Key Takeaways & Executive Findings
- •• Six HEA binders (e.g., CoCrFeNiMn) were successfully used to fabricate WC–HEA cemented carbides via mechanical alloying and two-step spark plasma sintering. • WC–HEA hardmetals exhibit superior hardness and fracture toughness compared to WC–metal or WC–intermetallic counterparts, overcoming the traditional hardness-toughness trade-off. • Thermal conductivity of WC–HEA is significantly lower than that of conventional WC–Co, which may be advantageous for thermal barrier applications. • The excellent HV–KIC relationship of WC–HEA suggests potential for engineering structural applications where both wear resistance and toughness are critical.
Abstract
The binder phase performs critically on the comprehensive properties of cemented carbides, especially the hardness (HV) and fracture toughness (KIC) relationship. There are strong motivations in both research community and industry for developing alternative binders to Co in cemented carbide system, due to the reasons such as price instability, property degeneration, and toxicity. Herein, six kinds of high entropy alloys (HEA) including CoCrFeNiMn, CoCrFeMnAl, CoCrFeNiAl, CoCrNiMnAl, CoFeNiMnAl, and CrFeNiMnAl were employed as the alternative binder for the preparation of WC–HEA cemented carbides through mechanical alloying and two-step spark plasma sintering. The impacts of HEA on the microstructures, mechanical properties, and thermal conductivity of WC–HEA hardmetals were determined and discussed. WC–HEA hardmetals exhibited both superior HV and KIC to WC–metal or WC–intermetallic cemented carbides, indicating that HEA alloys were not only harder but also tougher in comparison with traditional metal or intermetallic binders. The HEA bonded hardmetals yielded thermal conductivities much lower than that of traditional WC–Co cemented carbide. The excellent HV–KIC relationship of WC–HEA facilitated the potential engineering structural application of cemented carbides.
1. Introduction
Cemented carbides, also named as hardmetals, were considered as one of the most successful engineering composite materials by means of powder metallurgy since it was firstly developed by Karl Schroeter in 1923, which has been widely used as metal and wood machining tools, moulds, as well as wear-resistant mechanical parts [1–3]. Generally, cemented carbide is essentially a composite of hard carbide phase and soft metal phase. The carbide phase is responsible to the high hardness, while the metal phase critically influences the fracture toughness of cemented carbide. It is the combination of hardness and fracture toughness that makes the cemented carbide system uniquely different from either brittle ceramics or ductile metal alloys. Specifically, the cemented carbide is tougher and more impact resistance than ceramic matrix, whereas it is much harder in comparison with metal alloys. The metallic binder plays a critical role for cemented carbide achieving superior combination of mechanical properties.
In the past decades, the metal Co has been considered as the most popular binder phase for cemented carbide, as a function of the excellent wettability of Co on WC, high yield strength and work hardening ability of Co, the plasticity of Co in the system, as well as the interfacial strength between Co and WC [4–6]. However, because of the combined influence of raising cost, hardness/corrosion/oxidation resistances deterioration, and negative effects on health, there is a strong motivation in both academia and industry for investigating alternative binder to Co in cemented carbides [7–8]. In other words, the design of WC–Co materials must balance a host of properties with respect to the intended applications. Up to now, metal, intermetallic compound, and ceramics (metal carbide and oxide) have been used to replace Co in cemented carbide systems [9–14]. However, whilst initially appealing, none of them, to date has been commercialized and produced on an industrial scale. Generally, the WC–metal exhibited unsatisfactory hardness and wear resistance, while WC–intermetallic and WC–ceramics yielded poor fracture toughness. For example, WC–9.6wt%Ni–0.4wt%Co possessed an excellent fracture toughness of 12.5 MPa·m1/2 with a poor hardness of 11.6 GPa [15], whereas WC–10vol% Fe3Al and WC–10wt%Al2O3 exhibited high hardness of 24.1 and 20 GPa but inferior fracture toughness of 7.5 and 5.9 MPa·m1/2 [16–17]. Advanced alternative binder to Co should be effective not only in facilitating the densification of WC, but also overcoming the balance between hardness and fracture toughness of cemented carbides.
Very recently, high entropy alloy (HEA), also named as multiple principal element alloy or compositionally complex alloy, has been attempted to be employed as the rather potential substitute binder for Co in cemented carbides, due to its superior thermal stability, room/high temperature mechanical properties, and tunable properties.
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Jialin Sun, Xiao Li, Le Zhao, Jun Zhao (2025). Effects of high-entropy alloy binders on the microstructure and mechanical/thermal properties of cemented carbides. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-2942-4
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Frequently Asked Questions
What are high-entropy alloy (HEA) binders in cemented carbides?
High-entropy alloy binders are multi-principal element alloys (e.g., CoCrFeNiMn) used as substitutes for traditional cobalt (Co) in cemented carbides. They aim to improve mechanical properties and overcome issues like cost and toxicity associated with Co.
How are WC-HEA cemented carbides fabricated?
WC-HEA cemented carbides are typically fabricated via mechanical alloying of WC and HEA powders followed by two-step spark plasma sintering (SPS), which allows densification while controlling grain growth.
What are the advantages of using HEA binders over Co?
HEA binders can provide superior hardness and fracture toughness compared to traditional metal or intermetallic binders, potentially overcoming the hardness-toughness trade-off. They also offer better thermal stability and may reduce health and environmental concerns.
How does the thermal conductivity of WC-HEA compare to WC-Co?
WC-HEA hardmetals exhibit significantly lower thermal conductivity than conventional WC-Co cemented carbides, which could be beneficial for applications requiring thermal insulation.
What are the potential applications of WC-HEA cemented carbides?
Due to their excellent combination of hardness and toughness, WC-HEA cemented carbides are promising for engineering structural applications such as cutting tools, molds, and wear-resistant parts, especially where both wear resistance and impact resistance are required.
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