Microstructure, mechanical properties and corrosion behavior of W-B-Ni-Fe shielding cermets synthesized by reactive boride sintering

Abstract

In this work, a novel type of nuclear shielding material capable of shielding γ rays and neutrons, W-B-Ni-Fe cermets, was synthesized using W, NiB, and Fe powders by reactive boride sintering. The cermets possessed a constant (Ni + Fe)/B atomic ratio of 1.50 and various W/B atomic ratio (ARWB) of 8.26, 3.25, 1.88 and 1.24, respectively. Microstructure and mechanical properties were characterized and analyzed, and corrosion behavior was discussed using electrochemical method in 1.0 M H2SO4 aqueous solution. After sintering, the cermets were composed of orthorhombic W2(Ni,Fe)B2 hard phase, W phase and Ni based binder phase. The homogeneous microstructure with both fine W2(Ni,Fe)B2 and W particles was obtained when ARWB was 3.25. At room temperature (RT), the hardness increased monotonically with ARWB decreasing, while the compressive and bending strengths peaked when ARWB was 3.25 due to the cooperative effect of hard-phase and grain-refinement strengthening. At high temperature (500 ℃), the presence of ductile W phase enabled an increase of bending strength compared to that at RT. The corrosion of cermets in 1.0 M H2SO4 solution began with active dissolution of Ni based binder phase, and then the passivation process occurred with the formation of blue WO3-x phase. With ARWB decreasing, Icorr was first sharply decreased and then sharply increased. The impedance value of cermet was lowest when ARWB was 3.25 which is due to the relatively lower forming ability of passive film.

Keywords

• W-B-Ni-Fe cermets
• Reactive boride sintering
• Microstructure
• Mechanical properties
• Corrosion behavior