A study of the manganese-tungsten binary phase diagram

摘要

The current work investigated the manganese -tungsten binary system by studying the microstructure of a mechanical alloy of tungsten-35 at.% manganese, sintered at 1225, 1275, 1350, and 1425 degrees C. Consistency of the results is evaluated through thermodynamic modeling of the manganese-tungsten phase diagram. The micro structural constituents were characterized qualitatively and quantitatively in terms of the type of phases and the content of manganese in the tungsten rich-phase using X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDS). The XRD patterns revealed peaks associated with a tungsten-rich phase and manganese oxide (MnO) in the first set of samples while the patterns of the second set showed the strong peaks related to a manganese-rich phase and manganese dioxide (MnO2). Backscattered images showed a distinct two phase microstructure in the first set of samples as compared to a three-phase microstructure in the second set of the samples. The maximum observed solubility of manganese in tungsten is 12 +/- 3 at.% after sintering at 1350 degrees C for 90 min, compared to 9.3 at.% at 1268 degrees C based on a thermodynamic model. The maximum observed solubility of tungsten in manganese is about 10 at.% in the high temperature solid, compared to 7.4 at.% and 4.6 at.% in the solid and liquid phases respectively at the peritectic temperature of 1268 degrees C.