| Nickel-based single crystal superalloy is widely used as the preferred material for advanced aeroengine turbine blades because of its excellent high temperature performance and structural stability.Its innovation and manufacturing level are an important reflection of national core competitiveness to measure national economic development and national defense security.China's long-term innovation model,which relies on experience accumulation and cyclic trial and error,often leads to a longer cycle and a higher cost.In recent years,the Material Genome Project(MGP),which is based on high-throughput characterization of a large number of material samples at different scales,can not only provide digital data for the material performance and structure database,but also verify the correctness of the theories and models used and shorten the development cycle of new materials.Therefore,the study of quantitative characterization of the structure and the relationship between composition,structure and properties of new single crystal superalloys can not only lay a foundation for the process and application research,but also provide data support for the establishment of a rich material database.In this paper,metallographic microscopy,scanning electron microscopy(SEM),electron probe(EPMA),nanoindenter and stress-rupture machine are used to characterize the microstructure parameters of ?' phase,? matrix,carbide and(?+?')eutectic by quantitative metallographic characterization techniques.The effects of heat treatment and W element on the evolution of composition,structure and properties of single crystal superalloys were studied by combining the composition distribution and the macro and micro mechanical properties of materials.A three-dimensional reconstruction method for dendrites of single crystal superalloys was established preliminarily.The results show that:1)The dendritic segregation of the alloy was effectively reduced by heat treatment,which has the greatest influence on Hf,Ta and W elements,the segregation degree is reduced by 167%,28.1%,12.9% respectively.In the ? and ?' phases,the average segregation ratios of Al,Cr,Co and W decreased by 26.12%,16.18%,9.08% and 20.91%,respectively.The average segregation ratios of Ta and Re increased by 21.18% and 45.98% respectively.After heat treatment,petal-shap and plate-like(?+?')eutectic structure disappeared basically;strip and granular carbides were decomposed into small blocks or particles,and the content of carbides decreased from 0.2% to less than 0.1%.The morphology factor of the particles is close to ?2 and the average size is about 0.4 um.At the meantime,the cubic degree and homogeneity of the particles increase,and the volume fraction is close to 60%.The elastic modulus of the alloy is close to 230 GPa,and the hardness is about 4.5 GPa.Heat treatment has no effect on the nanoindentation properties.2)The increase of W content leads to the aggravation of element segregation of dendrite and interdendritic in as-cast alloys.The W element is the most and the degree of segregation is increased by 41.2%.After heat treatment,the diffusion of alloying elements is more uniform,with the greatest effect on Re and W decreasing by 10.7% and 11.1% respectively.The segregation degree of Re and Al to ? phase in as-cast structure increased by 25% and 60% respectively,while that of Co and Cr to ?' phase increased by about 20% and the distribution ratio of W remained basically unchanged.After heat treatment,the segregation of Re,Al and Co to the ? phase remained basically unchanged,and the segregation of W element in the ? phase increased by 85%.With the increase of W content,the primary dendrite spacing decreases by 17.68 um,(?+?')eutectic structure content increases by 1.5 times,and a small amount of plate-like(?+?')eutectic still exists after heat treatment.The increase of W content has little effect on the morphology and content of carbides and the width of gamma channel.The volume fraction of the ?' phase increases by 10%.The ?' phase particles have larger size(0.44 um),uniformity and cubic degree.W element has little influence on the nanoindentation properties of the micro-area.3)After the stress-rupture test,the structure of the two alloys is rafted.The rafting integrity of the alloys with high W content is closer to 1,and the topological inversion coefficient is greater than 1.The ? phase is replaced by the ?' phase as the continuous phase.W element promotes the rafting process of the alloys.The content of precipitated TCP phase is about 1%,and most of them are granular,which has little effect on the properties of the alloys.The creep rate decrease caused by dislocation climbing mechanism and the solution strengthening caused by W element make the alloys with high W content have good durability at 1037°C,173 MPa/200 MPa/220 MPa.The alloys with high W content still have 63.33 h stress rupture life at 220 MPa.However,both elongation and section shrinkage of the alloy are reduced.4)The three-dimensional morphology of dendrites of two alloys with different W content was reconstructed by continuous slicing technology.The detailed steps and experimental parameters of continuous slicing were described.And the post-image processing and threedimensional reconstruction were also explained. |
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