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研究了平均晶粒尺寸为25μm的锻造Inconel718镍基高温合金在4K、77K和293K温度下的高周疲劳性能。在该材料中,在λ晶界处析出片状δ相,合金基体中析出粗大的富铌碳化物(MC型)。该合金的屈服强度和极限抗拉强度随温度下降而提高,而延伸率或断面收缩率并未下降。即使在各温度下,甚至在约10~7周次也没出现疲劳极限,但是高周疲劳强度同样随温度降低而提高。疲劳裂纹产生于试样表面附近,并在裂纹源处形成小穿晶断面。疲劳裂纹主要源于粗大的富Nb碳化物,而且小穿晶断面与这些碳化物相关。然而,在较低的应力振幅试验中,小穿晶断面通过穿晶裂纹源而形成并生长。这种特殊裂纹产生行为可能会降低该合金的低温高周疲劳强度。
The high cycle fatigue properties of forged Inconel 718 nickel-base superalloy with an average grain size of 25 μm at 4K, 77 K and 293 K were investigated. In this material, a plate-like δ phase is precipitated at the λ grain boundary, and coarse niobium-rich carbide (MC type) is precipitated in the alloy matrix. The yield strength and ultimate tensile strength of the alloy increased with decreasing temperature, while the elongation or reduction of area did not decrease. The fatigue limit did not appear even at about 10 to 7 weeks at each temperature, but the high cycle fatigue strength similarly increased with decreasing temperature. Fatigue cracks occur near the surface of the specimen and form a small transgranular fracture at the source of the crack. Fatigue cracks mainly originate from coarse, Nb-rich carbides, and small, transgranular fractures are associated with these carbides. However, in the lower stress amplitude test, small transgranular fractures formed and grew through the source of transcrystalline cracks. This particular crack initiation behavior may reduce the low temperature high cycle fatigue strength of the alloy.