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 G
f
c, 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 G
l
c measurements. The fracture toughness of these materials has also been compared to the microstructure by quantitative metallography. A relationship of G
l
c
and 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 G
l
c for all the materials.