ICMCTF 2021 Virtual Conference Session B5: Hard and Multifunctional Nanostructured Coatings

The development of PVD technologies is often related with creation of new multicomponent materials that are used as precursors in deposition process. Particularly relevant is the manufacture of cathodes made of ceramics & composite materials. Since the doping of coatings by structure modifiers, such as B or Si, for example, is a non-trivial task. Among the methods of ceramic cathodes manufacturing can be noted the pressing+sintering & hot pressing technology. Self-propagating high-temperature synthesis (SHS) is the cost effective & convenient method for manufacturing of composite cathodes [1].

The SHS method allows obtaining a wide range of materials & cathodes have a high density & a low content of impurities due to self-cleaning effect in the combustion wave. In present review, the several types of advanced coatings deposited with the SHS-materials were demonstrated.

It was shown that the follow nanocomposite coatings can be produced in various energy regimes, including rigid, due to the use of functionally graded & reinforced SHS-materials (FGM & RM):

a) hard oxidation resistant MoHfSiB, MoZrSiB, & TaZrSiB coatings were obtained by DC magnetron sputtering (MS) & pulsed MS of (MoSi₂-HfB₂-MoB)/Mo, (MoSi₂-ZrB₂-MoB)/Mo, & (ZrB₂-TaSi₂)/Mo FGM disk targets [2] b) hard optically transparent TaSiCN coatings - by MS of TaSi₂-TaC-SiC-Si₃N₄ RM disk targets c) hard corrosion resistant CrB₂ & TiAlNiCN coatings - by HIPIMS using CrB₂ & TiC-NiAl disk targets [3]. d) hard wear resistant TiCrBN coatings - by ion implantation (MEVVA) or pulsed cathodic arc evaporation (PCAE) of (TiB-Cr₄Ti₉B-Cr₂Ti )/(Ti+TiB) ring FGM targets [4]. e) hard oxidation & corrosion resistant coatings - by PCAE method using CrB₂ & Cr₃C₂-NiAl rod targets. f) hard TiAlSiCN & TiCrSiCN coatings with high thermal stability/oxidation resistance - by MS of TiAl₃-TiC-Ti₅Si₃-AlN & TiC-Cr₃C₂-Ti₅Si₃ disk targets at high currents [5]. g) hard wear resistant soft magnetic FeTiB films - by MS of Fe/TiB₂ segment target [6] h) hard oxidation resistant SiBCN films - by ion sputtering (IS) & MS of SiC-B₄C disk SHS-targets [7].

The research was carried out under the financial support of the Russian Science Foundation in the framework of project No. 19-19-00117.

1. E.A. Levashov et al. Int Mater Rev 62 (2017) 203

2. Ph. Kiryukhantsev-Korneev et al. Corros Sci 123 (2017) 319

3. Ph. Kiryukhantsev-Korneev et al. Ceram Int (2019) doi.org/10.1016/j.ceramint.2019.09.152

4. Ph. Kiryukhantsev-Korneev et al. J. Phys.: Conf. Ser. 1238 (2019) 012003

5. K. Kuptsov et al. Acta Mater 83 (2015) 408

6. E. Sheftel et al. Phys Status Solidi 13 (2016) 965

7. Ph. Kiryukhantsev-Korneev et al. Prot Met Phys Chem 53 (2017) 873

As the demands for the quality and speed of machining increase, the application of protective coatings on cutting or forming tools becomes increasingly important. Currently used protective coatings exhibit sufficient hardness, but this trait is often coupled with distinct brittleness. Recently a material combining seemingly mutually exclusive high hardness and moderate ductility has been theoretically predicted [1]. This material contains atoms of a transition metal (X), boron (B) and carbon (C) in X₂BC stoichiometry ordered in a complex high aspect ratio unit cell. The arrangement of the unit cell provides for high hardness of the material due to strong ionic-covalent bonds together with enhanced ductility owing to planes with only metallic bonds providing for plastic deformation of the cell. The properties of X₂BCs with different transition metals were calculated; however, experimental synthesis of only crystalline Mo₂BC was reported so far [2,3]. Apart from post-deposition annealing [3], HiPIMS was shown to be an effective way to prepare crystalline Mo2BC at industrially relevant deposition temperatures [2]. Other X₂BC such as W₂BC have been predicted to exhibit better mechanical properties compared to Mo₂BC, however, this comes at the cost of near-zero formation enthalpy predicting problems with the crystallization of this phase. On the other hand, systems such as Nb₂BC should exhibit lower hardness and ductility, but they should be significantly easier to be synthesized in the correct crystalline form.

This contribution reports on HiPIMS driven deposition of different X₂BC systems covering systems with low as well as higher negative formation enthalpies. Coatings prepared at ambient temperature as well as those prepared elevated temperatures > 700 °C will be compared. The correlation between the deposition parameters, the structure of the coatings and their mechanical properties will be shown.

