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The wear rates of self-mated alumina couples show that friction as well as wear is largely determined by the above-mentioned hydro-thermal conditions. The presence of water and its amount available in the surrounding system either in liquid or in gaseous form plays a key role for friction and wear behavior and can be beneficial for the tribological profile of steam degradation resistant materials. Hot steam enhances the tribo-chemical formations of oxides and hydroxides on MgO-ZrO2 alumina and antimony impregnated carbon.
Das tribologische Profil von binderlosem NbC und mit 8% bzw. mit 12% Cobalt oder 12% Fe3Al gebundenem NbC wird unter unidirektionaler Gleitreibung (v= 0,1-10 m/s, T= 22°C und 400°C) und unter oszillierender Gleitreibung vergleichend gegenüber Ingenieurkeramiken und Hartmetallen dargestellt. Zusätzlich werden die 4-Punkt-Biegebruchfestigkeit, elastische Eigenschaften (E,G) bis 1.000�C die lastabhängige Mikrohärte sowie die Phasenzusammensetzung und Gefügestrukturen vorgestellt. Die Verschleißkoeffizienten des binderlosen NbC lagen bei T unterhalb von 10-6 mm³/N?m, während diejenigen der cobaltgebundenen NbCs mit ansteigender Gleitgeschwindigkeit von 2-4 10-6 mm³/N?m bei 0,1 m/s auf 5-7 10-7 mm³/N.m bei 10 m/s abnahmen. Die Verschleißkoeffizienten bei 400°C lagen für die NbCs generell unterhalb von 10-6 mm³/N.m. Das tribologische Lasttragevermögen im Trockenlauf, ausgedrückt als PV-Wert, nimmt mit ansteigender Gleitgeschwindigkeit auf 100 W/mm² zu. Bedingt durch die geringe Löslichkeit von NbC in Legierungen offenbarten erste Zerspanversuche mit verschiedenen Stählen eine gegenüber WC-basierten Schneidstoffen signifikant angehobene Zerspanungsvolumina. Somit offenbart NbC in offenen und geschlossenen Tribosystemen Anwendungspotentiale.
Wälzbeständigkeit von ta-C Dünnschichten unter hohen Hertzschen Beanspruchungen bis zu 3000 MPa
(2010)
Testing friction and wear of the tribosystem piston ring and cylinder liner outside of engines
(2008)
An OEM-driven working group started in January 2004 to elaborate the philosophies, concepts and test procedures for testing piston ring and cylinder liner materials as well as engine oils outside of engines using the SRV (abbreviation for German: Schwingung, Reibung, Verschleiß; in English: Oscillation, Friction, Wear) test equipment. The different SRV test philosophies in use by OEMs are compiled. The working group focuses on (i) ASTM fuel economy sequence by ageing oils; (ii) friction and wear in the top-dead-centre region under mixed/boundary lubrication; (iii) extreme pressure load under mixed/boundary lubrication; and (iv) hydrodynamic friction. Tribological test results and precision data are presented.
The use of alternative base oils, like esters or polyglycols, with more intrinsic properties for the lubrication of automobile engines has a potential for ecological and technical advantages. Being in competition with hydrocarbon-based formulations, detailed knowledge of several thermophysical and viscometric properties as well as tribological properties over a large temperature range are required (mapping). The tested polymer-free polyglycols and ester-based formulations displayed no visible tribological weaknesses regarding wear resistance and EP-behavior as well as offering significant advantages in order to meet metal- and ash-free and bio-no-tox criteria. Especially the formulated polyglycols without friction modifiers also showed an intrinsic retention of low coefficients of friction and a hydrodynamic film forming behavior comparable to hydrocarbon-based factory-fill oils. The wear resistance and EP-behavior of low-additivated polyglycols, but also of esters, can be enhanced by means of triboactive materials. Lubricious oxides or triboactive materials and polar base oils, or a combination thereof, may substitute the EP and AW properties realized by the additives, thus enabling long drains and responding to eco-tox or bio-no-tox requirements as well as restrictions from the chemical box.
