Mechanical Properties of Cr<SUB>3</SUB>B<SUB>4</SUB> Cermets Cemented by Different Metallic Binders

Abstract

Cr 3 B 4 cermets cemented by cobalt and iron as a metallic b inder up to 20 wt% were prepared by hot pressing at 1500 and 1800℃ under a pressure of 14 and 41 MPa for 1hr. The binder addition enhanced the densification of Cr 3 B 4 cermets due to the formation of liquid metal and its flow into the pores. It is also found that the temperature and pressure have a pronounced effect on densificat ion. The densification of Cr 3 B 4 is enhanced by the addition of cobalt and iron due to the liquid phase format ion, therefore, the hardness and fracture toughness were improved, to a certain extent. A composite with a both high Vickers hardness of 35.98 GPa and a modest fracture toughness of 2.5 MPa.m 1/2 could be obtained by the addition of 8 wt% cobalt at 1500 o C and 14 MPa. There is an overgrowth of the boride grains which surly reduces the hardness but has less impact on the fracture toughness.

Tailoring the Mechanical Properties of Earth-Abundant Transition Metal Borides via Bonding Optimization

“…Knowing the elastic constants also allows an estimation of the Vickers hardness (H V ) based on the calculated B DFT and G DFT using the parametrized relationship shown in eq 1, where κ is Pugh's ratio (G/B). 16 Using eq 1, the estimated H V,Chen for Cr 3 B 4 is 27 GPa, which is in agreement with the experimentally measured value (H V,exp ≈ 26 GPa), 34 compared to other high hardness transition metal borides like WB 4 (H V,exp ≈ 43 GPa) 49 and OsB 2 (H V,exp ≈ 22 GPa). 52 This supports the fact that Cr 3 B 4 is ultraincompressible, but it is not a superhard transition metal boride.…”

“…Cr 3 B 4 is a prime example of earth-abundant 3d transition metal boride with moderate experimentally measured hardness (H V = 26 GPa). 34 In this work, we explored the opportunity of enhancing the mechanical properties of Cr 3 B 4 by computationally investigating the chemical bonding through COHP calculation, which revealed that the compound is too electron rich. Therefore, V substitution is employed to optimize the chemical bonding in Cr 3 B 4 by reducing the VE count.…”