The Influence Of Cooling Method To The Organizations And Properties Of Fe₃Al Intermetallic Compound

In this paper,Fe₃Al intermetallic compounds was preparing in the atmospheric environment by the use of medium frequency induction melting furnace,the metal liquid was cooled and solidificated in the water glass sand, stainless steel mold and water-cooled copper mold.At last the block wedge of the test.was obtained.By the use of X-ray diffraction(XRD),optical microscope, universal testing machine,pendulum-type impact testing machine and hardness machine,studied alloy phase,mechanical properties,and by the use of scanning electron microscopy(SEM) and electron microprobe(EPMA),observed the alloy microstructure,the fracture morphology and the oxide layer morphology.The experimental results show that:as-cast,in the water glass sand,the organizations was distributed evenly in the alloy and the grains was big.In stainless steel mold,the organizations were small and uniform.In the water-cooled copper mold,the organizations and the grains were distributed unevenly and regional segregation was existed.Firstly,homogenization annealing was done at the 1000℃and remained 15h.Secondly,the temperature was reduced to 600℃and remained 1h.After heat treatment,netted segregation neat the grain boundary was eliminated,Cr,B can be soluted in the matrix,and enhanced the strength of the internal crystal,so that the hardness of alloy can be improved and the mechanical properties of alloys be increased.However,either as-cast state or heat treatment state,the plasticity of the alloy at the room temperature has no significant improvement.With the increase in the cooling rate,the alloy fractured from the characteristics of the intercrystal fracture to the mixed fracture characteristics that be made up of the intercrystal fracture and transgranular fracture.High-temperature oxidation tested that oxidation kinetics of alloy followed the parabolic law,but there be some negative bias.The experimental results show: In the water glass sand and stainless steel metal mold,cross-section morphology of the oxide layer be basically the same,the outer layer is composed of Al₂O₃,Fe₂O₃ and Cr₂O₃,inner layer is Fe₃Al matrix,between oxide layer and matrix there be no phenomenon of wrinkling and peeling off.The surface oxide layer of the alloy on the in the stainless steel metal type be thin and dense.In the water glass sand,the thickness of the surface oxide layer be uniform.The antioxidation of the alloy solidificated in the stainless steel metal be slightly higher than the antioxidation of the alloy solidificated in the water glass sand.