Easily tiltable B-Al-B linear chain: The origin of unusual mechanical properties of nanolaminated MAB phases (CrB2)nCrAl

The present work deals with first-principles simulations on the shear responses of nanonaminated (CrB2)(n)CrAl (n = 1-3) MAB phases. The simulated results show that the ideal shear strengths Tm of basal plane shears are much lower than those of non-basal plane shears, indicating that dislocations tend to nucleate in basal planes. The lower resistance against basal plane shear is associated with the easily tiltable nature of B-Al-B linear chains, which may result from the local open structure around Al layers. In addition, the easily tiltable nature of B-Al-B chains also well explains the reduction tendency of Tm with the increase of boride nano-layer thickness under basal plane shears. It suggests that the easily tiltable B-Al-B chains facilitate the release of shear strains in Al layers, which may give rise to MAB phases with the unusual mechanical properties in analogous to MAX phases, including readily machinability, thermal shock resistance, and damage tolerance. (C) 2017 Elsevier B.V. All rights reserved.