Ab initio supported development of TiN/MoN superlattice thin films with improved hardness and toughness

• Motivated by density functional theory (DFT)-derived ductility indicators for face centered cubic (fcc, rocksalt) structured TiN/MoN0.5 superlattices and Ti0.5Mo0.5N0.75 solid solutions, TiN/MoNy superlattice (SL) thin films with bilayer periods lambda of 2.4, 3.9, 6.6, 9.9, and 23.0 nm and corresponding solid solutions were developed by DC reactive magnetron sputtering. These SLs allow for improved hardness H and critical fracture toughness K-IC, with both peaking at the same bilayer period lambda of 9.9 nm (where the MoN0.5 layers crystallize with the ordered beta-Mo2N phase); H = 34.8 +/- 1.6 GPa and K-IC = 4.1 +/- 0.2 MPa root m. The correspondingly prepared fcc-Ti0.5Mo0.5N0.77 solid solution has H = 31.4 +/- 1.5 GPa and K-IC = 3.3 +/- 0.2 MPa root m. Thus, especially the fracture toughness shows a significant superlattice effect. This is suggested by DFT-by the increase of the Cauchy pressure from -19 to + 20 GPa for the 001-direction (while that in the 100-direction remained high, above 83 GPa) upon increasing lambda from 3 to 4 nm.& nbsp;Together, experimental and computational investigations prove the importance of optimized bilayer periods for highest strength and fracture toughness, as well as optimized N-content for the solid solutions.

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NATURVETENSKAP  -- Kemi -- Oorganisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)

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