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Abstract: A fracture toughness test for intermediate toughness materials is developed. The test configuration is a wedge-driven double cantilever beam, with design guided by analytical solutions for the energy release rate and compliance. Actual toughness measurements require finite element methods. To promote crack stability, a pre-cracking fixture is employed. The method is illustrated for a brazed joint. Measurements of the fracture resistance used both fractographic and compliance methods to ascertain crack length. The ensuing fracture resistance, Γ R ≈1kJm−2, is significantly greater than that for the intermetallic constituents. Approximately half of the toughening is attributed to plastic stretch of the ductile phase within the eutectic. The remainder is attributed to dissipation within a plastic zone that forms in the primary γ-Ni regions. A rationale for improving toughness is presented. [Copyright &y& Elsevier]

[Display omitted] • Room temperature moduli of most Nb-alloys agree well with mole fraction weighted rule-of-mixture calculations. • A single, linear temperature dependence of the elastic properties is suggested for all Nb-alloys considered in this study. • A single Smith-Palmer equation adequately describes the thermal conductivity most of the Nb-based alloys investigated. • Thermal conductivity of WC-3009 is significantly lower than the thermal conductivity than the other Nb-alloys investigated. • A performance index is introduced for lightweight, panel-shaped applications subject to thermal gradients or transients. There is renewed interest in refractory alloys that possess higher service temperatures than incumbent Ni-based superalloys (⪆1100 °C). Thermophysical property data for six Nb-alloys are gathered from the literature and reviewed, and new data are provided for two Hf-containing Nb-alloys; elastic modulus, thermal expansion, thermal conductivity, and heat capacity are presented for C103, and new thermal conductivity data are provided for a higher strength alloy, WC-3009. Comparisons with Ni-superalloys and other refractory-metal based alloys provide context. Physics-based models are provided that describe the temperature dependencies of the Young's modulus, coefficient of thermal expansion and density, and thermal conductivity; such that fair comparisons can be made across alloys for any given condition. The results suggest a need for improved understanding of the temperature dependence of the elastic modulus. A performance index is introduced for making informed materials selection decisions in the context of lightweight, panel-shaped applications subjected to sharp thermal transients or steep thermal gradients, and the significant strain rate sensitivity of Nb-alloys is highlighted. Ultimately, the relative value of current commercial alloy, C103, as well as the promise of specific Nb-W-Zr alloys are highlighted. [ABSTRACT FROM AUTHOR]

The microstructure, mechanical properties (at 25 °C, 1000 °C, 1200 °C, 1400 °C and 1600 °C) and oxidation behavior (at 1600 °C) of a binary Hf-27%Ta alloy and three ternary alloys, Hf-21%Mo-21%Ta, Hf-21%Nb-21%Ta and Hf-21%Ta-21%W (compositions are in atomic percent) are reported. The alloys were produced by vacuum arc melting, hot isostatically pressed under a high-purity argon pressure of 207 MPa at 1400 °C for 3 h and slow cooled to room temperature. The Hf-27Ta alloy had a microstructure consisting of coarse primary HCP particles and a monotectoidally transformed matrix consisting of a nano-lamellar mixture of the Ta-rich BCC and Hf-rich HCP phases. The Hf-21Mo-21Ta alloy consisted of a BCC matrix phase and HCP precipitates. Hf-21Nb-21Ta had a microstructure consisting of a BCC matrix phase, spherical nano-precipitates inside the matrix grains and two-phase BCC lamellar regions at grain boundaries, with no HCP phase detected. The Hf-21Ta-21W alloy had a three-phase structure consisting of a Hf-rich HCP matrix, W-rich cubic Laves phase and monotectoidally transformed regions consisting of nano-lamellae of Ta-rich BCC and Hf-rich HCP phases. The alloys had limited ductility at room temperature but they all were well workable at T ≥ 1000 °C. Among the studied alloys, the binary Hf-27Ta was the strongest at room temperature and the Hf-21Mo-21Ta was the strongest at high temperatures. The oxidation kinetics of Hf-27Ta, Hf-21Mo-21Ta and Hf-21 W-21Ta were similar, with 30–40 mg/cm2 mass gain per 1 h holding at 1600 °C. The Hf-21Nb-21Ta alloy exhibited much higher (~230 mg/cm2/h) mass gains at 1600 °C. The ternary alloys all showed evidence of the formation of gaseous and/or liquid species in the oxide scales. • Hf-27%Ta, Hf-21Mo-21Ta, Hf21Nb-21Ta and Hf-21Ta-21W alloys have a complex, multi-phase microstructure. alloys0 • Hf-27%Ta is the strongest alloy at room temperature, but it shows the lowest strength at 1200–1600 °C. Hf-21Mo-21Ta is the strongest alloy at 1000–1600 °C. • Hf-27Ta, Hf-21Mo-21Ta and Hf-21Ta-21W have a fairly good oxidation resistance at 1600 °C. • Hf-21Nb-21Ta shows poor oxidation behavior at 1600 °C. [ABSTRACT FROM AUTHOR]