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

1998 Fiscal Year Final Research Report Summary

• Project/Area Number: 09650717
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Physical properties of metals
• Research Institution: Osaka University
• Principal Investigator: MINAMINO Yoritoshi Osaka University Department of Adaptive machine systems, Professor, 大学院・工学研究科, 教授 (30116107)
• Project Period (FY): 1997 – 1998
• Keywords: diffusion / NiAl phase / Intermetallic compound / high pressure / activation volume / B2-type ordered structure / activation energy / diffusion profile

Research Abstract

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 %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.