Self-healing of creep-induced damage in a ternary Fe-3Au-4W alloy
During creep, quasi-spherical micron-sized cavities form preferentially at the grain boundaries oriented perpendicular to the load direction. These cavities subsequently grow and coalesce into micro and macro cracks, which ultimately lead to failure. The concept of self healing provides a new principle to extend the creep lifetime. Supersaturated solute atoms can selectively segregate at the free internal surface of the grain boundary cavities and fill them, thereby preventing the coalescence of cavities. This reduction in coalescence rate leads to an extended lifetime.
In our previous research, several binary model systems, including Fe-Cu, Fe-Au, Fe-Mo and Fe-W, have been proven to be effective in autonomously healing of creep damage and extending the creep lifetime. In the present study, we explore the damage behaviour of a ternary Fe-3Au-4W (wt.%) alloy containing two healing elements: the fast diffusing Au and the slower diffusing W. The composition of the ternary alloy was selected such that at the testing temperature of 550 °C both elements show 1 at.% supersaturation. Precipitation at the external surface is investigated to demonstrate the tendency of the solute atoms to segregate at the free surface and to evaluate the self-healing potential. Creep tests at elevated temperatures with different constant applied stresses are applied to evaluate the creep properties of the new ternary alloy. The results are compared with those for the Fe-Au and Fe-W binary alloys. This ternary alloy provides new insight in the interplay between two separate healing agents in the same system.