Effect of heat input on precipitation characteristic and order degree of Ni 3Al in light beam surfacing layer

Abstract

With the use of SEM, EDS and X-ray diffraction, the microstructure and phase composition of Ni 3Al intermetallic coating obtained by light beam surfacing were investigated. Moreover, the effect of heat input on the precipitation characteristic and order degree of Ni 3Al was also analyzed. The results show that with the Ni and Al mixed powder of 3:1 atomic ratio as surfacing material, the light beam surfacing layer cannot entirely consist of Ni 3Al owing to the oxidation burning loss of aluminum and the dilution of the molten pool by base metal. The surfacing layer with lower heat input (3000 J/mm) is composed of the eutectic of Ni 3Al and γ-(Fe,Ni). The increase of heat input (4200 J/mm) leads to intensified dilution of molten pool and increased oxidation burning loss of aluminum, which results in the reduced aluminum content in molten pool. The microstructure of the surfacing layer with higher heat input is the hypoeutectic of Ni 3Al and γ-(Fe,Ni), a lot of particle α-Fe precipitates within γ-(Fe,Ni) phases, and the order degree of Ni 3Al increases. With the increase of heat input, the microstructure of transition zone between surfacing layer and base metal changes from γ-(Fe,Ni) to lath martensite with hardness of HV740.