Abstract
The orienting of α″-Fe16N2 platelets in α-iron single crystals has been studied by ageing experiments at around 180°C, both with and without magnetic fields up to 1˙7 MA m−1. Ageing without an external magnetic field leads to some local orienting, initially because of the elastic interaction between the particles, and later because of the influence of the spontaneous magnetization of the matrix. By ageing in an external magnetic field, α″ becomes completely oriented within large crystal regions by selective coarsening, whereas after nucleation and primary growth no such orienting is detectable. These effects are interpreted in terms of a new theoretical evaluation of the interplay of the chemical driving forces and the physical orienting forces.