Hardening and Coherent Precipitates Size Evolution with Aging Fe-12Al-12V Alloy

Fe-Al based alloys have a remarkable potential for high temperature structural applications, provided that the limitation of their low creep resistance is solved. Third element addition (Nb, Ti, Zr or Ta) has proved to perform the task, at the expense of a low ductility. In previous works we have investigated ferritic alloys in the Fe-Al-V system with coherent precipitation of L2₁ phase (Fe₂AlV) and have identified phases in equilibrium at the vertical section Fe_1-2xAl_xV_x. We have found that a wide two-phase field is present in the composition range 0.10≤x≤0.15 (x: atomic fraction) till 720 °C. In this work we study the feasibility of a structural application at high temperatures of the Fe-12Al-12 V alloy. We look for ageing conditions leading to a stable coherent precipitation that could strengthen the ferritic matrix. In this way, we measured vickers hardness of coherent L2₁ precipitates at 600, 650 and 700 °C. In all cases hardness has a typical behavior with hardness maximum located at longer times and higher intensities as temperature decreases. We measured size evolution with time through Transmission Electron Microscopy of precipitates at 700 °C ageing temperature. As a further result, we could calculate from these measurements the activation energy for precipitate growth.