Precipitation of Fe2W Laves Phase in Fe-Ni-Based Alloy HR6W without Carbon

The age-hardening behavior of the Fe-Ni-based alloy HR6W without carbon was investigated at temperatures between 973 and 1173 K for a maximum of 3000 h to clearly identify the nose temperature of the Fe2W Laves phase. The microstructure observation was carried out for the aged alloys using field-emission scanning electron microscopy. One-step increase of hardness was detected for the alloy, which corresponds to the precipitation of Fe2W phase. It was found that the Fe2W phase precipitates with a flake-like morphology within gamma grain interior and with a granular morphology at grain boundaries. The TTP (time-temperature-precipitation) diagram for the alloy is established based on the results of hardness measurements and microstructure observations, and the C curve representing the time required to initiate precipitation of the Fe2W Laves phase within gamma grain interior was determined. The nose temperature of the C curve was identified as 1100 K, and the precipitation starts at 20 h at the nose temperature. The precipitation of the Fe2W phase at grain boundaries occurs for one order of magnitude earlier than that within gamma grain interior at temperatures below 1100 K. [doi:10.2320/jinstmet.J2022023]