Ni-B合金亚稳晶粒形成及其生长热—动力学效应研究
发布时间：2019-04-17 06:31
【摘要】：提高微晶、纳米晶材料的热稳定性是发挥其力学性能优势以及实现其广泛工程应用的关键。因而对微晶,纳米晶在成型过程和处理过程中的各项稳定性特征的研究具有重要意义。本文以低固溶度的Ni-B合金为研究对象,从实验出发并结合理论模型深入研究了其亚稳晶粒的形成和稳定化的机制。得出的主要结论如下:(1)利用循环过热和熔融净化的深过冷法制得了微晶Ni-1at.%B合金,其凝固组织形貌在ΔT80 K前经历了一个由枝晶向条状晶再到等轴细晶的过程。通过对不同过冷度下Ni-B合金的多项微观结构进行分析和表征,我们分析了不同过冷度的合金组织在凝固的不同阶段的晶粒细化机理。同时以合金中溶质拖拽力,溶质的钉扎作用以及初始过冷度的相互作用为基础,分析了Ni-B微晶合金凝固过程中固态变化过程中的晶粒生长机理,即随着过冷度的增加(80-230 K),在快速凝固之后到淬火之前,Ni-B合金微晶组织的生长方式经历了一个由正常到异常再变为正常的过程。(2)立足于有关激活能和晶界移动性的Arrhenius方程,建立了一个合金稳定化过程中的激活能变化的新模型,模型的验证和分析以纳米RuAl合金基础。同时,我们以晶粒生长的抛物线模型为基础,将热力学模型与动力学模型相结合,通过多种方法对晶粒生长的热动力学模型进行了建立和讨论。(3)通过对等温退火处理后的Ni-B微晶合金的晶粒、晶界形貌以及合金中溶质成分、组成物相的分析,合金的稳定性得到了研究。在长时间的退火过程中合金的组织经历了一个生长到初始稳定和再生长到最终稳定的过程,在退火过程中晶粒的二次生长与晶界处第二相沉淀的产生密切相关,其对晶粒的二次生长具有一定的促进作用。通过对Ni-B微晶合金晶粒生长进行拟合计算和稳定化过程中晶界能变化的分析,整个退火过程中晶粒的生长机理得到了研究。退火过程中,溶质原子B在晶界处的偏聚和富集使得合金组织得到了初始的稳定;但随着第二相沉淀在晶界处形成,其使得原先减小的晶界能又重新增加,进而为晶粒的二次生长提供了新的驱动力;同时沉淀相也具有拖拽力的作用,当拖拽力PZ逼近与驱动力PD时,微晶合金晶粒达到最终的稳定。
[Abstract]:Improving the thermal stability of microcrystalline and nanocrystalline materials is the key to give full play to their advantages in mechanical properties and to realize their extensive engineering applications. Therefore, it is of great significance to study the stability characteristics of microcrystals and nanocrystals in the process of forming and treatment. In this paper, the mechanism of metastable grain formation and stabilization of Ni-B alloy with low solid solubility was studied by experiments and theoretical model. The main conclusions are as follows: (1) Microcrystalline Ni-1at.%B alloy was prepared by means of cyclic superheating and melting purification. The solidification microstructure of the alloy experienced a process from dendrite to striped grain to equiaxed fine grain before 螖 T _ (80 K). By analyzing and characterizing the microstructure of Ni-B alloy with different undercooling degree, we have analyzed the grain refinement mechanism of the alloy with different undercooling degree at different stages of solidification. At the same time, based on the solute drag force, solute pinning and the interaction of initial undercooling degree, the grain growth mechanism of Ni-B microcrystalline alloy during solidification was analyzed. That is, as the degree of undercooling increases (80? 230 K), after rapid solidification to pre-quenching, The growth mode of microcrystalline structure of Ni-B alloy has undergone a process from normal to abnormal and then to normal. (2) based on the Arrhenius equation concerning activation energy and grain boundary mobility. A new model of activation energy variation during alloy stabilization was established. The verification and analysis of the model were based on nano-RuAl alloy. At the same time, based on the parabola model of grain growth, we combine the thermodynamic model with the kinetic model. The thermodynamic models of grain growth were established and discussed by various methods. (3) the grain size, grain boundary morphology, solute composition and composition of Ni-B microcrystalline alloy after isothermal annealing were analyzed. The stability of the alloy has been studied. During the long annealing process, the microstructure of the alloy has undergone a process of growth to initial stability and re-growth to final stability. During annealing, the secondary growth of grains is closely related to the formation of the second phase precipitation at the grain boundary. It can promote the secondary growth of grain. The grain growth mechanism of Ni-B microcrystalline alloy during annealing has been studied by fitting calculation and analyzing the variation of grain boundary energy in the process of stabilization. During annealing, the segregation and enrichment of solute atom B at the grain boundary makes the initial microstructure of the alloy stable. However, with the formation of the second phase at the grain boundary, the original reduced grain boundary energy increases again, thus providing a new driving force for the secondary growth of the grain. At the same time, the precipitate phase also has the effect of drag force. When the drag force PZ approaches to the driving force PD, the grain size of the microcrystalline alloy reaches the final stability.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG146.15
