TY - JOUR

T1 - Hardness and fracture toughness enhancement in transition metal diboride multilayer films with structural variations

AU - Vidis, Marek

AU - Fiantok, Tomas

AU - Gocnik, Marek

AU - Svec, Peter Jr

AU - Nagy, Stefan

AU - Truchly, Martin

AU - Izai, Vitalii

AU - Roch, Tomas

AU - Satrapinskyy, Leonid

AU - Sroba, Viktor

AU - Meindlhumer, Michael

AU - Grancic, Branislav

AU - Kus, Peter

AU - Keckes, Jozef

AU - Mikula, Marian

PY - 2024/3/21

Y1 - 2024/3/21

N2 - The simultaneous enhancement of hardness (H) and fracture toughness (KIC) through the formation of super- lattice structures challenges the conventional belief that these quantities are mutually exclusive. Here, this approach has been applied to the transition metal diborides, whose inherent brittleness severely restricts their application potential. The mechanical properties of TiB2/TaB2 systems as a function of bi-layer period Λ are investigated, combining theoretical and experimental approaches. Density Functional Theory is used to inves- tigate the structural stability and mechanical properties of stoichiometric hexagonal TiB2/TaB2 superlattices for Λ = 3.9 – 11.9 nm. The calculations predict the highest H = 38 GPa and KIC (100) of 3.3 MPa.m1/2 at the value of Λ = 5.2 nm. Motivated by the theoretical results, multilayer films with Λ = 4–40 nm were prepared by direct current magnetron sputtering. Due to the sputtering effects, the deposited diboride films differ significantly from the view of stoichiometry and structure. A detailed structure investigation reveals TiB2/TaB2 in form of super- lattices exhibiting coherent interfaces for Λ = 4 nm. For higher Λ, parts of TaB2 layers transform from the crystalline to the disordered phase. These transformations are reflected in the mechanical properties as measured by nanoindentation and micromechanical bending tests. The evolution of hardness follows Hall-Petch behavior, reaching a maximum of 42 GPa at Λ = 6 nm. Enhancing fracture toughness involves more complex mechanisms resulting in two KIC maxima: 3.8 MPa.m1/2 at Λ = 6 nm and 3.7 MPa.m1/2 at Λ = 40 nm.

AB - The simultaneous enhancement of hardness (H) and fracture toughness (KIC) through the formation of super- lattice structures challenges the conventional belief that these quantities are mutually exclusive. Here, this approach has been applied to the transition metal diborides, whose inherent brittleness severely restricts their application potential. The mechanical properties of TiB2/TaB2 systems as a function of bi-layer period Λ are investigated, combining theoretical and experimental approaches. Density Functional Theory is used to inves- tigate the structural stability and mechanical properties of stoichiometric hexagonal TiB2/TaB2 superlattices for Λ = 3.9 – 11.9 nm. The calculations predict the highest H = 38 GPa and KIC (100) of 3.3 MPa.m1/2 at the value of Λ = 5.2 nm. Motivated by the theoretical results, multilayer films with Λ = 4–40 nm were prepared by direct current magnetron sputtering. Due to the sputtering effects, the deposited diboride films differ significantly from the view of stoichiometry and structure. A detailed structure investigation reveals TiB2/TaB2 in form of super- lattices exhibiting coherent interfaces for Λ = 4 nm. For higher Λ, parts of TaB2 layers transform from the crystalline to the disordered phase. These transformations are reflected in the mechanical properties as measured by nanoindentation and micromechanical bending tests. The evolution of hardness follows Hall-Petch behavior, reaching a maximum of 42 GPa at Λ = 6 nm. Enhancing fracture toughness involves more complex mechanisms resulting in two KIC maxima: 3.8 MPa.m1/2 at Λ = 6 nm and 3.7 MPa.m1/2 at Λ = 40 nm.

KW - Superlattices

KW - Hard films

KW - Fracture toughness

KW - DFT

KW - TiB2/TaB2

U2 - 10.1016/j.mtla.2024.102070

DO - 10.1016/j.mtla.2024.102070

M3 - Article

VL - 2024

JO - Materialia

JF - Materialia

SN - 2589-1529

IS - 34

M1 - 102070

ER -