A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> TiAlN/VN superlattices are potential candidates for dry machining due to their high hardness and excellent tribological properties. It has been reported that VN easily oxidizes at relatively low temperatures and forms V2O5 having lubricious properties. The aim of this work is to investigate the effects of vanadium oxides on tribological properties of TiAlN/VN superlattices at high temperatures. During differential scanning calorimetry (DSC) in an argon/oxygen atmosphere it was found that the coatings oxidize at approximately 450 degreesC. Melting and boiling point of the formed oxides could be determined by DSC to approximately 635 degreesC and 1400 degreesC, respectively. It was observed by DSC and X-ray diffraction that the melting phase, a V2O5, containing oxide, transforms into a VO2 containing oxide causing the loss of the liquid phase. Dry sliding tests showed that up to 500 degreesC the friction coefficient increases from 0.55 to 0.95. It drops to approximately 0.18 at 700 degreesC and remains there as long as a liquid surface oxide is present. If most of V2O5 is converted into lower-oxidized vanadium the friction coefficient increases to a steady state value of approximately 0.55 at 700 degreesC. The results obtained show that addition of VN to hard coatings has high potential to achieve a low friction effect due to the formation and melting of a V2O5 containing oxide, in addition to its conversion into easily shearable lower-oxidized vanadium phases. (C) 2003 Elsevier B.V. All rights reserved. <s> BIB001 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> Ti-Al-V-N coatings are potential candidates for dry machining applications due to the combination of superior mechanical properties of the Ti 1-x Al x N phase and the lubricating effects of vanadium oxides formed between 500 and 700 °C. The aim of this work was to prepare Ti-Al-V-N coatings with a high V content (25 at.% V in the Ti-Al-V target) to evaluate the influence of the oxides formed, on the friction behaviour during tribological tests up to 700 °C. The coatings were deposited by DC magnetron sputtering of a powder-metallurgically produced Ti-Al-V target in an Ar+N 2 discharge. High temperature ball-on-disc tests were used to investigate the tribological properties against alumina balls. Up to temperatures of 500 °C only minor changes in tribological properties compared to Ti 1-x Al x N coatings could be observed. Increasing the testing temperature to 600, 650, and 700 °C yields a continuous reduction of the friction coefficient from around 1 to 0.27, respectively. However, during the experiment at 700 °C the friction coefficient increases to a constant value of 0.45. Thus, main emphasis was laid on the examination of the formed oxide phases to elucidate their relation to the changing friction coefficients. Scanning electron microscopy investigations, X-ray diffraction and Raman spectroscopy shows that first a V 2 O 5 phase is formed which is responsible for the reduction of the friction coefficient. The further oxidation to form TiO 2 and AlVO 4 on the surface and especially in the wear track (due to the higher local flash temperatures) controls the ongoing oxidation. <s> BIB002 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> J. Mayer, J. Microscopy 1998, 194, 71. [21] J. F. Ziegler, J. P. Biersack, U. Littmark, The Stopping Range of Ions in Matter (Pergamon Press, New York, 1985). [22] H. Gao, Y. Huang, W. D. Nix, J. W. Hutchinson, J. Mech. Phys. Solids 1999, 47, 1239. [23] H. Mughrabi, Mater. Sci. Eng. A 2004, 387–389, 209. [24] B. von Blanckenhagen, P. Gumbsch, E. Arzt, Phil. Mag. Lett. 2003, 83, 1. [25] R. Sedlacek, Mater. Sci. Eng. A 2005, 393, 387. [26] D. Hull, D. Bacon, Introduction to Dislocations Elsevier Butterworth-Heinemann, Oxford, 2004. [27] L. H. Friedman, D. C. Chrzan, Phil. Mag. A 1998, 77, 1185. [28] E. O. Hall, Proc. R. Soc. Lond. 1951, B64, 747. [29] N. J. Petch, J. Iron Steel 1953, 174, 25. [30] E. Arzt, G. Dehm, P. Gumbsch, O. Kraft, D. Weiss, Prog. Mater. Sci. 2001, 46, 283. [31] S. P. Baker, A. Kretschmann, E. Arzt, Acta Mater. 2001, 49, 2145. [32] N. Kalyanasundaram, M. C. Moore, J. B. Freund, H. T. Johnson, Acta Mater. 2006, 54, 483. <s> BIB003 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> Abstract The binary systems of Mo–N and W–N offer a high potential to enhance the tribological properties of common hard coatings, owing to their ability of forming lubricious oxides (often also referred to as Magneli phases) at elevated temperatures. The aim of this work is to characterize Mo–N and W–N hard coatings prepared by reactive unbalanced magnetron sputtering, and to verify the concept of solid/liquid oxide lubrication. Oxidation of the coatings and possible melting of the oxides are investigated by dynamical thermo-gravimetric analysis and differential scanning calorimetry (DSC) up to 900 °C in air. During heating the samples, the exothermal reactions, detected during the DSC measurements, indicate oxidation in the temperature range between 200 and 750 °C. These exothermic reactions are superimposed by endothermic melting