A Correlation of Material Toughness, Thermal Shock Resistance, and Microstructure of High Tungsten, Silver-Tungsten Composite Materials

The electrical erosion resistance of composite silver-tungsten materials seems to improve with finer dispersions of the silver and tungsten; however, these materials with the finer dispersions exhibit a higher tendency to fail by catastrophic crack propagation during arc erosion testing. A fracture mechanics approach is taken to determine Gfc, the critical strain .energy release rate for crack extension under plane strain conditions for several compositions and particle size distributions of silver-tungsten materials. A qualitative analysis of resistance to crack propagation in the same materials under severe arcing agrees with the Glc measurements. The fracture toughness of these materials has also been compared to the microstructure by quantitative metallography. A relationship of Glcand the mean free path between tungsten particles has been found to agree on only a porton of the materials. A more complex term involving contiguity, volume fraction silver and mean free path has a good correlation with Glc for all the materials.