Study of the influence of deformation temperature on the mechanical behaviour and fracturing behaviour of the cast TNM-B1 alloy

The paper covers the study of β-solidifying TiAl-based alloys, which are extremely promising materials for the aviation industry with an operating temperature of up to 850 °C, have high specific strength characteristics. The authors studied the influence of tensile deformation temperature in the range of T=25–1000 °C on the mechanical properties, phase composition and crack formation in the cast β-solidifying TNM-B1 alloy. It is found that the cast TNM-B1 alloy is characterised by a complex microstructure, including (α2+γ) lamellar colonies and interlayers of β(B2)+ω phases, the evolution of which at elevated deformation temperatures determines the material behaviour. It is shown that the ω-phase dissolution and the precipitation of dispersed secondary β-phase particles at T>950 °C have a significant influence on the mechanical characteristics. A pronounced temperature dependence of strength and ductility is identified: the maximum strength is observed at 800 °C, while the greatest relative elongation in the studied temperature range is achieved at 1000 °C. The transition from brittle to viscous fracture occurs in the temperature range of about 950 °C. Moreover, a dependence of the crack propagation mechanism on the orientation of lamellar colonies relative to the deformation axis is revealed: with an increase in temperature, the differences are leveled, and at 1000 °C, complete suppression of crack formation with the formation of pores along the boundaries of colonies and clusters of secondary β-phase particles is observed. The obtained results demonstrate the important role of microstructural transformations in the formation of deformation behaviour and mechanical properties of the TNM-B1 alloy based on gamma-titanium aluminide, which is of practical importance for the development of technologies for its thermomechanical processing.