Study Of Casting Structure In Superalloy Blade Made By Precision Casting And Optimization Of Heat Treatment

The K444nickel-base superalloy we studied in this paper is used for gas turbine blade. Because of its extremely working condition, the material for blade need stricter requirement for their performance. The materials must have certain intensity, corrosion resistance and long lasting performance at medium and high temperature. This excellent performance must be supported by controlling the microstructure of the alloy. The purpose of this article is to study the organization of casting state, and comparing the organization in different part of the blade. At the same time, the defects in the as-cast structure of the blade was explored, and the structure was optimized by heat treatment.The microstructure and phase components of K444superalloy are observed and analyzed by optical microscopy, scanning electron microscopy and X-Ray diffraction(XRD). It is found that the structure grows in dentrite manner. The structure of different parts are various, the secondary dendrite arm spacing decrease with wall thickness of the blade. The as-cast structure is made up of matrix phase,(y’), carbide phase and eutectic phase (y’+y). The eutectic is harmful for the permanent use of the alloy, the strengthening phase distributes uneven in the microstructure, this leads to dendritic segregation in the alloy.Because of the detects in the as-cast structure, the homogeneity of the structure is poor, it is need to optimize the microstructure by heat treatment. This paper research of the effects of different treatments on the as-cast structure, the result shows that the structure is optimized after the heat treatment. The heat treatment used in the paper concludes solution, primary aging (1050℃,4.5h) and aging(850℃,16h). Compared with the structure, we found the strengthening phase dissolved more with the temperature increasing in a appropriate range(1150℃-1190℃), and the strengthening phase in the structure after the aging process distribute dispersed and homogeneous. The ideal solution temperature is1190℃for this material. The solution time also influences the structure. The structure is more homogeneous with the solution time increasing. The ideal solution time is4.5h. The Mechanical Properties of heat treatment samples are tested.It is that compressive strength increased with the increasing of solution temperature. The strength increased weakly with the increasing of solution time.