第一原理合金热力学问题研究

IMR OpenIR

	第一原理合金热力学问题研究
	张会
学位类型	博士
导师	王绍青
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料物理与化学
关键词	合金材料热力学第一原理 Alloy Material Thermodynamic First-principles
摘要	"计算材料学的最终目的可能就是可以完全按照人们愿望来设计材料。要实现这个目标，需要对材料行为的基本机制完全的了解，尤其是需要了解热力学、形核、相稳定性等热力学方面的信息。以密度泛函理论为基础的第一原理计算方法，不需要任何实验参数，在本质上具有预测性。本论文采用第一原理计算方法，对若干合金材料的热力学性质进行了研究，包括相稳定性、相变以及合金相的力学性质等等。本论文共分八章。第一和第二章分别介绍了第一原理合金热力学方法的研究现状、理论和研究方法。在第三和第四章中，我们应用第一原理合金热力学方法研究了晶格振动效应对Al-Ti-和Al-Zr两个二元系中合金相稳定性的影响。计算出的Al-Zr系中的共析相变温度与实验结果符合得很好。我们的工作表明，晶格振动对某些合金系在高温下的相稳定性起着关键的作用，第一原理合金热力学方法，可以在不依赖实验数据的条件下，成功地预测合金的相平衡关系。 Al-Sc一般被用作高强度材料。Al-Sc合金的优良性能源于Sc在铝合金中能够析出稳定的L12 Al3Sc有序相。在周期表中与Sc近邻的元素M (M=Y，Ti, Zr, V, Nb, Ta...)经常被添加到AlSc合金中，以进一步提高其机械性能和降低成本。目前，添加元素M在Al3Sc中的占位以及Al3(Sc1-xMx)固溶体的稳定性还不清楚。在第五章中，我们的第一原理计算发现，Ti, Zr, Y 和 Ta倾向于替换Al3Sc中的Sc 原子，而Ni和Si 则倾向于替换Al原子。镁合金是航空航天工业中使用较多的轻质结构材料，近几年其在汽车工业中的应用受到了更多的关注。如何提高镁合金的高温抗蠕变性能是当下镁合金研究的热点之一，具有很重要的理论和应用价值。如今应用最广泛的镁合金为Mg-Al合金，人们主要采用添加合金元素的方法来强化Mg-Al合金，提高其抗蠕变性能。Mg-Al合金中加入Ca元素可以显著提高其抗蠕变性能，却同时发生了热裂缺陷。在第六章中，我们探讨了Mg-Al-Ca合金的热裂机制，发现，Mg2Ca的热膨胀行为与Mg基体比较接近，而Al2Ca的热膨胀系数则小得多，计算结果定性地揭示出了Al2Ca在合金热裂形成过程中扮演着重要的角色。添加稀土元素可以有效地提高镁合金高温抗蠕变性能。La和Nd是镁合金常用的合金化元素，但两种合金强化相的种类不同，二者强化机理也不完全一样。在第七章中，我们应用第一原理计算方法，研究了Mg-La和Mg-Nd二元合金中的化合物的相平衡关系，计算了La和Nd在Mg中的溶解度，以及强化相的弹性常数。我们的工作丰富了Mg-La和Mg-Nd的相图信息，有助于理解不同稀土元素在镁合金中的强化机理。第八章对本论文的研究内容做了总结。"
其他摘要	" Possibly the loftiest goal of materials science is the ability to design alloys with specific technological properties. To accomplish this goal it is necessary to have a thorough understanding of the fundamental mechanisms underlying materials behavior. In particular, one must acquire the information about thermodynamic, kinetic behavior and phase stability. The first-principles method, based on the density function theory (DFT), is predictive in nature, with little or without any experiment input. In this dissertation, first-principles calculations are carried out to investigate the thermodynamic properties of advanced structural materials, including phase stability, phase transformations, and the mechanical properties of compounds, etc. The dissertation is divided into eight chapters. In the first two chapters, an overview on the first-principles alloy thermodynamics method is given, including its research status, theories and methodologies.In Chapters 3 and 4, the first-principle alloy thermodynamic method is used to investigate lattice vibration effects on the phase stability of the two binary systems Al-Ti and Al-Zr. The calculated phase transition temperature of eutectoid reaction agrees very well with the experiments. The lattice vibration is proved to play a critical role in phase stability at high temperatures. The first-principles alloy thermodynamic method can predict the phase equilibrium in alloys without any experimental input. Al-Sc alloys are generally used as high-strength materials. The excellent properties of Al-Sc alloys are mainly attributed to the cubic L12 Al3Sc formation. The elements M (M=Y, Ti, Zr, V, Nb, and Ta etc.) near Sc in the period table are widely added to Al-Sc alloys in order to further improve mechanical properties and decrease the cost. At present, the site preference of the added elements M in Al3Sc and structural stability of Al3(Sc1-xMx) is not clear yet. The first-principles calculations in Chapter 5 show that Ti, Zr, Y and Ta tend to substitute for Sc in Al3Sc, while Ni and Si prefer to substitute for Al. Magnesium alloys are the light-weight structural material used in aerospace industry. In the past a few years, the application of magnesium alloys in automotive industry has attracted more attentions. How to improve the high-temperature creep resistance property is a central issue of study on magnesium alloy and has an important theoretical and application value. Mg-Al alloys have been attempted extensively. Many other elements are alloyed to Mg-Al alloys to elevate their high-temperature creep resistance. Adding Ca element significantly improves the creep resistance of Mg-Al alloys, but concurrently leads to the occurrence of severe hot crack defect. The hot-crack mechanism of Mg-Al-Ca alloys is discussed in Chapter 6. The calculations show that the thermal expansion of Mg2Ca is very close to Mg, whereas that of Al2Ca is much too lower than both Mg and Mg2Ca. Al2Ca is proved to play a critical role in hot crack formation. Rare earth elements addition can effectively improve the poor high-temperature creep resistance property of magnesium alloys. La and Nd are the two elements usually added to magnesium alloys. However, the kinds of the strengthening phase are different, and the strengthen mechanism is not completely identical. In Chapter 7, first-principles calculations are made to investigate the phase equilibrium in Mg-La and Mg-Nd binary systems. In addition, the solubility of La and Nd in Mg is discussed and the elastic constants of the strengthening phases in Mg-La and Mg-Nd alloys are calculated. Our work provides much additional information on Mg-La and Mg-Nd phase diagrams, and is of important significance to understanding strengthening mechanism of different rare earth elements in magnesium alloy. Chapter 8 summarizes the research contents in this dissertation."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64476
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	张会. 第一原理合金热力学问题研究[D]. 北京. 中国科学院金属研究所,2012.