Microstructure Formation Mechanism And Numerical Simulation Of Fe-Al-Ta Eutectic Composites

Fe-Al intermetallic compound can be used in the high temperature structural materials due to low density,good corrosion resistance,high temperature strength and creep resistance.However,its industrial application is limited by room temperature brittleness and poor process ability.To solve these problems,many studies show that FeAl-Ta ternary eutectic alloy can be obtained by mixing Fe-Al-Ta together through alloy component design,and then Fe-Al-Ta eutectic in-situ composites is produced by directional solidification technology.In this paper,ProCAST software was used to simulate the directional solidification process of Fe-Al-Ta eutectic composites,and the influence of solidification rate on the temperature field and microstructure of the solidification process of Fe-Al-Ta eutectic composites was explored.The results of temperature field simulation show that the maximum temperature gradient exists in the contact area between the casting and the cooling medium when the casting just touches the cooling medium.With the increase of the length of the casting extending into the cooling medium,the temperature gradient gradually decreases and tends to be stable.When the solidification rate is different,the temperature gradient increases with the increase of solidification rate.The results of microstructure simulation show that the columnar grains with good orientation can be prepared by the directional solidification technique,and the size of columnar grains decreases with the increase of solidification rate.At the lower solidification rate of 6μm/s,the microstructure of the castings is columnar,while at the higher solidification rate(30μm/s,100μm/s,200μm/s),there is a certain cold zone at the bottom of the castings,the microstructure of this region is fine equiaxed grains,and the middle and upper parts of the castings are a large number of columnar grains.In this paper,the solidification process of Fe-Al-Ta eutectic alloy under different cooling rates was observed in situ by an ultra-high temperature laser confocal microscope,and the change processes of sample surface at different temperatures were recorded,so as to study the crystal growth mechanism of Fe-Al-Ta eutectic.Through in situ observation,it is found that the crystal growth of Fe-Al-Ta eutectic shows obvious eutectic growth,and the solid-liquid interface continues to grow into the liquid phase with a cellular solid/liquid interface.With the increase of cooling rate,the curvature of the cellular solid/liquid interface increases.Metallographic analysis of the longitudinal section of the samples after in-situ observation show that the solidified microstructure at30℃/min and 100℃/min show obvious eutectic structure,and the size of the eutectic colonies decreases with the increase of the cooling rate.At the cooling rate of 200℃/min,there are eutectic and divorced eutectic structures.