1. Solidification Processing and Properties of Advanced Single Crystal Superalloys, Gerhard E. Fuchs, University of Florida, DMR 0353952 Carbon additions to single crystal Ni-base superalloys have been shown to increase their castability. The carbon additions were reported to reduce solidification segregation. Results from this study have shown that the resulting carbides form network in the mushy zone during solidification, blocking fluid flow which reduces the defects due to thermal-solutal convection. The carbide networks also resulted in increased porosity. MC-type, tantalum carbides in both blocky and acicular morphologies are observed. Increased carbon levels, above about 0.05wt% C, eventually result in a continuous interdendritic carbide network. Mechanical property testing has indicated that the presence of the carbides results in significant reductions in HCF, creep and tensile properties. Broader Impact: These results can be used to develop next generation alloys for increased efficiency and reduced energy consumption and emissions

2. Solidification Processing and Properties of Advanced Single Crystal Superalloys, Gerhard E. Fuchs and R. Abbaschian, DMR 0353952 Carbon and boron additions have been used to increase the castability and defect tolerance of single crystal Ni-base superalloys. However, the mechanism for these increases in castability and defect tolerance are not clear. This study utilizes additions of boron and nitrogen to modify the carbide morphology to examine the effect of carbide morphology and composition on segregation and solidification defect formation. Boron additions to carbon- containing Ni-base superalloys did not result in any significant change in morphology of the MC- type carbide. Preliminary results do not match predictions from computational techniques. Nitrogen additions to carbon- containing Ni-base superalloys resulted in more blocky MC-type carbides. 0.05C 0.05C+ B 0.05C + N

3. Solidification Processing and Properties of Advanced Single Crystal Superalloys, Gerharde E. Fuchs, University of Florida, DMR 0353952 Nitrogen and boron additions to carbon-containing Ni-base superalloys had no effect on solidification partitioning or carbide composition. Carbon addition resulted in increased dendrite arm spacing and decreased defect incidence from 35% to 25%. Boron and carbon additions resulted in lowered carbide melting point by ~7  C, decreased defect incidence from 35% to 25%. Nitrogen and carbon additions resulted in altered morphology to blocky, nodular carbides, increased solidification defects—40% defects. → Carbide morphology influences defect formation. Broader Impact: New, improved Ni-base superalloys can be developed for aircraft engine and industrial gas turbine applications that exhibit increased castability and defect tolerance. More complex and larger single crystal castings can then be produced economically. The resulting single crystal components will allow for higher operating temperatures, longer component lifetimes, reduced fuel consumption, reduced reliance on off-shore energy sources and reduced emissions. In addition, this work has resulted in the training of several undergraduate and graduate students in this critical technology area.