Microstructure of Undercooled Ni-B Eutectic Alloy of Non-equilibrium Solidification

Microstructure evolution of Ni-3.6%B alloy at different undercooling and cooling rates was studied by combination of molten-glass and cyclic superheating.The results show that both undercooling and cooling rate play an important role in evolution of microstructure morphology.When undercooling increased from 16 K to 301 K,the break-up α-Ni dendrites evolved from rod to granular and the eutectic transferred from lamellar to anomalous dot.As the increase of the cooling rate i.e.from nature cooling,water quench,Ga-In quench to Cu mold chilling,a transition of microstructure morphology from anomalous dot to lamellar eutectic was observed.Further theoretical analysis indicates that the microstructure morphology of Ni-3.6%B alloy is controlled by undercooling in small undercooling,whereas,by cooling rate in large undercooling.