13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- Figure 5. EBDS analysis showing recrystallization or subcell formation in AISI 316L after SSRT at 650°C to fractured using a strain rate of 10-6/s, a) showing analyzed area, b) EBSD analysis displaying local misorientation (bright patterns) tighter with crystallographic orientation in a inversed pole figure (white color means zero-solution), c) local misorientation legend where the y-axis is frequency and x-axis is misorientation angle [°] and d) inversed pole figure legend showing crystallographic orientation. 3.2. Precipitates effect on damage Both materials undergo precipitation due to the elevated temperature during the long deformation process. Alloy 617 has evenly distributed γ´ precipitates in the matrix and σ-phase in the grain boundaries [14]. AISI 316L get precipitates as Cr-rich carbides, that probably are M23C6 or M6C, also σ-phase precipitate and they appear both in the matrix and grain boundaries [15]. The deformation time depends on material properties and strain rate, the deformation time varied from 1 minute to 130 hours. The size and amount of precipitates varied with the deformation time or strain rate and temperature, from no precipitate at high strain rates to more and bigger precipitates at the slower strain rates. Damage corresponding to the precipitation can be seen in fig.3 and fig. 6. At low strain rate and elevated temperature, the interaction between a moving dislocation and a precipitate can cause damage in the material. Fig. 6 display internal cracks that have initiate and propagate in the grain boundaries due to deformation and embrittlement from precipitates (Fig.6 c) and d)). Precipitates act as crack initiation points due to high local stress caused by the interaction between dislocations and precipitates. c) d) Load direction a) b)
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