Structure and Defects of Quasicrystals

9732567广泛这笔赠款支持准晶合金性能的理论研究。含有过渡金属的富铝合金形成错综复杂的晶体结构和准晶。这些合金表现出独特的机械性能，如低摩擦系数、低温下的高硬度和高温下的延展性。准晶已经增强了外科合金的强度，最终可能会在传统金属表面涂覆一层，这些金属容易因摩擦而磨损，如油炸疼痛和汽车发动机部件。这项研究将试图了解大块准晶、它们的缺陷和表面的原子相互作用、原子结构和由此产生的力学性质。基于电子结构的金属间化合物对和多体相互作用势允许对复杂的晶体和非周期结构进行可靠的总能量计算。本研究对Al-Mn、Al-Cu-Co、Al-Ni-Co和Al-Cu-Fe等合金家族的这些相互作用进行了评估和应用。有了相互作用，我们将评估复杂晶体结构以及十方和二十面体准晶的力学和热力学稳定性。我们将改进目前对原子位置的理解，并理解特定结构的能量偏好。为了了解这些相的平衡热力学，我们将评估低能激发，如空位、化学无序和原子振动。准晶材料具有被称为相子涨落的额外类型的结构激发。相子涨落在原子位移方面的确切含义目前还不是很清楚。对热力学性质进行建模的一种策略涉及推导平铺哈密顿量。这些都是基于对小单胞结构的能量和熵的仔细评估而计算大的非周期结构的自由能的近似。利用平铺哈密顿量，我们可以研究相子的弹性和固态相变。前人的理论和实验研究涉及准晶的力学性质，包括缺陷的作用。这项研究考察了晶界和孪晶界的位错和能量的结构和长程应变场。准晶与真空或其他金属之间界面的结构变化需要注意。除了这些纯粹的结构问题外，上面讨论的低能激发还影响着原子扩散和位错运动等动力学性质。这笔拨款研究的是这些缺陷。从简化的瓦片和Lennard-Jones原子模型开始，我们最终将瓦片哈密顿量和原子结构模型联系起来。%这笔赠款支持准晶合金性质的理论研究。含有过渡金属的富铝合金形成错综复杂的晶体结构和准晶。这些合金表现出独特的机械性能，如低摩擦系数、低温下的高硬度和高温下的延展性。准晶已经增强了外科合金的强度，最终可能会在传统金属表面涂覆一层，这些金属容易因摩擦而磨损，如油炸疼痛和汽车发动机部件。这项研究将试图了解大块准晶、它们的缺陷和表面的原子相互作用、原子结构和由此产生的力学性质。***

9732567WidomThis grant supports theoretical research into the properties of quasicrystalline alloys. Aluminum-rich alloys containing transition metals form intricate crystal structures and quasicrystals. These alloys display unusual mechanical properties such as low coefficients of friction, great hardness at low temperatures, and ductility at high temperatures. Quasicrystals already strengthen surgical alloys, and may eventually coat surfaces of conventional metals subject to wear by friction, such as frying pains and automobile engine parts. The research conducted here will attempt to understand the atomic interactions, atomic structure and resulting mechanical properties of bulk quasicrystals, their defects and surfaces. Electronic structure based pair and many-body interaction potentials for intermetallic alloys allow reliable total energy calculations for complex crystalline and aperiodic structures. This research evaluates and applies these interactions for such alloy families as Al-Mn, Al-Cu-Co, Al-Ni-Co and Al-Cu-Fe. With the interactions in hand, we will evaluate mechanical and thermodynamic stability for complex crystalline structure and decagonal and icosahedral quasicrystals. We will improve current understanding of the atomic positions, and understand the energetic preference for particular structures.To understand the equilibrium thermodynamics of these phases we will evaluate low energy excitations such as vacancies, chemical disorder and atomic vibrations. Quasicrystalline materials possess additional types of structural excitations known as phason fluctuations. The precise meaning of a phason fluctuation in terms of atomic displacements is presently not well known. One stategy for modeling thermodynamic properties involves deriving tiling Hamiltonians. These are approximations for calculating the free energy of large aperiodic structures based on careful evaluation of energy and entropy for small unit cell structures. With the tiling Hamiltonian we can study phason eleasticity and solid state phase transformations.Forefront theoretical and experimental research addresses mechanical properties of quasicrystals, including the role of defects. This research examines structures and long range strain fields at dislocations and energetics of grain boundaries and twin boundaries. Structural modifications at interfaces between quasicrystals and vacuum or other metals require attention. Beyond these purely structural questions, the low energy excitations discussed above influence dynamical properties such as atomic diffusion and dislocation motion. This grant studies such defects. Starting with simplified tiling and Lennard-Jones atomistic models, we eventually link with the tiling Hamiltonians and atomic structure modeling.%%%This grant supports theoretical research into the properties of quasicrystalline alloys. Aluminum-rich alloys containing transition metals form intricate crystal structures and quasicrystals. These alloys display unusual mechanical properties such as low coefficients of friction, great hardness at low temperatures, and ductility at high temperatures. Quasicrystals already strengthen surgical alloys, and may eventually coat surfaces of conventional metals subject to wear by friction, such as frying pains and automobile engine parts. The research conducted here will attempt to understand the atomic interactions, atomic structure and resulting mechanical properties of bulk quasicrystals, their defects and surfaces. ***