Effect Of Heat Treatment On Microstructure And Mechanical Properties Of Novel Ni-based Superalloy

With the increasing thrust-weight ratio of aerospace engines,the temperature before the turbine is getting higher and higher,which requires the new turbine disk alloy to have to have more excellent comprehensive mechanical properties.Because the actual working conditions of the turbine disk are very complex,a high-performance superalloy is needed.Therefore,a new type of nickel-based superalloy is designed and developed as a material for turbine disk.The new nickel-based superalloy is a kind of superalloy by solid solution strengthening,precipitation strengthening,fine grain strengthening and microtwins strengthening.The strengthening phase of precipitation phase strengthening is γ′ phase,and its suitable size,morphology,quantity and distribution can make the alloy have good comprehensive mechanical properties.Therefore,the suitable heat treatment process is the key factor to obtain the ideal microstructure and mechanical properties of the alloy.In this paper,the new nickel-based superalloy was taken as the research object.The effects of heat treatment process on the morphology,quantity,size and distribution of the strengthening phase γ ′ phase of the new nickel-based superalloy were systematically studied by OM,SEM,EBSD,TEM and other characterization methods.The relationship between heat treatment process parameters,microstructure and mechanical properties was established.The evolution of mechanical properties and deformation mechanism of the novel nickel-based superalloy at intermediate temperature was studied.The main conclusions are as follows :1.With the increasing solution temperature from 1060 °C to 1130 °C,the microstructure of the novel nickel-based superalloy can be divided into the following three types: a finegrained microstructure dominated by the γ′ phase,a transition-zone microstructure dominated by the γ′ phase and twins,and a coarse-grained microstructure dominated by twins.The superalloy treated with solution temperature at 1080 ℃ exhibit the highest tensile strength due to the increase in the size and area fraction of the secondary γ′ phase and the combination of various strengthening mechanism.2.At room temperature,the tensile reinforcement mechanism of the novel nickel-based superalloy after 1130 ℃ solution treatment is the deformation mechanism of the slip band,and the tensile strength decreases with the increase of tensile temperature.In the tensile test conducted at 750 ℃,the deformation mechanism was the interaction between microtwins,SFs and γ′ phase.At room temperature and 750 °C,the tensile fracture mechanism of the new nickelbased superalloy is similar,both of which change from ductile fracture mechanism to ductilebrittle mixed fracture mechanism.3.The novel nickel-based superalloy after 1080 ℃/4 h/AC+650 ℃/24 h/AC+760 ℃/16h/AC of double-stage aging heat treatment,the γ′ precipitates is bimodal in size to obtain higher hardness.4.The suitable size,morphology,quantity and distribution of the γ′ phase can be adjusted through the heat treatment system to achieve the purpose of adjusting the mechanical properties of the novel nickel-based superalloy.5.After solution treatment at 1080 ℃,the yield strength and elongation rate of the alloy were 1176 MPa and 22.5 % respectively at room temperature.At room temperature,the main deformation mechanism is that a large number of dislocations slip,and the partial dislocations shear the γ′ particles into isolated stacking faults.When the temperature reaches 650 ℃,it is observed that microtwins shearing through the secondary γ′ particles and γ matrix,and the continuous stacking fault shearing secondary γ′ particles and γ matrix deformation.At 700 ℃-750 ℃,the secondary γ′ particles and the γ matrix are sheared simultaneously by continuous stacking faults and microtwins,and the density of stacking faults and microtwins increase with temperature.In the 650 ℃-750 ℃ range,the mechanism for shearing a γ′ particles once transitions from APB to isolated stacking faults.