Effect Of Heat Treatment System On Microstructure And Properties Of DD6 Nickel-based Single Crystal Superalloy

Nickel-based single crystal superalloys are widely used in the manufacture of turbine blades in ground aviation engines due to their excellent high temperature oxidation resistance and good corrosion resistance.The advantages and disadvantages of turbine blade performance are extremely important technical indicators of the engine level,and its materials and preparation technology represent the level of a country in the aviation field.Therefore,how to improve the service life of engine turbine blades under high temperature and high pressure has become the most important issue.The??phase is a strengthening phase precipitated on the?matrix,and is completely coherent at the same time.They form the microstructure of the single crystal superalloy together.And the distribution,size,number,and morphology of the??phase can be used to achieve the optimal state through heat treatment and the alloy can obtain the best mechanical properties finally.In this test,the as-cast DD6 alloy in the[001]direction was prepared in a high-gradient vacuum induction directional furnace by a spiral crystal selection method.First,the as-cast DD6 alloy was subjected to standard heat treatment,that is,a solution heat treatment plus two aging heat treatment.The single crystal specimens after standard heat treatment were placed at 900-1300? for 10min,30min and 1h respectively.Observing the microstructure of alloys after different heat treatments,it is concluded that there is no secondary precipitation of?'phase in the alloy after standard heat treatment.After holding at 900-1200?,the size of?'phase gradually increases with temperature.However,the size of the?'phase obtained after holding at 1100? for 30 minutes was moderate,and after holding at 1100 and 1200?,secondary?'phase began to appear in the matrix.When the alloy is kept at 1300?,all of the?'phase is dissolved back into the matrix,and it is re-precipitated into a new?'phase during the cooling process.In the atmospheric environment,the three alloys that were kept at 1100? for 10min,30min,and 1h were subjected to high-temperature oxidation tests at 900?/125h and1000?/125h.The study found that no matter which temperature,XRD phase analysis after holding at 1100?for 30min showed that the oxides were mainly NiO,Al₂O₃,Co₃O₄ and CrTaO₄.EDS analysis found a certain amount of oxides of Ni,Al and Cr.The proportion of the inner layer of the oxide film is small,dense and continuous distribution,and the proportion of the outer layer is cracked,distributed in a loose porous shape.High temperature creep tests were performed on the alloys after standard heat treatment and 1100? for 30 min after standard heat treatment under the conditions of 760?/785MPa and 980?/250MPa.The alloys were found to have an effect on the creep properties in the temperature range.The study found that the creep experiment of the??phase has a negative effect on the creep deformation and distortion,and the existence of the secondary??phase has a negative effect on the creep life.However,the creep life of the alloy is within the normal fluctuation range.