Microstructure and materials properties of understoichiometric TiBx thin films grown by HiPIMS

• Published in: Surface & coatings technology 2020-12, Vol.404, p.126537, Article 126537
• Main Authors: Thörnberg, Jimmy, Palisaitis, Justinas, Hellgren, Niklas, Klimashin, Fedor F., Ghafoor, Naureen, Zhirkov, Igor, Azina, Clio, Battaglia, Jean-Luc, Kusiak, Andrzej, Sortica, Maurico A., Greene, J.E., Hultman, Lars, Petrov, Ivan, Persson, Per O.Å., Rosen, Johanna
• Format: Article
• Language: English
• Subjects: Borides; HiPIMS; Mechanical properties; Microstructure; Stoichiometry; Titanium
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.126537

TiBx thin films with a B content of 1.43 ≤ x ≤ 2.70 were synthesized using high-power impulse magnetron sputtering (HiPIMS) and direct-current magnetron sputtering (DCMS). HiPIMS allows compositions ranging from understoichiometric to overstoichiometric dense TiBx thin films with a B/Ti ratio between 1.43 and 2.06, while DCMS yields overstoichiometric TiBx films with a B/Ti ratio ranging from 2.20 to 2.70. Excess B in overstoichiometric TiBx thin films from DCMS results in a hardness up to 37.7 ± 0.8 GPa, attributed to the formation of an amorphous B-rich tissue phase interlacing stoichiometric TiB2 columnar structures. We furthermore show that understoichiometric TiB1.43 thin films synthesized by HiPIMS, where the deficiency of B is found to be accommodated by Ti-rich planar defects, exhibit a superior hardness of 43.9 ± 0.9 GPa. The apparent fracture toughness and thermal conductivity of understoichiometric TiB1.43 HiPIMS films are 4.2 ± 0.1 MPa√m and 2.46 ± 0.22 W/(m·K), respectively, as compared to corresponding values for overstoichiometric TiB2.70 DCMS film samples of 3.1 ± 0.1 MPa√m and 4.52 ± 0.45 W/(m·K). This work increases the fundamental understanding of understoichiometric TiBx thin films and their materials properties, and shows that understoichiometric films have properties matching or going beyond those with excess B. •B deficiency accommodated by Ti planar defects in understoichiometric TiBx.•Superior mechanical properties for understoichiometric TiBx•Deposition fluxes in HiPIMS and DCMS gives rise to widely different compositions.