Enhanced thermal stability of a cobalt-boron carbide nanocomposite by ion-implantation

A first investigation of the thermal stability in a wear resistant cobalt-boron carbide (Co-B4C) nanocomposite has been performed by the combination of calorimetry and transmission electron microscopy. The calorimetric measurements show that the thermal stability of Co-B4C is not influenced by the presence of the 10 vol.% mu m-sized boron carbide particles. However, grain growth is shifted to significantly higher temperatures during in-situ annealing (in the transmission electron microscope), and abnormal grain growth is not observed to be as extensive as in conventional nanocrystalline Co. This effect is mainly attributed to the observed implantation of Ga atoms during transmission electron microscope specimen thinning by focused ion beam. Grain boundary segregation mechanisms are discussed as possible reasons for the retarded grain growth.