Structure of alloys of the Nb—Mo—В system in the region Nb—NbB—MoB—Mo

Abstract

As-cast and annealed alloys containing to 50% (at.) В were studied by X-ray diffraction technique and scanning electron microscopy with electron microprobe analyses. Temperatures of incipient melting were measured with pyrometry after Pirani— Alterthum. Basing on the data obtained, the Nb—Mo—В solidus surface projection was constructed in the range Nb—NbB—MoB—Mo for the first time. The boride (Nb₃B₂) was found to become stable on the solidus surface after dissolution of more 9,5% (at.) Mo in it, and the compositions between (Nb_0,84Mo_0,16 )₃B₂ and (Nb_~0,3Mo_~0,7 )₃B₂ separate from the melt. This boride forms superfine eutectics (Nb, Mo) + (Nb₃B₂) and (Nb, Mo) + (Nb₃B₂) + (Mo₂B).