Effect of Higher Silicon Content and Heat Treatment on Structure Evolution and High-Temperature Behaviour of Fe-28Al-15Si-2Mo Alloy

This paper describes the structure and properties of cast Fe3Al-based alloy doped with 15 at. % of silicon and 2 at. % of molybdenum. The higher content of silicon is useful for the enhancement of high-temperature mechanical properties or corrosion resistance of iron aluminides but deteriorates their workability due to increased brittleness. It was found that the presence of both alloying elements leads to an increase of values of the high-temperature yield stress in compression. The heat treatment (annealing at 800 degrees C for 100 h) used for the achievement of phase stability causes the grain coarsening, so the values of the high-temperature yield stress in compression are lower at 600 degrees C and 700 degrees C in comparison to values measured for the as-cast state. This stabilization annealing significantly improves the workability/machinability of alloy. Furthermore, the higher silicon content positively affects the values of the thermal expansion coefficient that was found to be lower in the temperature range up to 600 degrees C compared to alloys with lower content of silicon

Fe–Al–Si-Type Iron Aluminides: On the Strengthening by Refractory Metals Borides

The effect of boron addition into Fe–28Al–5Si–X (X = -, 2Mo, or 2Ti) on the structure and high-temperature yield stress was investigated. Generally, the alloying of binary Fe3Al-type iron aluminides by silicon significantly improves high-temperature mechanical properties by solid-solution strengthening. On the other hand, the workability and ductile properties at room or slightly elevated temperatures get worse with the increasing silicon content. Boron alloying together with titanium or molybdenum alloying is one of the ways to improve the workability of this type of alloy and, at the same time, ensure the formation of a sufficient amount of secondary phase particles required for effective strengthening. In this paper, the influence of 1 at. % of boron on high-temperature yield stress is evaluated in response to structural changes and compared with results obtained previously on the same type of alloy (Fe–28Al–5Si–2X, X= -, Mo, or Ti) but without boron alloying. It can be concluded that the network structure of borides of refractory metals formed due to boron alloying works more effectively for alloy hardening at higher temperatures than a mixture of silicides and carbides present in the boron-free alloy of the same composition