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Structural Materials

Overview

An 18R long-period stacking ordered (LPSO) structure comprised of an HCP magnesium matrix with layers containing zinc and yttrium.

An important avenue of improving energy efficiency in transportation is the development of lighter and/or more efficient materials that compose the body of the vehicle. For automobiles, a promising possibility is to replace the aluminum alloys that make up a large portion of the mass of the car with lighter magnesium alloys. Unfortunately, magnesium alloys tend to have poorer mechanical properties than their aluminum counterparts. However, advances in processing and doping magnesium alloys show potential in improving the strength of magnesium alloys, such as the formation of long-period stacking ordered precipitates and the use of rare earth dopants. Another avenue we are exploring for improving efficiency in transportation is next-gen superalloys for jet engine tubrine blades based on Co. Calculating the thermodynamic and kinetic properties of these alloys allows us to understand the physics of the strengthening mechanisms and suggest novel compositions and processing mechanisms with improved strength.

Impurity volume in hcp Mg vs. formation energy of Mg3X L12 for many elements from DFT. The red elements are those that strengthen Mg by the formation of LPSO precipitates. New elements that may do the same thing could be those near the red elements.
Through the use of density functional theory (DFT), two important questions can be answered. The first is why do these phenomena improve mechanical properties?  DFT can predict properties that are difficult or impossible to determine experimentally, such as charge density, enthalpy of formation, diffusion coefficients, interfacial energy, etc. Having these properties helps to reveal fundamental strengthening mechanisms. This then leads into the second question: are there stronger alloy compositions? This is a very difficult question to answer experimentally as there are MANY elements in the periodic table and systematically investigating them all would be prohibitively expensive in cost, time, and materials. Once the critical properties that govern strengthening mechanisms are known, systematic predictions of those properties with DFT can be readily performed across the entire periodic table. These predictions guide new experiments which can then guide new calculations. This process is often called Integrated Computational Materials Engineering (ICME).




GP zones can strengthen Mg alloys.  DFT can be used to calculate the formation energies of GP zones as a function of the number of Mg planes (left).  Using these calculations, we can make predictions about the optimum number of Mg planes between GP layers, and so gain insight into the precursors of precipitates in Mg-Ca-Zn alloy. 




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