Effect Of Trace Mounts Of Zr On Microstructure And Properties Of K4169Alloy

K4169casting alloy has the same composition with Inconel718alloy ofthe United States， Which is the Ni-Fe based superally by precipitated thephase B.C.T.γ " and F.C.C. γ′.The alloy has good performance such as highstrength， plastic， good resistance to corrosion and good performancewelding performance and casting process performance in a wide range oflow temperature (253~700℃).But when service temperature is above650℃，the γ" phase besomes incoherent whit matrix alloy，and then aggregates，grows up and transforms to stable δphase， so many propertes such asstrength and plasticity rapidly deteriorate.In recent years， with the rapidlydevelopment of aircraft engine，especially the gas turbine parts，the higherrequest of application of alloy is made.however， the domestic and foreignresearch workers tried to adjust the content of Al、 Nb、 Ti、 Fe、 Mo、 Ta、Cr、Co、W and other major alloy elements in order to obtain better stabilityof organization and work at a higher temperature.In this thesis， the K4169alloys are added different content of Zr by manual electric arc furnace. Theeffect of Zr on microstructural of casting alloy，uniformity processing，stateof standard heat treatment， fracture failure compressive properties wereinvestigated by metallurgical microscope (OM)， transmission electronmicroscope (TEM)， scanning microscope (SEM)， energy dispersive X-raydetector (EDX)， X-ray diffraction (XRD) and mechanical property testings.The research conclusions are as follows:(1) After increasing the element of Al and Co in K4169alloy, themicrostructure of as-cast alloys are the same to the as-cast master alloyK4169, includes branches crystal of γ matrix、dispersion distribution of γ′inmatrix、 nitride and Laves phase;The element of Zr promotes eliguation ofNb、 Mo and increases the count of phase type in as-cast.(2) The element of Zr promotes the precipitation of grain boundaryprecipit, as increasing of the content of Zr, the segregation degree of Al, Nb,Mo and Ti elements become ease, when the content of Zr exceeds by0.09%,branch crystal segregation is promoted and the content of Nb, Mo in lavesphase is increased; The segregation in as-cast alloy is serious, Matrix andLaves phase both are solid solution, a large number of carbon atoms andalloy elements are solute atoms, so primary carbide is less in as-cast alloys; Zr promotes the formation of nitride, makes the counts of nitrides group andthe size of nitrides increased;The hardness of as-cast alloy shows a trend ofdecrease with the increasing of Zr content.(3)The element of Zr improves the incipient melting temperature oflaves phase of K4169, alloy melting point becomes lower; Temperature andsample thickness of alloy have great influence on homogenization treatment;Laves phase disappears during the treatment process, and nitrides can’t beeliminated because of its higher melting point; Hardness of alloy shows thetrend of reduce at beginning and then increase with the processing timeextending. Even after5hours, alloy is overburnt; Eventually the processingis confirmed as:1150℃×3.5h.(4) The components of heat treatment alloy is uniform, the segregationreduces and the crystallization is better, the count of phase type reducesthan as-cast alloy, but secondary carbide phase appears,Zr elements canchange the shape of grain boundary precipitat, grain-boundary carbide areshort clavite without Zr element in heat treatment alloy, while it is roundparticles in heat treatment alloy ally with Zr element, the main componentsof carbide is NbC; Zr increases the lattice distortion between granularseparation phase and matrix and causes microstructure defects increasedaround nitrides particles, After heat treatment, microscopic defects aroundgroup cluster particles become holes which is adverse to alloy performance.(5) Alloy strength can be improved when added appropriate amount ofZr element.With the increase of the content of Zr, standard heat treatmentstate alloy hardness and tensile strength show the trend of increase at firstand then reduce, and the extended is contrary trend; During tensile process,alloy second phase strengthening has a significant effects, carbide andnitride particles prevent relative slipping between different grain. Whencontent of Zr beyond0.09%, the hole defects increased which lead to alloyintensity decrease.