The deposition of ternary nitrides with the incorporation of carbon atoms into its structure has demonstrated to be a promising approach in the pursuit of wear-resistant and self-lubricating ...coatings. Firstly, both TiAlN and TiAlCN monolayers were deposited using direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) onto quenched and tempered AISI H11 tool steel to be used as references. Acetylene was used as a carbon precursor, producing DCMS and HiPIMS TiAlCN coatings with 9.0 and 21.7 at.% C, respectively.
Subsequently, TiAlN/TiAlCN multilayers of various designs were also developed as follows: 5×10/500, 5×50/500 and 5×100/500 nm. Residual stresses of the coating systems were determined by X-ray radiation utilising an ETA-diffractometer with a Cu-Kα radiation source applying the sin2ψ method. Additionally, residual stresses depth gradients of the substrate before and after the deposition of the coatings were determined in a LEDDI 8-circle diffractometer equipped with a W-X-ray tube and operated in the energy-dispersive mode of diffraction. Great reduction of the compressive residual stresses in the coatings was observed after the introduction of carbon into the TiAlN coating structure, shifting from −1047 ± 149 to −307 ± 211 MPa for the DCMS and from −7035 ± 1361 to +989 ± 187 MPa for the HiPIMS coatings. In the multilayer coatings, compressive residual stresses increase along with the increment of the TiAlN interlayer. Additionally, residual stresses of the substrate in the near-surface are dragged from low compressive stresses (−218 ± 61) to tensile stresses in the range of 1000 to 2000 MPa for all the DCMS/substrate systems, a behaviour only presented in HiPIMS by the TiAlN monolayer. Wear coefficients of all the evaluated HiPIMS systems are notoriously lower than their DCMS counterparts. Compared to TiAlN, TiAlCN HiPIMS presented a lower coefficient of friction but a higher wear coefficient, which in turn was not reduced by the introduction of the multilayer systems. Finally, Scratch test and Rockwell C adhesion tests have shown higher adhesion of DCMS coatings than HiPIMS coatings, and a detriment of the monolayers adhesion by the implementation of TiAlN/TiAlCN multilayer systems. The understanding of the residual stresses, both in the coating and in the substrate, and the way they affect the tribomechanical performance of the system coating/substrate continues to be of great importance, especially for coatings deposited by new technologies such as HiPIMS and self-lubricating coatings.
•Great reduction of compressive residual stresses with the carbon inclusion in TiAlN.•High superficial residual stresses on the substrate after DCMS deposition.•Adhesion of DCMS coatings systems to AISI H11 is always higher than HiPIMS.•Ceramic/ceramic multilayer designs did not improved adhesion or wear.
Combining materials with a self-lubricating character is a promising approach for an environmentally friendly lubrication. Therefore, Cu was incorporated in HiPIMS synthesized non-stoichiometric MoSx ...thin films. By increasing the Cu concentration up from 3.09 ± 0.09at.-% to 31.93 ± 0.12at.-% by an increased target power, the structure and the tribological properties were evaluated depending on the chemical composition. The results show, that an increased Cu content in the films in combination with the target setup during the deposition process leads to a preferred (002) basal-plane crystallite orientation and a densification of the microstructure in comparison to MoSx. Due to these structural properties, the dry friction behavior is improved under humid conditions. In combination with the transferfilm formed on the surface of the 100Cr6 counterpart, the lowest coefficient of friction of μ=0.092 ± 0.003 is seen at a target power of 1.5kW. Additionally, Cu tends to agglomerate the generated wear particles, which contributes to a high amount of tribomaterial with a MoSx character in the tribo track and thus a low wear. At a target power of 2.5kW the lowest wear coefficients with k=(0.64 ± 0.22) x 10−5mm2/Nm for the coated sample and k=(0.17 ± 0.02) x10 −5 mm2/Nm for the 100Cr6 counterpart were achieved. Therefore, the modification of MoSx films with Cu is promising to reduce the sensitivity of the friction on the environment and improve the tribological properties.
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•With an increasing Cu target cathode power (cpCu) an over-stoichiometric composition is set•A preferred (002) basal-plane crystallite orientation of the MoSx:Cu films is caused by the substrate rotation and the target arrangement•A high cpCu reduces friction and wear due to an increased amount of film material in the tribo track and the transferfilm on the 100Cr6 counterpart.
