Mechanical Properties and Microstructure of Fe-Co-W Sintered Alloys after Heat Treatment

摘要

Various heat treatments and their effects on the microstructure and the properties of sintered Fe-Co-W ternary alloys prepared from elemental powders are described. Isothermal sections in the range of 1383K～1653K are investigated by means of powerful techniques in order to bring arguments in the critical fields of composition. The experimental approach is supplemented by thermodynamic calculations using the Calphad method. Specimens in the composition range of 10 to 20 mass%W and 20 mass%Co are investigated after quenching and tempering between 473K and 1073K during 1h to 3 days. The μ phase (Fe,Co)_7W_6 is found as an equilibrium precipitate in many alloys. The formation of martensite during quenching and the precipitation sequence during tempering is discussed. It is shown that the investigated alloys can effectively be hardened by heat treatments. The formation of the microstructures in these sintered alloys is discussed in the light of the established phase equilibria and the structural change during tempering.