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Eingeladener Vortrag
- nein (110)
Die Wälzbeständigkeit von Kohlenstoffdünnschichten (DLC, Diamond Like Carbon) ist im Lauf den letzten Jahren wesentlich verbessert worden. Gleichwohl sind weitere Leistungssteigerungen nötig besonders bezüglich der Temperaturbeständigkeit und der prozessbedingten Oberflächenrauheit der abgeschiedenen Schichten. Dieser
Beitrag stellt ein neuartiges Schicht-Substrat-System vor. Dieses ist mit unlängst entwickelten DLC-Dünnschichten unter geschmierter Wälzbeanspruchung in einem Benchmark verglichen worden. Eine der zirkonium-basierten Dünnschichten erweist sich als wälzbeanspruchbar und -beständig unter hohen anfänglichen Hertzsche Pressungen bis P0max = 3.500 MPa und offenbarte in einem Erstbefüllungsmotoröl bei 120°C auch geringe Misch-/Grenzreibungszahlen. Als Vergleich erreichen die DLC Schichten 10 Millionen Zyklen bei RT bis maximalen Hertzsche Pressungen von P0max = 2.940 MPa. Einige DLC-Schichten erzielen diese hohe Belastbarkeit auch bei 120°C. Die Zr-basierten Dünnschichten erfordern keine darauf angepaßten Schmierstoffformulierungen. Diese nanostrukturierten Dünnschichten beruhen auf einer Architektur und einem Prozess, die sich zusammen für die Großserie eignen.
Zirkonium-basierte Dünnschichten in hochbeanspruchten Wälzkontakten als Alternative zu DLC und ta-C
(2009)
Zirkonium basierte Dünnschichten in hochbeanspruchten Wälzkontakten als Alternative zu DLC und ta-C
(2009)
Die Wälzbeständigkeit von Kohlenstoffdünnschichten (DLC. Diamond Like Carbon) ist im Lauf den letzten Jahren wesentlich verbessert worden. Gleichwohl sind weitere Leistungssteigerungen nötig besonders bezüglich der Temperaturbeständigkeit und der prozessbedingten Oberflächenrauheit der abgeschiedenen Schichten. Dieser Beitrag stellt ein neuartiges Schicht-Substrat-System vor. Dieses ist mit unlängst entwickelten DLC-Dünnschichten unter geschmierter Wälzbeanspruchung in einem Benchmark verglichen worden. Eine der zirkonium-basierten Dünnschichten erweist sich als wälzbeanspruchbar und -beständig unter hohen anfänglichen Hertzsche Pressungen bis POmax = 3.500 MPa und offenbarte in einem Erstbefüllungsmotoröl bei 120°C auch geringe Misch-/Grenzreibungszahlen. Als Vergleich erreichen die DLC Schichten 10 Millionen Zyklen bei RT bis maximalen Hertzsche Pressungen von Pomax = 2.940 MPa. Einige DLC-Schichten erzielen diese hohe Belastbarkeit auch bei 120°C. Die Zr-basierten Dünnschichten erfordern keine darauf angepassten Schmierstoffformulierungen. Diese nanostrukturierten Dünnschichten beruhen auf einer Architektur und einem Prozess, die sich zusammen für die Großserie eignen.
The steam technology has attracted attention for recovering energy from waste heat in transportation systems. 40% of the calorific value of the fuel is wasted through the tailpipe. The use of waste heat recovery systems (WHRS) in cars and especially in trucks corresponds to possible energy savings in terms of less fuel consumption in the range of 7 – 18 %. This relates not only to the savings of fuel but also to the non-production of green house gas CO2. Steam expander form tribosystems, which can´t be lubricated with oils, as hot steam hydro-cracks these fluids. Suited tribomaterials as well as their tribo-oxidatively reaction layers must be first steam degradation resistant and for the tribotesting of such candidate material, tribological testing devices for a hot steam environment are needed. Not much is known so far about the tribological properties of any material system running under pressurized hot steam conditions. For these reasons and for being able to evaluate tribological properties in hot steam, BAM has developed and built a new and sealed tribometer for hot steam allowing evaluating tribological properties up to 700°C and 10 bars in gaseous atmospheres like hot steam or ethanol.
Experimental results on the wear of self-mated aluminum oxide and MgO-ZrO2 couples show that friction as well as wear is largely determined by the above mentioned hydro-thermal conditions. In this system the presence of water and its amount available in the system either in liquid or in gaseous form plays a key role for wear behavior and can beneficial. Ethanol and/or water-ethanol mixtures can form beneficial tribofilms, also on specific diamond-like carbon films.
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.
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.
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.
The tribological profile of alumina (99.7%) mated against rotating disks in two niobium carbide (NbC) grades were determined in unidirectional sliding tests (0.1 m/s to 7.5 m/s; 22°C and 400°C) as well as in oscillation tests (f= 20 Hz, δx= 0.2 mm, 2/50/98% rel. humidity, n= 106 cycles) under unlubricated (dry) conditions. In addition, the microstructure and mechanical properties of NbC were determined as well. The reason for testing hot-pressed NbC was to avoid side effects generated by sintering additives and/or second phases. The tribological data obtained were benchmarked with different ceramics, cermets and thermally sprayed coatings. NbC exhibited low wear rates under dry sliding associated with high load carrying capacity. The tribological profile established revealed a strong position of NbC under tribological considerations and for closed tribo-systems against traditional references, such as WC, Cr3C2, (Ti,Mo)(C,N), etc.
Thermally sprayed TiO2-x coatings under mixed lubrication and unlubricated sliding conditions
(2004)
The ways/paths to low friction, low wear and high load carrying capacities in gear and engines
(2013)
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.
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 present work deals with Niobcarbid (NbC). Strategic reflections on tungsten carbide and more and more stringent toxicological restrictions for cobalt associated for both with spiraling stock market prices have attracted recently some attention for Niobium carbide as a substitute for tungsten carbide in machining.
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.
Niobium is today largely available. The initial NbC grade was substoichiometric, SPS sintered and cobalt bonded. The NiMo-bonded stoichiometric NbC1.0 grades enable the substitution of cobalt by nickel, SPS by conventional sintering and NbC0.88 by NbC1.0 in view of functional properties. Nickel bonded NbC grades have improved toughnesses versus cobalt NbC grades, but lose hardness. NiMo and NiMo2C bonded NbC1.0 grades compensated the loss in hardness while keeping the toughness.