ICMCTF 2025 Session MA-ThP: Protective and High-temperature Coatings Poster Session

To enhance the restricted oxidation resistance of transition metal diboride (TMB) ceramics, alloying with Si and disilicide phases is an effective method, resulting in the formation of highly dense and protective SiO₂ scales. This phenomenon has been well documented in the context of bulk ceramics [1, 2], and recent studies have also corroborated its occurrence in thin-film TMBs, including CrB₂, HfB₂, and TiB₂ [3, 4]. The incorporation of Si, TaSi₂ or MoSi₂ into TiB₂ results in a significant reduction in oxidation kinetics, while exhibiting only minor effects on the mechanical properties. In the case of quaternary TiB₂-based coatings, hardness values of 36 GPa (TaSi₂) and 27 GPa (MoSi₂) have been achieved, in comparison to approximately 38 GPa for the binary system. All of the aforementioned coatings exhibited α-AlB₂ crystal structure, with a preferred (0001) orientation being a key factor in achieving the highest hardness. Nevertheless, the fracture characteristics of these Si-alloyed TMBs remain largely unexplored.

The objective of the present study is to elucidate the fracture characteristics, particularly K_IC, of these Si-containing TMBs at elevated temperatures up to 850 °C through the application of in-situ micromechanical testing techniques. Accordingly, a series of Ti-TM-Si-B_2±z coatings was deposited via non-reactive DC magnetron sputtering using a variety of composite targets, including TiB₂, TiB₂/TiSi₂ (90/10 & 80/20 mol%), TiB₂/TaSi₂ (90/10 & 80/20 mol%), and TiB₂/MoSi₂ (85/15 & 80/20 mol%). To gain a deeper understanding, additional detailed structural investigations were conducted using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and elastic recoil detection analysis (ERDA).

In comparison to the binary TiB_2+z and the quaternary Ti-Ta-Si-B_2±z, the Si and MoSi₂-containing coatings exhibited a distinct onset of plastic deformation at approximately 600 °C. This phenomenon can be attributed to the precipitation of silicon-containing phases, which underlines the significance of conducting material testing at temperatures relevant to their intended applications.

[1] GB. Raju, et al,. J Am Ceram Soc. 2008;91(10):3320–3327.
[2] GB. Raju, et al., Scr Mater. 2009;61(1):104–107.
[3] T. Glechner, et al., Surf. Coat. Technol. 434 (2022) 128178.
[4] A. Bahr, et al., Materials Research Letters. 11 (2023) 733–741.

In the present work, the influence of Si addition on the oxidation behavior of high-entropy carbide thin films based on the system(Hf, Ta, Ti, V, Zr)C is investigated. High-entropy carbides thin films were deposited on sapphire (Al₂O₃) as well as low-alloy steel substrates using magnetron sputtering. Additionally, powdered free-standing coating materials were also produced. All the as-deposited thin films exhibit a single-phase face-centered cubic (FCC) structure (Fm-3m, space group number 225). During non-isothermal oxidation using DSC-TGA, onset-temperature shifted from 490 ^oC to 502 ^oC while mass gain was reduced from 11% to 8.88 % with Si addition. Furthermore, the oxide-peak intensities in the obtained XRD patterns are decreased indicating a smaller fraction of formed oxide phases. All samples were fully oxidized during isothermal oxidation but the samples alloyed with Si show denser and thinner oxide scales compared to the samples without Si.

Using DC magnetron co-sputtering, we synthesized CrMnFeCoNiAg thin films with systematically varied silver content. X-ray diffraction (XRD) patterns reveal distinct non-mixing behavior with the emergence of pronounced peaks corresponding to both silver and Cantor alloy phases. Cross-section bright-field TEM micrograph and SAED patterns revealed a dense structure with Ag precipitates dispersed throughout the 900-nm-thick film. HRTEM micrographs showed a nanoprecipitate morphology with fine-scale linear precipitates, while STEM-HAADF imaging highlighted the internal structure, revealing characteristic modulated patterns with striations parallel to the basal plane, indicative of spinodal decomposition with cuboidal particles and tweed-like contrast patterns.

