Analytical Electron Microscope Study of Low Temperature Diffusion Couples

The microstructrual features，crystallographic orientation relationships and compositional variations across the interface in diffusion couples bonded at low annealing temperatures were investigated by analytical electron microscopy(AEM)。The surface activated bonding(SAB)method was used as a technique to produce the diffusion couples.The surface of the sample was ion-beam sputtered before diffusion bonding in order to clear-off the oxide layer or contamination at the bonded interface.In the Ni/Ni I D 23 i D 2 A1 diffusion couples prepared by the SAB method，the Ni-rich solid solution phase(γ)grows towards the Ni I D 23 i D 2 Al-based intermetallic phase(γ‘)during diffusion annealed.Theγ/γ‘interphase interface is flat and parallel to the bonded interface in the couples prepared by the SAB method。Theγandγphases in the Ni/Ni I D 23 I D 2 A1 diffusion couple annealing at 1123 K has the same crystallographic orientation。On the other hand，theγandγphases in the Ni/Ni y D23齐埃D2A1 diffusion couple prepared without sputtering and diffusion annealed at1123K has a different crystallographic orientation.It is clear that the sputtering of bonding interface has a large effect on the growth process of phases in the diffusion couples.Fine-grained aluminum alloys were processed by the equal-channel angular pressing(ECAP)technique and the grain boundary diffusion was examined using the diffusion couples prepared by the SAB method.The interdiffusion coefficients in the fine-grained diffusion couples are significantly larger than those in coarse-grained couples particularly at lower annealing temperatures.The activation energy of diffusion in the fine-grained diffusion couple was estimated to be about two third of that in the coarse-grained one。It is clear that the SAB method is very useful to prepare the diffusion couples at lower bonding temperatures and enables to study the low temperature interdiffusion process by analytical electron microscopy.

The microstructrual features, crystallographic orientation relationships and compositional variations across the interface in diffusion couples bonded at low annealing temperatures were investigated by analytical electron microscopy (AEM). The surface activated bonding (SAB) method was used as a technique to produce the diffusion couples. The surface of the sample was ion-beam sputtered before diffusion bonding in order to clear-off the oxide layer or contamination at the bonded interface. In the Ni/NiィイD23ィエD2A1 diffusion couples prepared by the SAB method, the Ni-rich solid solution phase (γ) grows towards the NiィイD23ィエD2Al-based intermetallic phase (γ') during diffusion annealed. The γ/γ' interphase interface is flat and parallel to the bonded interface in the couples prepared by the SAB method. The γ and γ phases in the Ni/NiィイD23ィエD2A1 diffusion couple annealing at 1123K has the same crystallographic orientation. On the other hand, the γ and γ phases in the Ni/NiィイD23ィエD2A1 diffusion couple prepared without sputtering and diffusion annealed at 1123K has a different crystallographic orientation. It is clear that the sputtering of bonding interface has a large effect on the growth process of phases in the diffusion couples. Fine-grained aluminum alloys were processed by the equal-channel angular pressing (ECAP) technique and the grain boundary diffusion was examined using the diffusion couples prepared by the SAB method. The interdiffusion coefficients in the fine-grained diffusion couples are significantly larger than those in coarse-grained couples particularly at lower annealing temperatures. The activation energy of diffusion in the fine-grained diffusion couple was estimated to be about two third of that in the coarse-grained one. It is clear that the SAB method is very useful to prepare the diffusion couples at lower bonding temperatures and enables to study the low temperature interdiffusion process by analytical electron microscopy.