Search

The NiAl-Cr(Mo) eutectic alloy doped with Dy was prepared by suction casting technique and its microstructure and mechanical properties were investigated. It is found that with the addition of Dy, the Ni5Dy phase is formed along the NiAl/Cr(Mo) phase boundary in the intercellular region. By the suction casting method, the microstructure of the alloy get well optimisation which can be characterised by the fine interlamellar spacing, high proportion of eutectic cell area and fine homogeneous distributed Ni5Dy phase, The compression test results reveal that the room temperature and high temperature mechanical properties of the suction cast alloy improve significantly, compared with the conventionally cast alloy, [ABSTRACT FROM AUTHOR]

The effects of micro-Ru alloying addition on NiAl alloys were investigated by optical microscopy, SEM, X-ray diffraction and powder X-ray diffraction. The mechanical properties were characterised by Vickers microhardness measurement and compression tests at room temperature and various elevated temperatures. Micro-Ru alloying addition does not modify the crystal structure of NiAl alloys. However, local electronic structure may be modified owing to the specific site occupancy preference of Ru, smaller size difference between Ru and Al and different electronic nature of Ru and Ni. This is partially verified by the decrease of the long range order degree accurately measured via powder X-ray diffraction. As a result, a maximum softening effect occurs at 0·5 at.-%Ru addition indicated by Vickers microhardness measurement and compression testing results. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of polycrystalline Ni76Al23Zr alloy was studied as a function of heat treatment, environment, and temperature. It was found that the tensile ductility was very sensitive to temperature, the alloy showing low ductility at temperatures from 700 to 1000°C both in air and vacuum. Environmental embrittlement could be alleviated for those specimens with elongated grains. The ductile transgranular fracture was explained by stress concentration at the intersection of slip bands and grain boundaries. It was also found that an oxide layer, formed during tensile testing at elevated temperature, affected the environmental embrittlement of Ni3Al(Zr) alloy. An adherent Al rich oxide film was effective in protecting the underlying alloy from oxygen penetration. [ABSTRACT FROM AUTHOR]

The mechanical behaviour and microstructural evolution in tension of NiAl - 9Mo eutectic alloy at 1100 ° C and strain rates from 10[sup -5] to 10[sup -3] s[sup -1] have been investigated. High values of strain rate sensitivity index, but relatively small elongations between 150 and 200%, have been observed. Tensile specimens with various strains were quenched in water to preserve the dislocation structures for TEM examination. The TEM results show that the dislocation configuration and density change significantly with an increase in strain rate, and therefore correspond to different deformation mechanisms. At a low strain rate (5[sup .]5 × 10[sup -5] s[sup -1]), the dislocation density is relatively low and dislocation activity is regarded as an accommodation mechanism for grain boundary sliding. In contrast, the high density of dislocations as well as clear subboundaries observed in grains at a high strain rate (5[sup .]5 × 10[sup -4] s[sup -1]) suggest that the dislocations are active directly in response to the applied stress as well as participating in the relaxation process of grain boundary sliding by subboundary formation. Thus, grain boundary sliding is mainly responsible for superplastic deformation at a low strain rate, while superlastic deformation at a high strain rate is controlled by the combined operation of both grain boundary sliding and dynamic recovery. [ABSTRACT FROM AUTHOR]

The microstructure of a multiphase NiAl-33.5Cr-0.5Zr intermetallic alloy was examined by SEM with energy dispersive spectroscopy and TEM. The tensile creep behaviour of the hot isostatically pressed NiAl-33.5Cr-0.5Zr alloy was studied. The results of the creep test indicated that all of the creep curves under the present test have similar characteristics: a short primary creep stage, a dominant tertiary creep stage, and nearly identical creep strains (~45%). The apparent stress exponent and the apparent activation energy were analysed and discussed. The mechanism of the creep deformation was also analysed by the observation of TEM. [ABSTRACT FROM AUTHOR]