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Ultrafine Ti(C, N)-based cermets are vacuum-sintered by refining the particle size of raw materials and tailoring the WC/TaC ratio to achieve the improvements in comprehensive mechanical properties and cutting performance. The hardness, flexural strength and tool lifespan of ultrafine Ti(C, N)-based cermets are substantially higher than those of submicron Ti(C, N)-based cermets with the same composition because of the refined grains and the improved distributions of both metal phases and residual stress. The hardness attenuation behavior and strengthening mechanism in Ti(C, N)-based cermets at different test temperatures have been proposed. At 400 ℃, the hardness attenuation of Ti(C, N)-based cermets depends mainly upon the softening of metal phases. However, at 800 ℃, the hardness attenuation of Ti(C, N)-based cermets is mainly related to the reduced bearing capacity of hard ceramic phases and interfacial sliding. The addition of refractory TaC is beneficial for the improvement of high-temperature mechanical properties and the tool lifespan, attributed to the strengthening of the ceramic framework by tantalum atoms. • The strategy on synergistic refinement of raw powders with various constituents in ultrafine Ti(C, N)-based cermets is proposed for the first time. • The comprehensive properties of ultrafine Ti(C, N)-based cermets are substantially higher than those of submicron Ti(C, N)-based cermets. • The hardness attenuation behavior and strengthening mechanism in Ti(C, N)-based cermets at different test temperatures are proposed. [ABSTRACT FROM AUTHOR]

The composition complexity of Ti(C, N)-based cermets poses a great challenge to the controllability of their sintering process. The effects of both refractory TaC addition and original particle size of starting materials on densification behavior and microstructural evolution of Ti(C, N)-based cermets were investigated during liquid phase sintering. The particle rearrangement only plays a very limited role in promoting densification of Ti(C, N)-based cermets at the initial stage of liquid phase sintering, whereas the pore-filling in the presence of liquid phase becomes a dominant densification mechanism in the middle stage or even earlier. Enhanced densification of ultrafine Ti(C, N)-based cermets is realized by introducing refractory TaC additive based on the grain growth-induced liquid phase pore-filling mechanism, which is also verified by an extended study using other refractory carbide additives such as NbC, ZrC and HfC. This work provides a novel idea for the development of fully densified ultrafine Ti(C, N)-based cermets with outstanding mechanical properties, which are highlighted in machining applications of difficult-to-machine materials as well as other wear-resistant parts operating in high-temperature and high-stress environments. [Display omitted] • The effects of both TaC addition and the particle size of starting materials on the densification behavior of Ti(C, N)-based cermets are clarified. • Enhanced densification of ultrafine Ti(C, N)-based cermets is realized by introducing refractory TaC additive. • This work provides a novel idea for the development of fully densified ultrafine Ti(C, N)-based cermets. [ABSTRACT FROM AUTHOR]

The pursuit of efficient and stable electrochemical catalysts based on transition metals (TMs) for the hydrogen evolution reaction (HER) is of paramount importance. Herein, a novel partially amorphous NiMoB/NiMoO 4−x catalyst with dense nanoparticle assemblies has been prepared with B doping and reduction by one step NaBH 4 treatment of smooth nanorod-like NiMoO 4 precursor. Benefiting from the MoNi 4 alloys partially reduced from NiMoO 4 precursor, optimized electronic state through B doping and partially amorphous structure, NiMoB/NiMoO 4−x obtained splendid activity for HER with a lower overpotential of 26.2 mV at 10 mA cm 2 coupled with a narrow Tafel slope of 66.75 mV dec 1, in contrast to NiMoO 4 precursor catalyst (260.24 @10 mA cm 2, 149 mV dec 1) in alkaline solution. Additionally, the self-supported NiMoB/NiMoO 4−x electrode exhibits remarkable stability, maintaining a current density of 50 mA cm 2 for a minimum of 40 h attributed to mixed phases of MoNi 4 and amorphous NiMoO 4−x for accelerating the H 2 evolution and enhancing water adsorption. This work offers a facile avenue to rationally design high-performance electrocatalysts for enhancing hydrogen evolution with NaBH 4 accompanying borate doping and reduction. [Display omitted] • Partially amorphous NiMoB/NiMoO 4−x was constructed by one step hydrothermal. • MoNi 4 alloys accelerate H 2 evolution assisted by amorphous NiMoO 4−x. • Oxygen vacancies (O v) can enhance the conductivity and hydrogen spillover effect. • B doping effectively modulates the electronic structure of NiMoB/NiMoO 4−x. [ABSTRACT FROM AUTHOR]