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

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_&lt；Li-1&gt；·[{1-(1-B·k_&lt；i-1&gt；)fs_i}/{1-(1-B·k_&lt；i-1&gt；)fs_&lt；i-1&gt；}]^&lt；(ki-1-1)/(1-Bki-1)，where k_&lt；i-1&gt；is partition ratio at C_&lt；Li-1&gt；，B is given as follows：B=2αfor 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，andα=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_&lt；Ti&gt；，k_&lt；Cr&gt；)，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_&lt；65&gt；Cr_&lt；10&gt；Ti_&lt；25&gt；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.

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.