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Review

Recent Developments in Self-Lubricating Thin-Film Coatings Deposited by a Sputtering Technique: A Critical Review of Their Synthesis, Properties, and Applications

by
Sunil Kumar Tiwari
1,2,*,
Turali Narayana
3,
Rashi Tyagi
4,
Gaurav Pant
5 and
Piyush Chandra Verma
6,*
1
BEST Centre, UPES, Dehradun 248007, Uttarakhand, India
2
Department of Mechanical Engineering, School of Advanced Engineering, UPES, Dehradun 248007, Uttarakhand, India
3
Department of Mechanical Engineering, Aditya Institute of Technology and Management, Tekkali 532201, Andhra Pradesh, India
4
Department of Mechanical Engineering, Galgotias University, Greater Noida 203201, Uttar Pradesh, India
5
Department of Mechanical Engineering, GLA University, Mathura 281406, Uttar Pradesh, India
6
Department of Mechanical Engineering, BITS Pilani, Hyderabad Campus, Hyderabad 500078, Telangana, India
*
Authors to whom correspondence should be addressed.
Lubricants 2025, 13(8), 372; https://doi.org/10.3390/lubricants13080372
Submission received: 26 June 2025 / Revised: 11 August 2025 / Accepted: 20 August 2025 / Published: 21 August 2025
(This article belongs to the Special Issue Advanced Surface Treatments and Coatings for Friction and Wear Reduction)
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Abstract

In response to the demand for advanced materials in extreme environments, researchers have developed a variety of bulk and thin-film materials. One of the best-known processes for altering the mechanical and tribological properties of materials is surface engineering techniques. These involve various approaches to synthesize thin-film coatings, along with post-deposition treatments. The need for self-lubricating materials in extreme situations such as high-temperature applications, cryogenic temperatures, and vacuum systems has attracted the attention of researchers. They have fabricated several types of thin films using CVD and PVD techniques to meet this demand. Among the various techniques used for fabricating self-lubricating coatings, sputtering stands out as a special one. It contributes to developing smooth, homogeneous, and crack-free dense microstructures, which further enhance the coatings’ properties. This review explains the need for self-lubricating materials and the different techniques used to synthesize them. It discusses and summarizes the concept of synthesizing various types of self-lubricating films. It shows the different types of self-lubricating material systems, like transition metal-based nitrides and carbides, diamond-like carbon-based materials, and so on. This work also reflects the governing factors like the deposition temperature, doping elements, thickness of the film, deposition pressure, gas flow rate, etc., that influence the deposition results and, consequently, the properties of the film, as well as their advanced applications in different areas. This work reflects the self-lubricating properties of different kinds of films exposed to various environments in terms of their coefficient of friction and wear rate, emphasizing how the friction coefficient affects the wear rate.

1. Introduction

The need for materials with high durability and smart performance has attracted the attention of researchers toward different classes of materials, including the surface properties of those materials [1,2,3]. Considering the cost of investment during material development, researchers are working extensively in the area of thin film technology to tailor the surface properties of materials. One of the most investigated and studied properties is self-lubricating properties [4,5,6,7]. Typically, liquid lubricants are used when two parts come into contact. However, the use of these liquid lubricants limits the application of different materials in complicated cases such as vacuum application, food and packaging industries, microelectronics, and paper industries, and creates environmental hazards [4,8]. In order to overcome these problems for a variety of applications, including cryogenic and high-temperature applications, a lot of research has been conducted in the area of developing solid lubricant coatings [9,10,11,12]. Among these solid lubricants, the idea of developing self-lubricating materials through different technologies in the form of bulk and thin films emerged; these materials are capable of reducing friction and wear, and eliminating the use of additional lubricants when used under diverse conditions, including high loading, high temperatures, and vacuum environments [13,14,15]. To obtain the thin deposited surface providing lubrication, it is reported that a layer providing lubrication should consist of a thick layer that separates the sliding parts from coming into direct contact [16,17,18]. However, there are broad categories of materials that provide self-lubricating effects even if they are thin in their dimensions. There are various processes that can develop thin films with self-lubricating properties, including chemical vapor deposition (CVD) and physical vapor deposition (PVD) [19,20,21]. Some of the various deposition techniques for developing self-lubricating thin films are shown in Figure 1.
These coating processes are capable of producing various types of coatings, including alloy coatings, composite coatings, and doped coatings [22,23,24]. Different classes of materials are used as the matrix material or dopant to produce these coatings. The broad categories of materials used for synthesizing self-lubricating coatings are illustrated in Figure 2 [13]. The selection of materials is crucial in synthesizing coatings for specific applications.
For example, MoS2 coatings deposited as a matrix material and MoS2 doped with other materials are excellent self-lubricating coatings with enhanced tribological properties [25,26]. However, these coatings can lose their properties in moist environments due to the formation of oxides. Similarly, graphite acts as a self-lubricating material because of its low shear strength.
One challenge faced by these materials is their lack of stability in terms of mechanical properties, despite their lubricating properties. Therefore, it is important to understand the key features that a self-lubricating material should possess when selecting materials for specific applications. The major features of self-lubricating materials include [23,27]
(a)
Stability of mechanical and tribological properties, and thermal and corrosion resistance;
(b)
Enhanced ductility and low shear strength in the sliding direction;
(c)
Low and controlled diffusion to minimize the depletion of the solid lubricant.
Furthermore, in response to industrial demands, researchers have developed various types of self-lubricating coatings tailored to specific temperature ranges. These coatings are broadly categorized as follows [13]:
(a)
Low-temperature self-lubricating coatings;
(b)
Moderate temperature self-lubricating coatings;
(c)
High-temperature self-lubricating coatings.
The synthesis of low-temperature self-lubricating coatings aims to deposit self-lubricating composites for use in the temperature range of −200 °C to room temperature (RT), primarily for cryogenic applications. These coatings are commonly utilized in aerospace, space satellites, and shuttles for their cryogenic systems [28,29,30]. Research has shown that incorporating MoS2, graphite, or a combination of both, along with additives such as polycarbamide, polysiloxane, epoxide, UFAR, and polyurethane, enhances the self-lubricating properties of MoS2-based coatings for low-temperature applications. On the other hand, self-lubricating coatings developed for moderate temperature applications are designed for use in the temperature range from RT to 500 °C [5,31,32,33]. From the class of materials shown in Figure 2, transition metal dichalcogenides (TMDs), tungsten and molybdenum disulfides, polymer coatings, oxide coatings, and diselenides have proven to be effective coating materials in this temperature range. The application of self-lubricating coatings applicable for use beyond 500 °C falls under the category of high-temperature self-lubricating coatings. Some of the classical materials used for this purpose are oxides, sulfates, fluorides, or their combination in optimized forms [31,34]. One of the challenges for these coatings during application is that they lose their self-lubricating properties when the temperature falls below a certain limit.
Considering the demand for precision manufacturing of self-lubricating materials, sputtering is one of the techniques used to deposit these coatings with enhanced microstructural features and mechanical and tribological properties [35,36,37]. Sputtering is a PVD process that involves sputtering atoms from solid target materials, which can be confined in a defined direction by the use of magnets (magnetron sputtering) and are condensed over the substrate to produce a thin film. A typical schematic diagram of magnetron sputtering is shown in Figure 3 [38,39]. The major components of the technique include a vacuum chamber, a high vacuum pump, a substrate holder, sputtering guns, a chiller, and a substrate heating element. Depending on the vacuum pump used, the typical base pressure of the chamber can reach up to 10−7 mbar, whereas the working pressure can be controlled between 10−2 to 10−6 mbar as per the requirements. The working of the sputtering equipment involves the introduction of high-purity inert gas or reactive gas (in the case of reactive sputtering) in the vacuum chamber in a controlled manner by the use of mass flow controllers (MFCs) [39,40]. Thereafter, a voltage is applied between the cathode (sputtering target) and the anode (substrate and chamber), which ionizes the gas, resulting in the formation of charged ions. These ions strike the target material and release the atoms as a result of bombarding the ions on solid targets, which are further ejected from the target and condensed and grown on the substrate.

