Superhard oxidation-resistant Ti1-xAlxBy thin films grown by hybrid HiPIMS/DCMS co-sputtering diboride targets without external substrate heating

• Published in: Materials & design 2024-02, Vol.238, p.112727, Article 112727
• Main Authors: Wicher, B., Pshyk, O.V., Li, X., Bakhit, B., Rogoz, V., Petrov, I., Hultman, L., Greczynski, G.
• Format: Article
• Language: English
• Subjects: HiPIMS; Ion mass spectrometry; Magnetron sputtering; Mechanical properties; Oxidation resistance; Transition metal diboride thin films
• ISSN: 0264-1275
• DOI: 10.1016/j.matdes.2024.112727

[Display omitted] •Near-stoichiometric in B content, Ti1-xAlxBy films with 1.81≤y≤2.03 are designed by utilizing a hybrid HiPIMS/DCMS method.•The B/metal ratio decreases with increasing Al content due to changes between the angular distribution of Ti and Al atoms•A much higher ionization of the Al-DCMS flux also undercut the B/metal in grown TiB2-HiPIMS/AlB2-DCMS Ti1-xAlxBy thin films.•A 15-times improvement in 800 °C-oxidation resistance of single-phase occurs with increased Al-alloying, from 0.36 to 0.74.•The best compromise between low O-scale thickness (90-180 nm) and high hardness (34-38 GPa) is presented within 0.58≤x≤0.67. Ti1-xAlxBy films (0.40 ≤ x ≤ 0.76, and 1.81 ≤ y ≤ 2.03) combining good mechanical properties and high-temperature oxidation resistance are demonstrated. Layers are grown using a hybrid high-power impulse and dc magnetron co-sputtering employing two target configurations (AlB2-HiPIMS/TiB2-DCMS and TiB2-HiPIMS/AlB2-DCMS) and no external substrate heating. Near-stoichiometric B content are achieved by co-sputtering two diboride targets. Time-resolved ion mass spectrometry analyses reveal that the ionization of the DCMS flux (Al) is much higher during TiB2-HiPIMS/AlB2-DCMS. The effect is caused by the difference in the first ionization potentials and the ionization probabilities of sputtered metals and results in lower B/metal ratios in films grown in this configuration. The B/metal ratio in the single-phase Ti1-xAlxBy decreases with increasing Al content, which is explained by the change between angular distribution of Ti and Al atoms. Alloying with Al improves the high-temperature oxidation resistance: the thickness of the oxide-scale forming after 1 h anneal at 800 °C decreases more than 15 times upon increasing x from 0.36 to 0.74. Ti1-xAlxBy films with 0.58 ≤ x ≤ 0.67 offer the best compromise between high-temperature oxidation resistance and mechanical properties with an average oxide scale thickness 90–180 nm and the hardness of 34–38 GPa.