【作者】 张艳华；

【导师】 刘永长；

【作者基本信息】 天津大学 ， 材料学， 2008， 博士

【摘要】 非平衡凝固合金由于其特殊的微观结构导致其具有许多优异的性能。随着航天航空及运输工具轻型化的迅速发展,具有较高比强度的Al基快速凝固合金尤其是Al基非晶合金表现出广阔的应用前景。晶化动力学模型在分析非晶相的形成过程及热稳定性方面具有重要的价值,因此一直受到研究者的关注,如何提高模型在实际分析过程中的精确度从而得出正确的分析结果是非晶晶化模型追求的主要目标。论文系统研究了非平衡凝固条件下冷却速度和合金成分对Al-Fe-Si合金凝固组织的影响规律;通过制备Al-Fe-Si-(Zr)非晶合金,研究了该合金中纳米晶/非晶复合结构的形成及其动力学机理;为进一步精确描述动力学过程,对等时动力学模型进行了改进,发展了多峰转变模型和孕育动力学模型。研究结果表明:非平衡凝固过程中,冷却速度和合金成分对合金的凝固组织具有显著地影响。其中,亚快速凝固条件下,冷却速度决定了Al-Fe-Si合金中凝固组织的相选择,并对其凝固组织中金属间化合物的形貌、尺寸、分布及体积分数有显著影响;快速凝固条件下,Al-Fe-Si-(Zr)合金的冷却速度越高,越有利于非晶相的形成。此外,快速凝固Al-Fe-Si-(Zr)合金中,Fe和Zr元素的含量对非晶相的形成也有明显的促进作用,两者促进非晶相的形成原因却有所不同。快速凝固条件下,对Al-Fe-Si-Zr合金的微观组织观察可知,此时的合金为10 nm左右的纳米Al颗粒随机分布在非晶基体中的纳米晶/非晶复合结构中。等时晶化过程动力学分析结果表明其晶化过程分两步进行,且两步晶化过程进行的难易程度大致相当。对传统的等时晶化动力学模型进行改进,同时建立了适用于晶化过程中普遍存在的多相转变的多峰转变模型,并以此对具体合金体系的晶化过程进行了研究。结果表明,特别是在具有较小转变温度范围的非晶合金体系中,改进的等时晶化模型和多峰转变模型均具有较高的精确度。此外,还建立了较为完善的晶化孕育动力学模型,并用于具体非晶合金的孕育动力学,分析结果和实验数据保持了较高的一致性。更多还原

【Abstract】 Compared with conventional crystalline alloys, non-equilibrium solidified alloys show outstanding mechanical properties due to their special microstructure. The rapidly solidified Al-based alloys, especially the Al-based amorphous alloys, are highlighted because of their specific strength, tunable corrosion resistance and high fracture strength. It makes Al-based glasses to be very promising materials for potential aerospace applications. The crystallization kinetic model has been used to improve the analysis result accuracy and get the correct conclusion about crystallization process, which is very important for studying the formation mechanism of amorphous alloys and their thermal stability.This thesis mainly focus on the contents below: the solidification behavior of Al-Fe-Si-(Zr) alloy under sub-rapid or rapid solidification, such as the influence of cooling rate on the microstructural evolution of alloy (Chapters 2 and 3); the effect of cooling rate and the composition of alloy on the crystallization of amorphous phase, which formed during the rapid solidification (Chapter 4); the formation and crystallization of nano/amorphous Al-Fe-Si-Zr alloy (Chapter 5); improvement of isochronal crystallization kinetics model and its application to the amorphous alloy (Chapters 6 and 7); establishment of multi-peak transformation kinetics model and incubation kinetics model and the study on their validity in the practical application in chapter 8. The results indicate that:The cooling rate and components of alloy agents influence the microstructure of alloy under non-equilibrium condition. In the sub-equilibrium condition, the cooling rate affects no only the phase selection, but also the volume fraction, shape and size of the intermetallic compounds. The increase of cooling rate and component of Fe or Zr in Al-Fe-Si-(Zr) both contribute to the formation of amorphous phase.In the as-spun Al89Fe8Si2Zr ribbons, a composite nanocrystalline/amorphous structure formed companied with the average size of nano Al particles of about 10 nm and the crystallization of as-spun composite Al89Fe8Si2Zr was investigated by the continuous heating annealing DSC analysis. The result showed that the crystallization process two progresses, which with the approximately same reaction rates.An improved analytical model for isochronal transformation kinetics has been developed. The proposed treatment for the temperature integral and the consequent analytical model for isochronal transformation kinetics have been proved to be more effective than the previous model especially in a narrow temperature interval by numerical method. Moreover, both the multi-peak transformation kinetics model and incubation kinetics model established here show the validity and precision during their practical applications.更多还原