2. Self-Lubricating Films Synthesized by Sputtering

Several materials have been synthesized for their self-lubricating properties at both room temperature and elevated temperatures [6,22,41,42]. Some of these materials are shown in Figure 2, which have been synthesized in the form of bulk or thin-film alloys or composites. These materials possess low friction along with low mechanical and tribological properties. A variety of metallic, non-metallic, and polymeric coatings have been fabricated using different synthesis techniques with self-lubricating properties [18,25,43,44,45]. While fabricating self-lubricating coatings, the major problem faced is that the deposited films lose their mechanical and tribological properties as well as their adhesion strength, based on their service and application conditions. For example, nitrides can be used as self-lubricating coatings, but the doping of foreign materials in the matrix of nitrides leads to the degradation of their existing mechanical and tribological properties [19,21,46]. On the other hand, diamond-like carbons (DLCs) do not lose their mechanical and tribological properties even when prepared for use in lubricating environments, but the challenge in using them is due to their limited applications and low adhesion strengths [47]. While there are many ways to fabricate self-lubricating coatings, this section particularly focuses on the synthesis of various self-lubricating coatings using sputtering techniques.

2.1. Nitride-Based Coatings

Nitride-based coatings are used as self-lubricating coatings, as they provide superior strength in terms of mechanical and tribological properties. These coatings are thermally stable, but their higher coefficient of friction and wear limit their use in industries. For example, V and VN have been proven as potential materials for their use in industries when it comes to high-temperature applications. Their addition to many matrix materials like CrN makes them coatings with self-lubricating properties and enhances their tribological properties. Athamani et al. deposited a series of Nb-V-N coatings over a silicon substrate for their application at high temperatures. They found that adding V into NbN produces a substitutional solid solution, along with increasing the hardness up to ~28 GPa [48].
Huang et al. deposited TiAlCN coatings using reactive sputtering under different gas environments of Ar, N2, and CH4. Films were deposited at a substrate temperature of 400 °C using the alloy target of TiAL (50 mol% each). They found a preferred phase of (111) in TiAlN coatings, which became randomly oriented at higher concentrations of carbon, providing the possibility of self-lubricating properties [45].
Guleryuz et al. synthesized TiN thin films containing solid lubricants in their matrix using reactive magnetron sputtering. The film was deposited over a Si wafer, and a micro-beading technique was used to create reservoir islands of lubricant. Before the actual film deposition, a layer of Ti was deposited with a thickness of ~30 nm to enhance the adhesive properties of the coatings. Once the deposition was complete, the photoresist was removed to create the holes in the coatings. The coefficient of friction of the film was studied with the number of cycles as the influencing factor, as shown in Figure 4b. It was found that samples with graphite as a lubricant and alumina as a counter face showed a minimum coefficient of friction of ~0.2 to 0.25. However, an in-depth study of the first 500 cycles for all the films showed almost the same coefficient of friction, which changed beyond it up to 2000 cycles. The microscopic investigation confirmed that the lubricant was less spread after 2000 cycles, even if the holes in the tracks were filled. They also stated that indium showed superior performance in terms of self-lubricating properties when deposited using sputtering [46].
Martinez et al. developed Ti (C, N)-based hard coatings using a double magnetron sputtering process. The films were deposited in two different phases, where in the first case, Ti and graphite targets were sputtered in the presence of an Ar/N2 mixed gas environment, whereas in the second case, they were sputtered in an Ar atmosphere. They found that the incorporation of graphite into Ti (N) led to a dramatic reduction in the friction coefficient of the films from 0.7 to 0.3. The results of the friction coefficients with respect to the wear rates are shown in Figure 4c. They also stated that the film exhibited self-lubricating performance after the introduction of amorphous carbon in the TiN matrix, which reduced the friction coefficient and wear rate of the coatings [49]. This is attributed to the higher degree of crystallinity and hard amorphous phases in the coating. Additionally, it is reported that TiN and graphite always contribute to enhancing the mechanical and tribological properties of films. Tillmann et al. [43] synthesized TiAlVN coatings by industrial magnetron sputtering in an environment of Ar and Kr. In order to fabricate nitride coatings, N2 was introduced into the vacuum chamber as a reactive gas. They deposited samples by varying the flow rate of N2 to 50, 100, and 150 mL/min at heating powers of 10 kW and 5 kW individually in the set of three samples. The results showed that the thickness of the films increased with increasing N2 flow rates, whereas the mechanical properties increased with an increase in the high-temperature powder inside the coating chamber. They also found that the friction coefficient of the film performed well when tested at 500 °C up to 1000 cycles, as shown in Figure 4d. This is attributed to the formation of the V2O5 oxide layer at 500 °C, which contributes well to enhancing the self-lubricating properties.
While the need for self-lubricating coatings in sophisticated machining is crucial, it is also essential to consider hard-to-machine specimens in industries. Achieving a balance between self-lubricating, mechanical, and tribological properties is key [5,50,51]. There is a significant amount of literature demonstrating the synthesis of transition metal nitride coatings, which have shown promise in providing self-lubricating properties [19,43,51,52]. Fernandes et al. studied the impact of vanadium addition in Ti-Si-N films on their mechanical and tribological properties. Films were deposited on silicon substrates using deep oscillation magnetron sputtering at two different peak powers of 110 kW and 28 kW. The results of the tribological tests conducted at room temperature are depicted in Figure 5. The researchers discovered that the Ti-Si-N coating exhibited a lower wear rate when deposited at a higher peak power of 110 kW compared to the film deposited at 28 kW. However, the introduction of vanadium into the matrix of Ti-Si-N resulted in a significant decrease in wear rate for the film deposited at a peak power of 28 kW, while the film deposited at 110 kW showed a consistent wear rate initially, followed by a decrease [18].

