Numerical simulation on directional solidification of Al-Ni-Co alloy based on FEM

The ratio, of the temperature gradient at the solidification front to the solidification rate of solid-liquid interface, plays a large part in columnar grain growth. The transient temperature fields of directional solidification of Al-Ni-Co alloy were studied by employing a finite element method. The temperature gradient at the solidification front and the solidification rate were analyzed for molten steels pouring at different temperatures. The results show that with different initial pouring temperatures, the individual ratio of the temperature gradient at solidification front to the solidification rate soars up in the initial stage of solidification, then varies within 2,000-6,000 ℃.s.cm2, and finally goes down rapidly and even tend to be closed to each other when the solidification thickness reaches 5-6 cm. The simulation result is consistent with the practical production which can provide an available reference for process optimization of directional solidified Al-Ni-Co alloy.

Lamellar morphology of directional solidified Ti–45Al–6Nb–xW alloys

Directional solidification of Ti-45Al-6Nb-xW（x=0,0.4,0.8;at%） alloys was performed by Bridgeman method with the stable growth rate of 5,10,and 20 μm·s^（-1）.The differential scanning calorimeter（DSC） results indicate that both the eutectic temperature and the transition temperature of α（Ti_3Al） to γ（TiAl） increase with W content increasing from 0 at%to 0.8 at%.For the stable growth rate of 10 μm·s^（-1）,the orientations of α_2（Ti_3Al）/γ（TiAl）lamellae change from 45°（0 at%W） to 0° and near 0°（0.4at%and 0.8 at%W） to the crystal growth direction,and the spacing of α_2/γ lamellae decreases with W content increasing from 0 at%to 0.4 at%,while it increases when W content is 0.8 at%.With the increase in growth rate from5 to 10 and 20 μm·s^（-1）,the lamellar spacing of α_2/γbecomes smaller,and the lamellar thickness becomes more uniform.

Growth rate and composition of directionally solidified intermetallic TiAl–Nb alloys with different solidification conditions

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.