M. Woydt, H. Mohrbacher

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

Introduction

The background for the use of hartmetals and mmcs based on niobium carbide (nbc) as cutting tools and for wear resistant tribosystems. Niobium Carbide (NbC) hardmetals & MMCs for cutting tools and wear-resistant tribosystems. Investigate mechanical, dry-sliding properties, hot hardness, and composite performance.

Abstract

In this present study, the mechanical properties (strength, hardness, moduli) and the drysliding properties of stoichiometric and sub-stoichiometric NbC were compared. Microhardnessand elastic properties of NbC depend from the C/Nb ratio, because the binaryphase diagram Nb-C shows a region of homogeneity of NbCx of 0,72≤ x ≤1.0. At RT, hardmetals of stoichiometric NbC have an elastic modulus E of ~440 GPa, those of substochiometricNbC0,88 an E of 405 GPa. The hot hardness of sub-stoichiometric NbC is above600°C higher than of WC. The dry sliding wear resistance (0,1-7/10 m/s) of the presentFe3Al-NbC0,94 with ~61 vol.-% NbC as hard phase was close to those known of NbC-basedhard metals. No grain pull-outs or fragmentations of the NbC grains were seen in the weartracks of the Fe3Al-NbC composite (MMC), as a metallurgical interphase was formedbetween matrix and NbC grains. Stoichiometric and sub-stoichiometric niobium carbideshave at RT and 400°C under dry sliding a prone intrinsic wear resistance more or less independentfrom sliding speed, either as hardmetal or as hard phase in metal matrix composite,associated with an exceptional high load carrying capacity.

Review

This paper presents a compelling investigation into the potential of Niobium Carbide (NbC), both stoichiometric and sub-stoichiometric, as a foundational material for high-performance cutting tools and wear-resistant tribosystems. The authors meticulously compare the mechanical and dry-sliding properties of different NbC compositions, leveraging the known homogeneity region of NbCx. The work is highly relevant given the ongoing search for alternatives to conventional hardmetals like Tungsten Carbide (WC), particularly in applications demanding enhanced high-temperature stability and wear resistance. The study's scope, encompassing fundamental property comparisons and an exploration of Metal Matrix Composites (MMCs), positions it as a significant contribution to the field of advanced materials. The findings detailed in the abstract are robust and particularly promising. A key revelation is the dependency of microhardness and elastic properties on the C/Nb ratio, with specific elastic moduli provided for different NbC variants. Crucially, the sub-stoichiometric NbC exhibits superior hot hardness above 600°C when compared to WC, a critical advantage for high-temperature applications. Furthermore, the dry sliding wear resistance of an Fe3Al-NbC composite (with ~61 vol.-% NbC) is shown to be comparable to NbC-based hardmetals, attributed to the formation of a stable metallurgical interphase that prevents grain pull-outs and fragmentation. The observed intrinsic wear resistance, largely independent of sliding speed for both hardmetal and MMC forms, coupled with an exceptional load carrying capacity, underscores the material's potential for demanding tribological environments. Overall, this study offers strong experimental evidence supporting the viability of NbC-based materials for advanced wear applications. The clear comparison with WC, especially regarding hot hardness, provides a valuable benchmark, and the detailed observations of the Fe3Al-NbC composite's wear behavior are particularly insightful. While the abstract effectively highlights the key results, the full paper would benefit from elaborating on the specific mechanisms responsible for the observed sliding-speed independent wear resistance and perhaps a more direct wear performance comparison with WC-based materials across various conditions. Nevertheless, the presented work is well-executed, provides significant new data, and makes a valuable contribution to the understanding and development of next-generation hard materials. It is clearly suitable for publication.

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