Study On Hot Deformation Behavior And Processing Map Of Ti₂AlNb-based Alloy

Ti2Al Nb-based alloy is advanced structural material applied in airline and industry and has comprehensively excellent mechanical properties in high specific strength, specific stiffness, fracture toughness and creep resistance.Therefore, Ti2 Al Nb-based alloy is a new study hot-spot in intermetallic compound research field with a great range of potential utilities and a prospect of development. However, Ti2 Al Nb-based alloy is difficult-to-deformation material.Its organization and property are extremely sensitive to the deformation parameters, so it’s hard to get products stable in organization and property, and the high cost of manufacture restricts its application range.This paper considers Ti2 Al Nb-based alloy. The isothermal constant strain rate compression experiments were conducted between 900~1110 ℃ and0.01~10s-1 deformation parameter. The author analyzed the true stress-strain curves, calculated this alloy’s activation energy and constructed a constitutive equation with high accuracy. Processing maps in different dependent variables were drew according to Prasad and Murty criterions. The author also studied the analysis diagram with the microstructure and got the instability regions, the better hot working area and its corresponding thermodynamic parameters and deformation mechanism. Main results are as follows.Flow stress curve of Ti2 Al Nb-based alloy has features like stress peak, flow softening and steady state flow. Flow stress decreases with the increase of deformation temperature and the decrease of strain rate. According to the calculation,Ti2 Al Nb-based alloy’s activation energy Q=358.24KJ/mol, which is obviously bigger than self diffusion activation energy of pure α titanium and pureβ titanium alloy. This shows that thermal deformation of Ti2 Al Nb-based alloy is controlled by processes eliminate high temperature diffusion. A constitutive equation with high accuracy is constructed, and the error analysis shows that in all the data points, data points of less than 15% errors accounted for 93.8% and90.8%.Processing maps in different dependent variables were drew according to Prasad and Murty criterions separately. By the comparison of these two kinds of processing maps, the author found that this two has a similar prediction of instability region, but when considered with the microsstructure, Prasad criterionis more reasonable than Murty criterion. Therefore, the author adopted the processing map based on Prasad criterion to optimize hot working process parameters of Ti2 Al Nb-based alloy.According to the processing map based on Prasad criterion and its corresponding microstructure, the process parameters of instability are:900~990 ℃,0.25~10s-1,1035~1100℃,0.39~10s-1 and 900~945 ℃,0.01~0.019s-1,and their corresponding deformation mechanisms are adiabatic shear bands, flow localization, large grained and β elongated grain. Better thermal processing parameter areas are: 1080~1110℃, near 0.01s-1 and 1035~1050℃, near 1s-1, and their corresponding deformation mechanisms are super plasticity, dynamic recrystallization and appear sub-grain.