Research On Adjusted Pressure Investment Casting For K4169 Superalloy Thin-walled Castings

With the rapid development of aeroengine technology, there are increasing demand for complex thin-walled structure components made by superalloys. All these components are designed to be larger and thinner. Corresponding to the higher requirements of the structure and properties, manufacturing difficulty of traditional gravity casting process is increasing greatly. Adjusted pressure casting process can be a very good solution to produce qualified thin-walled castings and improve the filling and feeding capacity of molten metal, which would greatly reduce casting defects including cold shut and shrinkage porosity. The casting process and solidification structure of adjusted pressure investment casting for superalloy thin-walled castings has been studied through both experimental and numerical methods in this dissertation. With numerical simulation method, the filling process and solidification process of filling sample under adjusted pressure investment casting were studied. To validate the simulation results and study the influence of process parameters on the casting quality, adjusted pressure casting experiments were carried out using process parameters chosen in numerical simulation. An innovative process scheme for superalloy bracket was presented and the casting process, shrinkage porosity distribution and microstructure were predicted. The main results as follows:Firstly, the filling process and solidification process and effect of process parameters on the casting quality of filling sample under adjusted pressure investment casting are studied by numerical method. The results showed that when pouring temperature, preheating temperature and gas flow rate was 1560°C, 955°C and 5kPa/s, the thin walled castings were filled completely. Also the results showed that the increase of as flow rate would improve the filling capacity of molten metal and the increase of crystallization would improve the feeding capacity of molten metal, which would reduce the number of shrinkage porosity defects in the castings.Secondly, adjusted pressure casting experiments were carried out using process parameters chosen in numerical simulation. The results showed that grain morphology of sheet samples from the top to the middle location were all equiaxed and became finer with the grain number increases significantly, while micro structure of the pouring gate position were columnar crystal with same orientation. With the growth of gas pour rate, grain size and hardness of sheet samples were enlarged, the SDAS were reduced; with the growth of crystallization pressure, grain size and SDAS were reduced and hardness were enlarged; with the growth of wall thickness, grain size and SDAS were enlarged and hardness were reduced. The experimental results were complied with simulation results.At last, an innovative process scheme for superalloy bracket was presented and the casting process, shrinkage porosity distribution and microstructure were predicted. The results showed that when pouring temperature, cooling method and gas flow rate was 1610°C, air cooling 10 min and 7kPa/s, the thin walled castings got best quality. Simulation results of macrosegregation and microstructure showed that adjusted pressure investment casting method could manufacturing homogeneous castings.