The Energy And Structure Of Low Index Twist Grain Boundary For Noble Metals Au, Ag And Cu

Grain boundary (GB) can affect materials especially those nano-materials significantly in their physical, chemical and mechanical properties, while it may be the decisive factor sometimes in mechanical properties and malfunctions of metals. The special character of GB comes from its special structure and energy which is different from the bulk material. Thus, the research in GB's structure and energy is the foundation for the knowledge of materials and then enable us to change some of their properties even to design new type of materials. In this dissertation, the unrelaxed energy and structure of the (001), (011) and (111) low index GBs for noble metals such as Au, Ag and Cu are calculated with the modified analytical embedded atom method (MAEAM), the relaxed energy and structure of the (001) GB are also included for these metals. The principal results of the calculation can be concluded as:(1) The unrelaxed (001), (011) and (111) low index GB energy of the three metals Au, Ag and Cu doesn't increase with the twist angle θ except the zero energy when 8 = 0, but oscillates for low 2 value (reciprocal planar coincidence density of crystal lattices) GBs and converges towards a constant value with the increase of 2 value, and the the energy oscillation is related to its planar spacing d₀, smaller value of d₀ corresponding to more violent oscillation. Which is related to da also is the energy order of the three boundaries that the GB with larger d0 shows lower energy, that is, the (011) GB energy is the highest of the three and the (111) GB energy is the lowest.(2) In-boundary translation of the twin-grains can result in periodic unrelaxed energy variation, the period is a square with the side length L_∑/∑ for (001), a rectangular with the side length L_∑¹ /2 and L_∑²/∑ for (011) GB, a rhombus with the side length L_∑ /∑ for (111) GB respectively. The lowest energy can't appear at other configurations except the structures when it is translated to the centre or corners of the quadrilateral or the centre of its sides which should be the slide direction in our prediction for the sliding between twin-grains. The energy variation caused by translation decreases with the planar spacing d0 the reciprocal planar coincidence density of crystal lattices ∑.