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MoCoB–Co cermets with varying Mo/B atomic ratios (AR Mo/B) and Co contents were fabricated, and their microstructure, mechanical properties, and corrosion behavior were investigated. The MoCoB hard phase exhibited the maximum grain size and anisotropy when the AR Mo/B was 0.84, which degraded the mechanical properties. For AR Mo/B ≥ 1.08, a third phase, Co 7 Mo 6 , and dense three-dimensional networks composed of stacking faults and ε-martensite plates were observed. These three-dimensional networks limited the dislocation slip in face-centered cubic γ-Co and ε-martensite, improving the hardness of the cermet and decreasing the transverse fracture strength (TRS). The corrosion resistance of the cermets was influenced by the MoCoB particle size, the Mo content of the binder phase, and the ε-martensite content. With an increase in the AR Mo/B , the corrosion resistance of cermets initially decreased and then increased. Additionally, as the Co content increased, the hardness gradually increased, whereas the TRS and fracture toughness steadily decreased. For AR Mo/B = 0.92 and a Co content of 45 at.%, the cermet displayed the best overall performance, with hardness, TRS, and fracture toughness values of HRA 89, 1720 MPa, and 13.2 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

WCoB based cermets were prepared by spark plasma sintering at sintering temperature among 600°C-1200 °C. The phase evolution was investigated by detecting density behavior, phase composition, microstructure and mechanical properties during sintering process. The sintering process can be divided into three stages: powder densification, solid phase reaction and liquid phase sintering. WCoB hard phase forms at 1000 °C during solid phase sintering, showing better mechanical properties than Co 2 B, especially on Vicker's hardness. WCoB hard phase forms on the basis of Co 2 B binary boride and its content increases in liquid phase sintering stage with high density. The Vicker's hardness and transverse rupture strength (TRS) reach the maximum value of 1262 Hv and 1212 MPa at 1200 °C and 1170 °C, respectively. The fracture toughness reaches the maximum value of 21.8 MPa m1/2 at 1050 °C, and the inter-granular fracture is the main fracture mechanism. [ABSTRACT FROM AUTHOR]

To find high-performance ternary borides as the hard phase of the cermets, first-principles calculation was applied to systematically investigate the structure, mechanical, electronic and thermal properties of 26 ternary borides MⅠ x MⅡB x (x = 1 or 2). The phase stability and mechanical properties were evaluated by formation enthalpy and elastic constants. Debye temperatures were calculated to study the thermal conductivity, and the hardnesses of the candidates were predicted via the overlap populations calculation and hardness model. The results show that all the candidates possess thermodynamic and mechanical stability. Most of the MⅠ x MⅡB x (x = 1 or 2) exhibit a better ductility than WC, except Ta 2 FeB 2 , Mo 2 MnB 2 , Nb 2 CrB 2 , Nb 2 FeB 2 and Ti 2 ReB 2. Moreover, sorted from high to low, Nb 2 CrB 2 , Mo 2 CoB 2 , W 2 MnB 2 , Mo 2 FeB 2 , Ti 2 ReB 2 , NbFeB, MoCoB, Mo 2 NiB 2 , Nb 2 FeB 2 , and Mo 2 NbB 2 have a larger Debye temperature than WC. All the candidate ternary borides exhibit a lower hardness than WC, with the maximum hardness of 26.3 GPa for MoCoB. The analysis of electronic properties indicates that all the MⅠ x MⅡB x (x = 1 or 2) exhibit metallic, ionic and covalent hybrid properties. The calculated results are expected to provide guideline for developing ternary boride-based cermets or coating materials that may replace WC-Co cermet. • Ternary boride-based cermets may replace WC-Co. • The mechanical and thermal properties of 26 MⅠ x MⅡB x (x = 1,2) were investigated. • A novel high hardness and thermal conductivity MoCoB-Co cermet was proposed. • A scientific foundation for accelerated design of tungsten substitutable cermets. [ABSTRACT FROM AUTHOR]

The influence of N 2 atmosphere on the microstructure of gradient zone in Ti(C,N)-Mo 2 C-Ni cermet was systematically investigated by the coupling analysis of experimental characterization and thermodynamic calculation. Under the guidance of calculated carbon window, the composition of Ti(C,N)-Mo 2 C-Ni cermet was designed, and the cermet was produced via liquid-phase sintering at 1450 °C for 2 h under N 2 pressure of 20, 200, 400 and 600 mbar. The microstructure and element distribution of cermet were analyzed by using Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray spectroscopy (EDX). A homogeneous microstructure was obtained for cermet sintered in 20-mbar nitrogen atmosphere, whereas the thickness of gradient layer increased with nitrogen pressure. EDX mapping demonstrate that Mo and Ti are enriched in gradient zone, while Ni is lacking and partially segregated near the surface. The diffusion of elements in cermet is caused by the different nitrogen activity between surface and interior. The carbonitride grains show typical black core and gray rim structure in the bulk of cermets, while it present light-gray core and gray rim in the surface gradient layer. In addition, the Vickers microhardness measurement was performed for the gradient zone of cermets, and the hardness increased for cermets sintered in higher nitrogen pressures, which exhibit slower grain growth phenomena. [ABSTRACT FROM AUTHOR]

