Research On Microstructure And Properties Of Rapidly Solidified TiAl/Ti Based Alloy

Ti-44A1-8Nb alloy fibers were successfully fabricated by melt extraction technique at different rotational speeds.The morphology and microstructure of the fibers were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectrometer(EDS)and transmission electron microscopy(TEM).It was found that the diameter of fibers decreased with the increase of rotational speed,and the surface Rayleigh wave defects became more serious.Ti-44A1-8Nb alloy fibers were mainly composed of ?2 phase and ? phase.Rapid solidification was helpful to the formation of ?2 phase.The effects of quartz tube on the preparation of Ti-44A1-8Nb fibers were discussed.It was found that the second phase Ti3Si was produced and accompanied by parallel slip displacement faults.The metal fiber forming process was analyzed by numerical simulation software ANSYS(FLUNET).The characteristics of the melting pool were calculated after the molten metal rose to the surface of the copper wheel.The phase field,temperature field,flow field and the formation mechanism of surface defects during metal fiber forming were studied.It is found that the uneven diameter is related to the surface stability of the melt.The key lies in the contact between the melt and the roller and the stability of the melt in the region where the melt moves together with the roller.Due to the gap between the upstream meniscus and the roll surface,as the fiber is formed and pulled out,the gap is gradually reduced,and the phenomenon of air entrainment in the process is likely to affect the fiber formation.The large temperature gradient causes the molten pool to stratify,and the surface near the roller is a supercooled layer,which is characterized by the slowest flow rate,the lower drawing layer and the fastest flow rate.Therefore,the metal fiber is easily formed to have a diameter fluctuation downstream,resulting in a diameter fluctuation.The surface quality is poor and a bamboo-like defect is formed.Ti-6A1-4V alloy ribbons were successfully prepared by melt rotation at different roller speeds.The effect of roller speed on the morphology and microstructure of Ti-6A1-4V alloy ribbons were studied by XRD,SEM and EDS.The effect of SiO2 on the structure and properties of Ti-6A1-4V alloy ribbons were discussed.The tensile mechanical properties of the strip obtained under different roller speeds were studied.It was found that the Ti-6A1-4V alloy ribbon consists of p phase with alternated distribution of ?' phase and ?" phase.Higher cooling rate promoted ?' phase formation.According to the energy spectrum analysis,it was known that there were surface embossings on the matrix mainly composed of ? phase.The Ti-6A1-4V material reacted with the quartz tube wall by electromagnetic induction melting,and it was found that Si segregated at the interface of the two phases.Tensile properties of Ti-6A1-4V alloy ribbons showed unique plastic deformation characteristics.Tensile curve had undergone linear and non-linear deformation stage.The strip prepared at 2300 r/min of roller speed exhibited high elastic strain and fracture strength.As the rotation speed of the roller increases,a thin strip stack phenomenon occured,and the stack caused defects in the inside of the ribbon to cause a decrease in strength.