Diffusion and its mechanism in B2-type ordered NiAl at high pressures.

为了制备(NiAl/NiAl-Fe)、(NiAl/NiAl-Ti)和(NiAl/NiAl-Mn)扩散偶，制备了NiAl、NiAl-Fe、NiAl-Ti和NiAl-Mn四种扩散偶。用电子探针仪测量了经3 Gpa高压退火后的扩散偶的扩散曲线。用霍尔法由扩散曲线确定了扩散系数。[LND/*P=-DELTAV_D/RT+r_GK_T]DELTAV_D是了解扩散机制的一个重要数值，也是了解扩散机制的有效信息，因为DELTAV_D是指与引起NiAl中扩散的缺陷相对应的物理量。研究结果如下：(1)NiAl中1623K下的Mn扩散的DELTAV_D(m^3/mol)：4.11x1O^&lt；-6&gt；43.6at%Al，5.87x10^&lt；-6&gt；45.8at%Al，6.70x10^&gt；-6&gt；在47.5at%A1，7.O8x1O^；-6&gt；在49.8at…(2)NiAl中Fe在1548K时的扩散曲线：3.27×10^-6&gt；在44.3at%Al，4.65×10^；-6&gt；在46.8at%Al，5.50x10^；-6&gt；在49.5at%Al，5.5Ox10；-6；在50.7at%Al和3.24×10^-6；在51.4at%Al，(3)钛在NiAl中的扩散在1598K：5.54x10^；-6；在44.0at%Al，6.06x10^；-6；在46.9at%Al，7.7x10^；-6；在49.7at%Al，5.86x10^；-6；在50.8at%Al和3.1Ox10；-6&gt；在51.4at%时，DELTAV_D值在化学计量成分处最大，为(6.O-7.7)V_0，其中V_0为摩尔体积。这有力地表明扩散是以复杂的空位扩散机制进行的。在富Ni侧，DELTAV_D随着Al成分的增加而逐渐减小。这表明，除空位外，单空位对扩散也有贡献。另一方面，在富Al侧，DELTAV_D随Al组分的增加而逐渐减小。DELTAV_D随Al组分的增加而急剧下降，这表明扩散主要发生在激活的迁移过程中，这是因为结构上的Ni空位促进了扩散，而激活的空位形成过程并不重要，从而对NiAl中的扩散机制有了上述认识。较少

The allays of NiAl, NiAl-Fe, NIAl-Ti and NiAl-Mn were prepared in order to make the diffusion couples of (NiAl/NiAl-Fe), (NiAl/NiAl-Ti) and (NiAl/NiAl-Mn).The diffusion profiles in the diffusion couples annealed at high pressures up to 3GPa were measured by an electron probe microanalyzer.The diffusion coefficients were determined from the diffusion profiles by Hall's method.The activation volumes, DELTAV_D, of diffusion in NiAl could be evaluated from the pressure dependence of diffusion coefficients by using the following equation ; *lnD/*P = -DELTAV_D / RT+ r_GK_T.The DELTAV_D is an important value and an effective information for understanding the diffusion mechanisms, because it indicates the physical amount corresponding to the defects which contribute to the diffusion in NiAl.The results of this research are as follows ; (1) DELTAV_D(m^3/mol) of Mn diffusion in NiAl at 1623K : 4.11x1O^<-6> at 43.6at%Al, 5.87x10^<-6> at 45.8at%Al, 6.70x10^<-6> at 47.5at%A1, 7.O8x1O^<-6> at 49.8at … More %Al, 3.1Ox1O^<-6> at 50.8at%Al and 2.49x10^<-6> at 51.3at%Al, (2) DELTAV_D of Fe diffusion in NiAl at 1548K : 3.27x10^<-6> at 44.3at%A1, 4.65x10^<-6> at 46.8at%A1, 5.50x10^<-6> 48.8at%Al, 6.06x10^<-6> at 49.5at%Al, 5.5Ox10^<-6> at 50.7at%Al and 3.24x10^<-6> at 51.4at%Al, (3) DELTAV_D of Ti diffusion in NiAl at 1598K : 5.54x10^<-6> at 44.Oat%Al, 6.O6x10^<-6> at 46.9at%Al, 7.71x10^<-6> at 49.7at%Al, 5.86x10^<-6> at 50.8at%Al and 3.lOx10^<-6> at 51.4at%Al.The DELTAV_D values have the maximum at the stoichiometric composition and they are (6.O-7.7) V_0, where the V_0 is the molar volume.This strongly means that the diffusion occurs by the complicated mechanism with the divacancies.In the Ni-rich side, the DELTAV_D decreases gradually with the Al composition.This indicates that the single vacancies contribute to the diffusion in addition to the divacancies.On the other hand, in the Al-rich side, the DELTAV_D decreases steeply with the Al composition.This reveals that diffusion occurs mainly under the activated process of migration because the structural Ni-vacancies contribute to diffusion and then the activated process of vacancy formation is not important.Thus, the diffusion mechanism in NiAl has been understood above. Less