The Flow and Fracture Behaviour of Sintered Iron

Abstract

The tensile fracture strength of sintered iron compacts cannot be simply related to the original pore content as proposed by many previous investigators. In a well-sintered compact, plastic flow precedes fracture and is localized at ligaments to a degree which increases as the sintered density decreases within the range of practical interest. Most ligaments deform without necking; some rupture to allow local pore coalescences. These effects cause the original pores to grow anisotropically. Fracture occurs when general plastic instability leads to internal necking and rupture of many ligaments, i.e. to the rapid coalescence of pores across a section of the compact. No macroscopic necking can be expected. Calculations reveal that pore growth due to the flow which precedes fracture may account for a large reduction in the effective load-carrying cross-section of the matrix.In lightly-sintered compacts, little macroscopic strain is seen, and fracture is concentrated at interparticle contacts. Microscopically, fracture may involve ductile coalescence of fine pores within the contacts, brittle grain-boundary separation, or a mixture of both mechanisms. Again, fracture strength cannot be related simply to pore fraction.