铌/硅化物原位自生复合材料微米棒状向纳米层片状共晶组织转变及其硬化行为

Transition from micro-rod to nano-lamella eutectics and its hardening effect in niobium/silicide in-situ composites

以Nb−18Si(摩尔分数,%)复合材料为研究对象,分析共晶组织几何形态对电子束表面熔化(EBSM)快速凝固条件的响应机理及其对材料硬度的影响规律。研究结果表明,Nbss/Nb3Si共晶在电弧熔炼凝固条件下以棒状形态为主,而在EBSM凝固条件下转变为层片状形态。利用原子尺度的扫描透射电子显微镜(STEM)和近原子尺度的三维原子探针(APT)对样品进行表征,获得纳米Nbss/Nb_(3)Si共晶的三维层片状结构特征及其组分。与棒状共晶相比,EBSM凝固条件下形成的层片状共晶组织显著细化(共晶间距为39.5 nm),Nbss相体积分数大幅增加(约41%)。随着显微组织由微米棒状共晶转变为纳米层片状共晶,材料硬度显著增加,达到13.9 GPa。

To improve the mechanical properties of niobium/silicide in-situ composites via rapid solidification,the evolution of eutectic geometry and the corresponding hardening effect in a prototype Nb−18Si(at.%)composite upon electron beam surface melting(EBSM),i.e.,a rapid remelting and solidifying sequence,were studied.Results show that rod-like Nb solid solution(Nbss)/Nb_(3)Si eutectics prevail in the arc-melted state,yet evolve into lamellar arrangements after EBSM.Atomic scale scanning transmission electron microscopy(STEM)and near-atomic scale atom probe tomography(APT)were employed to characterize the three-dimensional stacking of nano-laminated Nbss/Nb_(3)Si eutectics and their compositions.Compared with the rod-like eutectics,the lamellar eutectics via EBSM demonstrate a prominent eutectic refinement(39.5 nm in spacing)and an increased volume fraction of Nbss(~41%).Nano-indentation testing reveals that with the microstructural transition from micro-rod to nano-lamella eutectics,a significant increment in hardness up to 13.9 GPa is achieved.