Understanding the growth process and its correlation to the structure of MoSx thin films is essential to control the friction behavior. Nevertheless, structural changes related to kinetic and thermal ...processes occurring during the deposition are not yet fully understood within the context of MoSx sputtered thin films. Therefore, MoSx films were synthesized by HiPIMS (High Power Impulse Magnetron Sputtering) technique using the one factor at a time method. By systematically changing the bias-voltage (0 to −200 V), the argon pressure (200 mPa to 600 mPa) or the heating power (0 to 3000 W) the interaction between the deposition parameters and their impact on the structure and the tribological properties was analyzed.The results show significant differences regarding the influence of kinetic and thermal effects. The investigation of the crystallographic orientation by XRD measurements reveals that a high kinetic energy induced by a high bias-voltage favors the growth of the (100) edge plane. A deposition process with a low deposition temperature and thus a low deposition rate leads to a more pronounced (002) basal plane due to the lower surface energy of the (002) surface. A high kinetic energy is also related to a densification of the morphology and a decrease in the sulfur content, which results in a thicker tribofilm and thus a lower wear and friction. Films deposited with a high heating power on the other show a low friction, but at the same time a columnar microstructure and high wear. Thus, the structure affects the amount of generated wear particles during the sliding, but more important is the ability of keeping them in the contact area during the tribo-tests.
•All deposition parameters lead to random orientation of the MoSx thin films.•A high kinetic energy leads to the formation of the (100) edge plane.•The deposition of MoSx thin films with a high bias voltage or high heating power result in a decreased friction.•The generation of third body particles and thus the formation of the tribofilm are affected by the structure of the MoSx thin films.
•HiPIMS of MoS2 targets.•Current–voltage characteristics.•Characteristics of the discharge mode.
High Power Impulse Magnetron Sputtering (HiPIMS) as high ionization sputtering technique is widely ...used to tailor the structure and the properties of thin films. However, investigations of process related effects are mainly obtained by HiPIMS of metallic, one-component targets, whereas examinations of compound targets are rarely found. Therefore, HiPIMS of MoS2 targets was conducted under a variation of the pulse duration and pulse frequency. During the process the current and voltage values were measured in order to investigate the characteristics of the discharge mode. The time-dependent current waveforms reveal a working gas-sustained self-sputtering for HiPIMS of MoS2. By decreasing the pulse frequency or the pulse duration, the peak-current is increased and the contribution of self-sputtering and the related gas rarefaction is enhanced, which leads to a reduced deposition rate.
Understanding the interaction between the structure and the tribological properties of sputtered molybdenum disulfide films at elevated temperatures is essential for their use in industrial ...applications. Therefore, the friction and wear behavior up to of 400°C of one stoichiometric MoS2 and a sub-stoichiometric MoS1.6 film are investigated against 100Cr6 counterparts. With an increasing temperature up to 200°C, the friction decreases, which is attributed to a thermally activated water desorption and an increasing intensity of the (002) basal plane. Due to a passivation mechanism caused by the sulfur defect sites, the friction is lower for the sub-stoichiometric film. Above this temperature the friction increases for both films and failure occurs at 400°C. Therefore, the friction at elevated temperatures result from a complex interaction of re-orientation mechanisms, desorption and oxidation processes.
•Sulfur defects contribute to a lower friction at all temperature levels.•Re-orientation mechanisms are facilitated by the increased temperature.•Generation of third body particles occurs more easily due to an elevated temperature.•Transition temperature has to be found at 200 °C.
•The structure of the MoS_x:N films transforms from polycrystalline to amorphous•MoSx:N reveal an improved hardness and the Youngs’s modulus•Improved tribological properties due to the incorporation ...of nitrogen•Tribofilm formation not impaired by the incorporation of nitrogen
Incorporating nitrogen into non-stoichiometric molybdenum disulfide (MoSx) thin films is a promising approach in order to improve the mechanical properties. Nevertheless, the adhesion between the film and the substrate is still challenging and the interaction between the mechanical and the tribological properties is not fully understood yet. Subsequently, reactive High Power Impulse Magnetron Sputtering (HiPIMS) is used to deposit nitrogen doped MoSx thin films with different nitrogen amounts on 16MnCr5 steel. The interaction between the structural changes, the mechanical properties and the tribological behavior depending on the nitrogen amount is investigated. The results prove that an increasing amount of nitrogen significantly affects the structure and the tribo-mechanical properties of the thin films. X-ray diffraction analysis reveals a transformation from crystalline to amorphous with an increasing amount of nitrogen from (7.1 ± 0.3) at.-% to (19.5 ± 0.5) at.-%. This transformation is related to a suppression of the columnar microstructure as well as an increasing hardness and Young‘s modulus from (0.14 ± 0.02) GPa, and (5.28 ± 0.32) GPa for the undoped film, to (5.12 ± 0.32) GPa and (92.5 ± 6.2) GPa, for the film with the highest nitrogen amount. The results of the Rockwell indentation tests show that the films with a small amount of nitrogen exhibit an improved adhesion behavior. The wear coefficient can be reduced to a quarter of the value of the undoped MoSx film, whereas coefficients of friction are at similar level of 0.2 in ambient air. Reactive HiPIMS has proven to be promising to deposit nitrogen doped MoSx thin films on steel substrates, which reveal improved mechanical properties and an excellent transfer film built-up during the tribo-tests without failures.
