The Fundamental Research Of Vacuum-assisted Low Pressure Casting Process For Nickel-based Superalloys

The superalloys have the characteristics of high melting point,high density and high viscosity,its precise castings develop towards thin wall,complicated structure and near net shape,and widely applied to aerospace fields.The counter-gravity casting technologies,including low pressure casting,suction casting,counter pressure casting,adjusted pressure casting and so on,have excellent filling and feeding capacities and are appropriate for producing complicated and thin-walled superalloy castings.In foreign countries,the counter-gravity casting technologies for superalloys have become mature,and a large number of high quality complex thin wall castings have been produced.In China,the research of counter-gravity casting technologies for superalloys has started late and its development and application is still restricted by technological equipment,such as the stalk,and is still in the exploration stage.Based on the engineering background described above,the basic research work of vacuum-assisted low-pressure casting of nickel-based superalloys such as K4169 was carried out.Firstly,developing the material and preparation technology of the stalk,a kind of ceramic stalk with good thermal shock resistance and chemical stability was developed for vacuum-assisted casting of superalloys.Secondly,aiming at present situation that the interfacial heat transfer coefficient(IHTC)is only set as a constant value for the traditional numerical simulation of investment casting,the IHTCs between the K4169 alloy and ceramic shell mold were obtained through ProCast inverse computation module and the temperature measured from different positions with different thicknesses of the test sample.The IHTCs were applied to the numerical simulation of the test sample,and the results show that the error between calculated temperature and measured temperature is less than 3%.Finally,a complete turbine blade of K424 superalloy was obtained through process test,which verified the feasibility of the vacuum-assisted low pressure casting process flow.When the interfacial heat transfer coefficient,which obtained through temperature measuring and inverse computation,was used as a close heat transfer boundary condition,the positions of the shrinkage hole and porosity were accurately predicted.