Wear and Corrosion Behavior of Diamond-like Carbon Coatings in Artificial Saliva

Abstract

This study investigates the properties of diamond-like carbon (DLC) coatings deposited onto a Ti6Al4V titanium alloy using plasma-assisted chemical vapor deposition (PACVD). The research encompasses adhesion tests, hardness, surface characterization, as well as corrosion and tribological evaluations. Artificial saliva was employed as both the lubricating and corrosive medium. Microscopic examination revealed a uniform coating with a thickness of about 3.2 µm. Scratch test results indicated that the deposited DLC coating exhibited superior adhesion, lower frictional resistance, and reduced wear compared to the titanium alloy. The coating deposition increased the hardness of the Ti6Al4V alloy by about 75%. Friction coefficients, measured under dry and lubricated conditions, were approximately 80% lower for the DLC-coated samples. Corrosion studies revealed that both the coated and uncoated surfaces demonstrated typical passive behavior and high corrosion resistance in artificial saliva. For DLC coatings, the corrosion current density and the corrosion rate were reduced by 85%. Microscopic observations of wear tracks following tribological and scratch tests confirmed the inferior wear and scratch resistance of the titanium alloy relative to the DLC coating. Under both dry and lubricated conditions (with artificial saliva), the volumetric wear rate of the titanium alloy was over 90% higher than for the DLC coating.

1. Introduction

Titanium and its alloys have found widespread applications in various industries due to their favorable combination of low density, corrosion resistance, and mechanical properties [1,2,3]. Compared to stainless steels and cobalt-based alloys, titanium and its alloys exhibit a lower modulus of elasticity and superior biocompatibility, making them more suitable for medical applications [4]. However, their tribological properties, particularly low wear resistance, can limit the durability and functionality of implants in the demanding conditions of the stomatognathic system.

The oral cavity is characterized by complex and dynamic conditions, including varying mechanical loads, a moist environment, diverse microbial flora, and fluctuating pH levels, imposing stringent requirements on biomaterials. Elevated wear rates can lead to the release of metallic debris, potentially inducing adverse tissue reactions and bone resorption around the implant. Moreover, wear debris can contribute to aseptic loosening of the implant.

Therefore, there is a compelling need to develop surface modification techniques for titanium alloys to enhance their wear resistance and corrosion resistance while minimizing the risk of a biological reaction. The mechanical, tribological, and corrosion properties can be effectively improved by applying hard, wear-resistant coatings and surface layers. Various surface modification techniques have been employed for this purpose, including ion implantation [5], thermal oxidation [6], plasma spraying [7], and physical and chemical vapor deposition (PVD/CVD) [3,8]. Carbon-based materials are playing an increasingly significant role in the advancement of materials science. The exceptional properties of carbon nanomaterials have led to their widespread application, e.g., in the energy, electronics, defense, tooling, aerospace, and medical industries [9,10,11]. Carbon exists in numerous allotropic forms, including carbon nanotubes, graphene oxide, quantum dots, graphene, fullerenes, graphite, and diamond [12,13,14,15,16]. Among these, diamond-like carbon (DLC) coatings stand out due to their unique combination of low friction and wear resistance, inherited from graphite, and exceptional hardness, derived from diamond. Due to their unique properties, diamond-like carbon (DLC) coatings have also become emerged as prime candidates for medical applications, particularly in the oral cavity. Diamond-like carbon (DLC) coating type a-C:H is characterized by high hardness due to sp3 bonds (typical in diamond) and excellent lubrication properties due to sp2 bonds (typical in graphite) [17,18]. DLC coatings exhibit an exceptional combination of characteristics including high hardness, low friction coefficient, wear and corrosion resistance, chemical inertness, high refractive index, and a smooth surface [9,19,20,21]. Moreover, their biocompatibility makes them ideal for biomedical applications. These coatings can significantly enhance the functionality and durability of dental implants while reducing the risk of complications arising from material degradation. However, the application of DLC coatings in medical devices necessitates extensive in vitro and in vivo testing to assess biocompatibility, hemocompatibility, toxicity, and long-term stability. In vitro studies [22,23,24] have demonstrated that DLC coatings deposited on stainless steel 316L, CoCrMo, and Ti6Al4V can reduce wear and the release of harmful metal ions. Authors of [25] investigated the tribological and corrosion properties of DLC coatings deposited on various substrates, including Ti6Al4V titanium alloy. Tribological tests were conducted under reciprocating motion with a load of 2 N, a sliding speed of 2.1 cm/s, and phosphate-buffered saline (PBS) as the lubricant. An alumina ball served as the counterface. Corrosion tests included static immersion in PBS and dynamic polarization in 0.9% NaCl solution at 37 °C. The polarization curve was measured from −0.5 V to 1.0 V with a scan rate of 0.1 V/s. Tribological results indicated that the DLC coatings on Ti6Al4V exhibited superior adhesion and wear resistance compared to coatings on stainless steel or CoCrMo alloys. Corrosion studies revealed that DLC-coated samples demonstrated a higher corrosion potential and lower corrosion current compared to bare metal substrates, indicating effective corrosion protection. Corrosion resistance is crucial for metallic implants in vivo as corrosion can lead to the release of metal ions, inducing inflammation and implant rejection. The high density and chemical inertness of DLC coatings effectively prevent corrosion of the underlying metal substrate. Nevertheless, defects such as voids and cracks can form in DLC coatings, serving as potential sites for fluid ingress, corrosion initiation, metal ion release, and even delamination [26]. Given the long-term in vivo service life of implants, corrosion resistance, and long-term stability are critical.

