Environmentally assisted fracture of sintered nickel cartridges

The failure of sintered Ni 200 cartridges, which were used as filters to collect solid catalytic particles from an organic solution of disodium iminodiacetate, was investigated. The initial microstructure of the sintered filter is composed of twinned Ni-α grains and pores, but during use severe embrittlement of the cartridges was accompanied by an intense loss of material, leading to an increase in the volumetric fraction of pores (from 39% to 72%), and a change in the morphology of nickel powders from smooth spheres to sharp faceted crystals. During corrosion testing, there was an visible difference in the corrosion behaviour between the solid electrolytic nickel and sintered Ni 200, with the latter being more prone to dissolution (chelant corrosion) and crevice corrosion. Fractographic examination indicated that the sintered Ni cartridge was initially ductile, but its premature failure during use occurred by a brittle fracture mode, due to the action of a stress corrosion mechanism.