Study On Brazing Material And Process For A Ni₃Al-based Single Crystal Superalloy

At present,advanced high-temperature materials and welding process have been the key factors in the development of new aero-engines and others fields.Intermetallic compound superalloy is one of the development trends of high-temperature structural materials in the future.This paper investigated proper brazing materials and welding process for a novel Ni3Al single crystal superalloy in order to acquire the fine connection of the alloys.The study is innovative and valuable in engineering application.Based on this background,The main contents and results of this paper are as follow:(1)In this paper,four kinds of interlayer alloys with Si and B(as melting point depressant elements)were designed that based on the chemical composition of base metal.The microstructure of the interlayer alloys was observed by SEM.The phase constituent of interlayer alloys was determined by EDS and XRD.The result showed that there were y matrix,(Cr,Si)3Ni2Si phase and ?'-Ni3Al phase in the interlayer alloys with Si element.And there were ? matrix,Ni20Al3B6 phase and ?'-Ni3Al phase in the interlayer alloys with B element.(2)The solidus and liquidus temperature of various interlayer alloys were determined by DTA.The wettability of interlayer alloys on the substrate was evaluated by the sessile drop method.The result showed that the wetting angles were less than 20° in the experiment.The welding experiments were proceeded with four kinds of interlayer alloys respectively and all joints were consisted of eutectic zone,isothermal solidification zone and diffusion affected zone.The joints using Si-interlayer consist of MoNiSi phase,y matrix and ?' phase in the eutectic zone,? and ?' phases in the isothermal solidification zone,needle-like Ni-Mo-Si phase with Al and Cr elements in the diffusion affected zone.The joints using B-interlayer consist of Mo2NiB2 phase,Ni20Al3B6 phase,? and ?' phases in the eutectic zone,? and ?'phases in the isothermal solidification zone and lots of little grainy and needle-shaped borides in the diffusion affected zone.(3)Research on the influence of welding process on joint structure found:The area of eutectic zone and the isothermal solidification time can be reduced by increasing the welding temperature.The area of eutectic zone can be reduced by increasing the welding time,which was beneficial to the diffusion of elements.The isothermal solidification time can be shorten by reducing the welding gap,which was easier to obtain isothermal solidification joints.(4)The welding process of four interlayer alloys was determined based on the above research and the mechanical properties of the joints were tested.The tensile strength of the joints besides the Ni75Si5 joint was more than 60%of base metal at 900?.The stress rupture life of each joint was more than 60%of base metal at 900?/181MPa.In this paper,the welding materials and welding process of Ni3Al single crystal superalloy materials were studied primarily,which provides guidance and reference for the high-quality connection process of Ni3Al-based single crystal superalloys and engineering application.