Font Size: a A A

The Simulation Study Of Molecule Dynamics On Transition Of Microstructure During The Rapid Cooling Process Form Al Liquid State(943K)to Amorphous State

Posted on:2002-07-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:C X ZhengFull Text:PDF
GTID:1101360032457524Subject:Materials science
Abstract/Summary:PDF Full Text Request
The molecular dynamics computer simulation study of Al liquid state (943 K) system constituted of 50,000 atoms and the rapid cooling process from liquid to amorphous state was first completed. The polyhedrals and cluster structure model of liquid state and amorphous state was established to study the change of the microstructure during the rapid solidification from liquid state to amorphous state. The following are the main results: 1. Though the atomic arrangement in liquid state (943K) Al is out of order in a long rang, yet it is instantaneously orderly in a short range, because bonded atoms construct polyhedrals. (1) The system of liquid state (943) Al abounds in the following bond types: 1551,1541 and 1431. The percentages of them are 16.8%, 15.2% and 21.5% respectively. The sum of them reaches 54%. The amounts of bond types 1421 and 1422 that relate to the fcc and hcp crystals are about 3.4% and 7.0% respectively. The amount of bond types 1321,1311 and 1301 that relate to the rhombohedron is about 14%. The amounts of bond types 1441 and 1661 that exist in bcc crystals are about 4.8% and 5.1% respectively. The sum of nearly ionized state bond types 1201 and 1211 is about 1.3%. The sum of various bond types is about 95% at 943K. It means that the amount of atoms that exist in nearly ionized state is less than 5%. Atoms above 95% exist in various structures with strong or weak orderly bonds in the system. (2) Bonds 1551,1441 and 1661 construct various closed polyhedral structures according to the requirements of Euler?polyhedral formula. The most of them exists in the short-range orderly form ?the icosahedron type (12 0 12 0). The number of them is 186 at 943K. As the defective structure of icosahedron, there are many atomic triangular polyhedrals that arrange irregularly with coordination number 12, 13, 14, 15 and 16. The total number of them is 462 at 943K. (3) The surrounding atoms in polyhedrals can bond with the neighboring atoms according to certain types. or the polyhedrals combine one another to form a cluster structure with one polyhedral as the nucleus. (4) In view of microstructure, there are dense regions of atomic aggregates and rare regions of ionized atoms. (5) The above data fluctuate due to the thermodnamic fluctuation. The structures of polyhedrals and clusters are unstable. The boundaries and the sizes of dense regions and rare regions are alwa s changing. 2. During the rapid solidification of liquid Al, the system undergoes a series of state transformations: liquid state, super cooling liquid state and solid state. Different the bond types and polyhedrals appeared in the liquid structure have different transformation tendency. (1) When the temperature of the liquid system decreases to 3 00K, the number of bond type 1551 increases 75%; the number of bond type 1541 increases only about 5.4%; but the number of bond type 1431 decreases 3.8%. The sum of these three types is 67% of the total number of various bond types. The number of bond types 1421 and 1422 that relate to fcc and hcp crystals decreases. The total number of them is 7.4% at 300K. The total number of bond types 1331 and 1311 that relate to rhombohedral structure decreases. The total number of them is 9.3% at 300K. The numbers of bond type 1441 and 1661 are 3.85% and 5.54% respectively. The numbers of bond type 1201 and 1211 that are nearly ionized decreases to 1.67%. The total number of various bond types is about to 98% at 3 00K. From the above transformation tendency, we can see that the rapid co...
Keywords/Search Tags:rapid concretion, amorphous metal A, Bonding analysis, polyhedron and cluster, amorphous configuration model, molecule dynamics, computer simulation
PDF Full Text Request
Related items