准晶、准晶凝固及其在材料工程上的应用(一)

Quasicrystals,Quasicrystalline Solidification and It's Applications for Materials Engineering( 1)

准晶是不具有三维周期平移序,而只具有准周期长程平移序和旋转对称性的新固体结构形态。Shechtman发现准晶使人们对晶体的认识发生了根本性变化。正是因为如此,原来的"原子在空间的规则重复排列"的晶体定义已改为"具有本质的明锐衍射花样的任何固体"。准晶绝大多数出现在Al基合金中。准晶按热力学稳定程度分亚稳相和稳定相。在自然界还存在着一些天然态准晶。为此,准晶可由熔体快速凝固或慢速凝固予以制造,并且可以应用Bridgman和Czochralski等方法制取准晶单晶。准晶具有一些独特的特性。准晶在材料工程上应用的核心点是在材料组织中出现准晶会使其力学性能得到提高。对铝基合金相应的方法可获得以准晶相为主体的组织和在固溶体的基体上出现准晶相。对钢铁材料是通过合金成分设计和热处理方法研究使在材料基体上弥散析出准晶相。

Quasicrystal is a new solid configuration with a long-range quasiperiodic translational order and rotational symmetry but no three-dimensional translational periodicity. Shechtman＇ s discover makes the knowledge to crystal to occur essential changement. This does be such case,and the International Union of Crystallography in 1992 change the definition of a crystal from＂a regular repeating array of atoms＂to＂any solid having an essentially discrete diffraction pattern＂.It is known that the much majority of quasicrystal occurs in Al-based alloys. The quasicrystals can be classed meta-stable and stable quasicrystal according to their thermo-dynemics. Quasicrystals have been found in nature. Just so,quasicrystals can be made from rapid-solidification of melted alloy or slow-solidification,and the single quasicrystal can be performed through Bridgman and Czochralski methods.Quasicrystal is possessed of their unique properties. It is the main point for application in materials engineering that the mechanical properties of materials can be raised when the quasicrystals consist in their microstructure. The respective methods for Al-based alloys are：（ 1） to get the predominant quasicrystal-line microstructure.（ 2） to get the quasicrystalline precipitation in the Al-matrix. The respective methods for steels is dispersed quasicrystalline precipitation phases in the martensite-matrix by means of alloy content design and respective attainable heat treated methods.