The process window and range of functional properties of NbC is wide, because micro-hardness, hot hardness, sliding wear resistance, elastic modulus and toughness can be tailored by the C/Nb ratio, because Nb4C3, Nb6C5 and other short and long range ordered phases occur in the region of homogeneity of NbCx (0,75≤ x ≤1.0) in the binary Phase diagram, and by the type of binder. Further improvements enable the addition of secondary carbides. Supporting results from literature and different grades with varying C/Nb ratio or binder types were illuminated. Thus, the NbC system offers to producers a wider process window, than WC. The impact of these tailored properties on sliding wear and cutting performance was illuminated by tribological and machining results. NbC can be synthesized by carbothermal conversion of Nb2O5 or be metallurgically grown in melts and leached out as coarse NbC cubes. NbC provides comparably lower friction in many relevant tribo-contacts and displays low wear. NbC and Nb2O5 have so far no REACH classification related to human toxicology and are not listed as substances of very high concern contrary to WO3 and Co3O4.
Hydraulic oils are well established formulations developed around the pump test. Requirements for energy efficiency and also environmentally acceptable properties increased the demand for development. In the same time, system pressure and the used of servo-hydraulic vanes increased bringing specific formulations and materials to their limit.
The vane pump is a key component in hydraulic systems and many other tribosystems in hydraulic circuits operate under different tribological operating conditions. The concept for ranking of hydraulic oils consists in using existing SRV-based ASTM test methods for evaluation of friction, wear and extreme pressure properties: D6425, friction and wear of oils (homologue to DIN 51834-2), D7421, extreme pressure properties of oils and D7755, wear volumes of ball and disks (homologue to DIN 51834-3. The tribological properties are assessed under the regime of mixed/boundary lubrication The SRV-based concept of tribological profile generates the wear volumes on two triboelements (specimen) and the extreme pressure properties as well as the evolution of friction in the wear and extreme pressure load step test. Thus, the benchmark and validation of hydraulic oils bear on a wider range of tribological properties. Round robin test results using the aforementioned testing concept will be shown. Another outcome is tribological set limits for inclusion in hydrau¬lic oil speci¬fications.
In the state-of-the-art technology, the impact of additives on friction and wear is evaluated in recipes with fixed concentrations. For the development of formulations it is desirable to determine the lowest effective concentration or the concentration at which failure was initiated or excessive wear began. Through a new development of the SRV® machine it is now possible to change the lubricant composition of a test specimen in a reproducible manner, in sub-pro Mill steps during the SRV® testing. This technology is used in the present article to define the optimum additive concentration with regard to wear and friction in a system of base oil and additive. Exemplary selected base oil and additive variants are tested here. The load parameters during testing are selected in such a way that they correspond to later application. The new data acquisition capabilities enable new possibilities for optimizing lubricant formulations in practice-oriented model-tribometer tests. “Cliff“ testing aims to identify in engine or gear tests the induction time or off-set point (“cliff“) after which wear and friction increased of failure occurred. Explanations for friction and wear increased as well as failures, which occurred during engine tests, can be derived from SRV® testing of oil samples taken or collected at different engine test times and correlating these with their friction, wear and EP data in respect to depleting curves for specific additives or other oil properties. A “cause-root” analysis is done by plotting SRV® data versus functional properties. The collected oil samples must be fully SRV® tested and chemically analyzed.
Substituting tungsten carbide (WC) as cutting tools and for wear protection by niobium carbide (NbC)
(2016)
As a refractory carbide, niobium carbide (NbC) is today still a forgotten carbide with hidden properties, such as wear resistance, thus qualifying NbC for the group of tribological materials with enhanced wear resistance. Several phases, like Nb₄C₃, Nb₆C₅ and other short and long range ordered phases occur In the region of homogeneity of NbCx (0,75≤ x ≤1.0) in the binary phase diagram, which enable the tailoring of properties and offers a much wider process window than known from WC. The type binder (Co, Ni, NiMo) and its concentration as well as the sintering process (SPS, liquid phase sintering) determine the box “hardness-toughness”, which will be illuminated based on more than 100 grades.
