Ab-Initio Calculations of Structure and Properties of Nanolaminated MAX Phases

摘要

This report results from a contract tasking RWTH Aachen as follows: A new class of machinable ceramic materials had recently received attention due a unique combination of hardness, toughness, machinability, and oxidation stability. These materials are called MAX phases, where M designates a transition metal, A is mostly a IIIA or IVA element of periodic table, and X stands for C or/and N. MAX phases have a unique nanolaminated atom arrangement, which leads to a low shear modulus - a property critical for low friction materials. However, MAX phases for tribology have not yet been explored systematically. Most research has been done on the machinable Ti3SiC2 system. However, the list of theoretically possible MAX phases is extensive. Practically, it is resource intensive to synthesize every thinkable MAX phase searching for a material exhibiting advantageous tribological properties. A superior strategy is to calculate bonding, structure, and properties of possible MAX phase compounds and then selectively dedicate a synthesis effort to the phase with the best combination of properties. This project is based on state of the art (1998 Nobel Prize in chemistry) density functional theory calculation algorithms to build up models of MAX phases and provide predictions of their phase stability and expected properties. It is envisioned to systematically explore nanolaminated phases with the M2AlC formula to address the influence of the M elements (Y, Zr, Nb, Mo, La, Hf, Ta, W) on bonding strength, electronic structure, and shear modulus. Our aim is to contribute towards the development of novel tribological materials. We propose to study the relationship between the valence electron configuration of M = Y, Zr, Nb, Mo, La, Hf, Ta, and W in M2AlC and the shear modulus of this fascinating new class of nanolaminated materials.