Intermetallic Ti-xAl-8Nb(x = 41,43,45,47,49;at%) alloys were solidified unidirectionally upwards with a constant temperature gradient of G=3.8 K·mm~(-1)at wide range of growth rates of v=10-400 μm·s~(-1)using a Bridgman directional solidification(DS) furnace.Microstructural parameters including the primary dendrite arm spacing(λ_1),secondary dendrite arm spacing(λ_2),dendrite tip radius(R) and mushy zone depth(d) were measured statistically.The values of λ_1,λ_2,R and d decrease as the growth rate increases for a given composition(x).The values of λ_1,λ_2,R and v increase with the increase in x value,while the value of d firstly increases and then decreases with the increase in x value for a given v.The relationships between λ_1,λ_2 and R were analyzed by the linear regression.The average growth rate exponent of λ_1 is 0.29,which is in accordance with the previous experimental observations,and that of λ_2 is close to the previous experimental results,while those of R and d are lower than the results in other alloy systems.In addition,theoretical models for λ_1,λ_2 and R were compared with the experimental observations,and a comparison of the present experimental results with the theoretical models and previous experimental results was also made. Intermetallic Ti-xAl-8Nb (x = 41,43,45,47,49; at%) alloys were solidified unidirectionally upwards with a constant temperature gradient of G = 3.8 K · mm -1 at wide range of growth rates of v = 10-400 μm · s -1 using a Bridgman directional solidification (DS) furnace. Microstructural parameters including the primary dendrite arm spacing (λ_1), secondary dendrite arm spacing (λ_2), dendrite tip radius (R) and mushy zone depth (d) were measured statistically. Values ​​of λ_1, λ_2, R and d decrease as the growth rate increase for a given composition (x). The values ​​of λ_1, λ_2, R and v increase with the increase in x value, while the value of d first increases and then decreases with the increase in x value for a given v. The relationships between λ_1, λ_2 and R were analyzed by the linear regression. average growth rate exponent of λ_1 is 0.29, which is in accordance with the previous experimental observations, and that of λ_2 is close to the previous experimental results, while those of R and d are lower than the results in other alloy systems. In addition, theoretical models for λ_1, λ_2 and R were compared with the experimental observations, and a comparison of the present experimental results with the theoretical models and previous experimental results was also made.