Microstructure Effects on Tensile Properties of Tungsten-Nickel-Iron Composites

摘要

Tungsten heavy alloys are W-Ni-Fe or W-Ni-Cu metal-metal composites produced by liquid phase sintering elemental powders. The alloys possess high density, strength, and ductility which makes them useful for several applications, including kinetic energy penetrators. The composite microstructure consists of nearly spherical grains of body-centered cubic tungsten surrounded by a solidified face-centered cubic matrix phase containing Ni, Fe, and W, Although polycrystalline tungsten normally is brittle at room temperature, the matrix imparts ductility to the composite. Controlled processing of heavy alloys containing 88 to 97 pct W resulted in high sintered densities and excellent bonding between the tungsten grains and matrix. For these alloys, deformation and fracture behavior were studied via slow strain rate tensile testing at room temperature. The flow stress increased and the fracture strain decreased with increasing tungsten content. During tensile testing, cracks formed on the surface of the specimens at tungsten-tungsten grain boundaries. The crack density increased with plastic strain and tungsten content. The surface cracks, though initially blunted by the matrix, eventually increased in density until catastrophic failure occurred. Reprints. (jes)