Effect of casting wall thickness on microstructure and mechanical properties of K439B superalloy

This work studies the microstructure and mechanical properties of K439B nickel-based superalloy castings with a wall thickness of 1-10 mm. The results show that the melt feeding capacity in thin-walled castings is poor， there are many shrinkage porosity in the 1 mm and 3 mm thin-walled castings， and the 10 mm thick-walled casting has the lowest porosity. Due to the increase of melt solidification rate， all of the secondary dendrite arm spacing， grain size and γ' phase size of the castings increase with the increase of thickness. The tensile tests at room temperature show that the mechanical properties of thin-walled castings are significantly affected by the evolution of microstructure. Due to the synergistic effect of the fine grain strengthening mechanism and precipitate shearing mechanism， the 1 mm thick casting exhibits the highest ultimate tensile strength （1037 MPa） and elongation to fracture （5.6%）.The 3 mm thick casting shows the poorest tensile strength and ductility，with values of 890 MPa and 4.1%， respectively， which can be attributed to its highest porosity level and the resulting severe stress concentration. Although the coarsening of grains and γ' phase reduces the grain boundary strengthening effect of the 10 mm thick casting， the reduced porosity and limited dislocation localization effectively impede the crack propagation，thereby preventing a pronounced deterioration in elongation to fracture.