloy. It has been claimed that the microstructure Taosha Liang, Lei Wang, Yang Liu, and Xiu Song, School of Materials Science and Enginee