2.2. TMC-Based Coatings

Transition metal carbide (TMC)-based coatings are hard and wear-resistant coatings that also provide enhanced thermal and chemical stability. They have applications in biomedical implants, the automotive industry, and semiconductors. They act as self-lubricating coatings when nanocrystalline TMC phases are embedded in a C matrix [53]. Polcar et al. deposited W-S-C coatings of nearly ~300 nm thickness using RF magnetron sputtering. The tribological properties were studied using the pin-on-disc tribometer to understand the sliding behavior of the coatings. They found that the friction coefficient of the coatings decreases continuously with increasing load, independent of frictional heating, as shown in Figure 4a. Additionally, they stated that the coating with a higher content of carbon showed the maximum friction coefficient throughout the test [54].
Pimentel et al. [6] investigated the effect of doping Cr in the matrix of a W-S-C thin film deposited through the RF magnetron co-sputtering process. The films were deposited on tungsten substrates with grooves of 2–3 μm created using a repetitive process of electro-discharge machining (EDM). The preparation of the substrates is shown in Figure 6a. The pin-on-disc tribometer test (5 N for 5000 cycles) revealed that the coefficient of friction decreased with increasing load for non-patterned substrates. For patterned substrates, the friction coefficient was significantly influenced by the nature of the grooves prepared before deposition. The researchers noted that samples A and B had lower friction coefficients compared to the bare substrate, as the grooves acted as reservoirs and were filled with material during the tribological test. The role of grooves in the substrate in enabling the coating to act as a solid lubricant to a certain distance is evident from the results presented in Figure 6.
Vuchkov et al. also examined the impact of different environmental conditions on the frictional behavior of W-S-C self-lubricating thin films deposited by magnetron sputtering [55]. They utilized two graphite targets (99.99%), one WS2 target, and one Cr target to deposit the co-sputtered films on Si and AISI M2 steel. A thin layer of Cr (400 nm) was deposited at the interlayer and gradient layers to enhance the adhesion strength of the films. A DC power supply was used to sputter all the targets simultaneously for a total time of 120 min with substrates rotating at a speed of 10 rpm. The parameters of deposition and the results obtained in terms of thickness and elemental composition are shown in Table 1. The results of the mechanical properties indicated that the hardness of the films decreased with increasing substrate–target distance. However, the researchers observed that a maximum hardness of ~13 to 15 GPa was achieved at a substrate–target distance of 15 cm. The tribological test results showed that the friction coefficient decreased from 0.15 to 0.1 after 2500 cycles at an applied load of 5 N, then increased to 0.25 after 40,000 cycles, and subsequently dropped to 0.17. The average friction coefficient at an applied load of 35 N was 0.06. The tribological tests at elevated temperatures (100 to 400 degrees Celsius) demonstrated variation in the friction coefficient with the number of cycles. The results of the tribological tests at higher temperatures are depicted in Figure 7a,b. Additionally, the results of tribological tests under vacuum using a 100Cr6 bearing showed a friction coefficient of ~0.01 to 0.02 at a load of 2 N after 100 cycles, which increased to ~0.5 after 800 cycles, as shown in Figure 7c,d. This is attributed to the contribution of the WS2 phase in the coating, which is responsible for the low COF. Additionally, the results of the 3D profilometer revealed significant wear with the formation of scars with a diameter of 0.8 mm, while the profilometer on the wear track did not show any evidence of the presence of transferred material.
Cao et al. studied the tribological behavior of Cu-Al/MoS2 composite coatings deposited using magnetron sputtering [22]. The coatings were deposited onto SUS 201 steels using three different targets of Cu (DC power), Al (DC power), and MoS2 (RF power) via a co-sputtering process in the presence of Ar. A series of samples was prepared, as shown in Table 2. The coatings were further annealed to remove residual stress. It was observed that the MoS2 layers exhibited a crystalline nature at an annealing temperature of 350 °C.
Tribological studies were conducted on a ball-on-plate tribometer setup. The results of the tests revealed that the coefficient of friction for Cu/MoS2 initially decreased and then increased with an increase in power supply to the Cu target. However, it was noted that the friction coefficients of Cu10 and Cu20 were lower compared to bare MoS2 films. Additionally, the friction coefficient of Cu10 (200 °C) was lower compared to Cu10 (100 °C). However, the friction coefficient of Cu10 (0.07) was the lowest among the family of Cu/MoS2 films. The results of the friction coefficient of Cu/MoS2 are shown in Figure 8. This is attributed to the doping of Cu into MoS2, which reduces the friction coefficient of the MoS2-based composite coating. Additionally, for the Cu10 film, it was easy to achieve the basal plane (002) for MoS2, which is parallel to the substrate. Moreover, the formation of dense films with a laminar microstructure contributed more to maintaining the low coefficient of friction.
Furthermore, the results of the test after annealing in an Ar environment showed that the coefficient of friction increased compared to the results obtained from as-deposited samples, but the Cu10 annealed at a temperature of 500 °C demonstrated the lowest coefficient of friction (0.088) compared to the entire set of Cu/MoS2 coatings. It was also observed that the coatings with the composition of Al as Cu-Al/MoS2 showed the lowest coefficient of friction (0.083) compared to all the as-deposited and annealed coatings.
Chen et al. synthesized an Au-Ni/a-C nano composite coating using the magnetron sputtering process. They deposited these coatings onto CuCrZr alloy to study the impact of integrating carbon into the film. The films were deposited on silicon at room temperature (RT) using three targets: Au, Ni, and graphite [56]. They found that the hard coatings (400 HV) of Au-Ni/a-C exhibited enhanced resistance to wear compared to Au and Ni coatings under normal environmental conditions. The films containing 1.8 wt% of carbon showed the best wear rate of 2.2 × 10−6 mm3/N-m, which was almost half compared to the Au and Ni reference films.
Vuchkov et al. synthesized Mo-Se-C films using the unbalanced magnetron sputtering technique [57]. They investigated the effect of incorporating MoSex, substrate bias, and substrate–target distance on the mechanical and tribological properties of Mo-Se-C films. The results of the experiment showed that the film containing 50 at% of carbon had a hardness of ~8 GPa with a coefficient of friction of ~0.9 at room temperature and 0.04 to 0.04 in an N2 environment at 200 °C.

2.3. DLC-Based Coatings

Diamond-like-carbon-based coatings have been used for their self-lubricating and high wear-resistant properties. The presence of carbon in the matrix of the coatings forms diamond-like structures, providing higher hardness and an excellent friction coefficient, which makes these coatings self-lubricating for their use in machining industries. Moreover, the arrangement of carbon in tetrahedral structures with covalently bonded atoms makes the coatings thermally stable and a potential candidate for use as an electrical insulator [58].
Guo et al. deposited Si-doped DLC coatings over Si and YG6 substrates using HiPIMS and magnetron sputtering techniques to study their wear behaviors. It was observed that the hardness of the film increased with an increase in the Si content in the film. The maximum hardness of ~19.3 GPa was achieved when the concentration of Si was 27.1%, which confirms the formation of diamond-like structure too. However, a concentration of Si in the films of 24.43 gives an average coefficient of friction of 0.066, which enhances the wear resistance properties because of the absorption of oxygen atoms in the film during the tribometer test [59].
Zhang et al. synthesized Ti-doped DLC-based nanocomposite multilayer coatings over 17-4 PH and Si substrates using magnetron sputtering. The deposited film had an average thickness of ~1.2 μm. The results revealed that the hardness of the film increased with an increase in current supply to the Ti target and thus the Ti concentration. However, the coefficient of friction decreased dramatically, where the lowest coefficient of friction was observed as 0.02. The substrate with the current supply of 0.4 A to the Ti target showed the best corrosion-resistant properties [60].
Bewilogua et al. fabricated DLC-based coatings over steel and Si substrates using D.C magnetron sputtering in unbalanced mode. They observed an increase in the deposition rate with an increase in the gas flow rate of C2H2. Additionally, the minimum wear rate of the coatings was found for W-DLC coatings for W/C atomic ratios of 0.2 [61].
There are numerous research reports in the literature where authors have examined the self-lubricating properties of thin films deposited by sputtering or other PVD or CVD approaches in terms of the friction coefficient. Some studies also demonstrate the effects of various influencing factors that affect the self-lubricating behavior at room temperature or elevated temperatures. Some of the results of the tribological properties of the coatings are presented in Table 3.

