GH720Li alloy wear-resistant plate has high operating temperature and high temperature strength, and is the preferred material for high-performance deformed turbine disk around 750℃. Widely used in foreign aero engines, such as Rolls-Royce BR700 and Allison company's GMA2100, GMA3007, T406, T800 and other high-performance aero engine turbine disc, in our country a large number of high performance gas turbine disc materials.
The excellent performance of GH720Li alloy wear-resistant plate is mainly due to its fine crystal structure, the volume content of the strengthened phase γ' phase up to 50% and the reasonable matching of various sizes γ' phase, and the precipitation strengthening effect of γ' phase is especially important for the mechanical properties of GH720Li alloy wear-resistant plate. Because the nucleation and growth of γ' phase are extremely sensitive to the cooling rate after solution treatment, the cooling rate is closely related to the choice of cooling medium during solution cooling of disc forgings. In order to ensure the high performance, high stability and long life of batch gas turbine disks under service conditions, the researchers systematically studied the effects of three kinds of cooling media (air, oil and water) on the microstructure (mainly γ' phase) and mechanical properties of GH720Li alloy wear-resistant plate, providing a reference for optimizing heat treatment process parameters.
The test material was cut from the GH720Li alloy wear-resistant plate forging prepared by isothermal forging. The average size of the wrought original grain of the wear-resistant plate of GH720Li alloy used in the test is about 10μm(ASTM9-10 grade), and the distribution is uniform. The primary γ' phase of about 1 ~ 5μm is evenly distributed on the grain boundaries, and the cooled γ' phase below 500nm is dispersed in the crystal. The γ' phase precipitated during the cooling process after forging is dissolved back in the solid solution process. The γ' phase is then precipitated again during solution cooling and subsequent aging.
The samples were cut from the wrought disc of GH720Li alloy wear-resistant plate along the string by wire cutting. The samples were held in solid solution at 1090℃ for 4h, and then air-cooled, oil-cooled and water-cooled respectively to complete the solid solution treatment. Then the samples were uniformly aged (650℃×24h, AC+760℃×16h, AC). Used for grain size observation, γ' phase observation and typical mechanical properties (room temperature and 650℃ tensile properties) test. The test results are as follows:
(1) According to the test conditions, the cooling method has no effect on the grain size and primary γ' phase of GH720Li alloy wear-resistant plate; The cooling medium mainly affects the cooling γ' phase (secondary and tertiary γ' phases) precipitated during the solution cooling process. With the increase of cooling rate, the average size of the tertiary γ' phase which plays the main strengthening role is air cooled > oil cooled > water cooled, and the tertiary γ' phase density is air cooled < oil cooled < water cooled.
(2) With the increase of cooling rate, the room temperature and high temperature strength of GH720Li alloy wear-resistant plate are successively air cooled < oil cooled < water cooled, and the plasticity is successively air cooled > oil cooled > water cooled. The changes of strength and plasticity are closely related to the density and size of the three γ-phases precipitated during the solution cooling process.
(3) Under the premise of ensuring the strength and plasticity of the GH720Li alloy wear-resisting plate, oil cooling should be used after solution to reduce the risk of disk distortion or even cracking caused by thermal stress.