In the study by [27], they investigated the influence of DLC coatings on the tribological properties of Ti6Al4V titanium alloy for dental applications. The coatings were deposited using radio frequency plasma-assisted chemical vapor deposition (RF-PACVD). A 3 mm diameter Ti6Al4V titanium alloy ball served as the counterface in the tribological tests. A commercial artificial saliva solution at 20 °C was used as the lubricant. The results indicated that the introduction of the DLC coating into the tribological system led to a simultaneous reduction in the coefficient of friction and volumetric wear by 75% and 99%, respectively. Authors of [28] demonstrated that DLC coatings effectively prevent corrosion caused by fluoride ions, thus enhancing their service life in physiological environments.

Despite advancements in surface modification techniques, challenges persist in the application of coatings for medical implants and in extending their service life [8]. Each modification method has its advantages and limitations. For instance, techniques like PVD/CVD can degrade the physical properties of both the substrate and the coating (reduced ductility) due to excessively high deposition temperatures [29]. Moreover, while DLC coatings exhibit excellent wear resistance, their thickness may be insufficient to ensure adequate adhesion and prolonged service life [30]. The current state of knowledge indicates a continued need for coatings that combine the strength of ceramics with wear resistance while providing exceptionally durable bonding. Such solutions are particularly sought after in biomedical applications, where durability and reliability are paramount [23,30,31,32].

Previous studies have evaluated the tribological properties of DLC coatings in lubricated contact, employing simulated body fluids such as commercial artificial saliva, physiological saline, and Ringer’s solution at room temperature [8,25,33,34,35,36]. However, these investigations were not specifically focused on the application of wear-resistant coatings for components used in the stomatognathic system. Therefore, in this study, an artificial saliva solution at 37 °C was utilized for tribological and corrosion tests to more accurately replicate the in vivo conditions of the oral cavity. The study results demonstrate that surface modification of Ti6Al4V titanium alloy with DLC coatings improves both corrosion and wear resistance.

2. Materials and Methods

2.1. Diamond-like Carbon (DLC) Coating Preparation

The diamond-like coating type a-C:H was applied on Ti6Al4V (

Table 1. Chemical composition of Ti6Al4V titanium alloy [3].

Ti6Al4V, % Content
Ti	V	Al	Fe	C	N	O	H
Balance	3.5–4.5	5.5–6.75	max 0.4	max 0.08	max 0.05	max 0.2	max 0.0125

), a titanium alloy by plasma-assisted physical vapor deposition (PACVD) at ˂220 °C. Since the studied materials are of medical interest, they must meet the requirements imposed by the field of biomedicine [37,38].

Prior to DLC coating deposition, the Ti6Al4V alloy substrates underwent a thorough surface preparation process. This included grinding and polishing, followed by ultrasonic cleaning in ethyl alcohol for 10 min. The resulting surface roughness, as measured by the Sq parameter, was determined to be 0.02 µm, meeting the biomedical standards outlined in ISO 7206-2:1996 [39]. Subsequent to DLC coating deposition, the Sq value of the substrate increased to 0.06 µm. In the plasma-assisted chemical vapor deposition (PACVD) process, argon and methane gases were introduced into a vacuum chamber. An electric field was applied to ionize the gases, creating a plasma. The ionized particles diffused towards the substrate and deposited a coating. A schematic representation of the process is presented in [40].

