The effects of withdrawal rate (4, 5, 7, 9, 10 mm/min) on the microstmcture and mechanical properties of directionally solidified superalloy DZ445 were investigated. The results show that with the increase of withdrawal rate from 4 mm/min to 10 mm/min, both the primary and secondary dendrite arm spacing decrease gradually, and the average size of y' precipitates well-distributed in both dendrite core and interdendritic, decreases gradually. The average size of y'precipitates in dendrite core is smaller than that in interdendritic areas. The tendency of segregation of elements is more intense with the increase of withdrawal rate. At room temperature, the tensile properties of the DZ445 alloy under different withdrawal rates differ slightly, except at 4 mm/min. At 650 ℃, the tensile elongations at both too high and too low withdrawal rate decrease obviously. Besides, the withdrawal rate has an apparent effect on the stress-rupture properties of the DZ445 alloy. To sum up, the alloy under withdrawal rate of 7 mm/min has a good balance of tensile property, stress-rupture property and microstructure. Therefore, 7 mm/min is finally determined to be the optimal withdrawal rate. DZ445 columnar crystal alloy under the optimal withdrawal rate has better tensile property and stress-rupture property than K445 polycrystal alloy, which has the same composition as DZ445 alloy.%研究不同抽拉速率(4,5,7,9,10 mm/min)对定向凝固DZ445高温合金微观组织和力学性能的影响.结果表明:随着抽拉速率由4mm/min增加到10mm/min,一次枝晶臂间距λ<,1>和二次枝晶臂间距λ2逐渐减小,枝晶组织逐渐细化;枝晶干和枝晶间γ'相尺寸也逐渐减小,枝晶间γ'相的尺寸比枝晶干γ'相的大,这种差别随着凝固速率的增加而减小;合金元素的偏析随凝固速率的增大越来越严重;除抽拉速率为4 mm/min外,抽拉速率对DZ445合金室温拉伸性能影响不大;当抽拉速率太高或者太低时,合金650℃拉伸伸长率均明显降低;抽拉速率对合金的持久性能影响明显;当抽拉速率为7 mm/min时,合金的拉伸性能、持久性能和微观组织达到综合平衡,为最佳抽拉速率;DZ445定向柱晶合金比同成分K445等轴晶合金具有更好的室温和高温拉伸性能及持久性能.
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