Precipitation-Strengthened Fe-Ni-Based Austenitic Alloy Grain Boundary Composition Segregation And Corrosion Resistance

Precipitation-reinforced Fe-Ni-based austenitic alloys are widely used in aerospace,navigation and other fields for their excellent resistance to high temperature,corrosion and high fatigue strength,and are most widely used in engine blades.Along with the continuous progress of China’s aerospace technology,the engine blade has also put forward higher performance requirements,of which corrosion resistance is one of the key alloy performance requirements.In this paper,the twin grain boundary and grain boundary composition deviations of the solid solution Fe-Ni-based austenitic alloy are investigated after treatment at the same aging temperature and different aging times;followed by electrochemical corrosion tests to study the effect of aging treatment at different times on the alloy’s resistance to intergranular corrosion and pitting corrosion resistance,providing the necessary theoretical basis for improving the corrosion resistance of the alloy.The results of the study indicate that:twin grain boundaries and grain boundary composition bias are prevalent in the solid solution Fe-Ni-based austenitic alloy,and the composition bias at the interface between the two sides of the same twin grain is inconsistent,with one side showing a single element enrichment and the enriched element types being Ni,Al,C;the other side showing a single element depletion and the depleted element types being Ni,Al,Mo,Si,C.The grain boundaries show element depletion and the depleted element types being Ni,Al,C.The same Fe-Ni-based austenitic alloy in solid solution at 740°C was characterized for the same twin grain boundary or grain boundary component segregation by cumulative aging for 2 hours,4 hours,8 hours and 16 hours.It was found that with the increase in aging time,the component segregation phenomenon weakened and the segregated element species decreased,w here the twin grain boundary depleted element species were only Ni and Al at 16 hours of aging,and the segregation of Al elements on the enriched side basically disappeared.Only the Ni element is more obvious at 16 hours of ageing.When the aging time was extended,the γ′ precipitation strengthening phase[Ni3(Al,Ti)] began to precipitate along the twin grain boundaries and grain boundaries in an orderly manner,and after aging up to 16 hours,the γ′ phase was densely arranged in the twin grain boundaries and grain boundaries in an orderly manner,indicating that the precipitation and growth of the γ′ phase may be related to the weakening of the bias of the twin grain boundaries and grain boundary components when the aging time was extended.The Fe-Ni-based austenitic alloy in solid solution and after different aging times at 740°C was analysis for its resistance to intergranular corrosion,and it was found that the solid solution alloy had no reactivation peak and the passivation interval was the largest,with the best resistance to intergranular corrosion;as the aging time increased,the reactivation peak began to fluctuate,the passivation interval decreased and the corrosion tendency increased.The pitting resistance of the alloy was characterized and found to be much higher in the solid solution state than in the ageing state because the passivation film formed on the surface of the alloy in the passivation interval is the densest,i.e.the number of oxygen vacancies and ionic vacancies on the surface is the lowest,resulting in the greatest resistance to electron and ion transfer.