MICROSTRUCTURAL EVOLUTION AT LARGE DRIVING FORCES DURING GRAIN-GROWTH OF ULTRAFINE-GRAINED NI-1.2WT-PERCENT-P

The microstructural evolution during grain growth at large driving forces of an ultrafine-grained Ni-1.2wt%P solid solution (starting grain size of 7 nm) is evaluated for the temperature range 473 to 873 K. It is shown that the material is thermally stable as a nanocrystalline structure up to 623 K. At higher annealing temperatures the material transformed into a two-phase Ni + Ni3P microstructure and considerable grain growth was observed. The Ni matrix showed continuous grain growth and displayed a temperature-dependent grain growth exponent N. The effects of driving force, grain boundary mobility, and grain boundary pinning on the final microstructure are discussed.