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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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Binary phase diagrams represent a rich source of thermochemical information. The mathematical concept of equilibrium that underlies binary phase diagram construction is reviewed using the Sn-Bi and Mg-Si systems as examples. The common methods that provide experimental data useful to modelling include microscopic phase examination, X-ray diffraction (XRD), elecromotive force (emf), vapour pressure, scanning calorimetry and calorimetric techniques. Using the mathematical concept above, information resulting from these diverse techniques can be examined in a self-consistent way and all information contributes to the construction of the phase diagram. As commercial alloys typically contain several elements, the mathematical equations derived for binary systems can be combined and extrapolated to model these multicomponent systems. There are two general cases: a system with one dominant element such as lead acid battery alloys which are represented by the lead-rich region of the Pb-Ag-Ca-Sn system and the general case where the alloy cover the entire compositional domain, such as the phase relationships of noble metal inclusions in nuclear fuel rods, which are represented by the Mo-Rh-Ru-Pd-Tc system.Résumé -Les diagrammes de phase binaires représentent une source riche en information thermochimique. On examine le concept mathématique d'équilibre qui sous-tend la construction du diagramme de phase binaire en utilisant les systèmes Sn-Bi et Mg-Si, comme exemples. Les méthodes communes fournissant l'information expérimentale utile à la modélisation incluent l'examen de phase par microscopie, la diffraction par rayons X, la force électromotrice (fem), la pression de vapeur, la calorimétrie à balayage et les techniques calorimétriques. Utilisant le concept mathématique ci-dessus, on peut examiner de manière consistante les données qui proviennent de ces techniques variées et toute l'information contribue à la construction du diagramme de phase. Puisque les alliages commerciaux contiennent typiquement plusieurs éléments, on peut combiner et extrapoler les équations mathématiques établies pour les systèmes binaires afin de modéliser ces systèmes à composantes multiples. Il y a deux cas généraux: un système avec un élément dominant, comme les alliages au plomb pour pile qui sont représentés par la région riche en plomb du système Pb-Ag-Ca-Sn; ensuite, le cas général où les alliages couvrent le domaine compositionnel entier, comme les relations de phase des inclusions de métal noble des tiges de combustible nucléaire, qui sont représentées par le système Mo-Rh-Ru-Pd-Tc.

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