Microalloying in sintered steels by mechanical alloying: Evolution of nanostructure during attrition and thermal stability

Microalloying as a technique to improve the mechanical properties has been used for decades in bulk steels. In order to transfer some of the benefits of microalloying to sintered steels, microalloying elements (Nb in this case) are introduced in the iron powder by mechanical alloying. Since mechanical alloying is a solid state alloying technique, the microalloying elements can be added not only in elemental form (Nb) but also in the form of carbides (NbC). Moreover, the use or not of wax as a process control agent during milling is considered. This work studies the evolution of the powder characteristics and nanostructure during milling and the thermal stability of the resultant powder (since for further consolidation the powder will be exposed to temperature). The evolution of the powder characteristics as a function of milling time is monitored by apparent and tap densities, SEM, particle size distribution, DRX, crystallite size and internal strain. The thermal stability of the resultant nanostructured powder is analysed by means of DRX (crystallite size and internal strain) after annealing the milled powder at different temperatures. The purpose of this study is to investigate the temperature influence on crystallite features and the release of stored deformation energy.