Reinvestigation of isothermal sections in M (M = Mo, W)-Fe-B ternary systems at 1323 K

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 are-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), Mo1-xFexB(CrB-type, 0.13 less than or equal to x less than or equal to 0.18) from 6 to 9 at%Fe at a stoichiometric boron content of 50 at%, Mo1+xFe2-xB4(Ta3B4- type, -0.08 less than or equal to x less than or equal to 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 M0.2Fe2.8B is stable only in a limited temperature region 1353 < T<1383 K.