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Solidification Mechanism and Microstructure Control of L1_2-(Al, Cr)_3Ti Intermetallic Compound

L1_2-(Al,Cr)_3Ti金属间化合物的凝固机制及显微组织控制

基本信息

批准号：
13650802
负责人：
MORI Nobuyuki
金额：
$ 2.3万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650802/
关键词：
solidification microsegregation solidification pass Al-Ti-Cr intermetallic compound phase diagram dendrite single crystal

项目摘要

To overcome weak points of past analytical methods to analyze microsegregation of alloys, a newly proposed progressive-type solidification equation was used to analyze the solidification path of Al-Ti-Cr alloys, and the following results were obtained. Liquid composition(C_<Li>) at the solid fraction(fs_i) of a region i is calculated from the data of (i-1) region by the progressive-type solidification equation : C_<Li>=C_<Li-1>・[{1-(1-B・k_<i-1>)fs_i}/{1-(1-B・k_<i-1>)fs_<i-1>}]^<(ki-1-1)/(1-Bki-1), where k_<i-1> is partition ratio at C_<Li-1>, B is given as follows : B=2α for Flemings model, B=2α(1-exp(-1/α)) -exp(-1/2α) for Clyne-Kurz model, B=2α/(1+2α) for Ohnaka model for plate-like dendrite, and α=D・θ_f/L^2, D : solid diffusion coefficient, θ_f : local solidification time, L : effective length of volume element(=s・d_2/2, s : structure factor(=0.5〜1)). The above modified equation enabled analysis of precise solidification path by using variable partition ratio(ki) from i=1 to n in the solidification range by dividing it with enough number(n) for the precise calculation. The solidification path of Al-Ti-Cr alloys were analyzed by the above progressive-type solidification equation by using experimentally obtained partition ratios(k_<Ti>, k_<Cr>), which are the functions of liquid compositions, and the calculated results agreed well with the experimental results. Further, temperature dependence of yield strength of L1_2-Al_<65>Cr_<10>Ti_<25> single crystal was investigated by compression test, and yield strength versus temperature curve showed a plateau or anomaly in the intermediate temperature range. Deformation-induced dislocation structure in the specimen was examined by transmission electron microscopy (TEM) to explain the above phenomena.

针对以往分析方法在分析合金微观偏析时存在的不足，采用新提出的渐进型凝固方程对Al-Ti-Cr合金的凝固路径进行了分析，得到了以下结果。由<Li>（i-1）区的数据，通过渐进式凝固方程C_<Li>=C_<Li-1>·[{1-（1-B·k_<i-1>）fs_i}/{1-（1-B·k_）<i-1>fs_<i-1>}]^<（ki-1-1）/（1-Bki-1），计算出第i区固相分数（fs_i）处的液相组成（C_），其中k_<i-1>为C_处的分配比<Li-1>，B为：对于Flemings模型，B=2α，B=2α Clyne-Kurz模型为（1-exp（-1/α））-exp（-1/2α），Ohnaka模型为板状枝晶时为B=2α/（1+2α），α=D·θ f/L^2，D为固体扩散系数，θ f为局部凝固时间，L为体元有效长度（=s·d_2/2，s：结构因子（=0.5 × 1））。根据上述修正方程式，能够通过将凝固范围内的i=1 ~ n的分配比（ki）除以用于精确计算的足够的数（n）而使用可变的分配比（ki）来分析精确的凝固路径。利用实验得到的分配比（k_，k_）作为液相成分的函数，用上述渐进型凝固方程分析了Al-Ti-Cr合金的凝固路径<Ti><Cr>，计算结果与实验结果吻合较好。进一步，通过压缩实验研究了L1_2-Al_Cr_Ti_3单晶的屈服强度与温度的关系<65><10><25>，发现在中温区屈服强度随温度的变化曲线呈现平台或异常。用透射电子显微镜（TEM）观察了试样中的形变诱导位错结构，以解释上述现象。