Effect of solution cooling medium on microstructure and mechanical properties of high quality GH738 alloy
GH738 alloy, corresponding to Waspaloy alloy of the United States, is a typical Ni-base deformation superalloy strengthened by γ 'phase precipitation. It is widely used in aerospace, petrochemical and other hot end parts because of its good strength and toughness matching, strong fatigue creep interaction and high temperature long-term stability. At present, GH738 alloy is widely used in ground smoke turbine disc and blade materials. In recent years, while developing new deformation superalloys, a series of process optimization of old alloys such as GH738 has been developed to meet the requirements of high pressure, high temperature, high speed and other harsh service conditions of aeroengine turbine disc.
The researchers studied the effects of different solution cooling media (oil, air, cotton) and subsequent aging treatment on the microstructure and mechanical properties of high-quality GH738(HQGH738) alloys. The grain structure and γ 'phase distribution were observed by optical metallography microscope (OM) and field emission scanning electron microscope (FESEM), and the tensile strength was measured.
The results show that the cooling medium has no effect on the grain size of HQGH738 alloy, but mainly affects the re-dissolution and precipitation behavior of primary and secondary γ 'phases, and then affects the properties of HQGH738 alloy. In the solid solution stage, with the increase of cooling rate (oil quenching > air cooling > cotton cooling), the secondary γ 'phase in the alloy decreases, and the smaller the size, the tensile strength of the alloy decreases. After the stabilization treatment, the strength order of the alloy under the three cooling methods remains unchanged, but the difference decreases. After double aging, the tensile strength of the three is equivalent. The faster the cooling rate, the slower the coarsening of primary γ 'phase, so that more fine secondary γ' phase is precipitated during the double aging process, and the yield strength of the final alloy increases with the increase of cooling rate.
