液态金属铝的热历史对凝固微结构的影响

用分子动力学模拟研究了液态金属Al 系统的热历史对凝固微结构的影响.发现在同一系统中、不同的热历史条件下， 1551 键型和与1551键型相关的二十面体结构(12 0 12 0)在微结构的转变过程中均起着非常重要的作用. 特别有意义的是, 在每个温度的等温运行中能够重复出现的二十面体的数目不随温度的降低而增加, 并有一个极大值.该极大值点正好与其玻璃转变温度Tg相对应, 在不同的热历史条件下极大值的位置是能够移动的.结果还显示出, 热历史条件对微结构转变有严重影响, 且其作用主要是在玻璃转变温度点Tg以后才显示出来. 这就为我们理解和控制凝固过程中的微结构转变提供了一条新途径.

Effects of Thermal History of Liquid Metal Al on Its Solidification Microstructures

The effects of thermal history of liquid metal Al on its solidification microslructures have been studied by using molecular dynamics simulation. It has been found that under different thermal history conditions, in the same system, both the 1551 bond-type and the icosahedron (expressed by (12 0 12 0)) related to the 1551 bond-type play a remarkable role during microstructure transitions (see Fig. 4 ) . The number of re-peatable icosahedra not always increased with the decrease of temperature and has a maximum during the isothermal runs at given temperatures (see Fig. 6) . The maximum point corresponds to the glass transition temperature Tg, and can be moved under different thermal history conditions. It is also demonstrated that the thermal history conditions seriously influence the solidification microstructures and their effects are mainly demonstrated after the glass transition point. These results give a new way to understand and control the microstructure transitions during solidification processes.