一次枝晶间距对DD26单晶高温合金持久各向异性的影响

Effect of Primary Dendrite Arm Spacing on the Anisotropic Stress Rupture Properties in a Nickel-base Single Crystal Superalloy DD26

研究了取向对高速冷却法(DD26-HRS)和液态金属冷却法(DD26-LMC)制备的DD26单晶高温合金760℃/670 MPa条件下持久性能的影响。结果表明,DD26-HRS合金一次枝晶间距明显大于DD26-LMC合金,而且DD26-HRS合金持久各向异性更为严重。位错形貌显示靠近[001]-[012]边界试样变形以基体内多滑移为主。由于DD26-HRS合金γ′相尺寸较大,抑制了层错带剪切γ′相的变形机制,从而使得DD26-HRS合金持久寿命高于LMC合金。然而,靠近[001]-[112]边界试样变形以单方向层错剪切γ′相为主,基体内开动的位错较少,DD26-HRS合金枝晶间粗大的碳化物相周围易于位错的堆积,从而萌生裂纹并沿碳化物界面迅速开裂,造成DD26-HRS合金持久寿命低于DD26-LMC合金。

The orientation dependence of stress rupture behavior in a single crystal superalloy DD26 processed by high rate solidification （DD26-HRS） and liquid metal cooling （DD26-LMC） was investigated under the condition of 760 ℃/670 MPa. The results demonstrated that the primary dendrite arm spacing （PDAS） of DD26-HRS alloy was much larger than that of DD26-LMC alloy, and the creep anisotropy of DD26-HRS alloy was more serious than DD26- LMC alloy. The dislocation morphology showed that the deformation was dominated by multiple slipping when the orientation of specimen was near the [001]-[012] boundary in the standard stereographic triangle. Due to the larger size of r particles in DD26-HRS alloy, the deformation mechanism of stacking fault shear was inhibited. Therefore, the stress rupture life of DD26-HRS alloy was longer than DD26-LMC alloy. However, the deformation of specimen, whose orientation was near the [001]-[112] boundary, was predominated by single 1/3（112） dislocations shearing γ＇ particles, and little type of dislocations slipping in γ＇ matrix： Around the larger script carbide in DD26-HRS alloy, it was easy to pile up with dislocations and initiate cracks. As a result, the stress rupture life of DD26-HRS alloy is much shorter than DD26-LMC alloy.