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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]

Microstructural stability and microstructure-property relationship during long-term thermal exposure in K452 alloy (a new Ni-base cast superalloy with -21 pet Cr, 11 pct Co, 3.5 pet W, 2.5 pet Al, 3.5 pet Ti, and others) are investigated. It is found that exposure temperature and time have significant effects on the microstructure and properties of the alloy. During exposure, the microstructure is degraded by γ' coarsening, MC carbide (M mainly represents Ti, W, and Nb) degeneration, precipitation and evolution of grain interior (GI) M[sub23]C[sub6] carbide, evolution of grain boundary (GB) microstructure, and precipitation of η phase. Among them, the γ' coarsening is the leading reason for the decrease of strength of the alloy. The GJ M[sub23]C[sub6] and the η phase have negligible influence on the properties due to their relatively small populations. Blocky, closely spaced GB M[sub23]C[sub6] particles engulfed in γ' increase the stress-rupture life, whereas the formation of a continuous GB M[sub23]C[sub6] chain has an opposite effect. A life peak occurs when the M[sub23]C[sub6]/γ' structure at the GBs is in an optimal form. The degenerated MC is the preferred initiation site of microcracks. Its presence at the GBs promotes the onset of intergranular fracture, and leads to the decrease in mechanical properties. [ABSTRACT FROM AUTHOR]

Precipitation behavior of Heusler phase (Ni2AlHf) in a directionally solidified (DS) NiAl- 28Cr-5Mo-1Hf (at.%) alloy was examined using scanning electron microscope (SEM) and transmission electron microscope (TEM). In the as-cast alloy, the Ni2AlHf phase generally appeared on the NiAl/Cr(Mo) interface, which degraded the NiAl/Cr(Mo) eutectic structure. In the heat-treated alloy, the density of the intercellular Ni2AlHf phase was slightly reduced. In addition, the spherical Ni2AlHf phase precipitated heterogeneously in the NiAl matrix, but the Ni2AlHf phase did not precipitate in the lamellar Cr(Mo) phase. The precipitation behavior of the Ni2AlHf phase could be explained in terms of the interfacial energy. A lattice model was also proposed to explain the NiAl↔Ni2AlHf phase transformation. [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 orientation relationship (OR) between α[sub 2]-Ti[sub 3]Al precipitates in the B2 phase in a Ti-47at.% Al-2at.% W-0.5at.% Si alloy was determined by transmission electron microscopy. The OR is \[2110][sub α2] //\[111][sub B2] and (0221)[sub α2] //(110)[sub B2], in which the close-packed planes of the α[sub 2] and B2 phases are not exactly parallel to each other. This OR is precisely predicted from the invariant line theory and the reciprocal lattice overlap theory. [ABSTRACT FROM AUTHOR]