Reinvestigation of Isothermal Sections in M(M=Mo, W)-Fe-B Ternary Systems at 1323 K

Abstract

Phase equilibrium relations in the M(M=Mo, W)-Fe-B ternaries were determined in isothermal sections at 1323 K based on X-ray powder diffraction and quantitative EPM-analyses (Mo, Fe, B) on argon arc-melted or reaction-sintered alloys, which were subjected to long term annealing. The investigation confirmed the existence of three ternary compounds in the Mo-Fe-B ternary at 1323 K and established their range of formation: stoichiometric Mo₂FeB₂(ordered U₃Si₂-type), Mo_1−xFe_xB(CrB-type, 0.13≤x≤0.18) from 6 to 9 at%Fe at a stoichiometric boron content of 50 at%, Mo_1+xFe_2−xB₄(Ta₃B₄-type, −0.08≤x≤0.76) at rather Fe-rich concentrations from 13 to 25 at%Mo at a stoichiometric boron content of 57 at%. In the system W-Fe-B two ternary compounds were found to exist in accordance to the literature: WFeB (TiNiSi-type) and W₂FeB₂(W₂CoB₂-type). No indication of ternary tungsten compounds with B contents higher than 40 at% was found. For both systems metastable Fe₃B with the Ti₃P-type was stabilised by the substitution of Mo or W for Fe. In both phases M_0.2Fe_2.8B is stable only in a limited temperature region 1353<T<1383 K.