reactions between 650 and 850 °C. The formed oxide phases are investigated by X-ray diffraction after DSC and tribometer testing. To evaluate the effect of formation and melting of the oxides on the coefficient of friction, dry sliding experiments in the temperature range between 25 and 700 °C against alumina and austenitic stainless steel balls are performed using a ball-on-disc tribometer. All coatings investigated show lubricious oxide formation, resulting in a decreasing coefficient of friction at temperatures above 500 °C. For Mo–N, these beneficial properties suffer from the formation of the volatile oxide MoO 3 at temperatures higher than 500 °C. Nevertheless, the lubricious oxide concept within both systems strongly contributes to the reduction of friction, which is important for several industrial applications. We therefore infer that the addition of Mo–N and/or W–N phases to hard coatings can effectively improve their tribological properties, especially in the temperature range between 200 and 700 °C. <s> BIB004 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> Abstract The high-temperature tribological properties of a cathodic arc ion-plated (V,Ti)N coating have been investigated with a SRV high-temperature friction and wear tester. After heating in air at temperatures above 500 °C, V 2 O 5 and TiO 2 phases were identified on surfaces of (V,Ti)N coating with V 2 O 5 -type platelets as the major oxidized product. (V,Ti)N coatings exhibit a friction coefficient in the range of 0.53–1.08 and a wear rate in the range of 1.69 × 10 −7 –1.31 × 10 −5 mm 3 /Nm, depending on test temperature used. At low temperatures, the presence of oxide debris induced by tribological stressing on the load-bearing regions reduces direct contact between (V,Ti)N coating and Al 2 O 3 , and generates a mild wear, however, adherent and compacted wear-protective oxide layers are not developed. At temperature of 500 °C or above, the wear-protective oxide layers containing thermally-oxidized V 2 O 5 platelets deform plastically to produce a lubricious and smooth appearance to reduce friction. Raman spectroscopy was used to identify the structures of wear debris and coating surfaces after wear tests. Tribochemical reactions are the dominating wear phenomena at low temperatures. The wear debris generated during the wear process consists mainly of the V 2 O 5 -type tribo-oxides. <s> BIB005 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> The mechanisms for frictional self-adaptation of advanced hard coatings with optimum tribological properties are based on the formation of thin reaction films in sliding contacts. The aim of this work was to characterize VN and V coatings deposited by unbalanced magnetron sputtering and to determine the influence of oxide phase formation on their friction and wear properties during high-temperature exposure in ambient air. Dry sliding experiments were performed in the temperature range between 25 and 700 °C. Structural changes and oxide phases were identified by X-ray diffraction and Raman spectroscopy after tribometer testing. The friction coefficient of the V coatings decreases from about 1.05 at RT to 0.27 at 700 °C, while the VN coating has a lower coefficient of friction (∼0.45) at RT which further decreases at temperatures above 400 °C. The onset of rapid oxidation of V and VN coatings, as evidenced by differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA), occurred at 400–450 °C with the formation of vanadium oxides, which were identified by XRD as V2O5, VO2 and V6O13. For both coatings evaluated, a significant decrease of the friction coefficient at temperatures above 400 °C was observed reaching a value of 0.25–0.27 at 700 °C, due to the formation of V2O5, giving rise to solid lubrication, and subsequent melting of this phase at temperatures above 600 °C, leading to liquid lubrication. <s> BIB006 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> Ultrahard, wear-resistant coatings of thin-film AlMgB14 coatings could extend the service life of wear-prone components such as cutting tools and hydraulic pump vanes. Previous work with AlMgB14 has shown that it can have a hardness up to 46 GPa if alloyed with TiB2, and it can be coated as a thin film using pulsed laser deposition (PLD). These films have already shown promise in various industrial applications. Vane blades coated with AlMgB14 films via magnetron sputtering have significantly reduced the wear rate of the pump blades. Some research has been done on production of these films using nanosecond laser PLD, but this project was the first to use femtosecond pulsed laser deposition of coatings. In this work, research was conducted into methods to optimize the thin films’ wear resistance and lubricity. The addition of 70wt%TiB2 and/or a titanium interlayer was investigated to improve three parameters: wear-resistance, the steady-state coefficient of friction, and adhesion. The addition of TiB2 lowered the adhesion and increased the wear rate of the film. However, the films with the TiB2 addition did decrease the run-in time it took for the films to reach a steady-state coefficient of friction