13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Tensile Deformation Behavior of a Nickel-base Superalloy under Dynamic Loads Lei Wang1,*, Yang Liu1, Xiu Song1, Junchao Jin1, Beijiang Zhang2 1 Key Lab for Anisotropy and Texture of Materials, Northeastern University, Shenyang 110819, Liaoning, P. R. China 2 Department of High-temperature Materials, Central Iron and Steel Research Institute, Beijing 100083, P. R. China * Corresponding author: wanglei@mail.neu.edu.cn Abstract The tensile deformation behavior of a nickel-base superalloy under the dynamic loads was investigated the by the optical microscope, scanning electron microscope and transmission electron microscope. The results shown that the yield strength of the alloy increases with the increasing of strain rate, eapacily at the strain rate higher than 101 s-1. While with the increasing of strain rate, the fracture elongation decreases at first, then increases rapidly and shows a minimum value at the strain rate of 102 s-1. The manner in which the dislocations go through the strengthening phases may be different during the plastic deformation at different strain rates and it is the main reason of the appearance of inflection point in the change of the strength with the strain rate. The obvious increasing of plasticity of the alloy at high strain rate is depended on the deformation twining during the plastic deformation. Keywords Superalloy, Dynamic load, Deformation behavior, Dislocation 1. Introduction Superalloy is a kind of important metallic material for engines in the aerospace industry, which is the key point for determination of the thrust and thrust-weight ratio of advanced engines [1-3]. With the rapid developing aerospace industry, the working condition of the superalloy is becoming more and more severe. In traditional aeroengine manufacturing industry, the mechanical properties and deformation behavior of superalloy used for rotating parts under the actual dynamic load is not given full considerations during its designing of structure, composition and microstructure, which is significantly different compared with that under the static load [4-6]. In fact, the Young’s modulus, strength, plasticity and ductility will change with the increasing of strain rate [7-10]. Therefore, the study on the deformation behavior of the alloy under the dynamic load is important for the safety of rotating parts used under the service conditions. The aim of present study is to investigate the strain rate effects on the tensile deformation behavior of a precipitation strengthened nickel-base superalloy used for aero-engine combustor under dynamic loads. And the mechanism for strain-dependence on strength and ductility of the alloy was also discussed. 2. Experimental Procedures The chemical compositions (wt%) of the alloy are of 0.038 C, 19.970 Cr, 9.990 W, 5.120 Mo, 2.180 Al, 1.290 Ti, 0.020 Mn, 0.080 Si, and balance Ni. The alloy was double vacuum melted, then forged and hot rolled into plates with the thickness of 1 mm After solution treated at 1150 for 15 min, ℃ the alloy was long-term aged at 800 for 0 ℃ h, 100 h, 200 h, 500 h and 1000 h, respectively. The tensile tests of the alloy were performed at room temperature using MTS 810 testing machine and Zwick HTM 5020 high speed tensile testing machine at a strain rates range of 10-3 S-1 to 103 S-1. The resistance strain gage was setupped on the specimens for synchronous collection of the strains and loads during the dynamic deformation with a sampling frequency of 1 MHz. The microstructure evolution, grain size and the tensile fracture surfaces of the tensile specimen were examined using an optical microscope (OLYMPUS GX71), laser scanning confocal microscope (OLYMPUS OLS 3100) and field emission scanning electron microscope (JEOL 7001). The dislocation configuration near the fracture surface was examined by a transmission electron microscope (TECNAI G2).
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