Study On Electromagnetic Confining & Directional Solidification And Structural Characteristics Of γ-based TiAl Intermetallic

The purpose of this paper is to describe and analyze firstly the processing of contactless electromagnetic shaping of y-based TiAl intermetallic. Directional solidification characteristics of successfully shaped y-TiAl alloys is then presented and investigated in relation with the experimental parameters. To do this, directional solidification experiments without pollution of y-TiAl alloys were made on the experimental apparatus designed by ourselves through Electromagnetic Confinement & Directional Solidification processing using a selected Ti-48A1 alloy as research object, Detailed issues include two main aspects as follows:1. Exploring contantless process of directional solidification microstructure preparation of y-based TiAl intermetallic by stabilized electromagnetic shaping. Based on the achievement of contantless solidification procedure of stainless steel samples, the shaping system composed of inductor and screen for y-TiAl alloys is established and optimum temperature gradient and solidification rates are took into account. Thus, on the foundation of stable shaping of y-TiAl metallic molten in electromagnetic confinement, directional solidification of Ti-48Al(at.% ) samples without pollution is obtained by using the protocol described aboved.2. Identifying solidification characteristics of y-TiAl alloys under the conditions of sub-rapid directional solidification. Using modified directional solidification processing with mold, the influence of experimental parameters such as solidification rates on competition and choice of stable and metastable phase and the growing morphologies of solidification interface and so on is discussed. Besides, influence mechanism is analyzed subsequently, and desired processing parameters for controlling crystal structure are provided.In conclusion, by means of the above studies we are expected to achieve desired shapes with cleanish surface and directional solidification microstructure of y-TiAl alloys with circular section. Solidification regulations and their mechanisms of peritectic y-TiAl alloys are clarified basically. It is found that owing to low density, molten TiAl alloys are prone to be driven by intense electromagnetic stirring during EMC process, yet by controlling the processing parameters properly such as electric current intensity, drawing velocity and S/L interface position etc., electromagnetic shaping stability without contact can be performed. In addition, the interface morphology of y-based TiAl peritectic alloys evolves from cell to dendrite with the increase of solidification rate on the basis of the constant temperature gradient. Meanwhile, the primary phase also evolves from stable phase to metastable phase.Theprimary dendrite arm spacing decreased with increasing growth rate according to relationship λ1=K2V-0.25GL-0.5 , and the interlamellar spacing decreased withincreasing growth rate according to the relationship λ∝ 3.9x10-9V-0.46. Furthermore, the volume fractions of a2 and r phase can be changed with increasing solidification rate.