value. Films produced with a titanium interlayer were found to adhere to the M2 steel substrate better than films without the interlayer. The adhesion of the thin films to M2 tool steel substrates, assessed using the Rockwell C indentation adhesion test, was found to be substantially improved by the deposition of a titanium interlayer. The addition of the interlayer also lowered the steady-state coefficient of friction of the films. Ultimately, it was concluded that the film with the best properties was the pure AlMgB14 deposited for 20 minutes with a Ti interlayer. <s> BIB007 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> Abstract Coated tools constitute the majority of the tools applied in material removal processes, rendering the employment of uncoated ones as an exception. A broad growing market of coated cutting tools has been developed. Moreover, numerous material- and manufacturing-engineers have joint their expertise, aiming at developing coatings meeting the needs for processing the most difficult-to-cut materials at the most extreme cutting conditions. The emerging of new workpiece, tool and film materials, the evolution of sophisticated coatings’ characterization methods and the continuous need for higher productivity rates, maintain vivid the industrial and scientific interest for further advancing this field. <s> BIB008 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> Abstract Multi-element (TiZrNbHfTa)N and (TiZrNbHfTa)C coatings were deposited on C45 and M2 steel substrates by co-sputtering of pure metallic Ti, Zr, Nb, Hf and Ta targets in Ar + N2 and Ar + CH4 reactive atmospheres, respectively. TiN, TiC and TiZrNbHfTa metallic coatings were also prepared as reference. All the films were comparatively investigated for elemental and phase composition, texture, microstructure, hardness, friction and wear behavior. X-ray structural analysis revealed the formation of single-solution phases ((111) texture). As compared to the reference binary coatings (TiN and TiC), the multi-component films exhibited significantly higher hardnesses (a difference in hardness of about 10 GPa in the case of nitrides) and also superior wear performance. The best friction and wear behavior was found for the (TiZrNbHfTa)C film, for which the friction coefficient and wear rate were of 0.15 and 0.8 × 10− 6 mm3 N− 1 m− 1, respectively. <s> BIB009 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> A B S T R A C T Hard coatings deposited on forming tools are used to improve the forming process and to increase tool life. The decre ase of tool wear and reduction of friction are the main motivations for the development of self-lubricating coatings for forming applications at elevated temperatures. In the present study (Cr,Al,V)N (Physical Vapour Deposition) coatings with 5, 11 and 20 at % vanadium were deposited via a combination of HPPMS (High Power Pulse Magnetron Sputtering) technology and direct current (DC) Magnetron Sputter Ion Plating (MSIP) PVD. The hardness and Young's Modulus of the coatings were investigated by nanoidentatio n. Furthermore, high temperature Pin-on-Disk (PoD) tribometer measurements against Ck15 (AISI 1015) were realized at different temperatures and compared with a (Cr,Al)N reference hard coating. The samples were analyzed by means of SEM (Scanning Electron Microscopy) and XRD (X-Ray Diffraction) measurements after Pin-on-Disk (PoD) tests. Moreover TEM (Transmission Electron Microscopy) analyses were carried out after 4 h annealing at 800 °C in ambient air to investigate the diffusion of vanadium to the coating surface. The tribological results at 800 °C show no improvement of the friction coefficient for the pure (Cr,Al)N coating and for the layer with 5 at % V. A time-dependent decrease of the friction coefficient was achieved for the coatings with 11 at % V (µ=0.4) and 20 at % V (µ=0.4) at 800 °C. © 2012 Published by Faculty of Engineering <s> BIB010 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> article i nfo Nanocomposite films that consist of niobium nitride with silver nanoinclusions were created using unbal- anced magnetron sputtering to investigate their potential as adaptive, friction reducing coatings. The coatings were tribotested against a Si3N4 counterface in the 25 to 1000 °C temperature range. The coatings displayed coefficients of friction in the 0.15 to 0.30 range at T>700 °C. Post-wear testing structural and chemical char- acterization revealed that, in the low to mid-temperature range, silver migrated to the surface to reduce friction. At higher temperatures, oxygen, silver and the transition metal reacted to form lubricious binary metal oxide phases (silver niobate) in addition to pure silver. In situ Raman spectroscopy measurements were taken during heating and wear testing at 750 °C to identify the evolution of phases in the coatings surface and in the wear track. The analysis of the in situ Raman spectroscopy data revealed the various stages of formation of these binary metal oxides. The coatings were subsequently doped with MoS2 to investigate the effect of the introduction of a low temperature lubricant. The addition of MoS2 did not