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The major advancements in mechanical and thermal properties of the most recently developed single crystal (SX) superalloys can be attributed to the addition of specific refractory elements into base alloy compositions. The present study investigates the effect of modifying refractory addition levels on the solidification behaviour of SX superalloys systems. Specifically, a series of six Ni-base alloy compositions are set in a controlled manner, such that the chemical microsegregation effects of Re, W, and Ru can be independently assessed. Fabrication of grain-free SX bars from each alloy composition is achieved by utilizing a modified Bridgman casting process, with subsequent compositional analysis of the solidification structures via electron microprobe analysis (EPMA) methods. Further validation of these EPMA microsegregation results are supported by means of eutectic phase fraction analysis and differential scanning calorimetry (DSC) methods. Qualitative partitioning results indicate typical SX alloy segregation behavior with elements such as Cr, Co, Re, Mo, and W all segregating towards the dendrite core regions, while the forming elements of Al, Ti, and Ta partition to the interdendritic-eutectic regions. Both Ni and Ru exhibit ideal segregation behaviour with no favorable partitioning to either liquid or solid phase. Quantitative EPMA results indicate that as the nominal Re level increases, the severity of microsegregation to the dendrite core regions rises dramatically for Mo, Cr, and Re. Evidence is presented that demonstrates the role that Ru plays in counteracting the microsegregation effects of both increased Re and higher overall total refractory levels. In addition to experimental trials, chemical partitioning predictions are also presented for the alloy system, utilizing a solid-liquid phase equilibria model generated using a customized chemical thermodynamic database. Using this CALPHAD approach, a comparison of the computational predictions and the actual experimental segregation results is also provided for discussion.

Thermobaric explosives (TBXs) have been primarily used for their blast, rather than for their fragmentation, characteristics. This work reports on an investigation, using a flash X‐ray imaging technique, of the ability of TBXs to shatter metal casings and to propel the resulting fragments. Three casing materials were used, AISI 1026 steel, ductile iron, and grey cast iron, while two different TBX compositions were used, with C4 serving as a benchmark. The fracture behavior of the casings, as a function of explosive fill and material characteristics, was as expected. One TBX formulation exhibited a run distance to detonation. The Gurney equation was used to correlate and compare the final fragment velocities. It was found that a larger fraction of the explosive energy was available to propel fragments in these two TBX compositions than a comparable amount of C4. This fraction of energy was influenced by the confinement of the detonation products and the ignition delay of the metal powders. These two factors had a greater influence on the fragment velocities than did material characteristics.

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