铸态V-5Cr-5Ti合金在退火过程中的第二相行为研究

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

采用XRD、OM、SEM和TEM对铸态V-5Cr-5Ti合金退火处理后组织结构进行分析。结果表明:在退火过程中,随着退火温度升高,铸态V-5Cr-5Ti合金第二相发生分解、扩散、聚集。第二相形貌由层状组成树枝状第二相转变成针状组成团聚状第二相。随着时间的推移,针状第二相尺寸发生了粗→细长→短粗的转变。1100℃,2h退火处理后V-5Cr-5Ti合金组织中存在3种类型的第二相(1)条状第二相,宽度为80~100 nm,长度为几个μm,化学式记为V_2-CO。(2)针状第二相,具有fcc结构,晶格常数为0.4193~0.4256 nm,该第二相在晶内或平行或垂直排列。(3)椭圆状第二相,具有fcc结构,晶格常数为0.4203~0.4268 nm。铸态V-5Cr-5Ti合金退火过程中,树枝状第二相首先发生分解、扩散,随后合金元素脱溶沉淀,形成以针状第二相为特征的团聚状第二相。该第二相是以Ti、V元素为主,Cr元素为辅,具有fcc结构的、稳定的碳-氧-氮化物,化学式记为(TiV)-CON。

The microstructure of as-cast V-5Cr-5Ti alloy during annealing was analyzed by XRD, OM, SEM and TEM. The results show that with increasing the annealing temperature, V-5Cr-5Ti alloy secondary phases of as cast V-5Cr-5Ti alloy decompose, diffuse and aggregate. The dendritic phase made by lamellar secondary phase turns into the reunion phase made by acieular secondary phase. The shape of aeicular secondary phase changes in order of coarse-elongated-tubby over time. There are three kinds of the secondary phase in V-5Cr-5Ti alloy after 1100 ℃×2 h annealing, i.e. strip secondary phase, whose chemical formula can be expressed as V2（CO）; aeicular secondary phase, which has fee structure with the lattice parameter 0.4193-0.4256 nm; elliptical-shaped secondary phase, which has fee structure, with the lattice parameter 0.4203-0.4268 rim. In the process of annealing, the dendritic phase decomposes and diffuses firstly, and then the alloy matrix precipitates due to the alloy element desolvation and separation out of the reunite phases, which is the characteristic of acicular secondary phase. Finally, the secondary phase is chromium-alloyed stabilized precipitations of titanium-vanadium oxycarbonitride with fcc structure, whose chemical formula can be expressed as （TiV）（CON）.