This research has been supported by the project LO1411 (NPU I) funded by Ministry of Education, Youth and Sports of Czech Republic, project CZ.1.05/2.1.00/03.0086 funded by the European Regional Development Fund and GACR project 15-17875S.

[1] H. Bolvardi, J. Emmerlich, M. to Baben, D. Music, J. von Appen, R. Dronskowski, J.M. Schneider, J. Phys.: Condens. Matter 25 (2013) 045501

[2] H. Bolvardi, J. Emmerlich, S. Mráz, M. Arndt, H. Rudigier, J.M. Schneider, Thin Solid Films 542 (2013) 5-7

[3] L. Zábranský, V. Buršíková, P. Souček, P. Vašina, J. Dugáček, P. Sťahel, J. Buršík, M. Svoboda, V. Peřina, Vacuum 138 (2017) 199-204

High anti-wearing capability of friction coating is extremely important to any low friction and machinary industry, especially for highly automated production era coming, ”Industry 4.0”. Molybdenum disulfide (MoS₂) belongs to Transition-metal dichalcogenids, TMDs . It is composed of layered structures, providing excellent wear resistance due to layer sliding . In this study, a cheap and massive producible ammonium thiosulfate precursor ((NH₄)₂MoS₄) has been developed for coating MoS₂ layer onto the nano-porous anodic aluminum oxide (AAO) layer on the surface of 7003 series aluminum alloy. MoS₂ layer on the aluminum alloy surface is detected by scanning electron microscope (SEM). The ammonium thiosulfate precursor is pyrolyzed at 280, 375, 400 and 550°C, respectively to form the MoS₂ layer. The wearing experiment is tested by using the Surface Hardness Abrasion Tester. After 1440 m wear test, the wear rates (weight loss/original weight) of pure 7003 aluminum alloy, AAO and MoS₂ coated aluminum alloy pyrolyzed at 400°C are 0.339%, 0.017%, 0.0109%, respectively. The thickness of the molybdenum disulfide film sliced and observed by focused ion beam-transmission electron microscope (FIB-TEM) is about 40 nm. The surface hardnesses of AAO and MoS₂ coated aluminum alloy are 3~4 GPa and 5~6 GPa, respectively, measured by nanoindentation. As the result of the test, the coating of MoS₂ layer on the surface of aluminum alloy substantially enhances anti-wear capability and hardness. This coating technique is expected to be used in all kind of metal parts for improving the lifetime of automated equipment .

Recently, remarkable properties of the TiSiCN coatings namely low friction and good wear protection have been reported. Our study aimed at a comparison between different technologies (RF Magnetron Sputtering and High Power Impulse Magnetron Sputtering) used for the coating depositions. Operating in RF mode, a composite target Ti-Si-C was sputtered in Ar + N₂ atmosphere. In HiPIMS mode, the coatings were obtained from alloyed TiSi targets with different Si contents (15 and 25 at.%) in a gas mixture containing Ar + N₂ + C₂H₂. Tailoring the coating properties can be successfully performed with a help of the target ion-induced secondary electron emission (ISEE). Technical aspects of both technologies will be discussed in order to set a relationship between thin film properties and process parameters. Physicochemical analyses (XRD, SEM, XPS and RBS) were carried out to evaluate the coating composition, morphology and crystalline structure. Residual stresses were determined by the curvature method on glass plates. Nanohardness values up to 28 GPa and Young’s modulus values up to 216 GPa were obtained while the coefficient of friction exhibited values below 0.35 against steel in an unlubricating pin-on-disk setup. The process parameters have been optimized to maximize the ion bombardment of the substrate surface by a monitoring the bias current signal with a Rogowski coil probe. The coating thickness was set to one micron onto polished steel substrates.

[1] J. Musil, Surface and Coatings Technology 125 (2000 ) 322–330

[2] P. Mayrhofer et al., Progress in Materials Science 51 (2006) 1032–1114

Cubic transition metal (TM) nitrides and carbides are well-established protective coating materials due to their specific combination of remarkable thermo-mechanical properties but also chemical inertness. Nevertheless, their unique bonding nature – in particular combination of strong covalent and metallic bonds – is also the origin for their lack in fracture tolerance compared to metals and metallic alloys.