appreciably reduce the room temperature coefficient of friction, likely due to the miscibility of this compound with the transition metal nitride. However, the coefficient of friction was significantly reduced at high temperatures because of the synergistic lubricious effect of silver niobates and molybdates. <s> BIB011 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> The fundamental mechanisms of solid lubrication are reviewed with examples from well-known solid lubricants like the transition metal dichalcogenides and diamond-like carbon families of coatings. Solid lubricants are applied either as surface coatings or as fillers in self-lubricating composites. Tribological (friction and wear) contacts with solid lubricant coatings typically result in transfer of a thin layer of material from the surface of the coating to the counterface, commonly known as a transfer film or tribofilm. The wear surfaces can exhibit different chemistry, microstructure, and crystallographic texture from those of the bulk coating due to surface chemical reactions with the surrounding environment. As a result, solid lubricant coatings that give extremely low friction and long wear life in one environment can fail to do so in a different environment. Most solid lubricants exhibit non-Amontonian friction behavior with friction coefficients decreasing with increasing contact stress. The main mechanism responsible for low friction is typically governed by interfacial sliding between the worn coating and the transfer film. Strategies are discussed for the design of novel coating architectures to adapt to varying environments. <s> BIB012 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> Abstract There are several manufacturing processes, in which the employment of solid lubricants is limited. In addition, ecological damage and higher production costs are further consequences of using such solid lubricants. This work aims at using the great potential of thin film technology to deposit adaptive, self-lubricating coatings as an alternative to conventional solid lubricants. Using magnetron sputtering process several titanium aluminum vanadium nitride coatings (TiAlVN) were developed in this study. These quaternary coatings possess the ability of forming lubricious oxides, known as Magneli phases, at elevated temperatures, which significantly reduces the friction coefficient and surface wear. <s> BIB013 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> Abstract The lifetime of forming tools can be increased by surface functionalization using novel, nanostructured coatings. A special centre of focus of this is the tribological requirements on the coating. Within the framework of the BMBF project, the friction and wear behaviours of 3 newly developed nanostructured composite tool coatings: VAIN, VAlN/VCAlN and VAlN/VCAlN with a carbon-enriched top layer, were examined and compared to each other. Because a conventional wear test would have required a large number of tests (⪢10,000) with a concomitantly high consumption of sheet metal, the examinations were run in a model trial at an increased surface pressure of 150 MPa, to accelerate the wear of the tool. Wear analysis was carried out by considering the changes in topography and hardness of the tool surface. <s> BIB014 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Nitrides and their derivatives <s> Abstract Silver tantalate was investigated as a potential lubricious material for moving assemblies in high temperature tribological applications. Three different approaches were explored for the creation of such materials on Inconel substrates: (1) powders produced using a solid state which were burnished on the surface; (2) monolithic silver tantalate thin films deposited by magnetron sputtering; and, (3) an adaptive tantalum nitride/silver nanocomposite sputter-deposited coating that forms a lubricious silver tantalate oxide on its surface when operated at elevated temperatures. Dry sliding wear tests of the coatings against Si 3 N 4 counterfaces revealed friction coefficients in the 0.06–0.15 range at T ~ 750 °C. Reduced friction coefficients were found in nanocomposite materials that contained primarily a AgTaO 3 phase with a small amount of segregated Ag phase, as suggested by structural characterization using X-ray diffraction. Furthermore, cross-sectional transmission electron microscopy techniques determined that the reduced coefficient of friction at T ~ 750 °C was primarily the result of the formation of a lubricious AgTaO 3 phase that reconstructs during the wear process into a mechanically mixed layer of AgTaO 3 , Ta 2 O 5 , and Ag nanoparticles. <s> BIB015
