Microstructure, mechanical, and corrosion properties of Zr&lt;sub&gt;1-x&lt;/sub&gt;Cr&lt;sub&gt;x&lt;/sub&gt;B&lt;sub&gt;y&lt;/sub&gt; diboride alloy thin films grown by hybrid high power impulse/DC magnetron co-sputtering

Bakhit, Babak; Dorri, Samira; Kosari, A.; Mol, J.M.C.; Petrov, Ivan; Birch, Jens; Hultman, Lars; Greczynski, Grzegorz

doi:10.1016/j.apsusc.2022.153164

Microstructure, mechanical, and corrosion properties of Zr_1-xCr_xB_y diboride alloy thin films grown by hybrid high power impulse/DC magnetron co-sputtering

Title

Microstructure, mechanical, and corrosion properties of Zr_1-xCr_xB_y diboride alloy thin films grown by hybrid high power impulse/DC magnetron co-sputtering

Author

Bakhit, Babak (Linköping University)
Dorri, Samira (Linköping University)
Kosari, A. (TU Delft Team Yaiza Gonzalez Garcia)
Mol, J.M.C. (TU Delft Team Arjan Mol)
Petrov, Ivan (Linköping University; University of Illinois at Urbana Champaign; National Taiwan University of Science and Technology)
Birch, Jens (Linköping University)
Hultman, Lars (Linköping University)
Greczynski, Grzegorz (Linköping University)

Date

2022

Abstract

We study microstructure, mechanical, and corrosion properties of Zr_1-xCr_xB_y coatings deposited by hybrid high-power impulse/DC magnetron co-sputtering (CrB₂-HiPIMS/ZrB₂-DCMS). Cr/(Zr + Cr) ratio, x, increases from 0.13 to 0.9, while B/(Zr + Cr) ratio, y, decreases from 2.92 to 1.81. As reference, ZrB_2.18 and CrB_1.81 layers are grown at 4000 W DCMS. ZrB_2.18 and CrB_1.81 columns are continual from near substrate toward the surface with open column boundaries. We find that the critical growth parameter to achieve dense films is the ratio of Cr⁺-dominated ion flux and the (Zr + B) neutral flux from the ZrB₂ target. Thus, the alloys are categorized in two groups: films with x < 0.32 (low Cr⁺/(Zr + B) ratios) that have continuous columnar growth, rough surfaces, and open column boundaries, and films with x ≥ 0.32 (high Cr⁺/(Zr + B) ratios) that Cr⁺-dominated ion fluxes are sufficient to interrupt continuous columns, resulting in smooth surface and dense fine-grain microstructure. The pulsed metal-ion irradiation is more effective in film densification than continuous Ar⁺ bombardment. Dense Zr_0.46Cr_0.54B_2.40 and Zr_0.10Cr_0.90B_1.81 alloys are hard (>30 GPa) and almost stress-free with relative nanoindentation toughness of 1.3 MPa√m and 2.3 MPa√m, respectively, and remarkedly low corrosion rates (∼1.0 × 10^-6 mA/cm² for Zr_0.46Cr_0.54B_2.40 and ∼ 2.1 × 10^-6 mA/cm² for Zr_0.10Cr_0.90B_1.81).