Influence Of Geometrical Parameters Of Spiral Selector On Grain Selection By CAFE Method

Because grain boundaries is eliminated and the source of cracks is reduced, the thermal fatigue property, heat corrosion resistance and creep resistance of Ni-base single crystal superalloy have been significantly improved. Today, this superalloy has become the important material for producing aero engine blades. Ni-base single crystal superalloy is the face centered cubic crystal. The <001> crystal has the best mechanical properties in its <100>,<001>, <010> crystal orientation. Therefore, the way to make the <001> crystal orientation of single crystal and the principal stress axis in the same direction has become one of the key technologies of vane control.In this paper, the CAFE method is used to simulate the process of preparing the second generation of Ni-base single crystal superalloy by spiral selector. The simulation results of direct type, columnar type and compound type spiral selector are compared. And the influecce of geometrical of starter and spiral part on effect of grain selection is discussed. Conclusion are as follows:(1) The function of starter is to optimize the grain orientation. Selection of grains in starter mainly controlled by two factors: competitive growth at early stage of grain selection and geometry shape at later stage of grain selection. The effect of spiral part is to select a single crystal grain. It has no influence on orientation optimization. The grain selection in spiral part is only related with the location. The grain that located inside of spiral channel always will be selected as the final single crystal.(2) For the direct type, columnar type and compound type spiral selector, efficiency of grain selection of direct type spiral selector is the best, the columnar type is poor and the compound type is worst. The quality of grain selector of columnar type spiral selector is the best, the type is poor and the compound type is worst. The quality of grain selection increase with the hight of columnar transitional portion.(3) The reduction of diameter and increase of height of starter can improve optimizinggrain orientation. So that, the deviations orientation angle of grain that will grow into spiral part are small and the final single crystal selected to meet the requirements. But too small diameter and too large height also can make the grain number of grain that grows from starter to spiral part is less. The spiral part can not play its preferred role. According to the simulation results, the diameter of the seeded segment design in 24 ~ 30 mm, height design within 30 ~36mm is appropriate.(4) The geometrical parameters of spiral part, such as take-off angle, diameter of spiral part and diameter of helixes of spiral part, has no role on optimization of grain orientation.And this parameters have a significant impact on the efficiency of grain selection. With the increase of diameter of spiral part and the decreasing of take-off angle or diameter of helixes of spiral part, the efficiency of grain selection improved obviously. According to the simulation results, the take-off angle design should be within 25~35°, diameter of spiral part should be designed in the 11~16mm, the diameter of helixes of spiral part should be designed within 4~6mm, for the design of spiral part.