Forming and growing mechanisms of homogenization-solution pores in a single crystal superalloy

The forming and growing mechanisms of homogenization-solution pores in a single crystal superalloy were investigated. The microstructures were observed with optical microscope (OM) and field emission microscope (FEM) after homogenization-solution heat treated at 1328 °C and 1350 °C for 2 h, 6 h and 9 h. Results indicate that when heat treated at 1328 °C, pores appear at the interface of eutectic and matrix at first and then leave in the matrix with the shrink of eutectic. When heat treated at 1350 °C, incipient melting happens at first, and some of them have a pore in the center. After that, with the homogenization-solution process, incipient melting microstructure fades away gradually. By analyzing the results with thermodynamics and kinetics methods, it is concluded that some pores nucleate during directional solidification and then become larger and visible during homogenization-solution heat treatments; some pores are generated by incipient melting, yet such pores are difficult to be distinguished from other pores; imbalanced elements cross-diffusion induces to the forming and growing of pores too, and such imbalanced diffusion also plays an important part on the growth of all preexisting pores.