To overcome these limitations the formation of carbonitrides by substitutional alloying of the non-metallic sublattice exchanging C with N atoms is an interesting approach. The so obtained adjustment of the valence electron concentration has strong consequences on intrinsic material properties, e.g. Young’s modulus, melting temperature, phase decomposition as well as fracture toughness. Therefore, within this study the impact of non-metallic alloying – exchanging C with N atoms – has been explored systematically for two model systems, TaC and HfC, respectively. TM-C thin films were deposited via non-reactive magnetron sputtering, while ternary TM-C-N coatings have been deposited in mixed Ar/N2 atmospheres. We combined ab initio calculations (DFT by VASP) with experimental studies to correlate predicted properties such as fracture tolerance enhancement with increasing VEC (due to nitrogen alloying). The mechanical characteristics have been assessed by micro cantilever bending, pillar compression or splitting tests in correlation to well-established nanoindentation to gain a comprehensive view on the mechanical characteristics – also at elevated temperatures. Furthermore, detailed insights on the phase formation during coating synthesis (also considering influence of structural defects such as vacancies), and hence morphology as well as chemical composition has been studied via ERDA and SEM/HR-TEM, respectively.

The ever-growing need for improved mechanical and thermal resistance of protective coatings ask for their continuous enhancement and optimization. Recently, we showed that CeSi₂ or LaB₆ doping (<2 mol%) of well-known and used Ti–Al–N coatings leads to a considerable enhancement of their thermomechanical properties and oxidation resistance. The very positive effects of Ta for Ti–Al–N (with Ta/Ti ratios of ~1/3) are already well documented. Within this study, we further follow the alloying concept by preparing sputtered nitride coatings using Ti_0.45Al_0.45Ta_0.10 composite targets alloyed with 2 mol% CeSi₂ or 1 mol% CeSi₂ plus 1 mol% LaB₆. The thereby developed single-phase face centered cubic LaB₆ and CeSi₂ doped Ti–Al–Ta–N coatings outperform the previously studied Ti–Al–Ta–N coatings considerably.

In their as-deposited condition, the LaB₆+CeSi₂-doped Ti_0.44Al_0.42Ta_0.13N coatings exhibit a hardness (H) of 37.8±1.5 GPa and an indentation modulus (E) of 498±14 GPa (on polished sapphire substrates). Although the hardness after vacuum-annealing at 1100 °C is with 30.7±1.8 GPa below that of the solely LaB₆-doped Ti_0.43Al_0.57N (39.6±1.3 GPa), the oxidation resistance is simply outstanding. Even after exposure to ambient air at 900 °C for 25 h, the oxide scale thickness is only 800 nm. Thus, easily outperforming the solely LaB₆-doped Ti_0.43Al_0.57N, but also the already excellent oxidation resistance of Ti_0.44Al_0.44Ta_0.12N and Ti_0.43Al_0.42Ta_0.14Ce_0.01N, which showed 2.4 and 1.9 µm thick oxide scales after 25 h exposure at 900 °C in ambient air, respectively.

Based on our results we can conclude that knowledge-based alloying design is a powerful tool to meet the ever-growing demands of highly-sophisticated applications.

Recently, a novel nanostructured surface composed of patterned arrays of Al/a-Si core-shell nanostructures (CSNs) has been shown to have a desirable combination of ultra-low friction (COF ~0.015 against a diamond counter face) and high durability. When subjected to instrumented nanoindentation, the individual CSNs show an unusual mechanical response characterized by almost complete deformation recovery, even beyond the elastic limit. Fundamentally, this mechanical behavior is hypothesized to be a result of a back-stress that develops in the confined Al core during compression loading that causes nucleated dislocations to retrace their paths or otherwise annihilate during unloading. In this study, molecular dynamics simulations are utilized to investigate the role that geometry and material properties play on the unique mechanical behavior of CSNs, with special attention paid to the roles of the core material and core-shell interface structure, along with supporting stress calculations.

To meet the requirement and needs of seawater lubrication for mechanical components in marine industry, nanostructured coatings with simultaneously high hardness and toughness are expected to deposit on component surface to enhance working performance and lifetime. Hence, in this work, TiSiCN nanocomposite coatings were deposited on Si (100) and AISI 316L stainless steel wafers by high power impulse magnetron sputtering (HiPIMS) at various peak power of 4-8 kW and negative substrate bias of 0- -200V. Metal Ti and MAX phase Ti₃SiC₂ layers serve as adhesion and transition layers, respectively. Nanocrystalline (nc)-(TiN,TiC,TiCN)/amorphous (a)-(Si₃N₄, SiC, sp²-C) nanocomposite structure is obtained in TiSiCN nanocomposite coatings, which exhibits high surface/interface integrity and dense microstructure without distinctly preferred orientation. At 7 kW and -60 V, TiSiCN/ Ti₃SiC₂/Ti coatings with high H, H/E*, H³/E*² and adhesion exhibit high open circuit potential of -0.07 V, low COF of 0.25 and specific wear rate of 6.1×10^-7mm³N^-1m^-1, resulting from mild abrasive wear without the occurrence of pitting corrosion in 3.5 wt.% NaCl aqueous solution. Moreover, cycling tribocorrosion tests exhibit that passive films possess strong abilities of regeneration and repairation on sliding contact surface thanks to high surface/interface integrity and dense microstructure.