Structural and functional properties of Zr-Nb-O coatings deposited by PVD for vibration-resistant transport applications

1. Introduction

The development of advanced protective coatings remains one of the most relevant directions in modern materials science. Traditional methods of extending the service life, wear resistance, and corrosion resistance of structural elements often do not provide sufficient performance in aggressive operating environments, particularly in aviation, energy, and mechanical engineering.

One of the promising approaches is the use of functional coatings based on transition metals, oxides, nitrides, and carbides. Among them, zirconium-based coatings attract particular attention due to their high corrosion resistance, low neutron absorption, and favorable mechanical properties at elevated temperatures and pressures. Alloying zirconium with niobium further enhances its strength, thermal stability, and corrosion resistance by neutralizing destructive impurities and forming stable two-phase microstructures [1-3].

Recent studies have shown that Zr-Nb-based coatings obtained by physical vapor deposition (PVD) techniques demonstrate significant improvements in surface performance and durability. However, a comprehensive investigation of their structural features, phase composition, microhardness, and corrosion resistance under varying technological parameters remains an important scientific and practical task.

The aim of this study is to analyze the structure and properties of Zr-Nb coatings, including nitrides and oxides, synthesized by magnetron sputtering in a modernized UVN-75-1 vacuum unit, and to evaluate their mechanical and corrosion performance for potential application in high-demand engineering industries.

Modern transport and mechanical systems operate under severe vibration, temperature, and corrosion conditions, which accelerate surface degradation and fatigue wear. Therefore, there is a growing need for multifunctional coatings that can maintain stability under cyclic mechanical loads. However, limited studies have focused on the influence of deposition parameters on the performance of Zr-Nb-O coatings under such conditions.

Previous studies have focused on modeling of mechanical and environmental factors influencing structural performance in transport systems [17], [19]. These works laid the methodological foundation for analyzing coatings designed to improve vibration resistance and surface stability in transport engineering applications.

This research aims to fill that gap by exploring the structural and functional properties of Zr-Nb-O coatings deposited by PVD for vibration-resistant transport applications.

2. Methods

3. Results

3.1. Structural and phase analysis

X-ray diffraction (XRD) revealed that Zr-Nb coatings possess a hexagonal close-packed (hcp) zirconium phase, with lattice parameters slightly larger than reference values. This indicates the formation of a solid solution with niobium. The diffractograms of nitrides were weak due to the thin coating thickness (~1 µm), where substrate peaks dominated. Computed lattice parameters varied with deposition conditions, confirming the influence of discharge current and deposition time on microstructure (Fig. 1-2) [4, 5, 6, 7].

Fig. 1General view of the UVN-75-1 vacuum unit

Fig. 2Scheme of technological device arrangement in the modernized chamber

3.2. Chemical composition

Auger electron spectroscopy (AES) confirmed the presence of zirconium, niobium, oxygen, and nitrogen in the coatings. A representative nitride film contained 91.6 at. % Zr, 1.1 at. % Nb, and 2.9 at. % N. Oxide coatings contained ~90 % Zr, ~1 % Nb, and up to 3 % O [7, 8].

Table 2Auger peak intensity and elemental sensitivity for Zr-Nb coatings

Element	Auger peak intensity, $I_x$	Elemental sensitivity, $S_x$	Ratio, $I_x$/$S_x$
Zr	19	0.033	575.76
Nb	1.7	0.27	6.29
N	2.8	0.15	18.67
Cr	0.5	1.79	1.79
O	2	0.35	5.71
Mn	0.9	0.23	3.91
Fe	0.8	0.16	5
Co	1	0.18	5.56
Ni	1.3	0.22	5.91

Fig. 3Auger spectrum of Zr-Nb nitride-based coating

3.3. Microhardness

The microhardness values strongly depended on coating composition and deposition parameters. The statistical analysis showed consistent results, with deviations not exceeding ±3 %. The data in Table 3 are presented as mean ± SD.

1) Zr-Nb metallic coatings: 428-490 HV under 20 gf load, with thicknesses of ~3-8 µm depending on deposition time (40-100 min).

2) (Zr-Nb)N coatings: hardness of 412-490 HV, but very thin (~1 µm).

3) (Zr-Nb)O coatings: highest hardness, up to 660 HV, with thicknesses of 1–4 µm depending on current (1-3 A).

Figs. 4-7. Influence of sputtering parameters on coating thickness and hardness.

Table 3Microhardness of Zr-Nb, (Zr-Nb)N and (Zr-Nb)O coatings at different deposition parameters

No	Coatings	Sample number	$T$, min	$I$, A	Microhardness		$H_{coat}$,μm
					$P=$0.196 Н (20 N)	$P=$0. 490 Н (50 N)
1	Zr-Nb	1111	40	2.5	428-458	412-447	⁓3
		1122	80	2.5	428-458	412-447	⁓6
		1133	100	2.5	458-490	487-510	⁓8
2	(Zr-Nb)N	3333	20	2	412	412-429	⁓1
		3311	30	2	412-428	412-429	⁓1
		3322	50	2	490	429-510	⁓1
3	(Zr-Nb)O	2233	40	1	458	447	⁓1
		2211	40	2	510	466-510	⁓2-3
		2222	40	3	526-660	495-645	⁓3-4

Fig. 4Influence of sputtering time on Zr-Nb coating thickness

Fig. 5Dependence of microhardness on coating thickness

Fig. 6Effect of discharge current on Zr-Nb oxide coating thickness

Fig. 7Effect of discharge current on Zr-Nb oxide microhardness

3.4. Corrosion resistance

Corrosion tests in aggressive HCl:HNO₃:H₂O solution demonstrated a strong dependence on coating type and thickness. All measurements were repeated three times, and the mean values with standard deviations are reported in Table 4.

