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The influence of temperature and counterbody material on the tribological properties of a-C:H
coatings deposited on Cronidur 30 steel has been investigated in a lubricated ball on disk
contact situation with alpha-alumina and silicon nitride as counterbodies. The results show, that the wear volumes of the systems increase exponentially with increasing temperature, for alpha-alumina more than for silicon nitride. Two different wear mechanisms seem to have a
major influence: First, the abrasive action due to materials hardness and second, the tribo-oxidation when silicon nitride is counter material.
Niobium is today largely available. The initial NbC grade was substoichiometric, SPS sintered and cobalt bonded (NbC0.88-12Co SPS). The NiMo-bonded stoichiometric NbC1.0 grades enable the subtituion 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 bonded NbC grades, but lose hardness. NiMo and NiMo2C bonded NbC1.0 grades compensated the loss in hardness while keeping the toughness.
The present paper illuminates the metallurgical progress on niobium carbide based hard metal developments, which are characterized by: a.) the substitution of cobalt binder by nickel, b.) the change from SPS to conventional sintering and c.) by switching from lab to pilot scale. The toughness was increased in the frame of these develop¬ments without loosening the hardness level. Stoichiometric and sub-stoichiometric, submicron NbC powders were used. The hardness-toughness profile of NbC grades match those of WC and cermet grades. Apart from the aforementioned parameters, the properties depend from the powder processing and sintering conditions. The functional profile of NbC and WC grades bonded by cobalt and nickel are benchmarked by 4-point bending strength, elastic moduli and hot hardness until 1000°C, dry sliding wear (T= 22/400°C; v= 0,1-10 m/s), abrasive wear (G65) and cutting performances under emulsion and coolant-free turning and milling against different alloys (C60, 100Cr6, 42CrMo4, X90CrMoV18, 300WA, GG35).
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.
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.
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.