Ingenieurwissenschaften und zugeordnete Tätigkeiten
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- 2016 (17) (entfernen)
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- Niobium carbide (6)
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Eingeladener Vortrag
- nein (8)
Niobium carbide (NbC) is an alternative cutting material. The Federal Institute for Materials Research and Testing (BAM) and the Institute for Machine Tools and Factory Management (IWF) of the TU Berlin assessed the cutting suitability of NbC with cobalt (Co)-binder compared to WC with Co-binder in the machining of a wide range of materials.
Substitution of tungsten carbide by niobium carbide as cutting materials and for wear protection
(2016)
Several phases, like Nb₄ C₃ , 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 Co₃ O₄ .
Niobium carbide for wear protection - tailoring its properties by processing and stoichiometry
(2016)
Niobium carbide is a hardly explored carbide but its functional profile shows a high potential for wear protection and tribological applications, which are currently dominated by tungsten carbide. Surprisingly little information is available on niobium carbide (NbC). Niobium carbide can be either synthesized by carbothermal conversion of Nb2O5 or be metallurgically grown and leached out. Furthermore, NbC hardmetal grades can be bonded by all known metallic binders and processed and sintered in exactly the same way as WC-based hardmetals. Niobium is today largely available. NbC can be efficiently produced, 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. This contribution demonstrates the key characteristics of NbC and discusses its sustainability and reliable value chain.
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.