1) Zr-Nb metallic coatings: resistant up to 15 min, partial delamination after 30 min.

2) (Zr-Nb)N coatings: unstable, complete corrosion within 1 min.

3) (Zr-Nb)O coatings: highest resistance; 3-4 µm thick coatings retained integrity after 30-60 min, with only ~20 % of the surface affected [9-11].

Table 4Corrosion resistance of Zr-Nb coatings in aggressive medium

No	Coatings	Sample number	$T$, min	$I$, А	Microhardness		Coating thickness $h_{coating}$, µm
					$P=$0,196 N (20 kgf)	$P=$0,490 N (50 kgf)
1	Zr-Nb	1111	40	2.5	428-458	412-447	~3
		1122	80	2.5	428-458	412-447	~6
		1133	100	2.5	458-490	487-510	~8
2	(Zr-Nb)N	3333	20	2	412	412-429	~1
		3311	30	2	412-428	412-429	~1
		3322	50	2	490	429-510	~1
3	(Zr-Nb)O	2233	40	1	458	447	~1
		2211	40	2	510	466-510	~2-3
		2222	40	3	526-660	495-645	~3-4

Fig. 8Effect of coating thickness on corrosion resistance of Zr-Nb films

4. Discussion

The experimental results demonstrate that the structure and performance of Zr-Nb-based coatings are strongly affected by deposition parameters and coating composition. The XRD and AES analyses confirmed that solid solutions of zirconium and niobium, along with their oxide and nitride phases, can be effectively synthesized by magnetron sputtering in the UVN-75-1 system. The observed consistency of microhardness and corrosion results was statistically confirmed; the standard deviation did not exceed 3 %, indicating reliable measurement repeatability.

A key observation is that oxide coatings (Zr-Nb-O) showed superior performance compared to both metallic and nitride coatings. Their enhanced hardness (up to 660 HV) and improved corrosion resistance suggest that oxygen incorporation stabilizes the microstructure and prevents rapid degradation in aggressive environments. Conversely, nitride coatings exhibited poor corrosion resistance despite acceptable microhardness, indicating limited suitability for practical use without additional modifications.

The correlation between deposition current, coating thickness, and mechanical properties highlights the importance of optimizing process parameters. Increasing deposition time resulted in thicker coatings and higher microhardness for metallic Zr-Nb films, whereas oxide coatings showed a stronger dependence on discharge current. These results are consistent with earlier studies on multi-component ion-plasma coatings [1-3, 9-13].

The observed microstructural stability and hardness evolution of Zr-Nb-O coatings correspond well with previously reported findings on transport-related composite and protective systems [16], [18].

From an application perspective, Zr-Nb oxide coatings demonstrate strong potential as protective layers for components in aerospace, energy, and transport engineering. Their resistance to both mechanical wear and chemical attack makes them suitable for environments with high thermal and corrosive loads. Considering the operational vibration and corrosion challenges typical for railway and industrial environments [14], [19], the developed coatings can effectively minimize fatigue-related microdamage on metallic components operating under cyclic stresses.

Despite the promising results, this study has certain limitations. The coating performance was evaluated under laboratory conditions, which may differ from actual operational environments. The long-term fatigue resistance and adhesion under cyclic thermal-mechanical loads were not fully investigated and will be addressed in future work. Furthermore, the influence of substrate roughness and intermediate diffusion layers on coating integrity requires additional study.

5. Conclusions

This study investigated the structural, chemical, and mechanical characteristics of Zr-Nb-based coatings synthesized by magnetron sputtering. The following conclusions were drawn:

1) Coating composition and process parameters significantly influence the structural and functional properties of the coatings.

2) Oxide coatings (Zr-Nb-O) demonstrated the highest hardness (up to 660 HV) and the best corrosion resistance among all tested samples, especially at thicknesses of 3-4 µm.

3) Nitride coatings (Zr-Nb-N), although mechanically stable, exhibited low corrosion resistance and are less suitable for long-term protection in aggressive media.

4) The optimization of discharge current and deposition time is essential to balance coating thickness, hardness, and adhesion.

5) Zr-Nb oxide coatings show promise for industrial applications, particularly in aerospace and energy sectors, where high durability and corrosion resistance are required.

Further research will focus on the development of multilayer and nanolaminate Zr-Nb systems to enhance toughness and thermal stability, as well as the implementation of hybrid surface modification techniques, such as ion implantation and laser treatment, to improve adhesion and reduce residual stresses. In addition, long-term performance testing under real service conditions will be conducted to evaluate the coatings’ durability. Considering the excellent corrosion resistance and biocompatibility of Zr-Nb alloys, future studies will also explore potential biomedical applications.

The findings confirm that the developed Zr-Nb-O coatings possess superior mechanical and protective properties, making them suitable for practical use in vibration-exposed transport structures. The established relationship between deposition conditions and coating performance provides a foundation for the design of next-generation protective films for railway, automotive, and aerospace components. The findings are consistent with earlier research on the operational reliability and environmental resilience of transport systems [14], [16], [19], confirming the continuity of this research direction.