A Study On The Effect Of TiB₂ Addition On Microstructure And Propreties Of FGH97 Superalloy

FGH97 is the third-generation superalloy independently developed in Chian.The traditional preparation process is powder metallurgy hot isostatic pressing(HIP).The alloy has excellent corrosion resistance,oxidation resistance,good mechanical properties and creep properties.However,due to the large grain size of the alloy,the mechanical properties at room temperature are limited;the original particle boundaries generated during the preparation process will become the source of cracks;after the cracks are generated,the propagation speed is fast;the decomposition temperature of the strengthening phase ?? limits its using temperature.In this paper,FGH97 powder with a particle size of 75?150?m and 5?m ceramic phase Ti B2 powder are used to form a composite.The low energy ball milling process and hot pressing sintering method are combined to successfully prepare a FGH97-Ti B2 system composite with a network structure.The basic properties of the material such as hardness,elastic modulus,and thermal diffusivity are tested through different testing methods,and then metallographic microscope,scanning electron microscope(SEM),X-ray diffractometer(XRD),and electron probe microanalyzer(EPMA)are used and transmission electron microscopy(TEM)and other testing methods for microstructure characterization and fracture mechanism analysis of the prepared material.And the mechanical properties such as room temperature stretching,three-point bending,high temperature stretching,high temperature compression were tested,combined with the mechanical property results and fracture analysis to obtain a strengthening effect of the network structure on the composite.Observation of the microstructure through an optical microscope revealed that the composite material is denser than the alloy,and with the increase of Ti B2,the density of the composite material is further increased.The reinforced phase Ti B2 is beneficial to the densification of the composite material.Microstructure analysis found that the phases of FGH97 alloy mainly include ?(Ni Al)phase and ??(Ni3Al)phase,a small amount of M23C6 and MC carbides,and there are obvious primary particle boundaries(PPBs);in addition to ? and A clear network structure can be seen beyond the ?? phase,and a secondary structure can also be observed in the primary network structure.The “network structure” is the generated M3B2 type boride,and there is no PPBs.Through the room temperature tensile test,the network structure makes the FGH97-Ti B2 composite exhibit excellent room temperature mechanical properties.The 3wt.%Ti B2 composite has a tensile strength of 998.3MPa and a yield strength of 715.9MPa.The yield strength is increased by 7.4% compared with the alloy,,the elongation is decreased.Through the analysis of the fracture at room temperature bending test,the introduction of the network structure,the particles at the grain boundary have a good impediment to the crack growth,so that the crack only develops in the direction of the force,and does not expand in other directions.High temperature tensile performance test,650? high temperature tensile,the tensile strength of the composite material reached 1103 MPa,far higher than the alloy's 904 MPa,an increase of 22%,the yield strength was 822.6MPa,an increase of 14.2% compared with the alloy Slightly improved;750°C high temperature stretching,the composite's tensile properties are better than FGH97 alloy in all aspects,tensile strength increased by 22.5%,yield strength increased by 130.9MPa,elongation has increased.At 850°C,the strength of the composite material decreased rapidly,with a tensile strength of 756.2 MPa and a yield strength of 673.1 MPa,both higher than the alloy.The network structure makes the composite material have better ability to maintain performance at high temperature.Subsequent secondary hot pressing of the composite,the material after the secondary hot pressing has no obvious holes,the network structure changes slightly,and the grain size is well controlled.In terms of mechanical properties,the yield of the composite yields ahead of time due to work hardening,and the yield stage is longer.In terms of elongation,the 1wt.% Ti B2 composite after secondary hot pressing can reach 8%,which is similar to the elongation of the original alloy,the yield strength and tensile strength are higher than the alloy.The tensile strength can reach 1159.2MPa,which is 13.7% higher than that of the alloy,14.5% higher than that of the sintered composite,and the yield strength can reach 864.6MPa,which is 14.2% higher than that of the alloy,5% higher than that of the sintered composite material.