2.2. Microstructure and Surface Texture

The thickness and chemical composition of the deposited carbon layers were examined using a Phenom XL scanning electron microscope (Phenom-World, Eindhoven, The Netherlands). The microscope was operated at an accelerating voltage of 15 kV and a magnification of 20,000×. The surface texture before the tribological tests was observed using an AFM microscope (Veeco, New York, NY, USA). Surface topography analysis was performed based on 3D axonometric images, amplitude parameters (Sq, Sv, Sp, Ssk, and Sku) and surface profiles. The surface area under analysis was 0.008 mm². The results of the experiments are presented in Section 3.1.

2.3. Adhesion and Mechanical Parameters

The adhesion of the DLC coating was assessed using a scratch test performed on a Micro Combi Tester (Anton Paar, Baden, Switzerland). A Rockwell diamond indenter was employed to induce a 3 mm scratch under a 15 N normal load. Real-time measurements of friction coefficient, acoustic emission, and scratch profile were acquired during the test. A comparative scratch test was conducted on the titanium substrate. The instrumental hardness was measured using an Ultra Nanohardness Tester (Anton Paar, Baden, Switzerland). During the test, the samples were loaded with a force of 50 mN. Then, the Berkovich diamond indenter remained under load for 10 s, after which the sample was loaded. Young’s modulus, maximum indentation depth, elastic, and plastic work were also measured in these studies. The results are presented in Section 3.2.

2.4. Corrosion Properties

The corrosion resistance was assessed using the potentiodynamic polarization method. The electrochemical corrosion test by potentiodynamic polarization (PP) was carried out at 37 °C in the artificial saliva solution. The chemicals used were analytical grade. The test was performed in the conventional three-electrode cell system with a calomel reference electrode (SCE) and a platinum auxiliary electrode (Pt) using a corrosion measuring system (BioLogic, Seyssinet-Pariset, France) (Figure 1) with a PGZ 100 measuring unit.

Each specimen was immersed in the electrolyte for 10 min prior to testing to allow for stabilization. A 1 cm² area of the specimen was exposed to the electrolyte. Potentiodynamic polarization (PP) curves were recorded at a scan rate of 1 mV/s over a potential range of −0.3 to 2.0 V versus open circuit potential (OCP). At least three experiments were conducted for each surface condition (as received, DLC-coated) to ensure reproducibility. Representative PP curves are presented in Section 3.3.

2.5. Tribological Tests and Assessment of Surface Geometric Structure After Tribological Test

Tribological tests were performed using an Tribometer (Anton Paar, Baden, Switzerland). The test parameters are shown in

Table 2. Tribological test parameters.

Parameter	Value and Unit
Type of movement	oscillatory
Load	1 N
Frequency	1 Hz
Radius and angle	9 mm, 60°
Number of cycles, distance	25,000, 460 m
Humidity	50 ± 1%
Ambient temperature	23 ± 1 °C
Lubricant	without (TDF), artificial saliva (AS)
Lubricant temperature	23 ± 1 °C and 37 ± 1 °C
Counter sample	Al2O3 (Ø 6 mm)

All samples were subjected to a normal load—F_N, of 1 N, corresponding to the estimated initial contact pressures of around 0.51 GPa for Ti6Al4V and 0.75 GPa for DLC.

, and the friction pair in Figure 2.

The properties of Al₂O₃ are shown in

Table 3. Mechanical and physicochemical properties of Al₂O₃ [41].

Hardness, GPa	Compressive Strength, MPa	Resistance to Chemical Exposure	Density g/dm3	Thermal Conductivity, W/(m × K)
1365	300–630	good	3.9	28–35

. The chemical composition of the artificial saliva is presented in

Table 4. Chemical composition of the lubricant [42].

Artifical Saliva, g/dm3
NaCl	KCl	CaCl2 × 2H2O	NaH2PO4 × 2H2O	Na2S × 9H2O	Urea
0.4	0.4	0.795	0.780	0.005	1.0

. The results of the tribological tests are detailed in Section 3.4.

Observations of the sample after tribological tests were performed using a confocal microscope with DCM8 interferometric mode (Leica, St. Gallen, Switzerland). Surface topography was evaluated based on axonometric (3D) images and surface profiles.