3. Optimization of Parameters

The behavior and properties of self-lubricating composites fabricated using PVD processes, specifically sputtering, are governed by many influencing parameters [23,25,64,75]. These parameters can include the processing parameters of the system, materials used along with dopants, percentage of constituent elements, and, finally, the primary results of the deposition in the form of structural and compositional integrity [38,39,76]. At the primary level during synthesis, the optimization of process parameters like base and sputtering pressure, gas flow, substrate–target distance, substrate temperature, deposition time, bias voltage, and treatments after deposition plays an important role in altering the mechanical and tribological properties of the coatings.
To deposit oxidation-free coatings, it is crucial to evacuate the coating chamber to a low pressure. There are several results reported in the literature where researchers have evacuated the vacuum chamber to 10−7 or 10−8 mbar. Second, the purity of the inert gas or reactive gas plays an important role, along with maintaining the required working pressure, depending on the mean free path calculated for the customized chamber. In general, the practice of depositing self-lubricating thin films using sputtering requires a working pressure of 10−2 or 10−3 mbar [37,40,77]. However, research indicates that high pressure can lead to the scattering of sputtered particles, resulting in the formation of films with porous and inhomogeneous structures. On the other hand, low pressure can result in uniform deposition with a fine microstructure of the coating. Therefore, a balance in the selection of working pressure during the deposition is essential for optimization.
Another influencing parameter of deposition is the power supply used to sputter targets. These power supplies can vary as DC/RF and pulsed DC power [78,79]. Generally, higher power to the substrate leads to an increase in sputtering yield, which helps in increasing the thickness of the coating. However, a higher power supply can eject larger atoms in some cases, and due to the smaller substrate–target distance, the impact of the ejected atoms on the pre-deposited films in the process can be impacted. It can damage the microstructural integrity of the film and thus influence the mechanical and tribological properties [80,81]. Moreover, the choice of power supplies according to the nature of the target is also an influencing factor while depositing films via magnetron sputtering. The DC power supply at the same power to RF gives a higher sputtering yield, while the sputtering yield in the RF power supply is lower. At the same time, the formation of a crack-free homogeneous microstructure is found in RF sputtering [82]. In general, DC power can be used for metallic sputtering targets, while an RF power supply is used for non-metallic targets. Therefore, optimizing the power supply and substrate–target distance is important.
Along with these deposition parameters, the working pressure and the gas flow (reactive and non-reactive) also influence the quality of the film [83,84]. In order to optimize the gas flow inside the vacuum chamber, it is crucial to understand the mean free path at a particular pressure inside the chamber. Low pressure can result in the formation of a smooth and dense microstructure, enhancing the overall mechanical and tribological properties of the film. In the case of reactive sputtering, the optimization of the reactive gas with the non-reactive gas becomes important [85]. The selection of the reactive gas, depending upon the sputtering target used, also influences the properties of the deposited coatings. The mixture of these reactive and non-reactive gases also influences the formation of different phases in the coatings, and, therefore, their control using a device like a mass flow controller (MFC) becomes important [40]. Additionally, depending upon the application and thickness of the films required, one of the most important and influential parameters is the substrate temperature. Substrate temperature generally deals with the process of nucleation and grain growth during deposition. A higher substrate temperature helps in the mobilization of sputtered species, which further organize themselves, leading to the formation of highly oriented crystal growth, enhanced adhesion, and increasing crystallinity in the film [86,87]. Additionally, post-treatment of films after deposition also helps in altering the formation of phases due to the formation and accumulation of residual stresses in the coatings.
Considering the different requirements of self-lubricating properties, the understanding of choosing the matrix material and dopants in the films is also important. In some cases, looking at the application at room temperature and elevated temperature, it is required to have self-lubricating properties without losing much in mechanical properties. Therefore, the percentage of constituent elements in the film’s matrix becomes important, as individual elements can contribute individually to altering the mechanical and tribological properties of the films [25,65,67]. A brief of the deposition parameters and post-deposition parameters is shown in Table 4.

4. Advanced Applications

The development of functional and engineered materials has significantly expanded the range of different classes of materials. Specifically, the need for coatings that can withstand extreme environmental applications has led to the development of self-lubricating coatings deposited over various parent materials based on specific needs [7]. These self-lubricating materials demonstrate exceptional properties, such as a low friction coefficient, reduced rates of wear and abrasion, and increased service life of the products they coat. These findings are supported by research [9,12,20,88].
Among the various areas of application, some commonly identified areas where these coatings are used include aerospace and defense applications [89,90], marine and biomedical implants, automobile and industrial applications, frictional parts where coolant creates problems, and other areas of application, as shown in Figure 9.
Self-lubricating coatings such as metal nitrides, oxides, and transition metal dichalcogenides have been synthesized through diverse PVD/CVD methods, and they are extensively utilized in modern engineering applications [55,57]. The need for these types of self-lubricating coatings is particularly felt in vacuum systems, cryogenic applications, clean rooms, and other areas where external lubricants are ineffective. In terms of advanced applications of self-lubricating coatings, they are also utilized in the electrical and electronics sector. They are commonly used in contact bushes, small sliding contacts, micro electrochemical systems, various research equipment, and precision electronic systems [14,91]. Nitride- and oxide-based self-lubricating coatings find applications in transmission systems, ball bearings, dies, dry machining and milling, and heavy load equipment in mechanical and industrial settings. Additionally, they are used in defense and nuclear industries, particularly in reactors, traction devices, vacuum systems, and shielding applications to meet tribological needs. Coatings such as DLCs and WS2 are commonly employed in space satellites and aircraft for actuators, hinges, and vacuum bearings [33,73].
The demand for self-lubricating coatings has been steadily increasing over the past few decades. As a result, the synthesis and modification of these coatings to meet specific application requirements have also been on the rise. The utilization of these coatings in highlighted areas is depicted in Figure 9.

