再结晶对DD6单晶高温合金轴向高周疲劳性能的影响

为了研究再结晶对二代单晶高温合金DD6高周疲劳性能的影响,对标准热处理的DD6合金进行表面吹砂处理,然后分别在1120℃和1315℃保温4h,以获得不同类型的再结晶组织。在疲劳试验机上分别测试了光滑和含再结晶的DD6合金试样在1070℃的轴向高周疲劳寿命。采用SEM观察DD6合金再结晶组织及疲劳断口。结果表明:胞状再结晶和等轴再结晶降低了DD6合金的轴向高周疲劳性能,胞状再结晶作用小于等轴再结晶;含再结晶的DD6合金试样的轴向高周疲劳断裂机制为类解理断裂和枝晶间的局部韧窝断裂共存的混合断裂;再结晶使DD6合金试样变为多源疲劳断裂。高温条件下,再结晶晶界的存在加快合金试样的氧化损伤,显著缩短早期疲劳裂纹的萌生和扩展时间,降低合金的轴向高周疲劳性能。

Effect of recrystallization on axial high cycle fatigue properties of DD6 single crystal superalloy

In order to study the effect of recrystallization on the high cycle fatigue (HCF) properties of DD6 single crystal superalloy, the specimens of DD6 alloy after standard heat treatment were grit blasted and heat treated at 1120℃ and 1315℃ for 4h at vacuum atmosphere, respectively. Axial HCF tests on both raw and recrystallized samples were carried out, and then the recrystallization microstructures and fatigue fracture morphology of DD6 alloy were observed by SEM. The results show that cellular recrystallization and equiaxed recrystallization reduce the axial HCF properties of the alloy, and the effect of cellular recrystallization on the axial HCF properties is less than that of the equiaxed recrystallization. The axial HCF fracture mechanism of DD6 alloy with recrystallization is the maxed fracture of dimple fracture distributed in interdendritic region and cleavage-like fracture. Also, it is emphasized that DD6 alloy with recrystallization is a multiple fatigue crack initiation mechanism. Under high temperature conditions, the presence of recrystallization significantly promotes oxidative damage of alloy specimens, thereby accelerating the earlier crack initiation and propagation, which is responsible for fatigue degradation.