Status of Nickel Bonded Niobium Carbide (NbC) as a Substitute for Cobalt-Bonded Tungsten Carbide (WC) as Cutting Tools and for Wear Protection

摘要

In the binary phase diagram different pseudo-cubic phases aside NbC, like Nb_4C_3, Nb_6C_5, define a large range of homogeneity of NbC_x (0.75≤ x ≤1.0). 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. NbC and Nb_2O_5 have so far no REACH classification related to human toxicology and are not listed as substances of very high concern contrary to WO_3 and Co_3O_4. Niobium is today largely available. The initial NbC grade was substoichiometric, SPS sintered and cobalt bonded (NbC_(0.88)-12Co SPS). The NiMo-bonded stoichiometric NbCi.o grades enable the substitution of cobalt by nickel, SPS by conventional sintering and NbC_(0.88) by NbCi.o in view of functional properties. Nickel bonded NbC grades have improved toughnesses versus cobalt bonded NbC grades, but lose hardness. NiMo and NiMo_2C bonded NbCi.o grades compensated the loss in hardness while keeping the toughness. The tool lifes of uncoated NiMo- and NiMo_2C-bonded stoichiometric NbCi.o grades under dry turning 42CrMo4 and C45E were between +30% to +100% higher and up compared to WC-6C0 (fine grain). NbC grades displayed lower dry sliding friction over WC grades. The softer Ni- and NiMo-bonded NbCi.o -grades with lower toughnesses have a higher dry abrasive wear resistance (ASTM G65), as the tougher WC-Co grades.