| Changes in mechanical properties of W-NrFe heavy alloys were observed in accordance with a variation of composition and annealing condition Alloys of three compositions, 90W-3Ni-7Fe, 90W-5Ni-5Fe and 90W-7Ni-3Fe in wt% were liquid phase sintered at 1470℃ for 1 hr in H₂atmosphere and then annealed at 700, 900, 1000 and 1400℃ for 60 hr. All specimens of 90W-3Ni-7Fe composition showed a formation of an intermetallic phase, μ-phase (W_6Fe_7), between spherical tungsten grains and the ductile γ-phase matrix in microstructure which increased its amount with increasing annealing temperatures. The intermetallic phase drastically decreased tensile strength and elongation of the alloy. Alloys of 90W-5Ni-5Fe and 90W-7Ni-3Fe compositions were consisted of tungsten grains and a ductile γ-phase matrix and showed relatively good mechanical properties throughout the examining conditions. Fracture surfaces exhibited an intercrystalline or a transcrystalline fracture behavior depending on the annealing condition while the matrix phase always showed a really good ductility. |
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