Influencing the binder properties in tungsten heavy alloys (WHA)

Abstract

Tungsten heavy metal composites (WHA) have been in development for a long time as the high density and the high melting point of tungsten make these composites interesting for high-temperature applications. In this work, materials with Ni/Fe, Ni/Fe/Mo and Ni/Cu binder were investigated. These materials are already well studied, however, properties, such as specific electrical resistivity, thermal conductivity, saturation magnetization and Young's modulus should be further improved. Moreover, as seen in [1], thermal and electrical conductivity do not fit together, which is why further investigations on this relationship was done in this thesis.The aforementioned properties may be infuenced in two ways. One attempt is to address the interface between tungsten particles and the matrix and the other attempt is to infuence the binder itself. This was executed with different heat treatment schemes. The binder samples were produced with powder hot extrusion. The microstructures were analysed with scanning electron microscopy (SEM) and X-ray diffraction (XRD). In addition, tensile tests were carried out to detect possible segregation effects at the grain boundaries. Furthermore, the validity of the Wiedemann-Franz law was tested on binder materials. For this purpose, the electrical conductivity of the binder materials was measured between 4.2K and room temperature. The properties of WHAs were mainly changed by annealing the samples at temperatures from 1000 °C and annealing times of 20 h or 120 h. A correlation between the thermal and electrical conductivity is hardly discernible in WHAs. Kinetic effects are particularly effective with the material IT180. Hot extrusion made it possible to produce non-porous binder materials. SEM images of binder materials show that further heat treatment causes tungsten to dissolve in the binder. No major infuence of different heat treatments can be seen in the binder materials. The Wiedemann-Franz law does not seem to apply to this binder materials.