The continuous dynamic recrystallization(CDRX) through a progressive transformation of a subgrain structure into a grain structure with the increasing of misorientation occurred in the hot deformation of titanium allo...The continuous dynamic recrystallization(CDRX) through a progressive transformation of a subgrain structure into a grain structure with the increasing of misorientation occurred in the hot deformation of titanium alloy. A grain size model for CDRX of titanium alloy in hot deformation considering work hardening effect, dynamic softening effect and non-homogeneous deformation effect was established. The β grain size was described as functions of the deformation temperature, strain rate and strain by using the dislocation density as an internal state variable. The inside dislocation storage and dislocation annihilation,which respectively resulted from work hardening effect and dynamic softening effect, were described by the Kocks-Mecking and Picu-Majorell theories correspondingly. The dislocation density rate associated with non-homogeneous deformation effect was done in terms of the Ashby theory. The material constants in the present model were determined via genetic algorithm(GA)-based objective optimization technique. Applying the grain size model to the hot deformation of Ti-5Al-2Sn-2Zr-4Mo-4Cr, the maximum difference between the calculated and experimental β grain size was 8.2%. Moreover, the effect of deformation temperature and strain rate on the β grain size in the hot deformation of Ti-5Al-2Sn-2Zr-4Mo-4Cr was calculated, indicating that the β grain size increased with the increasing of deformation temperature and the decreasing of strain rate.展开更多
New TiAl alloys, containing 45 at.% Al, 7 at.% Nb, x at.% W, and 0.15 at.% B (x = 0, 0.2, 0.4, and 0.7) were prepared by arc melting and drop casting consequently. Using optical microscopy, scanning electron microscop...New TiAl alloys, containing 45 at.% Al, 7 at.% Nb, x at.% W, and 0.15 at.% B (x = 0, 0.2, 0.4, and 0.7) were prepared by arc melting and drop casting consequently. Using optical microscopy, scanning electron microscopy (SEM), and electron superprobe technologies, the effects of tungsten on the microstructural evolution of the TiAl alloys, including the colony size and lamellar spacing, were analyzed. It was found that cellular structures and dendrites were formed in the as-cast TiAl alloys, and heavy metals, such as niobium and tungsten, tend to segregate strongly at the interface of the cellu- lar structures and dendrites. Trace tungsten can effectively impede the grain growth and narrow the interlamellar spacing. 0.4 at.% tungsten is more effective in refining the microstructure of the TiAl alloys.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51475375)the Fund of the State Key Laboratory of Solidification Processing in NWPU(Grant No.KP201513)
文摘The continuous dynamic recrystallization(CDRX) through a progressive transformation of a subgrain structure into a grain structure with the increasing of misorientation occurred in the hot deformation of titanium alloy. A grain size model for CDRX of titanium alloy in hot deformation considering work hardening effect, dynamic softening effect and non-homogeneous deformation effect was established. The β grain size was described as functions of the deformation temperature, strain rate and strain by using the dislocation density as an internal state variable. The inside dislocation storage and dislocation annihilation,which respectively resulted from work hardening effect and dynamic softening effect, were described by the Kocks-Mecking and Picu-Majorell theories correspondingly. The dislocation density rate associated with non-homogeneous deformation effect was done in terms of the Ashby theory. The material constants in the present model were determined via genetic algorithm(GA)-based objective optimization technique. Applying the grain size model to the hot deformation of Ti-5Al-2Sn-2Zr-4Mo-4Cr, the maximum difference between the calculated and experimental β grain size was 8.2%. Moreover, the effect of deformation temperature and strain rate on the β grain size in the hot deformation of Ti-5Al-2Sn-2Zr-4Mo-4Cr was calculated, indicating that the β grain size increased with the increasing of deformation temperature and the decreasing of strain rate.
文摘New TiAl alloys, containing 45 at.% Al, 7 at.% Nb, x at.% W, and 0.15 at.% B (x = 0, 0.2, 0.4, and 0.7) were prepared by arc melting and drop casting consequently. Using optical microscopy, scanning electron microscopy (SEM), and electron superprobe technologies, the effects of tungsten on the microstructural evolution of the TiAl alloys, including the colony size and lamellar spacing, were analyzed. It was found that cellular structures and dendrites were formed in the as-cast TiAl alloys, and heavy metals, such as niobium and tungsten, tend to segregate strongly at the interface of the cellu- lar structures and dendrites. Trace tungsten can effectively impede the grain growth and narrow the interlamellar spacing. 0.4 at.% tungsten is more effective in refining the microstructure of the TiAl alloys.
