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In order to investigate the influence of the temperature increase due to frictional heating on the wear behavior of the nanostructured alloy Fe 30 Ni 20 Mn 25 Al 25 , which consists of alternating b.c.c. and B2 phases with interfaces aligned along 〈100〉, dry sliding pin-on-disk tests were conducted in air at several sliding velocities (0.1 m s −1 , 0.25 m s −1 , 0.5 m s −1 , 0.75 m s −1 and 1 m s −1 ) for 1 km. Disks of yttria-stabilized zirconia were used as the counterface. A combination of state-of-the-art techniques was used to characterize the pins, disks and debris after wear tests. It was found that the pins had much higher wear rates at a lower sliding velocity compared to a higher sliding velocity, although the wear rate of the zirconia counterface was higher at the higher sliding velocities. It was concluded, based on X-ray diffraction and transmission electron microscopy, that the increase in zirconia wear at higher sliding velocities was due to localized phase transformation of the zirconia caused by high frictional contact temperatures. The zirconia debris removed from the disk because of the phase transformation also contributed to the lower mass loss of the pins in wear tests at sliding velocities of 0.5 m s −1 or higher because zirconia embedded in the surface of the pins provided added protection against pin wear. [ABSTRACT FROM AUTHOR]

An isothermal section of the Fe-Mo-Ti ternary system at 1000 °C has been constructed using data acquired from a series of seven alloys. The limit of solubility of Fe in the continuous A2 phase field between Ti and Mo has been determined, as have the extents to which Mo may be accommodated in the B2 TiFe phase, and Ti in the D8 5 Fe 7 Mo 6 phase. The B2, D8 5 and C14 Fe 2 (Ti, Mo) intermetallics were found to have limited tolerance for non-stoichiometric compositions. The positions of the A2 + B2 + C14 and A2 + C14 + D8 5 three-phase fields were determined, along with the extents of the A2 + B2, A2 + D8 5 , A2 + C14, C14 + B2 and C14 + D8 5 two-phase fields. No ternary phases were observed in any of the alloys studied. [ABSTRACT FROM AUTHOR]

Eight multi-component Nb–Si based ultrahigh temperature alloys were prepared by vacuum non-consumable arc melting. The effects of Hf, B and Cr alloying on the phase selection, phase stability, both non-equilibrium and equilibrium microstructure, room-temperature fracture toughness, hardness and oxidation resistance at 1250 °C of the alloys have been investigated and estimated systematically. The results show that the addition of B or Cr promotes the formation of hypereutectic structures. The alloying with both Hf and B suppresses the formation of β(Nb,X) 5 Si 3 and promotes the formation of α(Nb,X) 5 Si 3 and γ(Nb,X) 5 Si 3 , while the alloying with Cr has no effect on the crystal structures of 5-3 silicides. The room-temperature fracture toughness of the alloys is always degraded by the addition of Cr but almost not influenced by the combined additions of Hf and B. The hardness of 5-3 silicides exhibits a tendency of γ > α > β. The macrohardness of the alloys increases with Cr addition, and it obviously reduces in the presence of Hf after 1450 °C/50 h heat-treatment. The best oxidation-resistant performance has been obtained for the alloy with both B and Cr additions. However, in the presence of B and/or Cr, the oxidation resistance of the alloys has been degraded by further addition of Hf. [ABSTRACT FROM AUTHOR]

A Zr-base bulk metallic glass (BMG) alloy with the base composition Zr–10 at.%Al–5% Ti–17.9% Cu–14.6% Ni (BAM-11) was used to study the effects of oxygen impurities and microalloying on the microstructure and mechanical properties. Oxygen impurity at a level of 3000 appm dramatically reduced the glass forming ability and embrittled BAM-11 at room temperature. The embrittlement was due to the formation of oxygen-induced Zr4Ni2O nuclei that triggered near complete crystallization of the metallic glass. Microalloying with 0.1 at.%B+0.2%Si+0.1%Pb was effective in suppressing the crystalline phase formation and alleviating the detrimental effect of oxygen. Microstructural analyses indicate that the beneficial effect of the optimum dopants was mainly due to stabilization of the glass-phase matrix even though it contained high levels of oxygen. Thus, microalloying is effective in reducing the production cost and is very useful for manufacturing good-quality Zr-based BMGs from impure charge materials. [Copyright &y& Elsevier]