Microstructure And Mechanical Property Of LEN98M Superalloy Fabricated By Laser Additive Manufacturing Technology

Nickle-base superalloy is a kind of key material for fabrication of advanced aero-engine and gas turbine blades.In traditional directional solidification method,there are some problems,such as deteriorated microstructures,high cost and low yield.However,present directional solidification block further development and increased produce cost of superalloy with difficulting in controlling micro structure,low pass percent of parts and so on.In this work,the novel three dimensional printing technology(3DPT)is employed to fabricate components of superalloy.It's expected to reduce fabricating cost and to improve micro structure by using 3DPT.LEN98M superalloy was fabricated by laser additive manufacturing technology.As compared,DZ98M superalloy with same composition to LEN98M's was produced by trainditional method.The y' phase's microstructure,elements segregation,precipitation phases,characteristics of the temperature of solidification and tensile properties and so on of superalloys are systematically investigated by using scanning electron microscope(SEM),optical microscope(OM),electron microprobe(EPMA),energy dispersive spectroscopy(EDS),differential thermal analysis(DTA),X-ray diffraction(XRD)and some other research methods.The main results are as follows:(1)The primary dendrite arm spacing of the LEN98M alloy is reduced as large 1/5 of the directional solidification alloy,which shows the 3D technology can refine dendrite because of rapid solidification.The secondary dendrite wasn't obvious in the LEN98M alloy.After heating treatment,the LEN98M alloy shaped still exists obvious differences between dendrite and interdendritic but DZ98M alloy is same between dendrite and interdendritic.(2)The result of DTA shows that the solidus of the LEN98M alloy does not change aboviouly,the liquidus of the alloy decrease lightly,which results to narrowing down thermal treatment of window(about 10%).In addition,the melting peak of MC carbides(The"M"mainly are elements of Ti and Ta based on detection of EDS)appears at about 1360?.(3)There are many pinholes in the LEN98M alloy.The larger number of eutectic ?/?'transformed into y'massive eutectic.But the precipitation of carbides disappeared in the as-casted LEN98M alloy.The more carbides precipitated in LEN98M alloy after heating treatment more than of the DZ98M alloy.(4)The as-casted LEN98M alloy has a serious segregation of elements.After thermal treatment process,the segregation of elments could be improved obviousy.(5)The morphology of Y'phase are irregular and the range of average dimension of y'phase are large in the LEN98M alloy,especially for interdendritic region.After thermal treatment,the morphology of y'phase changed to regular cube-like with average dimension of 0.30?m in dendrite area,while y'phase are irregular cube with average dimension being 0.43?m in the interdendritic area.(6)The two type of alloys performed from brittle rupture to ductile rupture in tension test with increasing testing temperature(from 21 to 1000?),The tension experimental results show that ulitimate tensile strength of the DZ98M alloy increased at first and then decreased.The highest peak is at 760? and a lowest peak is at 1000?.The LEN98M alloy ulitimate tensile arrives to the highest value 600?,and then decreases with increasing temperature.Yiled strength of the LEN98M alloy is less than that of the DZ98M alloy.