The impact of these tailored properties on sliding wear (T= 22/400°C; v= 0,1-10 m/s) and cutting performance will be illuminated by tribological and machining results. Cutting test results under emulsion and coolant-free operation of cobalt and Fe3Al bonded, straight NbC versus WC based inserts against different alloys (C60, 100Cr6, 42CrMo4, X90CrMoV18, 300WA, GG35) will be highlighted.
The wear rates of self-amted alumina couples show that friction as well as wear is largely determined by the above mentioned hydro-thermal conditions. The presence of water and ist amount available in the surrounding system either in liquid or in gaseous from plays a key role for friction and wear behavior and cabe benefical for the tribological profile of steam degradation resistant materials. Hot steam enhances the tribo-chemical formations of oxides and hydroxides on MgO-ZrO2, alumina and antimony impregnated carbon.
Several phases, like Nb₄C₃, Nb₆C₅ and other short and long range ordered phases occur in the region of homogeneity of NbCₓ (0,75≤ x ≤1.0) in the binary phase diagram. Properties, like micro-hardness, hot hardness, sliding wear resistance, elastic modulus and toughness can be tailored by the C/Nb ratio, the addition of secondary carbides and the type of binder. Supporting results from different grades with varying C/Nb ratio or binder types were illuminated. Thus, the NbC system offers to producers a wider process window, than WC. The impact of These tailored properties on sliding wear and cutting performance was illuminated by tribological and machining results. Niobium is today largely available. NbC can be synthesized by carbothermal conversion of Nb₂O₅ or be metallurgically grown and leached out, provides comparably low friction in many relevant tribo-contacts and displays low wear. NbC and Nb₂O₅ have so far no REACH classification related to human toxicology and are not listed as substances of very high concern contrary to WO₃ and Co₃O₄.
The differences between the binary phase diagrams W-C and Nb-C illuminate several parameters for tailoring the properties of NbC. In the region of homogeneity of NbCx, with Nb4C3 and Nb6C5 other Niobium carbide phases occur. Properties, like micro-hardness, hot hardness, sliding wear, elastic modules and toughness can be tailored by the C/Nb Ratio, secondary carbides and the type of binder. Supporting results from different grades with varying C/Nb ratio or binder types will be illuminated. Thus, the NbC system offers to producers a wider parameter window, than WC.
The wear rates of self-mated alumina couples show that friction as well as wear is largely determined by the above mentioned hydro-thermal conditions. The presence of water and its amount available in the surrounding system either in liquid or in gaseous form plays a key role for friction and wear behavior and can be beneficial for the tribological profile of steam degradation resistant materials. Hot steam enhances the tribo-chemical formations of oxides and hydroxides on MgO-ZrO2, alumina and antimony impregnated carbon.
Tribology in hot steam
(2017)
The wear rates of self-mated alumina couples show that friction as well as wear is largely determined by the above mentioned hydro-thermal conditions. The presence of water and its amount available in the surrounding system either in liquid or in gaseous form plays a key role for friction and wear behavior and can be beneficial for the tribological profile of steam degradation resistant materials. Hot steam enhances the tribo-chemical formations of oxides and hydroxides on MgO-ZrO2, alumina and antimony impregnated carbon.
The frictional response of molybdenum bis(C11-14 branched and linear alkyl) carbamodithioate oxo thioxo complex (Mo-dttc) versus bismuth dimethyldithiocarbamate (Bi-dtc) and bismuth dodecylbenzene Sulfonate (Bi-ddbsa) slip-rolling under mixed/boundary lubrication (T=120°C, n=10 millions of cycles, P0max=2.25 GPa) in PAO-based formulation against three different steel alloys were compared.