AlM2B2 (M=Cr, Mn, Fe, Co, Ni): a group of nanolaminated materials

TL;DR

This study combines theoretical calculations and experiments to analyze the stability, elastic properties, electronic structure, and hardness of a series of layered ternary borides AlM2B2 (M=Cr, Mn, Fe, Co, Ni), revealing their nanolaminated nature and delamination behavior.

Contribution

The paper provides the first comprehensive analysis of the phase stability, elastic properties, and nanolaminated structure of AlM2B2 borides, including experimental validation and insights into their mechanical behavior.

Findings

AlCr2B2, AlMn2B2, and AlFe2B2 are stable phases.

AlCo2B2 and AlNi2B2 are metastable.

Nanolaminated structure leads to delamination and reduced hardness.

Abstract

Combining theory with experiments, we study the phase stability, elastic properties, electronic structure and hardness of layered ternary borides AlCr2B2, AlMn2B2, AlFe2B2, AlCo2B2, and AlNi2B2. We find that the first three borides of this series are stable phases, while AlCo2B2 and AlNi2B2 are metastable. We show that the elasticity increases in the boride series, and predict that AlCr2B2, AlMn2B2, and AlFe2B2 are more brittle, while AlCo2B2 and AlNi2B2 are more ductile. We propose that the elasticity of AlFe2B2 can be improved by alloying it with cobalt or nickel, or a combination of them. We present evidence that these ternary borides represent nanolaminated systems. Based on SEM measurements, we demonstrate that they exhibit the delamination phenomena, which leads to a reduced hardness compared to transition metal mono- and diborides. We discuss the background of delamination by analyzing chemical bonding and theoretical work of separation in these borides.