ABSTRACT
This paper presents the results of a study of the morphology and structure at the weld interface in a brass-Invar bimetal, which belongs to the class of so-called thermostatic bimetals, or thermobimetals. The structure of the brass-Invar weld interface was analyzed using optical microscopy and scanning electron microscopy (SEM), with the use of energy-dispersive X-ray (EDX) spectrometry and back-scattered electron diffraction (BSE) to identify the phases. The distribution of the crystallographic orientation of the grains at the weld interface was obtained using an e-Flash HR electron back-scatter diffraction (EBSD) detector and a forward-scatter detector (FSD). The results of the study indicated that the weld interface had the wavy structure typical of explosive welding. The wave crests and troughs showed the presence of melted zones consisting of a disordered Cu-Zn-Fe-Ni solid solution and undissolved Invar particles. The pattern quality map showed that the structure of brass and Invar after explosive welding consisted of grains that were strongly elongated towards the area of the highest intensive plastic flow. In addition, numerous deformation twins, dislocation accumulations and shear bands were observed. Thus, based on the results of this study, the mechanism of Cu-Zn-Fe-Ni structure formation can be proposed.
ABSTRACT
A new technique for investigation of interfacial dislocations in nickel-base superalloys by scanning electron microscopy is presented. At high temperatures the pressure of interfacial dislocations against the gamma/gamma'-interface causes grooves. This 'fingerprint of the dislocation network' is visualized by deep selective etching, which removes the gamma'-phase down to the gamma/gamma'-interface. Compared with transmission electron microscopy, the proposed method has important advantages: observation of large sample areas, no superposition of dislocations lying in different specimen depths, possibility of three-dimensional view of dislocation configurations, information about the dislocation mobility, reduced time for preparation and visualization. The method can be applied for multiphase materials where the interface is grooved by interfacial dislocations.