Modifying MoS
2
thin films by additional elements shows great potential in order to adjust the property profile and to meet the increasing requirements regarding high wear resistance and low friction ...properties of industrial components. Within that context, MoS
x
:N:Mo thin films were deposited by a reactive hybrid dcMS/HiPIMS process. By systematically increasing the Mo target cathode power, an investigation of the structural and the mechanical properties was conducted to understand the evolution of the tribological behavior. A low Mo target cathode power of 1 kW is related to the formation of the preferential (002) MoS
2
basal-plane and thus a low friction with µ = 0.2. With an increasing amount of Mo, the film loses its solid lubricant MoS
2
properties and a nitride constitution of the thin film is developing due to the formation of crystalline Mo and MoN phases. Related to this transformation, the hardness and elastic modulus are increased, but the adhesion and the tribological properties are impaired. The film loses its plasticity and the generated film material is directly removed from the contact area during the sliding contact.
•The structure of a-C:X in a-C/a-C:X is not affected by the multilayer design.•a-C/a-C:X structures reveal a higher hardness than a-C:X monolayers.•a-C/a-C:Si shows a low friction as a-C:Si, but with ...significantly lower wear.•a-C/a-C:W has a similar wear rate as a-C:W, but exhibits a lower friction.•The multilayer design is beneficial in exploiting advantageous properties of a-C:X.
Designing the film architecture of amorphous carbon based systems is effective in tailoring the tribo-mechanical properties. For this purpose, alternating a-C and a-C:X layers, with X = Si or W, were grown with a layer ratio of 1, a bilayer period of ~200 nm, and a bilayers number of 5 in a magnetron sputtering process. By comparing with a-C(:X) monolayers, the structure and tribo-mechanical properties of alternating a-C/a-C:X films were evaluated.
Although the bonding state of the a-C network of a-C:X in a-C/a-C:X is comparable to monolayered a-C:X, the multilayer design significantly affects the tribo-mechanical properties. The a-C/a-C:X multilayers exhibit a higher hardness compared to a-C:X. With a coefficient of friction of 0.12 ± 0.01, a-C/a-C:Si shows a low friction as a-C:Si with 0.09 ± 0.01, but the wear rate is significantly lower for a-C/a-C:Si with (3.4 ± 0.7) × 10-7 mm³/Nm than a-C:Si with (8.3 ± 1.0) × 10-7 mm³/Nm. Contrarily, a-C/a-C:W and a-C:W provide similar wear rates of 1.2 to 1.4 × 10-7 mm³/Nm, but the coefficient of friction is lower for a-C/a-C:W with 0.29 ± 0.02 than a-C:W with 0.36 ± 0.01. Hence, the multilayer design is efficient in improving the tribo-mechanical properties of a-C:X based films.
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•Deposition of alternating a-C/a-C:Cu and a-C/a-C:Ag multilayers by sputtering.•a-C/a-C:Cu and a-C/a-C:Ag reveal higher hardness than a-C:Cu and a-C:Ag.•a-C/a-C:Cu and a-C/a-C:Ag ...films with lower friction and wear than a-C:Cu and a-C:Ag.
The modification of amorphous carbon (a–C) films by adding either Cu or Ag is a common approach to tailor the film properties. These films become less hard, while they demonstrate higher friction and lower wear resistance than a–C. To enhance tribologically relevant features, multilayers of alternating a–C and a–C:Cu or a–C:Ag layers are synthetized by magnetron sputtering. The a–C/a–C:Cu and a–C/a–C:Ag multilayers possess a bilayer period of ~200 nm, a layer ratio of 1, and a bilayer number of 5. These structures are characterized by higher hardness and lower friction and wear against 100Cr6 counterparts as compared to monolayered a–C:Cu and a–C:Ag.
Amorphous carbon (a-C) attracts great attention in tribology research and thin film technologies due to its versatile properties. However, high temperatures and mechanical stresses may cause ...significant changes in the structural ordering of the a-C network. We present an optical method to initiate structural ordering and to probe solid-to-solid structural transitions of element modified a-C films. A pulsed pump laser introduces heat into the film in a controlled manner, while a second laser probes confocally the first- and second-order Raman scattering signatures of the a-C network. For low pump power, the number of defects and non-sixfold aromatic rings is reduced. A further increase in the laser power leads to sharply evolved changes in the Raman scattering features, indicating a transition from a-C to defected graphite and an effusion of hydrogen. Moreover, graphite-dominant defect relaxation and an enhancement in hexagonal lattice areas occur and, in turn, activate second-order Raman scattering lines. A rising laser power subsequently results in progressive graphitization. Chemical modification of the films with Si or Cu enhances their thermal stability and even shifts the upper thermal limit of the film ablation, while the a-C:W film demonstrates a more efficient enrichment of nanocrystalline graphitic clusters.
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