5. Conclusions

The need for advanced materials, specifically self-lubricating films, represents a significant advancement in the field of surface engineering. Various films are deposited using different techniques, with an emphasis on the sputtering technique in this review. The advantage of sputtering lies in its ability to produce homogeneous and dense microstructures, flexibility in depositing different metallic and non-metallic coatings, and the ability to vary elemental composition, thickness, and mechanical and tribological properties.
In addition to sputtering, other processes have been used over the past few decades to meet the requirement for thicker films. Self-lubricating coatings made from polymeric materials are typically deposited using CVD processes, which can produce thicker films compared to sputtering. Common types of self-lubricating coatings include metal nitride coatings; carbide coatings; oxynitrides like TiN, CrN, TiSiN, TiCrN, and VN; as well as transition metal dichalcogenides like MoS2 and WS2.
The review also demonstrates different kinds of material systems like TMC-based coatings, TMN-based coatings, DLC-based coatings, etc., that provide unique advantages and benefits in reducing the friction coefficient and wear rate.
Optimizing process parameters is crucial as they can impact the mechanical and tribological properties of the coatings, especially under extreme conditions. These self-lubricating coatings find applications in the defense, space, marine, automotive, nuclear, and vacuum industries, where liquid lubricants may not be suitable.
There is a growing need for the development of self-lubricating materials to reduce the reliance on traditional lubricants in various applications. Some of the self-lubricating coatings with different material systems; their advantages, drawbacks, and additional lookouts into them; and the identification of the future scope of work are presented in Table 5.

Author Contributions

S.K.T.: conceptualization, writing—original draft, data curation, methodology, software. T.N.: validation, software, formal analysis. R.T.: data curation, review and editing, and visualization. G.P.: review and editing, software, data curation, formal analysis. P.C.V.: project administration, editing and review, visualization; methodology. All authors have read and agreed to the published version of the manuscript.

Funding

The research received no external funding.