Highlights: [•] Studying the W and Mo effect on the mechanical properties of Ti(C,N) cermets. [•] Studying the W and Mo effect on the electronic properties of Ti(C,N) cermets. [•] Distinguish the different property of hard phase and rim phase in Ti(C,N) cermets. [•] Explaining from theory the different property of Ti(C,N) and (Ti,Mo,W)(C,N) cermets. [ABSTRACT FROM AUTHOR]

Transition metal boride enable applications in fields of cutting tools as the hard phase, but their fabrication suffers from shortcomings in high temperature for binary and hard/soft phase balance. Here, we leveraged a WCoB-Co cermets prepared by using elemental powders of W, Co and B powders via in situ synthesis method and investigated the microstructure evolution of a composite structure of WCoB/Co. The phase evolution, microstructure evolution and mechanical properties were investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The complete sintering process consist of three solid-phase reaction stages and one liquid-phase sintering stage. The solid-phase reaction stage includes the following three reactions: B + 2Co → Co 2 B, 11 W +15 Co 2 B → 9WCoB + W 2 Co 21 B 6 , and 14 W + 2W 2 Co 21 B 6 → 12WCoB + 23Co + Co 7 W 6. The eutectic liquid phase, essential for the densification, forms at 1323 °C. The Rockwell hardness and density value reach 87.5HRA and 12.11 g/cm3, respectively. At 1380 °C, the traverse rupture strength (TRS) reaches the peak value of 1495 MPa. Moreover, the results show that transgranular fracture is the main fracture mode. The densification stage was completed at ~1400 °C. In particular, Co 7 W 6 phase was discovered during the study of the evolution of WCoB-Co cermets. An increase of the B content was found to be beneficial to eliminate the Co 7 W 6 phase that proved to be detrimental to mechanical properties. • WCoB-Co cermets were prepared using elemental powders. • The paper focuses on phase evolution and microstructure evolution. • Increasing the content of B element can improve the mechanical properties and eliminate Co 7 W 6 phase. [ABSTRACT FROM AUTHOR]

MoCoB–Co cermets with different Mn contents were synthesized using an in-situ sintering reaction, and the effect of Mn addition on the microstructure, interfaces, and mechanical properties was investigated. The addition of Mn inhibited the transition of the binder phase from fcc to hcp. Adding an appropriate Mn can increase the density of the material and refine the hard phase grain. With increasing Mn content, the hardness decreased marginally and then gradually increased, and the transverse rupture strength (TRS) and fracture toughness (K IC) gradually decreased. The cermet with 6 wt% Mn addition had the smallest grain size and lower porosity. The hardness of the cermet increased from HRA 89.0 to HRA 91.7. The interface bonding strength of MoCoB/hcp-Co is higher than that of MoCoB/fcc-Co. After isothermal aging treatment, the content of hcp-Co in the binder phase increased markedly; thus, the K IC and TRS increased from 11.3 MPa m1/2 and 1200 MPa–13.3 MPa m1/2 and 1750 MPa, respectively. [ABSTRACT FROM AUTHOR]

A first-principles study was performed to assess the potential of MAB 2 (M = Nb, Ta; A = Co, Ni) ternary borides as friction-resistance cermet. The formation energy, decomposition energy, phonon dispersion curves and elastic constants were calculated to evaluate stabilities. The bulk modulus, shear modulus, Pugh's ratio, Poisson's ratio and elastic anisotropy were adopted to analyze elastic properties. The Debye temperature was used to reflect thermal conductivity. The density of states, charge density and Mulliken population were performed to reveal physical mechanisms. Through calculational results, MAB 2 possesses structure and mechanical stabilities, and then MAB 2 has excellent elastic properties. Both NbNiB 2 and TaCoB 2 are ductile materials; in addition, the thermal conductivity of NbNiB 2 and NbCoB 2 are satisfying. The calculations imply MAB 2 is a mixture of covalent, ionic and metallic bonds, indicating covalent bonds are vital. Especially, the theory hardness of NbCoB 2 , NbNiB 2 , TaCoB 2 and TaNiB 2 are 25.30, 27.71, 30.78 and 31.91 respectively, indicating MAB 2 has high-hardness potential. The comprehensive properties are more outstanding in MAB 2 than in MAB. The method from atomic scale to macroscale can accelerate optimization of novel friction-resistance cermet. • Studying the potential of MAB 2 -type borides as friction-resistance cermet. • Ratio of B in MAB 2 borides playing a vital role. • MAB 2 borides belonging to a mixture of covalent, ionic and metallic bonds. • Covalency mainly affecting properties of MAB 2 Borides. • Optimization way from atomic scale to macroscale. [ABSTRACT FROM AUTHOR]