Effect of alloying composition on solidification microstructure and mechanical properties of TNM-based TiAl alloys

Abstract

It is quite sensitive for TiAl alloy to composition, and the solidification microstructure and mechanical properties may be changed by compositional minor-adjustment. In this paper, two TNM-based alloys with different solidification modes (TNM-45Al alloy and TNM-0.3Si-0.7C alloy) were obtained basing on TNM alloy via two different compositional minor-adjustment routes. Compared with TNM alloy, the effects of compositional minor-adjustment routes on localized segregation, solidification microstructure and compression properties at room temperature were investigated. It is found that the solidification mode of TNM-45Al alloy is still β solidification, compared with TNM alloy, localized segregation is evidently weakened, lamellar colonies are coarsened and solidification texture is strengthened, and the yield strength, compressive strength and fracture strain at room temperature are increased by 14.04 %, 30.21 % and 28.97 %, respectively. And the solidification mode of TNM-0.3Si-0.7C alloy is transformed into peritectic solidification, with regional polarization of localized segregation, rapid coarsening of lamellar colonies and severe strengthening of solidification texture, the yield strength increased by 16.51 % at room temperature, and the compressive strength and fracture strain decreased by 32.01 % and 71.31 %, respectively. It is indicated that the coarsening of lamellar colonies and the intensification of solidification texture of TNM-45Al alloy can be inhibited by the precipitation of TiB, but those of TNM-0.3Si-0.7C alloy can not be restrained by the TiB/Ti5Si3 symbiotic structure found for the first time and the precipitation of TiB. In addition, the change of localized segregation behavior is the main factor for the strengthening and toughening of TNM-45Al alloy, and the solid solution of Si/C atoms is the main factor leading to the embrittlement of TNM-0.3Si-0.7C alloy.