Indentation Strengths of Zirconium Diboride: Intrinsic versus Extrinsic Mechanisms

Abstract

Zirconium diboride (ZrB 2 ) is an important ultrahigh-temperature ceramic, which exhibits outstanding mechanical properties and is widely used in extreme environments. Extensive experimental studies, however, have found that synthesized ZrB 2 specimens show widely scattered indentation hardness values ranging from 8.7 to 26 GPa. We have performed comprehensive stress−strain calculations of ZrB 2 to explore its structural and stress responses and found that ZrB 2 possesses an intrinsic indentation strength of 32.7 GPa, which is on par with those of other transition-metal borides that exhibit higher indentation hardness values of ∼30 GPa. This result suggests that large variations in measured hardness are driven by extrinsic factors, and an analysis of available experimental data indicates that the quality of the crystallinity of specimens holds the key to realizing improved hardness corresponding to the predicted intrinsic indentation strength. These findings offer insights into the origin of the previously reported lower hardness values of ZrB 2 and raise the prospects of achieving superior strengths in well-crystallized ZrB 2 that approach or match those of other ultrahard transition-metal compounds.

Ternary Mg-Nb-H polyhydrides under high pressure

“…using the CALYPSO [34][35][36] code. The underlying calculations on structural relaxation, ab initio molecular-dynamics (AIMD) simulations, electronic and elastic properties are performed with aid of the PBE exchange correlation functional [37][38][39], as implemented in the VASP package [33]. The valence space for Mg, Nb, H are 2p 6 3s 2 , 4s 2 4p 6 4d 4 5s 1 and 1s 1 , respectively.…”

Computational Exploration on the Structural and Optical Properties of Gold-Doped Alkaline-Earth Magnesium AuMgn (n = 2–12) Nanoclusters: DFT Study

“…CALYPSO software ( Wang et al, 2010 , 2012 ) was utilized to search the initial geometries of AuMg n ( n = 2–12) nanoclusters. CALYPSO can perform predictions of the energetically low-lying isomers structures at given chemical compositions and pressure for nanoclusters ( Lv et al, 2012 ; Zhao et al, 2019 ; Lu et al, 2020 ) in gas-phase and crystals ( Lu and Chen, 2020a , 2020b , 2021 ; Sun et al, 2020 ; Chen et al, 2021 ) via particle swarm optimization (PSO) algorithm. To search for as many low-lying energy isomers of AuMg n ( n = 2–12) nanoclusters as possible, the following strategy will be employed.…”

Exploring the structure and electronic properties of germanium doped boron clusters using density functional theory based global optimization method

“…In the PSO methodology, we used 30 generations with each generation containing 30 structures to obtain around 900 configurations for each cluster size. Recent studies have revealed the PSO based approach in CALYPSO [85][86][87][88][89][90][91][92][93][94][95][96][97][98] to be highly efficient and precise in arriving at the ground state of clusters and chemical compounds. Following the PSO based optimizations, ten lowest energy configurations were reoptimized for each cluster with the help of B3LYP, TPSS and M06-L functionals and the TZVP basis set to find the ground state structure.…”