Study On Eutectic Transformation Of Non-eutectic Component Ni-B Alloy

As a non-eutectic alloy component with excellent comprehensive performance and widely used in industrial production,there are usually two or more microstructure transformations during solidification,and the current mature eutectic transformation mechanism can not be reasonably explained.Therefore,it is of great engineering value and practical significance to study the eutectic growth model of non-eutectic component alloys under non-equilibrium solidification conditions.The eutectic transformation process and mechanism of Ni-B binary alloy in deep undercooling solidification were systematically studied by combinating the glass adsorption purification,circulating heating and triggering nucleation.Using high frequency induction reheating furnace to smelt each alloy specimen,the solidification interface morphology was observed with the help of high speed photographer,and change patterns of interface growth rate was analyzed,and the temperature change of the solidification process of alloy specimen was monitored in real time by infrared thermometer,and the cooling curve in the process was recorded.According to this,the variation law of interfacial recalescence rate was analyzed,the internal relationship between the recalescence rate and interface growth rate is deeply analyzed by using the theoretical model of bonding and breaking bonds in solidification process.In addition,the microstructure of the sample after solidification was observed by metallographic microscope,transmission electron microscope and scanning electron microscope.After that,the Ni-B binary alloy amorphous ribbon was prepared by single-rolling belt method,and the strip was annealed differently.The pre-annealing test was studied byX-ray diffractometer,synchronous thermal analyzer and transmission microscope.The microstructure and thermal stability of the sample were measured and compared with the amorphous ribbon by microhardness tester.The main conclusions are as follows:By studying the deep undercooling solidification characteristics of Ni-B non-eutecticalloys,the variation law between recalescence rate,interfacial growth rate and composition,undercooling is obtained.The bond energy model is used to derive the positive proportional relationship of the recalescence rate and the interface growth rate.The recalescence rate and the interfacial growth rate increase with the rasing of undercooling;the closer the alloy composition is to the eutectic composition point,the recalescence rate and the interface growth rate are greater.According to the thermodynamic formula,the greater the undercooling,the larger the nucleation driving force,and the shorter of time required for the alloy to complete the eutectic transformation,so the greater the rcalescence rate and the growth rate.The temperature reaches the equilibrium phase diagram eutectic transition temperature,and the non-eutectic alloy will undergo a phase transition due to the undercooling of the component to the pseudo-eutectic region when the composition is closer to the eutectic point.By observing the evolution process of non-eutectic Ni-B deep undercooled solidification,the intrinsic relationship between the microstructure morphology and non-eutectic composition was found,and the volume fraction/mass percentage of the halo was analyzed by theoretical model.The two liquidus slopes(m?,m?),the two equilibrium partition coefficients(k?,k?),the eutectic composition point(Ce),and the composition of the sample(C0)are related.In the hypoeutectic alloy structure,the dendritic or rod-shaped ?-Ni phase accounts for a large proportion.The lamellar eutectic phase accounts for a large proportion in the hypereutectic composition.In the hypoeutectic Ni-B alloy,?-Ni is first nucleated and grows into coarse dendrites in the form of small planes;and as the composition increases,the intact dendrites gradually melt,and ?-Ni appears to be demelted.Due to the competitive growth mechanism,Ni3 B is the first phase and surrounded by the ?-Ni forming a halo structure in the hypereutectic composition.Ni-B amorphous alloy with high hardness was successfully prepared by high vacuum single roll belt method.The effects of crystallization temperature and crystallization time on the microstructure of amorphous alloy were analyzed.After high temperature and long time crystallization treatment,the Ni-B amorphous alloy gradually appeared sharp diffraction peaks,and the grain orientation increased continuously,and the precipitated phases were mainly determined to be ?-Ni and Ni3 B.After the crystallization treatment,the larger the composition of the strip,the higher the glass transition temperature,but the hardness and toughness of thestrip structure are lower than those of the same composition.At the same time,as the crystallization temperature increases,the surface of the Ni-B amorphous alloy is arranged in a disorderly and unorganized phase,and gradually becomes a regular arrangement,and gradually becomes a dendritic structure similar to the primary phase.As the crystallization time continues to increase,the more liquid undercooling of the Ni-B alloy rises,the more crystallinity gradually increases,and the faster crystal transformation process completes.