The volume of the removed material was measured and subsequently, the volumetric wear rate, W_V, of the coating-substrate systems was calculated using the following equation [43]:

$$W_V={\displaystyle \frac{V}{F_N\ast S}} \left[{\displaystyle \frac{{\mathrm{mm}}^3}{\mathrm{N}\ast \mathrm{m}}}\right]$$

(1)

where V—volume of material removed, ${\mathrm{mm}}^3$. $F_N$—normal force, N. S—distance, m. The results are presented in Section 3.5.

3. Results

3.1. Scanning Microscopy and Atomic Force Microscopy

Figure 3 shows a cross-sectional image of the DLC coating microstructure along with the linear distribution of elements. The thickness of the coating was determined from observations in five areas.

Linear analysis of the chemical composition of the a-C:H coating showed that the deposited layer was approximately 3.2 µm thick and the near-surface layer consisted of carbon and tungsten. At a depth of about 3.0 µm from the surface, chromium was observed, constituting the interlayer. Its function is to ensure adequate coating-to-metallic substrate adhesion.

Atomic force microscopy was employed to comprehensively analyze the surface topography. Figure 4 and Figure 5 present 3D surface plots (a) and corresponding profiles (b) for both the bare substrate and the DLC-coated surface. Medium profiles are marked in brown. Additionally, amplitude parameters extracted from the 3D images are summarized in

Table 5. The parameters of surface texture.

Parameter	Ti6Al4V		DLC
	Mean	Stand. Dev.	Mean	Stand. Dev.
Sq, μm	0.01	0.002	0.06	0.005
Sv, μm	0.09	0.015	0.53	0.017
Sp, μm	0.05	0.002	0.36	0.128
Ssk	−0.95	0.629	−1.82	0.575
Sku	7.42	2.43	12.97	0.825

.

The surface analysis revealed a significant alteration in the topography of the Ti6Al4V substrate following the deposition of the DLC coating. The 3D surface plots of the DLC coating exhibited features such as peaks and valleys in the order of 400–500 nm, as confirmed by the amplitude parameters in Table 5. Notably, the root mean square roughness (Sq), peak height (Sp), and valley depth (Sv) increased by more than 80%. Both the substrate and the coating displayed negative skewness (Ssk) values, indicating the presence of more profound valleys on the DLC coating compared to the substrate. While the kurtosis (Sku) values below 3 suggest a normal distribution of peaks and valleys for both surfaces [44], the DLC coating exhibited a higher Sku value (12.97) compared to the substrate (7.42), indicating a greater number and/or size of valleys. Although these valleys might initially appear as surface defects, they could potentially enhance the tribological performance by serving as reservoirs for lubricant or wear debris. In conclusion, the DLC coating is expected to exhibit superior tribological properties based on the observed surface characteristics.

3.2. Adhesion and Hardness

Figure 6 and Figure 7 present the results of the scratch tests performed on DLC coatings and Ti6Al4V titanium alloy substrates. The figures include optical images of the scratch tracks, as well as plots of the applied load (Fn), acoustic emission (Ae), friction force (Ft), scratch profile (Rd), and critical load values (Lc1–Lc2). A three-dimensional axonometric image illustrating the scratch are shown in Figure 8.

Adhesion is a crucial characteristic that determines the suitability of a coating for biotribological applications. The higher the adhesion of a coating, the better it protects the substrate from corrosion or wear. Additionally, to enhance the adhesion of DLC coatings, intermediate layers such as chromium are often employed. These intermediate layers serve to separate the hard coating from the significantly softer Ti6Al4V titanium alloy.

Scratch testing of the DLC coating revealed excellent adhesion to the Ti6Al4V substrate. The first acoustic emission event registered at a critical load of 3.55 N—Lc1. This signal was not indicative of coating delamination but was more likely associated with the indenter encountering an isolated surface defect. A second acoustic emission event at 9.18 N—Lc2 corresponded to the formation of cohesive cracks on both sides of the scratch. The maximum scratch depths were 3.56 µm for DLC and 5.54 µm for Ti6Al4V. Despite the scratch depth exceeding the coating thickness (approximately 2.8 µm), no delamination was observed, highlighting the high resilience of the DLC coating. In contrast, the titanium alloy graph exhibited minimal acoustic emission changes. However, the friction coefficient for the titanium alloy was approximately 45% higher than that of the DLC coating.

Table 6. Mechanical parameter test results.

