Precipitates in a Fe-Co-Mo alloy characterized by complementary methods

The precipitation hardening behaviour of a Fe-Co-Mo alloy, which is comparable to that of Al-alloys, has been investigated. In this alloy, hardening is achieved by the precipitation of nm-sized Mo-rich precipitates. The Fe-25%Co-15%Mo (m%) alloy exhibits a peak hardness of ∼68 HRC after solution annealing and subsequent continuous heating to 615 °C. This optimum state of hardness has been analysed by complementary methods to gain a thorough insight into the materials microstructure. Transmission electron microscopy (TEM) and three-dimensional atom probe (3DAP) investigations have been conducted to characterize size, shape, and chemical composition of the precipitates. Because the analyzed volume in TEM and 3DAP investigations is small, statistical information has been obtained by small-angle neutron scattering (SANS). For the analysis of the SANS data, additional information derived from 3DAP measurements was used. Combination and comparison of the results of TEM, 3DAP and SANS provide the possibility to describe the microstructure of the alloy in detail and lead to a better understanding of the strengths and limitations of each method.