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

制备NiAl、NiAl- fe、NiAl- ti和NiAl- mn合金，形成（NiAl/NiAl- fe）、（NiAl/NiAl- ti）和（NiAl/NiAl- mn）扩散对。用电子探针微量分析仪测量了在3GPa高压下退火后的扩散偶的扩散曲线。扩散系数由扩散曲线用霍尔法确定。根据扩散系数的压力依赖性，可以用下式计算NiAl中扩散的激活体积DELTAV_D；*lnD/*P = -DELTAV_D / RT+ r_GK_T。DELTAV_D是了解NiAl中扩散机制的重要数值和有效信息，它反映了NiAl中导致扩散的缺陷所对应的物理量。本文的研究结果如下：(1) 1623K时Mn在NiAl中扩散的DELTAV_D(m^3/mol): 43.6at%Al时为4.11 x10^<-6>， 45.8at%Al时为5.87x10^<-6>， 47.5at%A1时为6.70x10^<-6>；(2) 1548K时Fe在NiAl中扩散的DELTAV_D：在44.3at%A1时为3.27x10^<-6>，在46.8at%A1时为4.65x10^<-6>，在48.8at% A1时为5.50x10^<-6>，在49.5at%Al时为6.06x10^<-6>，在50.7at%Al时为5.5Ox10^<-6>，在51.4at%Al时为3.24x10^<-6>, (3) 1598K时Ti在NiAl中扩散的DELTAV_D：在44时为5.54x10^<-6>。Oat %, 6。O6x10^<-6>在46.9at%Al, 7.71x10^<-6>在49.7at%Al, 5.86x10^<-6>在50.8at%Al和3。lOx10^<-6> at 51.4at%Al。DELTAV_D值在化学计量组成时最大，为（6.0 ~ 7.7）V_0，其中V_0为摩尔体积。这有力地表明，扩散是通过具有间隙的复杂机制发生的。在富ni侧，随着Al组分的增加，DELTAV_D逐渐减小。这表明，除了空位外，单个空位对扩散也有贡献。另一方面，在富Al侧，DELTAV_D随Al组分的增加而急剧减小。这表明扩散主要发生在迁移激活过程下，因为结构上的ni空位有助于扩散，因此空位形成的激活过程并不重要。因此，在NiAl中的扩散机制已经被理解。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