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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以及凝固后的冷却速度密切有关。定向凝固可大幅度地提高合金的塑性、热疲劳性能和中温持久性能,使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是由于蠕变第二阶段的延长,而高温(～980℃)持久寿命的提高主要是由于蠕变第三阶段延长的结果。通过定向凝固改善高强度铸造镍基高温合金的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;另一个原因是获得[001]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度,延长蠕变第二阶段,从而进一步大幅度提高中温持久寿命,这主要是由于冷却析出的细小γ′相代替了铸态粗大γ′相的缘故。定向凝固及高温固溶热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倍左右。消除了横向晶界的定向凝固合金中,初生MC是蠕变裂纹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 effect of directional solidification on microstructure and properties of a high strength cast nickel base superalloy was investigated. It was found that the low magnification and the microstructure of the alloy are closely related to the rate of directional solidification and the rate of cooling after solidification. Directional solidification can greatly improve the plasticity of the alloy, thermal fatigue properties and long-lasting temperature properties, so that the instantaneous elongation and long-term high temperature performance has also been significantly improved. The increase in long-lived life at mid-temperature (~ 760 ° C) was mainly due to the second phase of creep, while the increase in long-term high temperature (~ 980 ° C) was mainly due to the third phase of creep. The main reason for improving the high-temperature mechanical properties of high-strength cast nickel-base superalloy by directional solidification is to eliminate the lateral grain boundaries perpendicular to the stress axis. Another reason is to obtain preferentially grown columnar crystals in the [001] direction. High-temperature solution heat treatment can reduce the creep speed in the second stage and extend the second stage of creep so as to further improve the medium-temperature long-term life greatly, mainly due to cooling instead of the as-cast coarse γ ’phase reason. Directional solidification and high temperature solution heat treatment can increase the alloy’s mid-temperature (~ 760 ℃) life expectancy and elongation of 3-4 times, thermal fatigue performance of about 5 times. Among the directional solidification alloys with transverse grain boundaries eliminated, primary MC is a source of creep cracks and thermal fatigue cracks. It is expected that reducing the carbon content of the alloy and hence the amount of MC will further improve the high-temperature mechanical properties of the alloy.