Data Availability Statement

No new data were created or analyzed in this study.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Different deposition methods for synthesizing self-lubricating coatings.
Figure 1. Different deposition methods for synthesizing self-lubricating coatings.
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Figure 2. Different classes of self-lubricating materials.
Figure 2. Different classes of self-lubricating materials.
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Figure 3. Typical schematic diagram of magnetron sputtering.
Figure 3. Typical schematic diagram of magnetron sputtering.
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Figure 4. (a) The load versus friction coefficient for a W-S-C coating in a humid air environment, (b) the friction coefficient versus the number of cycles obtained from a pin-on-disc tribometer setup, (c) the friction coefficient and wear properties of coatings, and (d) the friction coefficient versus the number of revolutions for TiAlVN coatings.
Figure 4. (a) The load versus friction coefficient for a W-S-C coating in a humid air environment, (b) the friction coefficient versus the number of cycles obtained from a pin-on-disc tribometer setup, (c) the friction coefficient and wear properties of coatings, and (d) the friction coefficient versus the number of revolutions for TiAlVN coatings.
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Figure 5. (a) The wear rate of Ti-Si-V-N coatings, (b) the friction coefficient results for Ti-Si-N coatings at a peak power of 28 kW, and (c) the friction coefficient results for Ti-Si-N coatings at a peak power of 110 kW.
Figure 5. (a) The wear rate of Ti-Si-V-N coatings, (b) the friction coefficient results for Ti-Si-N coatings at a peak power of 28 kW, and (c) the friction coefficient results for Ti-Si-N coatings at a peak power of 110 kW.
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Figure 6. (a) Types of grooves prepared on the substrates, (b) the friction coefficients of different samples after 5000 cycles, and (c–f) the friction coefficients of patterned and non-patterned samples after 5000 cycles.
Figure 6. (a) Types of grooves prepared on the substrates, (b) the friction coefficients of different samples after 5000 cycles, and (c–f) the friction coefficients of patterned and non-patterned samples after 5000 cycles.
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Figure 7. (a) Friction coefficient versus the number of cycles, (b) friction coefficients at different temperatures for 2500 cycles, (c) friction coefficients in vacuum and N2 environments, (d) specific wear rate in vacuum and N2 environments.
Figure 7. (a) Friction coefficient versus the number of cycles, (b) friction coefficients at different temperatures for 2500 cycles, (c) friction coefficients in vacuum and N2 environments, (d) specific wear rate in vacuum and N2 environments.
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Figure 8. Friction coefficients of Cu/MoS2 coatings.
Figure 8. Friction coefficients of Cu/MoS2 coatings.
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Figure 9. Applications of self-lubricating coatings.
Figure 9. Applications of self-lubricating coatings.
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Table 1. Deposition parameters and the resulting elemental composition and thickness.
Table 1. Deposition parameters and the resulting elemental composition and thickness.
CoatingS-T DistanceSubstrate Bias (V)Power Applied to Targets (W/cm2)Elemental Composition (at%)S/W RatioThickness (μm)/Deposition Rate (nm/min)
WS2C (x2)CSOW
WSC1-101002.12.644.028.54.922.61.262/16.7
WSC1-151502.12.640.232.55.222.11.472.3/19.2
WSC1-152502.12.638.135.15.821.11.661.6/13.3
WSC1-1010502.12.645.825.13.126.00.961.8/15
WSC1-1515502.12.648.224.02.825.00.961.7/14.2
WSC1-1525502.12.640.832.72.823.71.381/8.3
WSC1-101002.13.257.620.12.420.01.012/16.4
WSC1-151502.13.252.226.11.520.21.292/16.3
WSC1-152502.13.253.027.52.417.11.611.6/13.1
Table 2. Deposition parameters for Cu/MoS2 and Cu-Al/MoS2 films.
Table 2. Deposition parameters for Cu/MoS2 and Cu-Al/MoS2 films.
SamplePower Supply to Individual TargetsHeating Temperature
MoS2CuAl
Cu510050RT
Cu10100100RT
Cu20100200RT
Cu40100400RT
Cu50100500RT
Cu60100600RT
Cu10 100100100 °C
Cu10100100200 °C
Cu5Al510055RT
Cu5Al10100510RT
Cu10Al5100510RT
Cu10Al10100105RT
Cu10Al101001010RT
Cu5Al1010055100 °C