Binary hard coatings based on transition metal nitrides, like CrN or TiN, are widely used in different industries. These coatings exhibit good bonding to the substrate and offer moderate mechanical and thermal properties with an adequate deposition rate, and they are widely used in different industries. By adding other elements to the base composition, e.g. aluminium, ternary and quaternary coatings are formed (TiAlN, CrAlN and CrAlTiN), with increased hardness and remarkable improvements in high temperature strength and inertness BIB008 . TiAlN coatings exhibit high hardness and elasticity as well as high oxidation resistance, which enable such coatings to be employed in higher temperature applications, such as milling and metal forming tools. However the coefficient of friction of TiAlN is between 0.7 and 1.0 which makes the use of lubricants inevitable in most industrial applications. Moreover, the CoF of most transition metal nitride coatings is fairly high (0.6-0.8) and their tribological effectiveness is insufficient especially at elevated temperatures BIB003 . Therefore, more element additions like Si, Hf, Nb, Zr, V, B, Y or O have been investigated to adjust the tribological performance by varying the content of crystalline and amorphous phases BIB008  . Nanostructured hard coatings based on nitrides and carbides may contain up to eight different elements BIB009 . When exposed to air at elevated temperature, some of the nitrides in the coating can easily oxidise. In many cases, the oxidised products are rutile, anatase, and iron oxides, sometimes amorphous and sometimes nano-scale crystalline, which may lower friction, depending on counterpart, contact load and different environmental conditions. Vanadium has attracted particular attention because V 2 O 5 platelets formed by thermal oxidation at high temperature (i.e. 500°C) deform plastically to produce a lubricious contact areas between coating and counterparts BIB005 . In our research, vanadium was successfully deposited on a nickel based superalloy (CM247) surface with a novel active screen plasma nitriding process (ASPN-V), and the CoF of the treated surface against Al 2 O 3 ball was reduced from above 0.9 at room temperature to lower than 0.4 at 600°C as seen in Figure 1 . Compared with TiN, the VN coating deposited by unbalanced magnetron sputtering has a lower CoF against alumina counterface (~0.45) at RT, which further decreases at temperatures above 400°C, reaching a value of 0.25-0.27 at 700°C. This phenomenon is due to the formation of V 2 O 5 , which acts as a solid lubricant, and the subsequent melting of this phase at temperatures above 600°C, leading to liquid lubrication ( Figure 1 ) BIB006 . Vanadium was also incorporated into TiN based coatings via cathodic arc ion-plating, and the CoF of (V, Ti)N coatings against alumina counterface was reduced from 1.08 at room temperature to 0.53 at temperatures above 500°C BIB005 . The incorporation of V into the TiAlN coatings, either forming a solid solution (Ti-Al-V-N) BIB002 or a superlattice structure of hard and lubricating layers (TiAlN/VN or TiAlN/TiAlVN) BIB001 , decreased the CoF, especially at elevated temperatures (700°C), to values as low as 0.18 BIB013 . Based on a thermodynamic assessment, Becker suggested a metastable solid solution would be synthesized more easily in both the VN-AlN and the VC-AlN systems than in the established TiN-AlN system BIB014 . However the coatings' response to temperature was not discussed. Vanadium was also used to improve the tribological properties of CrAlN coatings. The CoF of a CrAlVN (20 at.% V) coating deposited by DC high pulsed power magnetron sputtering (HPPMS) was reduced from 0.6 at room temperature to 0.4 at 800°C BIB010 . However, the low coefficient of friction is strongly dependent on the existence of a liquid Magnéli phase oxide (V 2 O 5 ) on the surface. The oxygen deficient oxide is only formed between 500 and 700°C. Consequently, the lubrication effect weakens and diminishes once the oxide is converted into other form of oxide phase. Under 500°C, the CoF is persistently high (0.55-0.95). Similar to VN, hard coatings containing WN and MoN have the ability to form lubricious Magnéli phase oxides at elevated temperature. MoN and Mo 2 N coatings showed high hardness and relatively low CoF at low temperatures, but the formation of volatile MoO 3 at 500°C significantly limited its application in high temperatures BIB004 . On the other hand, WN coatings demonstrated a higher oxidation threshold at an expense of a higher CoF BIB004 . In the case of NbN, the CoF against Si 3 N 4 counterface steadily reduced from 0.9 at RT to 0.52 at 750°C and XRD revealed that NbN coating was completely oxidised into monoclinic Nb 2 O 5 which has Magneli's phases BIB011 . The CoF of TaN against Si 3 N 4 counterface displayed a similar trend as seen in Figure 1 BIB015 . A mixed phase of orthorhombic Ta 2 O 5 and TaN was identified by XRD after tribotest at 750°C. Finally, AlMgB 14 is a ceramic alloy that has a low coefficient of sliding friction, reaching a record value of 0.02 against AISI 52100 steel counterface in lubricated AlMgB 14 -TiB 2 composites   . Weak, van der Waals-bonded atomic layers of B(OH) BIB012 , a product of boron oxide with moisture, tend to slide against each other with little resistance to applied shear stresses which is the primary contribution to low-friction behaviour. Ultrahard, wear-resistant AlMgB 14 coatings have been coated on wear-prone components, such as cutting tools and hydraulic pump vanes, using pulsed laser deposition (PLD) to extend their service life by reducing friction BIB007 .