Parameter	Unit	Ti6Al4V		DLC
		Mean	Std. Dev.	Mean	Std. Dev.
Instrumental Hardness, HIT	MPa	4930	137.6	20,103	501.3
Young’s Modulus, EIT	GPa	127	2.6	144	1.6
Maximum Penetration Depth, hm	nm	697	6.3	429	3.6
Elastic Work, Welast	%	23	3.7	71	7.5
Plastic Work, Wplast	%	77	4.9	29	5.8

shows the mean values of mechanical parameters: hardness, maximum indenter penetration depth, Young’s modulus, and elastic and plastic work calculated based on ten measurement series.

The mechanical test results showed that the Ti6Al4V titanium alloy exhibited lower mechanical properties compared to the DLC coating. Their values were 4930 MPa and 127 GPa, respectively, and were about 75% and 11% lower than for diamond-like carbon coating. Given the results of the mechanical tests, it is assumed that the Ti6Al4V will have lower wear resistance than the DLC.

3.3. Corrosion

Figure 9 presents the potentiodynamic polarization (PP) curves for the as-received Ti6Al4V and DLC-coated samples. The corresponding PP parameters, including corrosion potential (E_corr), corrosion current density (i_corr), corrosion rate (v_corr), and polarization resistance (R_p) are summarized in

Table 7. Values of the potentiodynamic polarization parameters.

Parameter	Unit	Sample
		Ti6Al4V	DLC
Corrosion Potential, Ecorr	V vs. SCE	−0.299	0.114
Corrosion current density, icorr	µA/cm2	0.081	0.012
Corrosion rate, vcorr	mm/year	0.41 × 10−3	0.061 × 10−3
Polarization resistance, Rp	kΩ·cm2	552.318	608.125

. The E_corr, i_corr, and v_corr values were determined by Tafel extrapolation using EC-LAB software V11.62.5). The R_p values were calculated according Stern–Geary equation [45] using i_corr and Tafel slopes (βa, βc) values obtained from Tafel extrapolation. A higher E_corr value indicates greater thermodynamic stability of the material in the given solution. The i_corr value reflects the kinetic aspect of the corrosion process. The corrosion rate, v_corr, was calculated based on the i_corr value using Faraday’s law. The increase of R_p values point to higher quality of the surface film, and higher corrosion resistance of the material.

The polarization curves (Figure 9) and the corresponding electrochemical parameters (Table 7) indicate high corrosion resistance of both surfaces. Both surfaces displayed broad passive regions from approximately 0.32 V vs. SCE for the as-received surface and from 0.20 V vs. SCE for the DLC-coated surface.

A detailed examination of the polarization curves within the passive regions plotted in linear axes (Figure 10) enables an assessment and comparison of the real passive current density values. This comparison reveals significantly lower passive current densities (<0.002 mA/cm²) for the DLC-coated surface than the as-received surface, particularly below 1.15 V vs. SCE. This result together with much higher corrosion potential (E_corr) and lower corrosion current density (i_corr) and corrosion rate (v_corr) values (Table 7), indicate superior thermodynamic stability and slower corrosion kinetics of the DLC-coated surface. Excellent corrosion resistance of DLC coating on Ti6Al4V alloy at potentiodynamic polarization (0.9 wt. % NaCl solution, 37 °C) was also confirmed [36,46].

3.4. Tribological Tests

The tribological tests aimed to determine the coefficients of friction and linear wear of the friction pairs tested. Figure 11a,b shows the example plots of friction coefficient and linear wear as a function of the number of recorded friction pair cycles.

Figure 12 shows graphs of average friction coefficients and linear wear recorded during lubricated friction with artificial saliva solution.

The results clearly indicate that the DLC coating deposited on a titanium alloy Ti6Al4V improves the tribological performance of the surfaces in contact. Under both dry and lubricated conditions (artificial saliva), the DLC-coated samples exhibited significantly lower coefficients of friction 0.2 and 0.13 compared to the uncoated Ti6Al4V alloy. Moreover, the DLC-coated samples showed greater stability in friction coefficient and linear wear over time. At the same time, the DLC coating was characterized by the most stable curves of both parameters. In the case of the Ti6Al4V titanium alloy, the average friction coefficients were much higher and amounted to 0.94 during technically dry friction. The analysis of uncoated polished Ti6Al4V shows that the coefficient of friction was about 25% lower when the lubricant (artificial saliva) was present. Similar relationships were reported by the authors of [36,48,49].

