3 Characterization of Crack Tip Plasticity in IN-617 Using Indentation and Nano-Mechanical Raman Spectroscopy 15 Fig. 3.2 Stress distribution with microstructures obtained from EBSD of the notch tip under different bending loads of 500 mN, 2 N and 4 N at room temperature temperature of the sample during the test was 200 ıC, which was monitored by thermocouples. However, the temperature along the notch edge was little lower due to heat convection to the ambient air with obvious lower temperature inside the notch. And the difference of temperature at different area was due to difference of thermal conductivity that was affected by the precipitates on the surface, microstructure of surface and the stress conditions. After subtracting the temperature-induced Raman shift contribution, the remaining Raman shift was used to calculate stress. Stress values at every points around the notch tip was measured. Contour plots that depicted stress distribution of around the notch tip under loads of 500 mN, 2 N and 4 N at the overall temperature of 200 ıC were also shown in Fig. 3.3. The temperature field and stress distribution are affected by the microstructure of the notch area and the precipitates. In order to consider microstructure influence one needs to perform crystal plasticity type of simulations. However, dislocation systems data is very limited in this case. Therefore, an alternate approach is pursued in this work. For the purpose of finite element simulations, boundary conditions are shown in Fig. 3.4a. Microstructure of Alloy 617 has average grain size of approximately 150 microns. For each grain using spherical indentation, elastic-plastic stress strain curves were obtained with spacing of 50 microns by converting the experimental load-displacement data [18]. Figure 3.4b shows the
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