Zr-Sn-Nb合金第二相粒子结构特征及显微组织演变

摘要

Structure characteristics of the second phase particles of Zr-Sn-Nb alloy is studied by using first principles calculations combined with field emission scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction.Microstructure evolution of Zr-Sn-Nb alloy under the different temperature treatment is analyzed by using the horizontal metallographic microscopy combined with Zr-Nb binary alloy phase diagram.The results show that microstructure of Zr-Sn-Nb alloy has good stability when the temperature is 350 ℃, while the particles of α-Zr+β-Nb+Zr-Nb-F, α-Zr+β-Zr+Zr-Nb-Fe, α-Zr+β-Zr and β-Zr can be seen at 590,650,800 and 900 ℃, respectively.The second phase particles of Zr-Sn-Nb alloy are oval or circular, which is uniformly distributed in the grain and grain boundaries with the average size of 80.7 nm.Second phase with smaller size is β-Nb with cubic structure and that with larger size is Zr(Nb, Fe)2with ZrCr2 type six crystal structures, in which Nb atoms tend to occupy the position of Cr (Ⅱ), while Fe atoms tend to occupy the position of Cr (Ⅰ).Zr(Nb, Fe)2 phase under high temperature is not stable and dissolved in the matrix in the range of 650-800 ℃.Structure stability of β-Nb second phase is less than that of β-Zr, but better than that of α-Zr with the temperature increasing.Hence, when the temperature is low, microstructure of the matrix phase of Zr-Sn-Nb alloy is α-Zr.When the temperature increases, Zr(Nb, Fe)2 and β-Nb second phase both disappear and α-Zr matrix phase is gradually replaced by β-Zr.%采用场发射扫描电镜、透射电镜、X射线衍射仪结合第一性原理计算,研究Zr-Sn-Nb合金成品带材第二相粒子的结构特征,采用卧式金相显微镜结合Zr-Nb二元合金相图,分析成品带材不同热处理温度条件下显微组织的演变规律.结果表明,Zr-Sn-Nb合金成品带材第二相粒子为椭圆形或圆形,在晶粒内部和晶界呈弥散均匀分布,平均尺寸80.7 nm;尺寸较小的第二相为立方结构的β-Nb,尺寸较大的第二相为具有ZrCr2型六方晶体结构的Zr(Nb,Fe)2,Nb倾向占据Cr(Ⅱ)位置,Fe倾向占据Cr(Ⅰ)位置;成品带材350 ℃时具有较好组织稳定性,590 ℃时显微组织为α-Zr +β-Nb+Zr-Nb-Fe粒子,650 ℃时显微组织为α-Zr +β-Zr+Zr-Nb-Fe粒子,800 ℃时显微组织为α-Zr +β-Zr,900 ℃时显微组织为β-Zr;由于Zr(Nb,Fe)2第二相高温下结构不稳定,650~800 ℃发生溶解,β-Nb第二相随温度升高,其结构稳定性不及β-Zr,但优于α-Zr,因此 Zr-Sn-Nb合金成品带材温度较低时,显微组织中的基体相为α-Zr,随着温度的升高,Zr(Nb,Fe)2、β-Nb第二相消失,基体相α-Zr逐渐被β-Zr取代.