TY - JOUR

T1 - The MoN–TaN system: Role of vacancies in phase stability and mechanical properties

AU - Klimashin, Fedor

AU - Lobmaier, L.

AU - Koutná, Nikola

AU - Holec, David

AU - Mayerhofer, P. H.

PY - 2021/2/9

Y1 - 2021/2/9

N2 - Face-centred cubic (fcc-) Mo—N and Ta—N exhibit an inherent driving force for vacancy formation. To study their interaction and effects on structural evolution and mechanical properties, we synthesised Mo–Ta–N coatings by reactive magnetron sputtering using nitrogen-to-total pressure ratios, p N2/p T, of 0.32 and 0.69. Low p N2/p T results in high concentration of N vacancies, which stabilise single-phase fcc-Mo 1-xTa xN y up to x = 0.76. These solid solutions follow the MoN 0.5–Ta 0.875N 0.875 quasi-binary tie line. Compressive residual stresses, σ, indentation hardness, H, and toughness, K C, increase with Ta content, reaching their maxima of (on average) -2.0 GPa, 28 GPa, and 7.0 MPa√m, respectively, within the x range 0.38–0.69. Higher Ta contents favour higher concentration of metal vacancies deteriorating the properties. High p N2/p T favours the formation of fcc-Mo 1-xTa xN y rich in metal vacancies, which however always coexists with a hexagonal phase. Within the x range 0.33–0.66, the fraction of the hexagonal phase is negligible, and σ, H, and K C deviate from −1.0 GPa, 28 GPa, and 2.9 MPa√m, respectively, within the error of measurements. The combination of experimental and theoretical studies demonstrates the power of point defects in stabilising desired crystal structures and improving mechanical properties through the thereby tuned atomic configuration.

AB - Face-centred cubic (fcc-) Mo—N and Ta—N exhibit an inherent driving force for vacancy formation. To study their interaction and effects on structural evolution and mechanical properties, we synthesised Mo–Ta–N coatings by reactive magnetron sputtering using nitrogen-to-total pressure ratios, p N2/p T, of 0.32 and 0.69. Low p N2/p T results in high concentration of N vacancies, which stabilise single-phase fcc-Mo 1-xTa xN y up to x = 0.76. These solid solutions follow the MoN 0.5–Ta 0.875N 0.875 quasi-binary tie line. Compressive residual stresses, σ, indentation hardness, H, and toughness, K C, increase with Ta content, reaching their maxima of (on average) -2.0 GPa, 28 GPa, and 7.0 MPa√m, respectively, within the x range 0.38–0.69. Higher Ta contents favour higher concentration of metal vacancies deteriorating the properties. High p N2/p T favours the formation of fcc-Mo 1-xTa xN y rich in metal vacancies, which however always coexists with a hexagonal phase. Within the x range 0.33–0.66, the fraction of the hexagonal phase is negligible, and σ, H, and K C deviate from −1.0 GPa, 28 GPa, and 2.9 MPa√m, respectively, within the error of measurements. The combination of experimental and theoretical studies demonstrates the power of point defects in stabilising desired crystal structures and improving mechanical properties through the thereby tuned atomic configuration.

UR - http://www.scopus.com/inward/record.url?scp=85100984912&partnerID=8YFLogxK

U2 - 10.1016/j.matdes.2021.109568

DO - 10.1016/j.matdes.2021.109568

M3 - Article

VL - 202.2021

JO - Materials and Design

JF - Materials and Design

SN - 0264-1275

IS - April

M1 - 109568

ER -