Investigation Of High Strength Superalloy Used For Investment Casted Combustor Casing Of High Thrust-Weight Ratio Aeroengine

Latest high thrust-weight ratio aeroengine put forward higher requirements for enduring temperature of the structure material of the combustor casing.Inconel 718,among with the substituted alloys,couldn't meet the requirements of the latest high thrust-weight ratio aeroengine. Therefore,there is an urgent demand for the research and development of a kind of high-strength nickel-based cast superalloy,which should acquire the stability of microstructure and mechanical properties up to 700℃,and the yield strengthes of more than 1000MPa up to 700℃.Based on Inconel 718C and Rene 220,series of modified chemical compositions were designed through theoretical calculation and experiments. Effects of casting procedures and heat-treatment procedures on microstructures and mechanical properties,as well as effects of elements adjustment on mechanical properties,microstructure evolution and hardening behavior during long term exposure,were systematically investigated in experimental alloys.The results are showed as below.(1)Replacing Nb with same atom percent of Ta,improved strengthening effects and microstructure stability were obtained.With the same(Nb+Ta/2) %wt,increased Ta led to remarkable improvement of the tensile properties, stress-rupture properties,stability ofγ" and retarded precipitation ofδ.Also, the hardness peak,which occurred in the alloy with lower Ta%wt, disappeared in the alloy with higher Ta%wt.On the other hand,increased (Nb+Ta/2)%wt decreased the microstructure stability of the experimental alloy.With the same Nb%wt,increased Ta%wt improved the tensile and stress-rupture properties remarkably,while it decreased the stability ofγ" and accelerate the precipitation ofδ,and advanced the occurrence of hardness peak during ageing at 700℃.(2)With the same Mo%wt,increased W%wt show no evident improvement on tensile and stress-rupture properties,while it decreased the stability ofγ" and accelerate the precipitation ofδand the occurrence of hardness peak during ageing at 700℃.On the other hand,with the same(Mo +W/2)%wt,increased W led to remarkable improvement of the tensile properties,stress-rupture properties.In some extent,the precipitation ofδwas accelerated,while it was not as remarkably as that of the alloy with increased (Mo+W/2)%wt.And the hardness peak disappeared,which showed acceptable microstructure stability.(3)The alloy with increased Ti%wt showed evidently higher tensile strength at both room temperature and 700℃,decreased stress-rupture properties at 700℃,lower stability ofγ",accelerated precipitation ofδand hardness peak.Increasing Al%wt decreased the stress-rupture properties, while it showed no evident change on tensile properties,microstructure stability and aging hardening behavior.(4)Ni_56.415Cr_18.0Co_12.0Al_0.5Ti_1.0Nb_3.0Ta_5.0Mo_2.0W_2.0B_0.02Y_0.05C_0.015was the eventually chosen chemical composition.Its yield strength at 700℃exceeded 1000MPa,which was superior to that of Inconel 718C at 650℃.Comparing to Rene 220,experimental alloy also showed obvious advantage in properties: 35%and 29%improvement of yield strength and tensile strength at 25℃, 34%and 27%improvement of yield strength and tensile strength at 700℃and 355%improvement of stress-rupture life at 700℃/620MPa.Also,the modified alloy could maintain its mechanical properties even after long-time exposure at 700℃for 1000 hours.