Effect Of Solidification Rate On Solidification Structures And Properties Of Fe-Al-Ta Eutectic

Intermetallic compound is a potential new type of high-temperature structural functional material with long-term ordered structure,excellent resistance to oxidation,corrosion,wear and impact.Fe-Al intermetallic compounds have excellent oxidation and corrosion resistance as compared with stainless steel.Fe-Al intermetallic compounds also have better corrosion resistance in high temperature sulfur-containing atmospheres than that of high temperature nickel-based alloys,and have small density and low cost,which has been attracted widespread attention from materials scholars.However,intermetallic compounds generally have the disadvantage of high room temperature brittleness,and the strength and creep resistance of Fe-Al alloys are lower when the temperature is higher than 600?.These greatly limit the engineering application of the material.Based on the research progress of strengthening and toughening of Fe-Al intermetallic compounds and the development of directional solidification technology,Alloying and directional solidification technology were combined together in this paper to improve the room temperature plasticity and high temperature strength of Fe-Al alloys.According to the Fe-Al binary phase diagram,a certain amount of Ta was added to the Fe-Al intermetallic compound,and a modified Bridgman directional solidification technique was used to make the Fe-Al-Ta eutectic in-situ composite.The higher solidification rates effects on phase composition,evolution of phase interface,solidification structure characteristics,crystal orientation,and materials characteristics were analyzed.Influence mechanism of solidification rate on solidification structure and mechanical properties was investigated,and the eutectic solidification theory was further improved and developed.short rods and spherical mixtures are uniformly distributed in Fe-Al-Ta eutectic at the solidification rates of 650?m/s,700?m/s,800?m/s,and 900?m/s.As the solidification rate increases further,the spheroidization becomes more and more obvious,and the structure becomes more refined.At this time,the solid/liquid interfaces of the Fe-Al-Ta eutectic are still cellular structure.All the S???values of Fe-Al-Ta eutectic at different solidification rates were calculated to be positive ones according to the M-S and KF theory.Any wavelength disturbance will interfere with the stability of the interface.The solid/liquid interfaces still are cellular structure,and the theoretical calculation and Experimental results match well.In order to obtain the minimum interfacial energy,the eutectic structures at different solidification rates maintain their own unique morphologies under their respective preferred orientations.The lattice mismatch of the matrix phase and the enhanced phase was calculated to be10.3%,and the phase interface of the eutectic is a semi-coherent interface.As compared with the as-cast Fe-Al-Ta eutectic alloy and pure Fe₃Al,the hardness value of the Fe-Al-Ta eutectic after directional solidification increases significantly with the increase of the solidification rate.The elongation curves of Fe-Al-Ta eutectic at different solidification rates are very similar throughout the tensile loading process.There is no obvious plastic deformation feature,and the eutectic structure fractures are all brittle fractures.The tensile strength of the Fe-Al-Ta eutectic structure after directional solidification is significantly increased as compared with the as-cast alloy,and the performance is significantly improved.The fracture toughness value of Fe-Al-Ta eutectic at solidification rate of 650?900?m/s are higher than that of the low solidification rates.As the lower solidification rates,the eutectic fracture mode is still cleavage fracture,mainly along lamellar fracture,accompanied by transgranular fracture.The Fe-Al-Ta eutectic fracture is a cleavage-tough fracture at the solidification rate of 700?m/s with a toughness value of up to 18.12 MPa·m1/2.The main toughening mechanism of the structure is the result of the combined action of fine toughening and eutectic toughening.