Precipitation of an Intermetallic Phase in Mo-alloyed Tungsten Heavy Alloys

Abstract

Mo–Ni–Fe heavy alloys essentially is constant. 2,9,20) Accordingly, alloying by Mo reduces the solubility of tungsten in the liquid phase during sintering, which retards the growth of W grains, promotes refinement, and exhibits better mechanical properties. Kemp 2) analyzed the microstructural evolution and the kinetic process of grain growth of W–Mo–Ni–Fe alloys, and noted that during furnace cooling a new intermetallic phase precipitated in the interfaces between the W–Mo grains and the matrix phase, and modified the mechanical properties. However, its exact composition and structure were not identified. It was also noted that the intermetallic phase could not be eliminated through conventional heat treatment. The above-mentioned reports mentioned some phenomena in the liquid-phase-sintered W–Ni–Fe alloys. However, the detail of microstructural evolution of W–Mo–Ni–Fe heavy alloys during liquid phase sintering remains unclear, and the effect of the Mo addition has not been fully discussed. Furthermore, the precipitation mechanism of the intermetallic phase, and the relationship between the intermetallic phase and cooling rate has still not been clear yet. Therefore, this study aims to provide further analysis of the issues mentioned above. A transmission electron microscopy (TEM) with an attached Energy Dispersive X-ray Spectrometer (EDS) was used to perform more accurate analysis, because the electron beam of TEM was only 10 nm in diameter and the effective excitation volume was approximately 10 5 mm 3 . 21) As only few studies have used TEM with EDS to analyze the microstructures of the matrix phase in the sintered W–Mo– Ni–Fe heavy alloys, TEM with EDS were used as the primary tools to examine the above-mentioned questions.