The increasing demands for workpiece quality and cost-effectiveness in machining processes necessitate a comprehensive consideration of all relevant factors, including cutting parameters, materials, tool coatings, and geometry. Physical Vapor Deposition (PVD) manufactured CrAlSiN nanocomposite coatings, composed of CrAlN grains in a SiN_x matrix, represent a promising solution for improved tool life of milling tools. The elastic-plastic properties of the coating and the deformation behavior of the material composite thereby can be deliberately influenced by varying the silicon content.

CrAlSiN coatings with silicon contents of x_Si = 10, 15, 20, and 25 at.-% in the metal portion were fabricated on cemented carbide WC-Co substrates. The indentation hardness H_IT and indentation modulus E_IT of the coatings were measured through nanoindentation (NI) with a force of F_NI = 10 mN, using a Berkovich indenter. Additionally, crack resistance was evaluated using quasi-static high load (HL) nanoindentation tests under forces ranging from F_HL = 750 to 1,750 mN, with increments of ΔF_HL = 250 mN. A conical diamond indenter was used for the high load nanoindentation tests. The resulting indents were subsequently analyzed using scanning electron microscopy (SEM). The findings reveal that the indentation hardness H_IT remains unchanged at H_IT = (25.48 ± 1.59) GPa, while the indentation modulus increases with higher silicon content, ranging from E_IT = (222.64 ± 10.45) GPa for x_Si = 10 at.-% up to E_IT = (239.89 ± 7.78) GPa for x_Si = 20 at.-%. After high load nanoindentation all coatings exhibit no cracks at F_HL = 750 mN. With F_HL ≥ 1,000 mN on the other hand cracks can be observed in all coatings. Nevertheless, with rising silicon content, the maximum indentation depth h_max decreases, while the residual indentation depth h₀ remains constant. Furthermore, the proportion of plastic work shows a slight reduction as silicon content x_Si increases. These results indicate that the resistance against plastic deformation of the CrAlSiN coating increases with higher silicon content.

Coatings with high silicon content demonstrate promising resistance against plastic deformation at room temperature, highlighting their potential for further investigation. This initial test qualifies these coatings for additional studies under high-temperature conditions, aiming to enhance their applicability in machining processes. The insights gained from this research could lead to the development of more durable and efficient cutting tools, ultimately improving productivity in industrial applications.

In this study, high entropy nitride TiVZrNbTa thin films were prepared by DC reactive magnetron sputtering on silicon substrates at room temperature. The impact of varying nitrogen flow rateson the structural, microstructural, optical and electrical properties were investigated. X-ray diffraction technique revealed that all the deposited films exhibited a polycrystalline structure with fcc phase. However, the pure metallic samples displayed an amorphous structure [1]. Optical properties analysis showed a decrement of the reflectance compared with free-nitrogen sample in the infrared region, as determined by UV-VIS spectroscopy [2]. Hall-effect measurements indicate that the electrical resistivity for all samples remained within the range between 100 and 300 μΩ cm. Interestingly, samples deposited with applied substrate bias power during the deposition process did not show a significant change in resistivity. This suggests that substrate biasing has minimal effect on the electrical transport properties of the latter films. On the other hand, applying adjustable substrate bias led to a blueshift in the epsilon-near-zero (ENZ) wavelength. Furthermore, X-ray photoelectron spectroscopy (XPS) shows the effect of the nitrogen flow rate on the residual stress [3] and plasmon frequency. The impact of varying nitrogen flow rates on the microstructural properties were further investigated and explained.

References

[1] Cemin, F., de Mello, S. R., Figueroa, C. A., & Alvarez, F. Surface and Coatings Technology, 2021, 421, 127357.

[2] Von Fieandt, K., Pilloud, D., Fritze, S., Osinger, B., Pierson, J. F., & Lewin, E. Vacuum, 2021, 193, 110517.

[3] Pogrebnjak, A. D., Yakushchenko, I. V., Bagdasaryan, A. A., Bondar, O. V., Krause-Rehberg, R., Abadias, G., ... & Sobol, O. V. Materials Chemistry and Physics, 2014, 147(3), 1079-1091.