硼、铌元素在微合金钢与高纯镍中的晶界偏聚行为
发布时间：2018-12-23 20:35
【摘要】：硼(B)、铌(Nb)元素在合金材料晶界的偏聚行为,直接影响合金材料的机械性能。澄清B、Nb元素在晶界的偏聚机制,有助于精准控制其在晶界的偏聚行为,进而提高材料的性能。本论文综合运用飞行时间二次离子质谱、俄歇电子能谱、透射电子显微镜和电子背散射衍射等技术研究了高温变形高纯镍和连续冷却淬火的微合金钢中B、Nb元素在晶界的偏聚,并采用正电子湮没寿命技术分析了冷却过程中微合金钢中空位和位错等缺陷的行为。最后采用基于密度泛函理论的第一性原理研究了 B在bcc-Fe和fcc-Fe中的固溶方式和扩散机制。利用飞行时间二次离子质谱技术,在高温变形高纯镍中直接观察到B在一般晶界和退火孪晶界上均形成显著的偏聚,且偏聚区域的宽度随着变形温度的降低而增大。相同热处理工艺下,B在孪晶界上的偏聚明显比一般晶界上的偏聚弱。在一般晶界上观察到两种形态的偏聚:在1100℃变形(发生明显的再结晶行为)的样品中,B偏聚区域局限于晶界附近约1 μm范围内,偏聚程度较强;在700℃变形(未发生明显的再结晶行为)的样品中,B偏聚区域分布在晶界两侧约6 μm的范围内,偏聚程度较弱。在部分样品中的一般晶界上可以同时观察到这两种形态的偏聚。在微合金钢连续冷却过程中,随着温度的降低,Nb在原奥氏体晶界上的偏聚逐渐增强,同时利用正电子湮没寿命技术发现这一过程中伴随着材料内部空位型缺陷浓度的降低。分析认为冷却过程中空位向晶界的扩散和位错向晶界的移动可能均会促进Nb向晶界的偏聚。借助于飞行时间二次离子质谱技术,在连续冷却微合金钢的原奥氏体晶界上直接观察到了沿着原奥氏体晶界分布的Nb、Cu富集区。通过对原奥氏体晶界附近约40 μm范围内的所有富集区进行分析,发现Nb只在Cu富集区内出现富集,表明在微合金钢连续冷却过程中Cu元素促进了 Nb在奥氏体晶界的富集。利用透射电子显微镜在原奥氏体晶界上观察到了含Nb和Cu的析出物。根据第一性原理计算结果,在bcc-Fe中B既可以占据置换位置,又可以占据八面体中心位置,但以间隙机制进行扩散。所得扩散系数为,D_0=1.05×10~(-7)×exp(-0.75eV/kBT)m~2·s~(-1)与实验结果基本吻合。在fcc-Fe中B倾向于占据置换位置,计算所得B以B-单空位复合体机制扩散的扩散系数约为D_0=6.30× 10~6×exp(-2.01 eV/kBT)m~2·s~(-1)。
[Abstract]:The segregation behavior of boron (B), niobium (Nb) at the grain boundary of the alloy directly affects the mechanical properties of the alloy. Clarifying the segregation mechanism of BNb at grain boundary is helpful to accurately control the segregation behavior of Bnb at grain boundary and improve the properties of the material. In this paper, the time of flight secondary ion mass spectrometry, Auger electron spectroscopy, transmission electron microscope and electron backscattering diffraction were used to study the high temperature deformed high purity nickel and continuous cooling quenched microalloyed steel. The segregation of Nb elements at grain boundaries and the behavior of defects such as vacancies and dislocations in microalloyed steels during cooling were analyzed by positron annihilation lifetime technique. Finally, the solution mode and diffusion mechanism of B in bcc-Fe and fcc-Fe were studied by using the first principle based on density functional theory (DFT). By means of time of flight secondary ion mass spectrometry, it was observed that the segregation of B was observed at both general grain boundary and annealing twin boundary directly in high-purity nickel deformed at high temperature, and the width of segregation region increased with the decrease of deformation temperature. Under the same heat treatment process, the segregation of B on twin boundary is obviously weaker than that on general grain boundary. Two kinds of segregation were observed at general grain boundaries: in the samples deformed at 1100 鈩，
本文编号：2390229
[Abstract]:The segregation behavior of boron (B), niobium (Nb) at the grain boundary of the alloy directly affects the mechanical properties of the alloy. Clarifying the segregation mechanism of BNb at grain boundary is helpful to accurately control the segregation behavior of Bnb at grain boundary and improve the properties of the material. In this paper, the time of flight secondary ion mass spectrometry, Auger electron spectroscopy, transmission electron microscope and electron backscattering diffraction were used to study the high temperature deformed high purity nickel and continuous cooling quenched microalloyed steel. The segregation of Nb elements at grain boundaries and the behavior of defects such as vacancies and dislocations in microalloyed steels during cooling were analyzed by positron annihilation lifetime technique. Finally, the solution mode and diffusion mechanism of B in bcc-Fe and fcc-Fe were studied by using the first principle based on density functional theory (DFT). By means of time of flight secondary ion mass spectrometry, it was observed that the segregation of B was observed at both general grain boundary and annealing twin boundary directly in high-purity nickel deformed at high temperature, and the width of segregation region increased with the decrease of deformation temperature. Under the same heat treatment process, the segregation of B on twin boundary is obviously weaker than that on general grain boundary. Two kinds of segregation were observed at general grain boundaries: in the samples deformed at 1100 鈩，
本文编号：2390229
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