Cu5Al1010055200 °C
Table 3. Results of the tribological properties of coatings deposited by sputtering and other PVD and CVD techniques.
Table 3. Results of the tribological properties of coatings deposited by sputtering and other PVD and CVD techniques.
AuthorsMethod of FabricationMatrix MaterialDopantsFriction CoefficientSpecific Wear RateRemarksRef.
Kloos et al.Ion platingCopper,Pb, In, Ag0.08 for copper; 0.2 for Cu-In -Cu-In is better than Cu-Pb.[32]
Lugscheider et al.Magnetron sputter-ion platingV2O5 and WO2.9-A 2–5% oxygen and argon ratio gave the best results-O2 to Ar (0–50%) variation; substrate temperature of 400 °C[62]
Basnyat et al.Co-sputteringCrAlNAg0.233.0 × 10−8These results are for 8% Ag.[19]
Wang et al.AnodizationPTFEAl--The weight change after wear is 0.0022.[19]
Ma et al.PECVDTi-Si-C-N and Ti-Si-N-0.75 for Ti-Si-N and 0.35 for Ti-Si-C-N--[50]
Filip et al.Magnetron sputteringMoS2Ti and Mo0.05 for MoS2 coatings, 0.03 for Ti/MoS2 coatings, and 0.08 for Mo/MoS2 coatings-A tribological test was performed for 36,000 cycles.[63]
Incerti et al.Arc discharge and magnetron sputteringCrNAg0.75 for coatings at Rt and 0.78 for coatings at 400 °C-Ag clusters helped maintain a COF of 0.23.[51]
Ming et al.Plasma electrolytic oxidation (PEO) processTiO2 and graphiteOxygenThe COF for the uncoated substrate is ~0.35 to 0.45; the TiO2/graphite coating has a COF of 0.15.5.2 × 10−5 mm3/N m for the substrate and 1.7 × 10−5 mm3/N m for TiO2 coatingsThe substrate used was Ti6Al4V.[64]
Yan et al.Laser claddingCoTiC and CaF2~0.31 to 0.24 for Co-based coatings and 0.24, 0.19, 0.22 for 0%. 10%, and 20% CaF2, respectively.-Cr-Zr-Cu was used as a substrate; laser cladding was performed at 400 °C.[65]
Meister et al.Non-reactive RF magnetron sputteringWSe2WC0.07 in atmospheric air and 0.03 in a nitrogen environment2 × 10−5 mm3 Nm−1 for non-heated samples and 3 × 10−7 mm3 Nm−1 for modulated bias samplesCoatings were deposited on Si substrates. The hardness of the films was nearly 4 to 5 GPa.[66]
Gu et al.DC magnetron sputteringMoS2Carbon (graphite target)Less than 0.1 for MoS2-C coatingsThe wear rate of MoS2-C coatings was ~10−7 mm3/Nm.The sliding time for the tribological test was 3600 s.[25]
Fernandes et al.DC reactive magnetron sputteringTiNSilicon and vanadium~1.09 to 1.15 for TiSiN coatings and 0.5 for TiSiVN coatings-Films were deposited over Si and steel.[67]
Torres et al.Laser claddingNiCrSiB powderAg and MoS21.1 for most of the tests, but ~0.5 to 0.8 for 10 MoS2 and ~0.5 to 0.5 for Ag-10 MoS25.6 × 10−5 mm3/Nm for the nickel-based alloy and 2.7 × 10−5 mm3/Nm for the 5Ag-10MoS2 base alloyThe film was deposited over 1.4301 grade steel substrate.[68]
Bobzin et al.DC and high-power pulse magnetron sputteringCrAlNMo:S0.77 for the uncoated AISI M2 sample-Films were deposited on cold-worked steel substrates AISI D2 and AISI M2.[69]
Zhou et al.Laser claddingNi60-16.8TiC-23.2WS2 as the Ni coating and Ni60-19.6TiC-20.4WS2 as the N2 coatingNi and Cr as the main phase elementsThe COF of the N1 and N2 coatings at different testing temperatures of 20 °C, 300 °C, 600 °C, and 800 °C are 0.444/0.489, 0.393/0.433, 0.357/0.440, and 0.321/0.404, respectively.The wear rates of the N1 and N2 coatings at different testing temperatures of 20 °C, 300 °C, 600 °C, and 800 °C are 1.4 × 10−4/1.1 × 10−4, 5.9 × 10−5/4.8 × 10−5, 3.7 × 10−5/4.5 × 10−5, and 2.9 × 10−5/2.3 × 10−5 mm3/Nm, respectively. The films were deposited over Ti6Al4V substrates.[70]
Zhau et al.Laser cladding + vacuum pressure thermal diffusion weldingNiCrSiBWUs0.38 for the as-received substrate,
0.43 for NiCrSiB coatings,
0.14 for Cu-G coatings, and
0.12 for SSWC		1.09 × 10−3 mm3/Nm for SSWC,
~4.83 × 10−4 mm3/Nm for the substrate, and
3.28 × 10−5 mm3/Nm for NiCrSiB coatings		SSWC 316 L steel was used as a substrate.[71]
Gautam et al.Atmospheric plasma sprayNi-Al-Ag-MoS2hBN0.5 and 0.23 for Ni-Al-Ag-MoS2-5 wt% hBN at RT and 800 °C, respectively-The variation in hBN was fixed as 5 wt% hBN and 10 wt% hBN.[72]
Zhu et al.Magnetron sputteringWS2-0.06 before 1200 s of the test and 0.09 at the end of the test; 0.07 at 100 °C and 0.2 at 300 °C-Films were deposited over high-speed steel substrates with a thickness of ~2.2 μm.[23]
Yuan et al.Laser claddingNiCr/TiCCu and WS20.61 for NiCr/TiC,
0.4 for NiCr/TiC-Cu, and
<0.4 for NiCr/TiC-WS2		-Films were deposited over 30CrMnSi steel substrates.[73]
