摘要
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.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.
基金
financially supported by the National Natural Science Foundation of China(Nos.51271016 and U1204508)
the National Basic Research Program of China(No.2011CB605500)
the Doctoral Program of Higher Education of China(No.20120006120042)
the Fundamental Research Funds for the Central Universities(No.FRF-TP-14-062A2)
