Production and Properties of High Entropy Carbide Based Hardmetals

Abstract

Dense, high-entropy carbide cobalt-bonded hardmetals with two different compositions, namely (Hf-Ta-Ti-Nb-V)C-19.2 vol% Co and (Ta-Ti-Nb-V-W)C-19.2 vol% Co, were successfully manufactured by gas pressure sintering (SinterHIP) at 1400 °C and 100 bar Ar pressure. The microstructure of these hardmetals consists of a rigid skeletal carbide phase embedded in a tough Co binder phase. EDS mappings showed that the high-entropy carbide phase did not decompose and that a typical hardmetal microstructure was realized. Only in the case of the (Hf-Ta-Ti-Nb-V)C-Co hardmetal was some undissolved TaC and HfO2, as well as some clustered vanadium titanium carbide phase, found, resulting in a split-up of the HEC phase into two very similar HEC phases. This resulted in a reduced hardness to fracture toughness ratio for this composition. Measurements of magnetic saturation polarization showed values between 57.5% and 70% of theoretical magnetic saturation polarization, indicating marginal dissolution of the carbide-forming metal elements in the binder phase. The hardness value HV10 for (Hf-Ta-Ti-Nb-V)C-19.2 vol% Co was 1203 HV10 and 1432 HV10 for (Ta-Ti-Nb-V-W)C-19.2 vol% Co.

Low-temperature densification of high-entropy (Ti,Zr,Nb,Ta,Mo)C—Co composites with high hardness and high toughness

“…In general, compared to solid-state sintering of carbide ceramics, liquid-phase sintering through addition of Co and/or Ni can greatly reduce the densification temperature, down to ~1300-1600 ℃. For the case of high-entropy carbide ceramics, Pötschke et al [22] recently successfully manufactured dense (Hf-Ta-Ti-Nb-V)C-19.2 vol% Co composites by gas pressure sintering at 1400 ℃ and 100 bar Ar pressure, resulting in an increase in fracture toughness to ~8.5 MPa•m 1/2 . However, this approach sacrifices the high hardness of high-entropy ceramics due to the high metallic binder content (19.2 vol%) employed, with the hardness of the (Hf-Ta-Ti-Nb-V)C-19.2 vol% Co composites being only ~11.8 GPa [22].…”

“…For the case of high-entropy carbide ceramics, Pötschke et al [22] recently successfully manufactured dense (Hf-Ta-Ti-Nb-V)C-19.2 vol% Co composites by gas pressure sintering at 1400 ℃ and 100 bar Ar pressure, resulting in an increase in fracture toughness to ~8.5 MPa•m 1/2 . However, this approach sacrifices the high hardness of high-entropy ceramics due to the high metallic binder content (19.2 vol%) employed, with the hardness of the (Hf-Ta-Ti-Nb-V)C-19.2 vol% Co composites being only ~11.8 GPa [22]. A similar study has also been conducted by Liu et al [23], for a (Zr 0.25 Hf 0.25 Ta 0.25 Ti 0.25 )C-20 wt% Ni/Co composite system, which resulted in a moderately low hardness value of ~16.3 GPa.…”

Influence of different binder metals in high entropy carbide based hardmetals

“…The compositions of the HEC-based hardmetals investigated in this study are compiled in Table 1. The equimolar (Ta,Nb,Ti,V,W)C powder with a lattice parameter of 4.354 Å was prepared at Fraunhofer IKTS from commercial carbide powders by mixing, sintering of cold isostatic pressed bars at 2250°C and subsequent crushing to <45 μm by means of a vibratory disc mill (more details can be found in [17]). For the preparation of HEC-based hardmetals binder contents of 16 and 24 vol-% were selected, since they represent the same binder content as in WC-10 wt-% Co and in WC-15 wt-% Co, respectively.…”

“…With respect to hardmetals or cermets, this concept has mostly been applied by the use of HEA as metal binders, e.g. [14][15][16], while investigations using HEC as a hard phase are still very limited [17][18][19][20]. Different technologies have been applied for their preparation, including Sinter-HIP [17] spark-plasma sintering (SPS) [18], pressureless melt infiltration using SPS [19] and precipitation in a steel matrix [20].…”

High Entropy Materials: Challenges and Prospects

“…The article on high-entropy ceramics reports on the steps of making (Hf-Ta-Ti-Nb-V)C and (Ta-Ti-Nb-V-W)C high-entropy carbides, and then compositing them with the 19.2 vol% Co binder to make hard metals (also known as cemented carbides) as potential cutting tool materials [9]. Researchers also mix up the TiC and FeCoNiCuAl HEA with mechanical alloying and sinter the mixture into TiC-reinforced FeCoNiCuAl HEA composites with spark plasma sintering, whose hardness and wear performance are largely improved [10].…”