Microstructure And Mechanical Properties Of SiC Ceramic And K4169 Alloy Composite Castings

SiC ceramics have many excellent characteristics such as small thermal expansion coefficient,wear resistance,oxidation resistance,thermal shock resistance,high hardness and high temperature mechanical properties.They can be used as key materials for rocket nozzles,engine heat-resistant parts,gas turbine blades,etc.Due to the brittleness of the engineering ceramic material itself and the limitations of the preparation process,it is difficult to obtain a member having a large size and a complicated shape.K4169 is a widely used nickel-based superalloy,which has a certain complementary relationship with ceramic materials.Therefore,the realization of reliable connection of ceramics and metals has high engineering application value.In this paper,the casting process was used to realize the integrated forming of SiC ceramics and K4169 high temperature nickel-based alloy.Combined with the finite element simulation results,the effects of different process parameters and interface conditions on the microstructure and properties of SiC ceramics and K4169 alloy composite castings were studied.Based on ANSYS Workbench,a composite casting model of SiC ceramics and K4169 alloy was built.Considering 7 different interface structures,8 intermediate layers with different compositions,and 6 intermediate layers with different thicknesses,the model was optimized for the DM module.The maximum equivalent stress usually occurs at the ceramic end,so the structure is optimized for the purpose of reducing the maximum stress at the ceramic end.The comprehensive analysis results show two excellent interface parameters:sawtooth structure?3 cycles,groove depth 7.30?Mm,groove width 2.57mm,spacing 4.00mm)plus 0.6mmTi intermediate layer,sine wave structure?3.5 cycles,amplitude 3.49mm?plus 0.4mmTi-45Ni intermediate layer are two optimal structures,the maximum under the given boundary conditions The three-point bending strength is 112.9 MPa and 208.3 MPa,respectively.SiC ceramics and K4169 nickel-base superalloys were cast by gravity casting process at a vacuum of 10 Pa,1450°C and preheating of 900°C to obtain a good joint.The thickness of the interfacial reaction layer reached 200?m and was scanned by scanning electron microscopy?SEM?.The energy spectrum of the joint reaction zone was determined by the energy spectrome:K4169/free C+FeC/TiC/FexSi/NixSi/TiC/SiC.The control variables were studied in the process parameters.It was found that with the prolongation of the holding time,the elements were fully diffused and the thickness of the reaction zone gradually increased.The fine mesh-like FeSi and NiSi phases in the reaction layer began to grow and became lath-like,free.The number and size of SiC particles decreased significantly.With the increase of casting temperature,the number of thermal cracks in the near-slot area of ceramics increased,the interface of ceramics collapsed,and the SiC particles peeled off increased and spread to the K4169 side.Finally,the thermal fracture morphology of SiC ceramic base metal was analyzed.The Ti-45Ni intermediate layer is used to alleviate the thermal stress generated during the joining process of the SiC ceramic and the K4169 alloy.The results show that due to the addition of the intermediate layer,the SiC ceramic avoids direct contact with the high-temperature molten metal and does not break due to thermal shock;the intermediate layer material melts and wets the ceramic surface,and the joint interface is flat;the reaction layer of a certain thickness is formed.The gradient of the thermal expansion coefficient mitigates the thermal stress.The active elements can also promote the diffusion of elements and the progress of the reaction.The interface structure of the castings obtained by using the Ti intermediate layer is mainly:SiC/SiC particles+C/Ni ₂ Si+Fe_xSi/TiC+Ti₅Si₃/residual Ti foil/TiC+Ti₅Si₃/K4160;The interface structure of the casting obtained by the NiTi intermediate layer is mainly:SiC/TiC+C/Ni₂Si/Ni₃Si+Ti₃SiC₂+Fe_xSi/FeC+?Nb,Cr?C/k4169.The casting temperature is 1450°C.With the increase of the thickness of the NiTi intermediate layer,the thickness of the reaction layer first decreases and then increases.The free C and SiC particles in the reaction layer gradually disappear,the interface bonding is more tight and gentle,and the bending strength of NiTi thickness is 350?m.The maximum is 120Mpa.