Liu et al.Laser cladding46% nickel-coated WC718-WC + 8% Ag0.20 for substrates, 0.379 for the coating at 700 W laser power, and 0.335 for the coating at 1000 W laser power3.68281 × 10−5, 1.59918 × 10−5, and 0.93687 × 10−5 mm3/Nm at RT for the substrate and 700 W and 1000 W laser power coatings, respectivelyCoatings were deposited on cast iron (RuT450) substrates.[74]
Table 4. Deposition parameters and their effects on coatings and their properties.
Table 4. Deposition parameters and their effects on coatings and their properties.
Influencing ParametersEffect on Coatings
Base pressureProtects from contamination (ex-oxidation)
Working pressureInfluences the mean free path
Sputtering powerInfluences the deposition rate and sputtering yield, and can generate stress in the coatings
Gas flow rateMaintains the required pressure; influences the sputtering yield
Substrate–target distanceImpact on the film thickness
Substrate temperatureEnhances crystallization and adhesion
Substrate rotationEnhances uniform and dense coatings
Bias voltageEnhances adhesion and film density; increases residual stress
Dopants usedAlters the chemical composition and affects the film’s properties
Power sourceAffects the film thickness and sputtering yield
Deposition timeAffects the film thickness and uniformity in microstructure
Post-deposition treatmentsAlters the microstructural, topographical, and film properties
Table 5. Different material systems used in self-lubricating coatings with their drawbacks, applications, and future scope.
Table 5. Different material systems used in self-lubricating coatings with their drawbacks, applications, and future scope.
SNMaterials UsedArea of ApplicationDrawbacksFuture Scope
1.Nitride coatings like VN, TIN, CrN, TiAlN, and WNMachine shops like cutting tools, bearings, dies, and actuatorsA high COF in a moist environment, with a challenge in lubrication at low temperaturesIt can be doped with V, W, and Mo, which enhance the lubricating properties
2.TMC-based coatingsEngine parts of an automobiles and aircraft, vacuum systems, and instrumentsProblem of oxidation at elevated temperaturesCan be fabricated in the form of nano-composite coatings, which possess improved oxidation-resistant properties
3.DLC-based coatingsGenerally used in bioimplants and precision toolsThe problem of adhesion between coatings and substrates, and the problem of high-temperature stabilityUse of high-temperature stable dopants in the matrix of DLC coatings
4.TMD-based coatingsUsed in cryogenic environments and dry bearing equipmentLoss of mechanical and tribological properties at different temperature rangesTMDs can be deposited in hybrid form using different metal layers
5.Oxide-based coatingsUsed in braking systems and structural parts of turbinesInstability of the phase formed and brittle behaviorThey can be deposited as toughened oxide coatings with healing properties
6.Composite coatingsUsed in marine industries and heavy machineryAchieving a smooth and homogeneous coating is a challengeCan be deposited using different techniques
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Tiwari, S.K.; Narayana, T.; Tyagi, R.; Pant, G.; Verma, P.C. Recent Developments in Self-Lubricating Thin-Film Coatings Deposited by a Sputtering Technique: A Critical Review of Their Synthesis, Properties, and Applications. Lubricants 2025, 13, 372. https://doi.org/10.3390/lubricants13080372

AMA Style

Tiwari SK, Narayana T, Tyagi R, Pant G, Verma PC. Recent Developments in Self-Lubricating Thin-Film Coatings Deposited by a Sputtering Technique: A Critical Review of Their Synthesis, Properties, and Applications. Lubricants. 2025; 13(8):372. https://doi.org/10.3390/lubricants13080372

Chicago/Turabian Style

Tiwari, Sunil Kumar, Turali Narayana, Rashi Tyagi, Gaurav Pant, and Piyush Chandra Verma. 2025. "Recent Developments in Self-Lubricating Thin-Film Coatings Deposited by a Sputtering Technique: A Critical Review of Their Synthesis, Properties, and Applications" Lubricants 13, no. 8: 372. https://doi.org/10.3390/lubricants13080372

APA Style

Tiwari, S. K., Narayana, T., Tyagi, R., Pant, G., & Verma, P. C. (2025). Recent Developments in Self-Lubricating Thin-Film Coatings Deposited by a Sputtering Technique: A Critical Review of Their Synthesis, Properties, and Applications. Lubricants, 13(8), 372. https://doi.org/10.3390/lubricants13080372

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