GOALI: Adhesion, Lubrication, and Wear of Aluminum

Arizona State University, Scottsdale AZ

Investigators

Abstract

0101840 Adams This award is a GOALI (Grant Opportunities for Academic Liaison with Industry) grant supporting research and education in the area of adhesion, lubrication, and wear of aluminum surfaces. This GOALI award involves collaborative research with the Aluminum Company of America (ALCOA) and General Motors (GM) and addresses fundamental tribological issues that impact aluminum processing and long-term durability of aluminum parts. Adhesion and wear processes are complex, and can involve many mechanisms. This project focuses on three important mechanisms, namely metal adhesion (when the lubricant and bulk oxide are penetrated), lubricant adhesion (how to maintain the lubricant on the surfaces during high stresses and temperatures), and wear processes (how material is removed, and the factors that control that removal). There are three major goals of the work. 1. Understand the factors that control metal-ceramic adhesion: In previous work, interfaces between aluminum and a model oxide and a model carbide were investigated. Density functional calculations explored many possible interface structures to determine the most favorable one. The PI investigated the electronic structure of these interfaces, using density of states, charge density, bond-order, Mulliken population analysis, and the Electron Localization Function, which, when combined, give a rich understanding of the type of bonding across the interface. The PI will extend this work from model systems to new carbide and nitride interfaces, as those materials are the most promising candidates for wear-resistant coatings. The effect of common alloying elements (Cu, Mg, Mn, Zn, and Si) on adhesion will be investigated because it is known that they have a major effect on adhesion and wear. In support of this work, GM will carry out experimental studies to measure interfacial adhesion energies for direct comparison with these calculations. 2. Investigate how lubricant boundary additives react with and bond to aluminum surfaces: These molecules are added to lubricants so that one end can bind to the surface while the other end is compatible with the lubricant, so that the lubricant is kept on the surface during high stresses. Previous work involved electronic structure investigations of how typical boundary additives (alcohols, carboxylic acids, and esters) react and bond to the surface. A combination of ab-initio molecular dynamics and geometry optimization enabled the determination of optimal reaction paths and typical products for several boundary additive species. This award will extend previous work that focused on additives used for metals processing to investigate additives used for automotive engine lubricants. A similar set of complementary simulations and calculations will be performed to determine optimal reaction pathways and final structures of typical bound species. The PI will also explore how high compressive and shear loads can cause some interfacial lubricants to react with and soften the surface. 3. Investigate the factors that control nanoindentation and wear: In previous work, empirical MD simulations were used to investigate many factors that affect nanoindentation, including temperature, surface orientation, indent load/speed, tip geometry, and tip-substrate interactions. Atomic scale deformation mechanisms, including local amorphization/melting and dislocation nucleation and motion, were visualized. Similar studies for asperity-asperity shear were also carried out. These calculations were complemented by experimental nanoindentation studies at GM, AFM tip dragging studies at ALCOA, and GM's continuum mechanics/finite element modeling of nanoindentation/wear. In this award, the PI plans to extend these nanoindentation and asperity-asperity simulations to include the effect of alloying elements (Cu and Mg), for both low concentrations (solid solutions) and high concentrations (precipitate formation), to see how those affect deformation mechanisms. Simulations of AFM tip dragging will be performed and compared with experimental results. The effect of thin native oxides on the surface, and boundary lubricants will also be explored. %%% This award is a GOALI (Grant Opportunities for Academic Liaison with Industry) grant supporting research and education in the area of adhesion, lubrication, and wear of aluminum surfaces. The research is a collaborative effort involving the University of Arizona, the Aluminum Company of America (ALCOA), and General Motors (GM) and addresses fundamental tribological issues that impact aluminum processing and long-term durability of aluminum parts. Adhesive and abrasive wear during bulk aluminum forming limits the stresses that can be applied, damages processing equipment, and impacts surface properties such as image clarity, spot weldability, and lubricant retention. Similarly, improvements in wear and lubrication of aluminum will enable greater use of aluminum in automobile engine applications, allowing weight reduction and increases in fuel efficiency, durability, and performance. The award supports interaction with industry on problems of fundamental and industrial interest using the tools of molecular dynamics simulation and electronic structure tools. The results will be tested at ALOCA and GM laboratories. The award provides an opportunity for graduate students trained in the use of materials simulation methods and electronic structure theory to tackle real-world problems and develop skills useful for industry and academe alike. ***