材料期刊网

在850—1050℃含有Ta或Nb离子的氟化物熔盐中,用电化学表面合金化的方法制备了Ta-Ni和Nb-Ni二元合金,分析表明合金层的成分是均匀的TaNi_3和NbNi_3化合物.利用恒电流间隙滴定技术(Galvanostatic Intermittent Titration Technique)证实了Ta-Ni二元系存在Ta_2Ni,TaNi,TaNi_2和TaNi_3四种化合物,测定了其生成电位和自由能;Nb-Ni二元系仅生成、NbNi和NbNi_3二种化合物.在熔盐电化学表面合金化的过程中,表面合金层的厚度与时间呈抛物线关系.测定了Ta-Ni和Nb-Ni合金中Ta和Nb的扩散系数,并建立了扩散系数随温度变化的Arrhenius方程

The electrochemically alloying on Ni surface with Ta and Nb was carried out In molten LiF-NaF-K_2TaF_7 or LiF-NaF-K_2NbF_7 at temperatures between 850 and 1050℃. In both cases only TaNi_3 and NbNi_3 stable phases are detected in the bulk of the layer. The intermetallic compounds of Ta-Ni binary system, including Ta_2Ni, TaNi, TaNi_2 and TaNi_3 have been identified and the Gibbs energy of formation of Ta-Ni compounds have been calculated. It is shown that the growth of the surface alloying layer follows a parabolic law versus the alloying time. The kinetic parameters of the intermetallic diffusion of Ta-Ni and Nb-Ni systems, including the dimensionless parameters which depends on the solid compositions at the boundary of the alloy layer and the intermetallic diffusion coefficients D have been estimated by combination of electrochemical measurements and diffusion equation. The following equations are confirmed: x~2=Kt and α=(K/D)~(1/2) where x is the thickness of the surface layer and K is the constant.