Jun Zhong

By Jun Zhong

In this chapter, density functional theory (DFT) is employed to identify the essentials of adhesive formation at the Al/Ceramic interfaces. Analyses of electronic structure in the DFT used for atomic bond evolution at interfaces, indicate that, adhesion energy mostly dominated by surface energy, may lead to formation of adhesives, which bind two type bulk-materials strongly together, especially for those polar systems involving cubic oxides, carbides and nitrides. In addition, ab-initio molecular dynamics (AIMD) based upon the DFT is adopted, for example, in the simulation of chemical reaction between two contacting reactive slabs: pure aluminum and iron-oxide. This may provide an insight into the dynamical formation of an adhesive (amorphous Al2O3-texture) occurring between two nascent material surfaces if lubricants are not present or are insufficient. Such a texture may bond onto a hard-roller surface as a protective thin film to resist the elevated temperature.

Part of the book: Adhesives

By Jun Zhong

In this chapter, to assist the design of aluminum processing, density functional theory is utilized to depict optimal adsorption geometries on an Al (111) surface for two commonly used boundary-layer lubricant additives: vinyl-phosphonic and acetic acids, i.e., tri-bridged, bi-bridged, and uni-dentate coordinations of these adsorbates are examined to determine the optimal binding sites on the surface. During these static analyses, charge density of states for molecular oxygen ions reacting with Al ions in the surface is applied to revealing the evolution essentials of molecular binding strength on surface. In addition, ab-initio molecular dynamics based upon density functional theory is employed to probe dynamic decomposition pathways on the Al (111) surface for two other important boundary-layer lubricant additives: butanoic acid and butanol alcohol. These decomposition pathways may occur upon molecular collisions with the surface, leading to formation of molecular pieces adhering on surface. Simulations are found to be in qualitative accord with existing experimental observations.

Part of the book: Tribology, Lubricants and Additives

By Jun Zhong

In this Chapter, a severely adhesive wear on a rough aluminum (Al) substrate is simulated by molecular dynamics (MD) under a high velocity impact of a hard-asperity (a hard-tip) with the Al-asperity. Multiple simulations include effects of four factors: the inter-asperity bonding, the geometry overlap between two asperities, the impact velocity between two asperities and the starting temperature of the Al-substrate. It is observed that the deformation mechanism on the Al-substrate would involve a local melting (from 1200 to 2500 K) which forms liquid type layers (amorphous textures) in the contact area between two asperities. Also, temperature profiles on the hard-tip and the Al-substrate is depicted. Moreover, a method in the Design of Experiments (DOE) is employed to interpret above all simulations. The DOE results indicate that the inter-asperity bonding and the geometry overlap between two asperities would substantially increase the wear rate (for about 53.56% and 67.29% contributions), while the starting temperature of the Al-substrate and the impact velocity between two asperities would play less important roles (about 10.30% and 6.61%) in raising the wear rate.

Part of the book: Tribology in Materials and Manufacturing