13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- Figure 5. Deformation twins near the fracture surface in the alloy aged for 500 h at strain rate of 5×102 s-1 At the same time, the thermal-softening effect often occur caused by heat generation during plastic deformation at higher strain rate [16, 17], which the dislocation moving resistance can be reduced, it also contributes to the increasing of the ductility of the alloy. 4. Conclusions (1) The yield strength of the alloy exhibits a slight increase when strain rate is lower than 101 s-1, while obvious increase when the strain rate is higher than 102 s-1. (2) The fracture elongation of the alloy shows obvious decrease when the strain rate is lower than 102 s-1, whereas it shows a rapid increasing when the strain rate is higher than 102 s-1. (3) The deformation resistance of the alloy increases with the increasing of strain rate during deformation at high strain rate due to the increasing of short-range resistance caused by acceleration of dislocation motion. When the strain rate is higher than 102 s-1, the significant increasing of the moving dislocation number is the main reason for the increasing of plastic deformation ability. In addition, the twinning deformations as well as thermal-softening caused by the temperature rising at high strain will contribute to the ductility of the alloy too. Acknowledgements This research was supported by National Basic Research (973) Program of China (No. 2010CB631203), National High Technology Research and Development (863) Program of China (No. 2012AA03A513) and National Natural Science Foundation of China (No. 51001021, 51171039). References [1] S. L. Soo, R. Hood, D. K. Aspinwall, W. E. Voice, C. Sage, Machinability and surface integrity of RR1000 nickel based superalloy. CIRP Ann-Manuf Techn, 60(2011) 89-92. [2] N. Fang , Q. Wu, A comparative study of the cutting forces in high speed machining of Ti-6Al-4V and Inconel 718 with a round cutting edge tool. J Mater Process Tech, 209(2009) 4385-4389. [3] R. Sharghi-Moshtagh, S. Asgari, The effect of thermal exposure on the γ′ characteristics in a Ni-base superalloy. J Mater Process Tech, 147(2004) 343-350. 200nm
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