DISPERSION-STRENGTHENED IRON BY GEL PRECIPITATION

Abstract

Metastable iron oxide particles containing calcium, magnesium, or zirconium in solid solution were produced by the gel precipitation method. These were reduced to metal with hydrogen/nitrogen mixtures in a fluidized-bed furnace at 800°C to yield iron powders containing dispersed oxide phases within each iron particle. The oxide phases were either 2CaO.Fe₂O₃, a solid solution of MgO and FeO, or ZrO₂, which appeared to be free from iron. Consolidation by compacting the powders into cans, sealing under vacuum, and hot extrusion yielded bars in which the oxide particles were dispersed. Hardness and tensile-test data for material heated to 1000°C for up to 100 h suggest that the oxides containing iron coarsen rapidly and contribute to strengthening only by maintaining a small matrix grain size. The iron-free ZrO₂ appears to be a true dispersion hardener and to restrain grain growth more than do the other oxides investigated.