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The 1200 °C oxidation behaviors of CrNb, CrNbTi and CrNbTaTi are reported. All alloys formed some combination of BCC and Laves phases. However, additions of Ti produced a unique inflection point where the microstructure inverts to a Ti-rich BCC matrix with Laves phase precipitates. Further additions of Ta to CrNbTi were found to increase the overall phase fraction of BCC phase. The oxidation kinetics for CrNb and CrNbTi were similar and nearly parabolic throughout the duration of exposure. CrNbTaTi exhibited inferior oxidation kinetics and mixed mode behavior throughout oxidation testing. All alloys formed intricate multi-phase oxide structures, consisting of a combination of both simple and complex oxides. The resulting microstructures are characterized using a variety of analytical techniques and the results are discussed relative to modeling predictions using ab initio density functional theory (DFT).

The microstructures and mechanical properties in compression (25 °C, 1000 °C and 1200 °C) of CrNb, CrNbTi and CrNbTaTi are reported. The CrNb alloy consisted of a Cr2Nb Laves phase matrix and Nb-rich BCC precipitates. After additions of Ti (CrNbTi alloy) the microstructure inverts to a Ti-rich BCC matrix, with Laves phase precipitates inside the matrix phase. Further additions of Ta to CrNbTi refined and decreased the volume fraction of the Laves phase particles in the CrNbTaTi alloy. CrNb exhibited limited ductility at 25 °C and 1000 °C, but became very ductile at 1200 °C and offered the highest compressive strength at all studied temperatures. CrNbTi and CrNbTaTi had better ductility, but suffered from a reduction in compressive strength.

The structures of Ca 60 Mg 15 Cu 25 , Ca 60 Mg 20 Cu 20 and Ca 60 Mg 25 Cu 15 metallic glasses have been investigated by neutron and X-ray diffraction. The correlation functions show a peak manifold in the region 2.2–4.5 A, arising from the various atom pairs for these glasses. The results show clearly that there are contacts between the solute atoms (Cu and Mg) which agree with a simple estimate of the maximum solute atom fraction beyond which solute–solute contact becomes topologically necessary. The Cu–Mg and Cu–Ca distances are consistent with the sum of covalent radii, whereas all other interatomic distances are consistent with the sum of metallic radii. The neutron and X-ray diffraction correlation functions were simultaneously fitted with a series of symmetric peaks to obtain coordination numbers and interatomic distances, but only the results from the first two peaks, Cu–Cu and Cu–Mg, are of reasonable reliability. The Percus–Yevick approximation for binary hard sphere systems has been used to simulate the results. This shows that the results of fits to the Cu–Cu and Cu–Mg correlations give a reasonable description for atoms which are in close contact, but do not include an additional contribution at longer distance due to atoms which are almost in contact. The fits to the Cu–Ca peak are strongly affected by overlaps with both the longer distance peaks used in the fit, and the broad trailing edge in the distributions of interatomic distances that is not taken into account by fitting with symmetric peaks. Final results show that copper has a total of 6.5 neighbours which are in close contact, but has a total coordination number of about 12–13, when atoms which are almost in contact are included.

Two refractory high entropy alloys with compositions near Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20, were produced by vacuum arc-melting. Despite containing many constituents, both alloys had a single-phase body-centered cubic (BCC) structure that remained not only stable after exposure to 1400 °C, but also disordered, as confirmed by the absence of superlattice reflections in neutron diffraction data. Compressive flow properties and microstructure development of these alloys were determined from room temperature up to 1600 °C. Limited compressive plasticity and quasi-cleavage fracture at room temperature suggest that the ductile-to-brittle transition for these alloys occurs above room temperature. At 600 °C and above, both alloys showed extensive compressive plastic strain. The yield stress of both alloys dropped by 30–40% between room temperature and 600 °C, but was relatively insensitive to temperature above 600 °C, comparing favorably with conventional superalloys.

Two refractory high-entropy alloys with near-equiatomic concentrations, W–Nb–Mo–Ta and W–Nb–Mo–Ta–V, were produced by vacuum arc melting. Despite containing many constituents both alloys have a single-phase body-centered cubic (BCC) structure. The lattice parameters a = 3.2134(3) A for the quaternary alloy and a = 3.1832(2) A for the quinternary alloy were determined with high-energy X-ray diffraction using a scattering vector length range from 0.7 to 20 A−1. The alloy density and Vickers microhardness were ρ = 13.75 g/cm3 and Hv = 4455 MPa for the W–Nb–Mo–Ta alloy and ρ = 12.36 g/cm3 and Hv = 5250 MPa for the W–Nb–Mo–Ta–V alloy. The exceptional microhardness in these alloys is greater than any individual constituent, suggesting the operation of a solid-solution-like strengthening mechanism.

A number of ternary Ca–Mg–Zn and Ca–Mg–Cu and quaternary Ca–Mg–Zn–Cu bulk metallic glasses were produced using recently developed specific criteria. Their glass forming ability was correlated to the alloy chemistry, melting temperature, and driving force for crystallization of super-cooled liquid. A structural assessment using the efficient cluster packing model was also applied and showed a good ability to represent these glasses. Glass transition temperature, crystallization temperature and heat of crystallization were also determined for the produced alloys. Compression tests were conducted on a quaternary alloy at room temperature and in the temperature range of super-cooled liquid.

The phase stability and transformations in Al 3 (Ti 1- x Zr x ) intermetallic alloys ( x =0–1) produced by arc melting were studied in the temperature range of 20 to 1100°C by using an in situ X-ray diffraction (XRD) method. Two phases, D0 22 and D0 23 , both having ordered tetragonal structures, were present at room temperature at zirconium concentrations from 1 to 10 at.% ( x =0.04–0.4). At higher concentrations of Zr (0.4 x 23 phase was detected. For the alloy with x =0.32, the D0 23 transformed to D0 22 on heating at temperatures 1100 °C and above. On cooling, the D0 22 phase was stable to ∼650 °C, and the D0 23 phase was formed again in the temperature range of 600–650 °C. The positional parameters of the D0 23 atomic structure in the alloy Al 3 (Ti 0.68 Zr 0.32 ) were determined using a full-profile XRD analysis. It was shown that zirconium atoms substitute titanium atoms and increase the lattice parameters of the D0 23 structure. Zr fractions as small as x =0.1 are required to stabilize the D0 23 structure. A low temperature phase modification, Al 24 Ti 8 , was also detected in the surface layer in the temperature range below 650°C and it was found to be a result of surface grinding. Mechanical properties of the alloys studied are also discussed.