K418C高温合金异常组织形成机制及其对凝固特性的影响

发动机涡轮增压器用镍基铸造高温合金K418C铸锭经快速感应重熔浇铸零件时发生开裂。运用光学显微镜、扫描电子显微镜(SEM)、电子探针微束分析仪(EPMA)和透射电子显微镜(TEM)对断裂铸锭表面进行了宏观形貌及显微组织分析,并对断裂原因进行探讨。结果表明:断口附近的显微组织异常,黑色块状析出相分布于基体上,伴有穿晶裂纹,电子衍射分析表明黑色块状组织为β-NiAl,铸锭局部Al偏高使得铸锭在凝固时析出脆性相,再次快速加热产生的热应力使得裂纹在β-NiAl相与基体之间萌生并快速扩展贯穿整个铸锭,导致瞬间断裂。

Formation Mechanism and Effects on Solidification Performance of Abnormal Microstructure for K418C Ni-base SuperaUoy

K418C Ni-based superalloy casting ingots for engine turbochargers fractured during casting. Macrostructure and mierostrueture were studied by optical microscopy, scanning electrical microscopy （SEM）, electrical probe micro-analysis （EPMA） and transmission electron microscopy （TEM）, and the fracture mechanism was discussed. The results show that there were an amount of abnormal black phases near the fracture of K418C casting ingot, which distributed on the matrix, companied with transgranular crack. The electron diffraction result indicated that the black phase is β- NiA1, which is brittle and resulted from local segregation of M during solidification. The cracks between β-NiA1 and matrix were induced by heat stress during rapid heating and propagated rapidly across the whole ingot. Finally, the casting ingot fractured instantly.