高Cr铸造镍基高温合金K4648与陶瓷型芯的界面反应研究

采用金相显微镜、扫描电镜及能谱、电子探针和X射线衍射对高Cr铸造镍基高温合金K4648等轴晶和定向凝固铸件的合金/陶瓷型芯界面反应进行了系统研究,获得反应时间与反应量关系的界面反应动力学曲线、不同反应时间的反应界面形貌及产物的种类。结果表明:高Cr铸造镍基高温合金K4648与铝基型芯不易发生反应,而与硅基陶瓷型芯发生剧烈的界面反应,反应产生金属瘤状凸起物,造成铸件内腔破坏。此外,白色的硅基型芯内部变成黑色,黑色反应区内含有一定量的Cr,Al,Ti元素。在反应的中、后期型芯黑色反应区内还存在着灰色区,该区的Cr,Al,Ti含量远高于黑色反应区。高Cr铸造镍基高温合金K4648合金与硅基陶瓷型芯反应分为:(1)富Cr,Al,Ti熔体向型芯内的渗入阶段;(2)富Cr,Al,Ti熔体与陶瓷型芯SiO2基体的反应;(3)富Cr,Al,Ti的熔体与型芯中Zr-SiO4颗粒反应三个阶段。反应过程中型芯存在局部液化现象。K4648合金/硅基陶瓷型界面反应产物主要为层状或树枝状Al2O3,块状Cr3Si金属间化合物、ZrO2,富Cr,Zr,Al,Ti的复合氧化物、共晶形态的富Cr,Si,Al,Ti的复合氧化物、块状或树枝状的富Ti,Al,Zr,Cr复合氧化物。反应产物中的Cr,Al,Ti元素来自合金熔体而Zr,Si,O来自陶瓷型芯。

Investigation of Interfacial Reaction between High Cr Content Cast Nickel Based Superalloy K4648 and Ceramic Cores

The interfacial reaction between alloy and ceramic core in equiaxed and directional solidified high Cr content cast Ni-base superalloy K4648 castings was systematically investigated by optical metallography(OM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),electron probe micro-analysis(EPMA) and X-ray diffraction(XRD).The kinetic curve which indicates the relationship between reaction time and amount was illustrated.The morphology of reaction interface and the reaction products at different time were also presented.The results shown that a severe interfacial reaction occurred between high Cr content cast Ni-base superalloy K4648 melt and silica-based core,whereas it did not happened to alumina-based core.The inner surface of the casting was destroyed due to the formation of the metallic abnormal knobs during the interface reaction.Furthermore,the color of silica-based core changed from the normal white to abnormal black.The black reacted region contained some metallic element from the alloy such as Cr,Al and Ti.It was noteworthy that the grey region distributed in the black reaction zone after long time reaction.The amounts of Cr,Al and Ti in the grey region were much higher than that in the black reacted zone.The interfacial reaction between K4648 alloy and silica-based core could be roughly divided into three stages:(1) The(Cr,Al,Ti) rich melts infiltration into ceramic cores.(2) The reaction between(Cr,Al,Ti) rich melts and SiO2 matrix in ceramic cores.(3) The reaction between(Cr,Al,Ti) rich melts and blocky ZrSiO4 in ceramic cores.Partially liquefaction appeared in the ceramic core region during the reaction.The main products of interfacial reaction between K4648 alloy and silica-based core were layer-shape or dendritic Al2O3,blocky intermetallic Cr3Si,ZrO2,(Cr,Zr,Al,Ti) rich oxides,eutectic(Cr,Si,Al,Ti) rich oxides,blocky or dendritic(Ti,Al,Zr,Cr)rich oxides.Among these reaction products,the elements Cr,Al and Ti were from the alloy melt and the Zr,Si and O from the ceramic core.