Solid Solution and Precipitation Hardening in Mg-Fe-O Alloys

Abstract

Iron was introduced into single crystals of MgO by diffusion to produce thin homogeneous slices of alloy crystals containing up to ∼4% Fe/(Mg+Fe). When the iron is present as Fe²⁺ the MgO crystal is not appreciably strengthened but 1% Fe³⁺ retained in solution by quenching approximately doubles the flow stress of the original crystal. The strengthening due to Fe³⁺ can be enhanced slightly by aging the crystal in air at 700° to 1000°C. This causes a precipitate of magnesioferrite to form as octahedra which are perfectly oriented within the MgO, the faces of the octahedra being parallel to {111} in the MgO. The fracture process is not greatly affected by the presence of this ``coherent'' precipitate. Continued aging reduces the strength and coarsens the precipitate without change in shape over a size range of 100 Å to 1 μ.