Study on the nucleation mechanism of carbonitrides on LaAlO3 in GH4742 superalloy

Abstract

In this study, focused ion beam (FIB) and transmission electron microscopy (TEM) were used to investigate the morphology, composition, crystal structure, and phase interface growth orientation of the LaAlO3-Ti(C,N)-(Ti,Nb,Mo)C complex inclusion in GH4742 alloy. Based on the theory of lattice mismatch and the thermodynamic model of inclusion formation, the formation mechanism of composite inclusions was studied. Crystallographic analysis showed that Ti(C,N) grew on the LaAlO3 substrate, and its growth was restricted by the parallel orientation relationship with the LaAlO3 substrate. The (0006¯)LaAlO3//(1¯11)Ti(C,N) was the lowest lattice mismatch plane between the two phases, with a 1D lattice mismatch of 9.68% and a 2D lattice mismatch of 10.05%. The distance difference between two parallel planes was compensated by dislocations and lattice distortions. Ti(C,N) had lower lattice mismatch with TiC and LaAlO3, making it easier to grow on the LaAlO3 nucleus. Thermodynamic calculations indicate that oxides exist in solid form within the molten alloy. As the temperature decreases, TiN precipitates in the alloy melt, while TiC precipitates during the solidification process. These results provide an explanation for the formation process of the complex three-layer structure of the complex inclusions.

Keywords

• GH4742 alloy
• Complex inclusion
• Lattice mismatch
• Thermodynamic