The rapid solidification of undercooled liquid Ni_(45)Fe_(40)Ti_(15)alloy was realized by glass fluxing technique.The microstructure of this alloy consists of primaryγ-(Fe,Ni)phase and a small amount of interdendritic pseudobinary eutectic.The primaryγ-(Fe,Ni)phase transferred from coarse dendrite to fragmented dendrite and the lamellar eutectic became fractured with the increase of undercooling.The growth velocity ofγ-(Fe,Ni)dendrite increased following a power relation with the rise of undercooling.The addition of solute Ti suppressed the rapid growth ofγ-(Fe,Ni)dendrite,as compared with the calculation results of Fe-Ni alloy based on LKT model.The microhardness values of the alloy and the primaryγ-(Fe,Ni)phase increased by 1.5 times owing to the microstructural refinement caused by the rapid dendrite growth.The difference was enlarged as undercooling increases,resulting from the enhanced hardening effects on the alloy from the increased grain boundaries and the second phase. The rapid solidification of undercooled liquid Ni_ (45) Fe_ (40) Ti_ (15) alloy was realized by glass fluxing technique.The microstructure of this alloy consists of primary γ- (Fe, Ni) phase and a small amount of interdendritic pseudobinary eutectic. The primaryγ- (Fe, Ni) phase transferred from coarse dendrite to fragmented dendrite and the lamellar eutectic became fractured with the increase of undercooling. The growth velocity ofγ- (Fe, Ni) dendrite increased following a power relation with the rise of undercooling. The addition of solute Ti suppressed the rapid growth of γ- (Fe, Ni) dendrite, as compared with the calculation results of Fe-Ni alloy based on LKT model. Microhardness values ​​of the alloy and the primary γ- (Fe, Ni) phase increased by 1.5 times owing to the microstructural refinement caused by the rapid dendrite growth. The difference was enlarged as undercooling increases, resulting from the enhanced hardening effects on the alloy from the increased grain boundaries and the second phase.