Abstract
Multicomponent or high-entropy ceramics show unique combinations of mechanical, electrical, and chemical properties of importance in coating applications. However, generalizing controllable thin-film processes for these complex materials remains a challenge. Here, understoichiometric (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr, 0.12 ≤ x ≤ 0.30) films were deposited on Si(100) substrates at 400 °C by reactive magnetron sputtering using single elemental targets. The influence of ion energy during film growth was investigated by varying the negative substrate bias voltage from ∼10 V (floating potential) to 130 V. The nitrogen content for the samples determined by elastic recoil detection analysis varied from 34.9 to 43.8 at. % (0.12 ≤ x ≤ 0.30), and the metal components were near-equimolar and not affected by the bias voltage. On increasing the substrate bias, the phase structures of (TiZrTaMe)N1–x (Me = Hf, Nb, or Mo) films evolved from a polycrystalline fcc phase to a (002) preferred orientation along with a change in surface morphology from faceted triangular features to a dense and smooth structure with nodular mounds. All the four series of (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr) films exhibited increasing intrinsic stress with increasing negative bias. The maximum compressive stress reached ∼3.1 GPa in Hf- and Cr-containing films deposited at −130 V. The hardness reached a maximum value of 28.0 ± 1.0 GPa at a negative bias ≥100 V for all the four series of films. The effect of bias on the mechanical properties of (TiNbZrMe)N1–x films can thus guide the design of protective high-entropy nitride films.
Highlights
High-entropy alloys (HEAs) constitute a large family of singlephase alloys comprising five or more elements in equal or nearequal proportion (5−35 at. % for each).[1,2] HEAs have been gradually extended to high-entropy ceramics by replacing or adding non-metal elements, such as nitrogen, carbon, boron, and oxygen
The majority of single-phase High-entropy nitride (HEN) films have so far been synthesized by cathodic arc deposition and sputtering techniques using a single compound target[4,6,8] or segmented[7,9] as well as mosaic targets[10] in mixed argon/nitrogen atmospheres
At Vbias ≤ −100 V, metal substitution does not induce a significant increase in hardness and elastic modulus compared with recent reports on HEN films showing values of 18−27 GPa.[9,20,32]
Summary
High-entropy alloys (HEAs) constitute a large family of singlephase alloys comprising five or more elements in equal or nearequal proportion (5−35 at. % for each).[1,2] HEAs have been gradually extended to high-entropy ceramics by replacing or adding non-metal elements, such as nitrogen, carbon, boron, and oxygen. The majority of single-phase HEN films have so far been synthesized by cathodic arc deposition and sputtering techniques using a single compound target[4,6,8] or segmented[7,9] as well as mosaic targets[10] in mixed argon/nitrogen atmospheres This includes material systems of HENs with metal components from (Ti, Zr, Hf, V, Nb, Ta, Mo and W) to late 3d-transition metals (Cr, Mn, Co, Fe, Cu, and Ni) plus the main-group elements Al and Si.[3] The strategy to replace or add more transition-metal components shows the diversity in designing HEAs,[11−13] including HEN thin films.[14−17]. Systematic investigations of the microstructure and mechanical properties were carried out for the four different material systems when varying the substrate bias voltage from floating potential to −130 V
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