A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Lubricious oxide with noble metal addition <s> Abstract Thin films of pure molybdenum oxide MoO 3 , vanadium oxide V 2 O 5 as well as phases originating from Ag 2 O–MoO 3 , Cu–V 2 O 5 and Ag–V 2 O 5 systems were deposited on alumina substrates by means of reactive magnetron sputtering. Structure and phase composition of deposits were characterised by X-ray diffraction (XRD) and Raman spectroscopy. High temperature (100–700 °C) friction tests were performed using ball-on-disc configuration in air of normal humidity. Among studied phases, the best results were observed for silver molybdate (Ag 2 MoO 4 ) and vanadium oxide bronze (β-Ag 0,33 V 2 O 5 ) coatings, which were chemically stable and allowed to decrease friction coefficient to the level of 0.2 at 450 and 600 °C, respectively. <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> Lubricious oxide with noble metal addition <s> Adaptive tribological coatings were recently developed as a new class of smart materials that were designed to adjust their surface chemical composition and structure as a function of changes in the working environment to minimize friction coefficient and wear between contact surfaces. This paper provides an overview of the current research developments in this field, including: (1) Chameleon nanocomposite coatings which are produced by depositing a multi-phase structure whereby some of the phases provide mechanical strength and others are lubricious; (2) Micro- and nano-textured coatings which consist of hard nitride films with highly ordered micropores and nanopores that are subsequently filled with solid lubricants using various techniques such as lithography, reactive ion etching, laser texturing, pulsed air arc treatment, and ceramic beads as placeholders for sputter deposition; and, (3) Carbon and nitride nanotubes that are filled electrochemically with solid lubricants. The frictional and wear properties of the above three classes of newly developed adaptive structures, tested in various controlled environmental conditions (temperature, humidity), will be discussed in detail. <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> Lubricious oxide with noble metal addition <s> ) thin ﬁlms and powders from 25 to 600 C. We show, using ab initiomolecular dynamics, high-temperature X-ray diﬀraction, high-temperature Raman spectroscopy and diﬀerential scanning calorim-etry in combination with sliding tests, that the layered atomic structure of silver molybdate facilitates sliding, resulting in a lowcoeﬃcient of friction (<0.2) from 300 to 500 C. 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. <s> BIB003
Silver (Ag) can also be added to transition metal oxides to form double metal oxides of the type Me x TM y O z , where Me is a lubricious metal like silver and TM is a transition metal. Such oxides were found to exhibit relatively low coefficient of friction (0.1-0.3) in the medium temperature range (500-700°C) BIB002 . Additionally, silver can form silver molybdate and silver vanadate at higher temperature. Thin films based on the Ag 2 O-MoO 3 , Cu-V 2 O 5 and Ag-V 2 O 5 systems were deposited on alumina substrates via reactive magnetron sputtering by Gulbiński et al.  BIB001 . As seen in Figure 6 , the coefficient of friction at high temperature was reduced for all the oxides, but it was persistently high at low temperature for most of the coatings. The only exception was Ag 2 MoO 4 which was chemically stable and the coefficient of friction consistently low in a whole temperature range. Ag 2 MoO 4 exhibits a layered structure, with alternating AgO and MoO 3 planes separated by a silver layer, with the molybdenum atoms occupying tetrahedral sites and the silver atoms occupying octahedral sites. The weaker Ag-O bridging bonds (220 kJ/mol) makes them more prone to shearing and/or breaking at relatively high temperatures than the stronger Mo-O bonds (560 kJ/mol) as seen in Figure 7 BIB003  . Stone et al. also found the layered structure of silver molybdate facilitates sliding, resulting in a low CoF (<0.2) from 300°C to 500°C BIB003 . Silver and copper vanadates (AgV x O y and CuMo x O y ) demonstrated a low CoF of 0.2 at temperature around 500°C BIB001 .