The background for the use of hartmetals and MMCs based on Niobium Carbide (NbC) as cutting tools and for wear resistant tribosystems

Abstract

In this present study, the mechanical properties (strength, hardness, moduli) and the dry
sliding properties of stoichiometric and sub-stoichiometric NbC were compared. Microhardness
and elastic properties of NbC depend from the C/Nb ratio, because the binary
phase diagram Nb-C shows a region of homogeneity of NbC_x of 0,72≤ x ≤1.0. At RT, hard
metals of stoichiometric NbC have an elastic modulus E of ~440 GPa, those of substochiometric
NbC_0,88 an E of 405 GPa. The hot hardness of sub-stoichiometric NbC is above
600°C higher than of WC. The dry sliding wear resistance (0,1-7/10 m/s) of the present
Fe₃Al-NbC_0,94 with ~61 vol.-% NbC as hard phase was close to those known of NbC-based
hard metals. No grain pull-outs or fragmentations of the NbC grains were seen in the wear
tracks of the Fe₃Al-NbC composite (MMC), as a metallurgical interphase was formed
between matrix and NbC grains. Stoichiometric and sub-stoichiometric niobium carbides
have at RT and 400°C under dry sliding a prone intrinsic wear resistance more or less independent
from sliding speed, either as hardmetal or as hard phase in metal matrix composite,
associated with an exceptional high load carrying capacity.