Additionally, the friction coefficient of the Ti6Al4V alloy exhibited an initial decrease to approximately 0.6 within the first 500 cycles, followed by an increase to an average value of 0.9 during dry sliding and 0.7 during sliding against artificial saliva. The strong affinity of titanium to oxygen leads to the formation of a passive layer, primarily composed of TiO₂, with a few nanometers of thickness on the titanium alloy surface [4,50,51]. The low friction coefficient value during the initial phase of the test is attributed to the presence of this oxide layer. As the test progressed, this layer underwent wear, resulting in a 30% increase in frictional resistance under dry sliding conditions and a 15% increase under lubricated conditions with artificial saliva. During operation, the TiO₂ coating experienced cracking and delamination, ultimately leading to excessive wear of the underlying substrate.

3.5. Assessment of Surface Geometric Structure After Tribological Tests

Three-dimensional axonometric images illustrating the wear tracks resulting from tribological tests are shown in Figure 13. Quantitative data, including average wear depth (W_D) and volumetric wear rates (W_v), are tabulated in

Table 8. Average values of wear depth and volume.

	Tribological Test				Scratch Test
	WD, µm		${\mathit{W}}_{\mathit{V}},$$\frac{m{m}^3}{N\ast m}$		WD, µm	V, mm3
	TDF	AS	TDF	AS
Ti6Al4V	42.7	64.5	3.9 × 10−4	4.30 × 10−4	5.54	6.06 × 10−4
DLC	0.29	0.23	7.39 × 10−8	2.97 × 10−8	3.56	3.36 × 10−4

.

The results demonstrate that the diamond-like carbon coating outperformed the substrate material regarding the two tribological properties. It exhibited lower friction coefficients and greater wear resistance. Additionally, introducing a lubricant led to a substantial reduction in volumetric wear for both the coating and the substrate, with the most pronounced effect observed for Ti6Al4V (W_V reduction of 90%). While deeper wear tracks were formed on Ti6Al4V lubricated with artificial saliva, the overall wear volume was still lower compared to dry sliding conditions. The 3D surface plots in Figure 13a–d revealed the presence of numerous grooves on the titanium alloy wear tracks, which are attributed to the abrasive action of wear debris (Ti6Al4V and Al₂O₃) within the contact zone, which intensified the wear process. The optical and 3D axonometric image analysis showed that adhesive wear was the dominant wear mechanism. However, in the case of the coating, the wear resistance was significantly higher.

4. Conclusions

The following conclusions were formulated based on the test results:

• Applying the chemical vapor deposition (PACVD) technique resulted in coatings with a thickness of approximately 3.2 µm. Microscopic examination indicated that the deposition of the DLC coating resulted in significant changes to the surface morphology of the Ti6Al4V alloy. The DLC-coated surface displayed a characteristic rough texture, characterized by numerous hills and valleys, in contrast to the smoother surface of the uncoated substrate. Analysis of amplitude parameters confirmed the increased roughness of the DLC coating, with values approximately 80% higher than those obtained for the uncoated Ti6Al4V alloy.
• Scratch test results indicated that the titanium alloy exhibited poor scratch resistance, while the DLC coating demonstrated good adhesion to the metallic substrate. The deposition of carbon coatings increased the instrumental hardness and Young’s modulus of the Ti6Al4V titanium alloy by approximately 75% and 11%, respectively.
• A comparison of the polarization curves demonstrated that both the DLC coating and the Ti6Al4V alloy exhibited passive behavior in the artificial saliva environment. However, the values of potentiodynamic parameters indicated superior corrosion resistance of the DLC coating, characterized by higher thermodynamic stability and slower corrosion kinetics compared to the Ti6Al4V alloy.
• The tribological tests and microscopic observations of wear tracks revealed that the DLC coating exhibited lower friction coefficients and volumetric wear than the substrate material. Moreover, the application of artificial saliva as a lubricant intensified this trend. The findings of this study indicate that DLC coatings outperform Ti6Al4V alloy in terms of wear and corrosion resistance when exposed to an artificial saliva solution.
• The application of DLC coatings improved the properties of the titanium alloy Ti6Al4V, particularly in terms of tribological and corrosion resistance in the analyzed artificial saliva environment, making DLC coatings promising candidates for application in the stomatognathic system. The findings of this research suggest that further studies are necessary. Future work could involve tribological testing in distributed contact configurations and with different material combinations, motion types, and lubricants.