Plan-view characterization of intergranular precipitates on grain boundaries by combination of FIB lift out method and TEM analyses: A case study in austenitic stainless steel.

A new characterization method is proposed to study intergranular precipitates of polycrystalline material in the planar manner. A dual beam focused ion beam (FIB) - scanning electron microscopy (SEM) was applied to fabricate thin FIB lamella with a grain boundary parallel to the lamella to investigate for transmission electron microscopy (TEM). Distributions, microstructures and compositions of intergranular precipitates of austenitic stainless steel were then examined by TEM, scanning transmission electron microscopy (STEM), and energy dispersive X-ray spectroscopy (EDS). This plan-view microstructural characterization methods would play important roles in the case of materials where the intergranular precipitates play key roles for their physical and chemical properties.

Structural and compositional study of precipitates in under-aged Cu-added Al-Mg-Si alloy.

Atomic scale characterization of fine precipitates in an under-aged Cu added Al-Mg-Si alloy was carried out by combination of atomically-resolved annular dark-field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. Two types of precipitates were observed in the alloy. In the case of ordered ß" precipitates, ß" was proposed as Mg5-xAl2+xSi4 (x ≈ 1) with solute Cu atoms replacing Al site of ß" precipitate. In the case of disordered precipitates, the precipitates were found to consist of ß" sub-unit cells, three-fold symmetric structure without Cu atoms, Cu containing structures termed as "Cu sub-unit cluster", and Q' sub-unit cells. Among these structures, the morphologies of three-fold symmetric structure without Cu atoms, Cu sub-unit cluster, and Q' sub-unit cell were almost the same, so that these structures should be the clusters of Q' phase. Since the areal density, length and diameter of precipitates were almost equal between Cu free Al-Mg-Si alloy and Cu added Al-Mg-Si alloy, the increase of hardness by Cu addition should be due to the precipitation of Cu related precipitates, such as Cu sub-unit clusters and Q' sub-unit cells.

Effect of heat treatments on the microstructure and formability of Al-Mg-Mn-Sc-Zr alloy.

Microstructures and formability of scandium and zirconium added Al-Mg-Mn alloy sheets with various heating conditions were examined to improve their mechanical properties. Formability of these samples were judged by the Lankford value, r-value. It was possible to fabricate mechanically balanced Al-Mg-Mn-Sc-Zr alloy with high hardness 76.2 Hv and with high formability with r=1.2, by not only adding scandium and zirconium but also optimizing the heat treatment conditions.

Three-dimensional studies of intergranular carbides in austenitic stainless steel.

A large number of morphological studies of intergranular carbides in steels have always been carried out in two dimensions without considering their dispersion manners. In this article, focused ion beam serial-sectioning tomography was carried out to study the correlation among the grain boundary characteristics, the morphologies and the dispersions of intergranular carbides in 347 austenitic stainless steel. More than hundred intergranular carbides were characterized in three dimensions and finally classified into three different types, two types of carbides probably semi-coherent to one of the neighboring grains with plate-type morphology, and one type of carbides incoherent to both grains with rod-type morphology. In addition, the rod-type carbide was found as the largest number of carbides among three types. Since large numbers of defects, such as misfit dislocations, may be present at the grain boundaries, which can be ideal nucleation sites for intergranular rod-type carbide precipitation.

Microstructural characterization of GdBa2Cu3O7-δ superconductor films with BaHfO3 artificial pinning centers by scanning transmission electron microscopy.

Critical current (IC) of superconductor films under magnetic field is strongly influenced by dispersions and morphologies of artificial pinning centers (APCs) in general [1]. BaHfO3 (BHO) is acknowledged as the best candidates of APCs for REBCO films, which shows utmost thickness dependence and isotropic angular dependence of IC values for REBCO films [2]. Moreover, several researchers have focused on the nanostrains caused by the lattice mismatch at the interface between APCs and REBCO matrix, which are also the source for enhanced vortex pinning of the REBCO films [3]. In this study, we investigated to examine the nanostrain at the interface using spherical aberration (CS) corrected scanning transmission electron microscopy (STEM).BHO introduced GdBa2Cu3O7-δ (GdBCO) film was fabricated by pulsed laser deposition (PLD) method. TEM samples were prepared by focused ion beam (FIB; Quanta 3D 200i, FEI) method followed by Ar ion thinning (NanoMill, Fischione) method. Atomic scale imaging was performed by spherical aberration corrected STEM (JEM-ARM200F, JEOL), then microstructures of BHO/GdBCO interface was then examined by Fourier transformation (FFT).BHO nanorods and nanoparticles were found dispersed in the GdBCO matrix, where {100} and {110} facets were present at BHO/GdBCO interfaces, as shown in Fig. 1. In the case of PLD process, most favorable growth direction of BHO is [001] direction, so that the regular quadrangular prism shaped BHO with {100} facets would be grown along [001] direction of GdBCO matrix [4]. {110} facets of BHO were formed to maintain the minimum surface area at BHO/GdBCO to reduce the interfacial energy.jmicro;63/suppl_1/i27-a/DFU082F1F1DFU082F1Fig. 1.Plan view HAADF-STEM image and FFT image showing facets at BHO/GdBCO interfaces. This work was supported by the Ministry of Economy, Trade and Industry (METI) as "Development of Fundamental Technologies for HTS Coils" and the JSPS KAKENHI (26600046).

Influences of calcination temperature on growth and superconducting properties of GdBa2Cu3O7-δ films fabricated by fluorine-free metal organic deposition method.

GdBa2Cu3O7-δ is one of the best candidates for the superconducting coated conductors because it has high critical temperature and high critical current density under high magnetic fields. In this study, superconducting GdBa2Cu3O7-δ films were fabricated by fluorine-free metal organic deposition method via two different calcination temperatures, 723K and 873K, to examine the influence of calcination temperature on film growth and superconducting characteristics. Critical temperatures and critical current densities of the sample calcined at 873K were superior to the sample calcined at 723K. In the case of the sample calcined at 723K, the mixture of amorphous and crystalline phases was observed, and that of a- and c-axis oriented grains after the crystallization. In the case of the sample calcined at 873K, the randomly oriented crystalline phases were observed, and the mixture of c-axis oriented grains and (Gd, Al)2BaO4 phase after the crystallization. These microstructural changes caused the differences in superconducting characteristics.