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研究了定向凝固对一种高强度铸造镍基高温合金的组织和性能的影响,发现合金的低倍和显微组织与定向凝固速度及凝固后的冷却速度密切相关。定向凝固可以大幅度提高合金的塑性、热疲劳和中温持久性能,瞬时拉伸及高温持久性能也有显著改善。中温(～760℃)持久寿命的提高主要由于蠕变第二阶段的延长,而高温(～980℃)持久寿命提高主要是蠕变第三阶段延长的结果。定向凝固改善铸造镍基高温合金高温机械性能的主要原因是消除了垂直于应力轴的横向晶界;另一原因是获得〈100〉方向择优生长的柱状晶。高温固溶热处理可降低第二阶段的蠕变速率,延长这个阶段,从而进一步大幅度提高中温持久寿命。这主要归因于冷却析出的细小γ′相代替了铸态粗大γ′相。通过定向凝固及高温固溶处理可提高合金的中温(～760℃)持久寿命和延伸率达3—4倍,热疲劳性能达5倍。消除了横向晶界的定向凝固合金中,初生MC是蠕变及热疲劳裂纹的策源地。预计降低合金的碳含量从而减少MC数量将进一步改善合金的高温机械性能。

The structure and properties of a directionally solidified high strength castnickel-base superalloy have been studied. Directional solidification significantly in-creased the resistance to thermal-fatigue and intermediate temperature rupture lifeas well as the ductility and the tensile strength and high temperature rupture lifeof the alloy. The improvement of rupture life at certain intermediate temperature(about 760℃) was found to be due to an extension of the secondary stage ofcreep, whereas at a high temperature (about 980℃) the same improvementcame from an extension of the tertiary stage. The absence of grain boundaries inthe transverse direction gave rise to better mechanical properties, in particular, the<100> preferred orientation of the columnar grains played an important part inthe increased strength at elevated temperatures. The secondary creep rate was lowered and the second creep stage extendedafter high temperature solution treatment. This was found to be due to the solu-tioning of the coarse γ' phase on heating and the subsequent reprecipitation of auniformly dispersed fine γ' particles in the cast alloy after cooling. In the above directionally solidified alloy, primary MC carbides seem to serveas the sites for creep and thermal-fatigue crack initiation. This rather suggests thatthe high temperature mechanical properties of the alloy may possibly be furtherimproved if its carbon content is lowered.