1. Characterization and Mechnical Properties of Nanocluster Strengthened Ferritic (NSF) Alloys Peter Sarosi and Michael Mills Materials Science and Engineering - OSU Joachim Schneibel Oak Ridge National Laboratories Support provided by: DOE-Office of Basic Energy Sciences

2. Bright Field (BF) STEM Imaging Advantages: BF-STEM images sensitive to sharp crystal curvatures (e.g. dislocations) and mass/thickness Not sensitive to gradual curvatures (e.g. bend contours) and grain orientation changes Thicker foils can be analyzed compared with conventional TEM Disk superalloy Blade superalloy BF detector Objective aperture Back focal plane specimen Convergent beam Diffracted/ Scattered beam Beam rasters across sample HAADF detector Transmitted beam Technique: Objective aperture selects direct beam which is detected by the BF detector Diffraction conditions relaxed due to converged beam and angular range of BF detector C-TEMBF-STEM Deformed Ni Microsample

3. Compression Creep Testing at 800 o C in Air Similar minimum creep rates for testing along longitudinal and transverse directions Minimal effect of grain shape on creep rate Alloy OE-14YWT 200 nm

4. Constant Strain Rate Compression at 800 o C in Air Strain rates: 1x10 -5 s -1 1x10 -6 s -1 Small rate sensitivity Significant strain hardening (  =A  n ; n~0.1) Alloy OE-14YWT TEM foils extracted in the longitudinal direction for analysis   TEM foil

5. Straight and pinned dislocations observed in fine grained regions Dislocation density inhomogeneous – similar to annealed case No twinning observed as in some nanoscale grain size materials Initial Characterization of Compression Samples

6. Large grains are nearly defect free! If present prior to deformation, why so resistant to deformation? Initial Characterization of Compression Test

7. Future work Strain Time 11 22  1   2 Substructure Controlled Mobility Controlled Transient creep testing as a “Micro-mechanical” probe: Form of strain transient following rapid stress change indicative of deformation mechanism. Upon stress increase: - Decreasing creep rate --> Substructure refinement - Increasing creep rate --> Increasing mobile dislocation density

8. 1 nm (a) e-e- Hole Foil 20nm Correlating Dislocations with Clusters Combine HRTEM imaging of dislocations with Energy Filtered TEM to locate clusters