| Nb-Si alloy has the characteristics of high melting point and low density.It has great potential in replacing the traditional Ni-based superalloy material and applying it to the turbine blade of a new aeroengine with high thrust-weight ratio.The results show that Nb-Si alloy has poor room temperature fracture toughness and high temperature oxidation resistance,so it can not be directly used as blade material.However,Nb-based alloys have good solid solubility for many elements,so their properties can be improved by alloying.In view of the deficiencies of Nb-Si-Ti alloy in fracture toughness and high temperature properties,this paper studies the composition optimization of Nb-Si-Ti-Mo-Hf-Al-Cr superalloy,studies the changing rules of composition and structure of different alloys at different temperatures,and then realizes effective control of structure,analyses the fracture toughness and high temperature mechanical properties of Nb-Si-Ti superalloy at room temperature,so as to obtain Nb-Si-Ti superalloy materials with superior comprehensive properties.Therefore,it will play a certain role in promoting the thrust-weight ratio of aero-engine and the development of materials application in other high temperature environments.Because we find that the fracture toughness at room temperature of Nb-17Si-20Ti-4Hf-8Ta-2Al-2Cr is as high as 12.8194 MPa·m1/2.In this paper,Mo element is used instead of Ta to study the optimum composition of Nb-Si-Ti-Mo-Hf alloy by orthogonal test.By observing the microstructure of Nb-Si-Ti-Mo-Hf based alloy with different composition,it was found that the structure of Nb-Si based alloy with different alloy element content was significantly different in phase morphology,size and distribution,and the eutectic structure was composed of Nbss and Nb5Si3.Elements Si and Ti can play the role of eliminating Nb3Si of metastable phase,and Ti can promote the transformation from?-Nb5Si3 to?-Nb5Si3,and Mo play the role of stable?-Nb5Si3,and Hf can effectively refine the primary phase.The fracture analysis of fracture toughness at room temperature shows that Nbss phase is plastic fracture,siliceous phase?Nb5Si3?is brittle fracture,at the same time the primary phase of A-6 alloy?Nb-16Si-22Ti-5Mo-3Hf-2Al-2Cr?with the best toughness is granular,and its eutectic structure is fine floral eutectic.The high temperature compression experiments show that A-5 alloy?Nb-16Si-20Ti-15Mo-1Hf-2Al-2Cr?with high Mo content and low Hf content has the maximum high temperature compression strength,and the plastic deformation stage of Nb-Si-Ti-Mo-Hf alloy is very short in the comoressing progress.When Nb-Si-Ti-Mo-Hf alloy is oxidized,Nbss is firstly oxidized,Silicides are more resistant to oxidation,and the oxidation products include Nb2O5,TiNb2O7,TiO2,HfO2 and so on.Hf element can effectively improve the oxidation resistance of the alloy.According to the test results of orthogonal test,the orthogonal range analysis method was adopted to calculate the optimized alloy?Nb-16Si-20Ti-5Mo-3Hf-2Al-2Cr?,After ablation of optimized alloy.The two-phase microstructure of the optimized alloy is relatively small,and the mechanical properties are excellent,especially the oxidation resistance is significantly improved.It is found that the ablation mechanism and mechanical ablation is mainly sublimation in the ablation center area,while the ablation edge area is mainly characterized by oxidation of the alloy.At the same time,singlely change the content of Si and Hf to get two ingredients alloys on the basis of optimizing the alloy,and tests their properties in all aspects.The results show that the optimized alloy has the best comprehensive properties. |
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