Microstructure And Formation Mechanism Of Fe-Al-Ta Ternary Alloy Prepared By The Near-rapid Directional Solidification

Intermetallic compound is a new-type potential high-temperature structural material with a series of features such as light density,high melting point,high strength,excellent anti-oxidation and anti-corrosion properties.Intermetallic compound has been paid more attention by researchers because of better resistance to temperature than high temperature alloy and higher toughness and machinability than ceramic.Among intermetallic compounds,Fe-Al Intermetallics become the focus in the field of high-temperature structural materials owing to its light density,low price and outstanding performance.In the present study Ta has been added into Fe-Al alloy to obtain Fe-Al-Ta eutectic composites by directional solidification technique.The technological parameters of directional solidification have effects on phase growth and selection mechanism,composition of phases,morphology of liquid-solid interface and revolution rules of eutectic microstructures,which has been investigated at a big range of solidification rates by the modified Bridgman directional solidification equipment and advanced measuring instruments.The relationship between the microstructure of Fe-Al-Ta eutectic in situ composite and mechanical property is also studied,and in the meanwhile the surface micro-hardness,fracture of room temperature and three-point bending and strengthening mechanism are studieded and analyzed.The microstructure of Te-Al-Ta at different solidification rates is composed of Fe(Ta,Al)matrix phase and Fe2Ta(Al)reinforcement phase both under vacuum induction melting technique and directional solidification.At different solidification rates,the longitudinal microstructure of steady state is refined and transforms from uniform morphology to random configuration.It can be concluded that the eutecticmorphology represents a transition from rod-like to spherical-like and then to out-of-order short rod-like.At the range of solidification rates from 90?m/s to 600?m/s,the volume fractions of Laves phase increase firstly and then decrease,and the minimum volume fraction is 36.11% corresponding to the solidification rate of 90?m/s.Eutectic spacing becomes smaller gradually and its relationship with the solidification rates can be simulated as ?=75.99R-0.79,which is in consistent with J-H model.The liquid-solid interface is nearly independent on solidification rate and the cellular interface plays the main role.But as the solidification rate is increased,transition of cellular dendrite occurs and the revolution process transforms from regular primary branch to multiple branches and then to irregular multiple branches.There is distinct difference of surface hardness at different solidification rates and it has the tendency to become greater.During the room temperature tensile test,Fe-Al-Ta eutectic alloy both under vacuum induction melting technique and directional solidification show brittle fracture.The large volume fraction of Laves phase,the gradually decreasing eutectic spacing and the higher undercooling are all beneficial to the improvement of tensile strength of directional solidified Fe-Al-Ta eutectic alloy,which make the maximum tensile strength much higher than that of casting alloy..The three-point bending stress-strain curves and facture morphology have been obtained.Those show that the fracture of Fe-Al-Ta eutectic alloy can be classified as cleavage fracture.But the small amount of dimples is observed under high-power microscope,which makes contribution to the improvement of fracture toughness of Fe-Al-Ta eutectic alloy.