V-5Cr-5Ti合金铸态组织中的第二相行为研究

Behavior of Secondary Phase of As-cast V-5Cr-5Ti Alloy

采用XRD、OM、SEM和TEM对V-5Cr-5Ti合金铸态组织进行分析,研究第二相的行为。结果表明:采用真空电子束熔炼制备的V-5Cr-5Ti合金铸态组织具有粗大的晶粒,晶粒内部存在以层状第二相堆垛成树枝状为特征的成分偏析区;金属钒和铸态V-5Cr-5Ti合金的晶格常数分别为0.30316和0.30375 nm,V的单胞体积膨胀约0.58%;存在2种类型的第二相:(1)短条状第二相,具有fcc结构,晶格常数为0.4182~0.4228 nm;(2)椭圆状第二相,具有fcc结构,晶格常数为0.4186~0.4242 nm。V-5Cr-5Ti合金凝固过程中,首先Ti元素与C元素反应析出具有立方结构的亚稳间隙相(Ti_2C)或V元素与C元素反应析出具有hcp结构的亚稳间隙相(V_2C),随后原子发生相互取代,最终形成以Ti元素为主,V、Cr元素为辅,具有fcc结构的碳-氧-氮化物,化学式记为(Ti_2-CON)。

The as-cast microstructure of the V-5Cr-5Ti alloy was analyzed by XRD, OM, SEM and TEM. The behavior of second phase was investigated. The results show that the V-5Cr-5Ti alloy, fabricated by vacuum electron-beam melting, has coarse grains, which possess the characteristics of dendritic crystal made by lamellar secondary phase. The lattice parameters of metal vanadium and V-5Cr-5Ti alloy are0.30316 and 0.30375 nm, respectively. The swelling of V cell volume is 0.58%. There are two kinds of secondary phase in the as-cast alloy,i.e. short strip secondary phase, which has fcc structure with the lattice parameter between 0.4182~0.4228 nm and elliptical-shaped secondary phase, which has fcc structure with the lattice parameter between 0.4186~0.4242 nm. In the process of solidification of the V-5Cr-5Ti alloy, Ti and C react to form metastable interstitial phase（Ti_2C）, which has fcc structure, or V and C react to form metastable interstitial phase（V_2C）, which has hcp structure. Then, atoms are substituted by each other. Finally, the secondary phases are formed, that is vanadium and chromium-alloyed precipitations of titanium oxycarbonitride, whose chemical formula is expressed as（Ti_2-CON）.