[Abstract]:Improving the thermal stability of microcrystalline and nanocrystalline materials is the key to give full play to their advantages in mechanical properties and to realize their extensive engineering applications. Therefore, it is of great significance to study the stability characteristics of microcrystals and nanocrystals in the process of forming and treatment. In this paper, the mechanism of metastable grain formation and stabilization of Ni-B alloy with low solid solubility was studied by experiments and theoretical model. The main conclusions are as follows: (1) Microcrystalline Ni-1at.%B alloy was prepared by means of cyclic superheating and melting purification. The solidification microstructure of the alloy experienced a process from dendrite to striped grain to equiaxed fine grain before 螖 T _ (80 K). By analyzing and characterizing the microstructure of Ni-B alloy with different undercooling degree, we have analyzed the grain refinement mechanism of the alloy with different undercooling degree at different stages of solidification. At the same time, based on the solute drag force, solute pinning and the interaction of initial undercooling degree, the grain growth mechanism of Ni-B microcrystalline alloy during solidification was analyzed. That is, as the degree of undercooling increases (80? 230 K), after rapid solidification to pre-quenching, The growth mode of microcrystalline structure of Ni-B alloy has undergone a process from normal to abnormal and then to normal. (2) based on the Arrhenius equation concerning activation energy and grain boundary mobility. A new model of activation energy variation during alloy stabilization was established. The verification and analysis of the model were based on nano-RuAl alloy. At the same time, based on the parabola model of grain growth, we combine the thermodynamic model with the kinetic model. The thermodynamic models of grain growth were established and discussed by various methods. (3) the grain size, grain boundary morphology, solute composition and composition of Ni-B microcrystalline alloy after isothermal annealing were analyzed. The stability of the alloy has been studied. During the long annealing process, the microstructure of the alloy has undergone a process of growth to initial stability and re-growth to final stability. During annealing, the secondary growth of grains is closely related to the formation of the second phase precipitation at the grain boundary. It can promote the secondary growth of grain. The grain growth mechanism of Ni-B microcrystalline alloy during annealing has been studied by fitting calculation and analyzing the variation of grain boundary energy in the process of stabilization. During annealing, the segregation and enrichment of solute atom B at the grain boundary makes the initial microstructure of the alloy stable. However, with the formation of the second phase at the grain boundary, the original reduced grain boundary energy increases again, thus providing a new driving force for the secondary growth of the grain. At the same time, the precipitate phase also has the effect of drag force. When the drag force PZ approaches to the driving force PD, the grain size of the microcrystalline alloy reaches the final stability.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG146.15
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