Modeling the formation of free volume at grain boundaries and triple junctions during nickel crystallization

Abstract

The molecular dynamics method was used to study the formation of free volume at grain boundaries and triple junctions during crystallization using nickel as an example. To simulate the crystallization process, crystalline nuclei were used-small ideal crystals with a fixed lattice. The orientation of the crystal lattice in the nuclei was set randomly, but so that tilt boundaries with the misorientation axis <100> or <111> were formed in the result of crystallization. It is shown that the free volume during crystallization is predominantly concentrated at grain boundaries and triple junctions, and more so in the latter ones, i. e. where the last solidification of the structure occurs and crystallization fronts are encountered. The reduced density of the structure at triple junctions compared with grain boundaries is explained by the fact that when three crystallization fronts meet, the volume is fixed, where the liquid phase having a density lower than that of the crystal solidifies. The velocity of crystallization front motion is several tens of times lower than the speed of sound in a metal, therefore, defects, as a rule, formed only in the last turn-when the fronts meet, i. e. at grain boundaries and triple junctions. Disclinations at triple junctions were not observed in this work. During crystallization, relatively small subgrains with an orientation different from the neighboring grains, and usually in a stretched state, sometimes appeared in the region of triple junctions. But they "healed" relatively quickly, being absorbed by neighboring growing grains.

Получение Фрагментированной Структуры Микро И Наноуровня В Чистой Меди После Волочения И Ркуп

“…Для достижения этой цели применяют интенсивную пластическую деформацию [1][2][3]. Представляет интерес получение объемных поликристаллических материалов с субмикрокристаллической структурой (50-200 нм) [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. В настоящее время нет единого понимания схемы разбиения субзерна размером 500 нм на более мелкие фрагменты [3].…”