D.H. Ping

HREM STUDY OF THE MICROSTRUCTURE IN NANOCRYSTALLINE MATERIALS

Abstract High resolution electron microscopy studies of nanocrystalline Pd and (Fe 0.99 , Mo 0.01 ) 78 Si 9 B 13 indicate that the atomic structures of the grain boundaries consist of both ordered and disordered regions. The microstructure in ordered regions of the grain boundaries shows curved and little distorted appearance. In some areas, however, nanovoids and imperfect or disordered regions are also observed at the grain boundaries. The defects in the grains, such as five-fold twins, edge and 60° dislocations, are also observed. The nature of these defects is similar to those normally observed in conventional coarse-grained polycrystals.

Microstructure and composition analysis of nanostructured materials using HREM and FEG-TEM

The microstructure in nanostructured (NS) materials synthesized by different methods have been characterized by electron microscopy methods. NS-Pd was prepared by inert-gas condensation and in situ compacting method (IGCC), NS-alloys by amorphous crystallization method (ACM) and NS-Cu and Cu100-xFe(x) alloy by mechanical alloying (MA) methods. The experimental results have revealed that different preparation techniques lead to different microstructures. The grain boundaries have ordered and disordered structures and high density of defects were frequently detected in NS-materials synthesized by IGCC and MA. For the NS-alloys produced by ACM, however, the structures of GBs are similar to those in coarse-grained materials and the grains have nearly perfect crystal structure. For immiscible systems, a supersaturated Fe-Cu solid solution can be obtained by MA, but it is difficult using IGCC.

HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY STUDIES OF THE MICROSTRUCTURE OF NANOCRYSTALLINE TI70NI20SI10 ALLOY

The microstructure of nanocrystalline Ti70Ni20Si10 alloy with various grain sizes was investigated by high resolution transmission electron microscopy (HRTEM). The nanocrystalline samples were prepared by annealing the amorphous precursor. At an initial stage of annealing, homogeneous nucleation of Ti2Ni stable crystalline phase was found to occur. In the later stage, Ti5Si3 and a small amount of alpha-Ti were found to coexist. Based on the HRTEM observations, most of the grain boundaries have ordered structures and no obvious disordered regions were detected at the grain boundaries. However, asymmetric tilt grain boundaries were often encountered The samples are essentially free from any porosity. No signs of lattice defects, such as twins, stacking faults or dislocations were found to be present inside the grains.

High resolution electron microscopy studies of the microstructure in nanocrystalline (Fe0.99Mo0.01)Si9B13 alloys

Abstract The crystallization process of an amorphous (Fe 0.99 Mo 0.01 ) 78 Si 9 B 13 alloy was examined by high resolution electron microscopy. Experimental results show that nanocrystalline alloys with average grain sizes in the range 30–50 nm are obtained after annealing at 560–620°C for 1 h, and four phases — α-Fe(Si,Mo), (Fe, Mo) 3 B, (Fe,Mo) 23 B 6 and Fe 2 B — coexist in the sample. Most of the Fe 2 B crystals are found no nucleate at the interfaces between α-Fe(Si,Mo) grains and the residual amorphous phase at 620°C. No disordered regions and nanovoids were detected at the grain boundaries. Defect structures in the nanocrystalline alloys are also discussed.

Microanalytical study of the hexagonal phase in an yttrium-containing low expansion superalloy

The resistance to stress-accelerated grain boundary oxygen embrittlement (SAGBO) in Fe-Ni-Co-Nb-Ti controlled low expansion superalloy has been improved by trace yttrium element addition. The platelet precipitates in the alloy have been studied by means of optical microscopy, transmission electron microscopy, convergent beam electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction technique. The crystal structure and the chemical composition of the platelet phase have been determined. The phase has a CaCu5-type crystal structure (space group P6/mmm) with lattice parameters a = 0.498 nm and c = 0.408 nm. The crystallographic orientation relationship between the phase and the matrix is found to be ( 1)(gamma)/(0001)(H), [(1) over bar 10](gamma)/[11 (2) over bar 0](H). High-resolution images show that the interface between the platelet phase and the matrix is semicoherent and some stacking faults have been found in the platelet phase

Precipitations in an yttrium-containing low-expansion superalloy

AbstractThe resistance to stress-accelerated grain-boundary oxygen embrittlement and notch-bar rupture strength in Fe–Ni–Co–Nb–Ti low-expansion superalloy has been improved significantly by trace yttrium addition. The precipitates in the matrix as well as along the grain boundaries have been studied systematically. The platelet precipitates in the matrix and along the grain boundaries have a hexagonal crystal structure (space group, P6/mmm) with lattice parameters a = 0.498 nm and c = 0.408 nm. The crystallographic orientation relationship between the phase and the matrix is found to be

Transmission electron microscopic characterization of zirconia reinforced with silicon carbide fibres

(\overline 1 {\text{ }}\overline 1 1 )_\gamma //(0 0 0 1)_H ,[\overline 1 1 0]_\gamma //[1 1 \overline 2 0]_H

The potential for ordered grain boundary sliding in nanocrystalline palladium

. The semi-continuous discrete precipitates along the grain boundaries have an orthorhombic crystal structure with lattice parameters a = 0.45 nm, b = 0.80 nm and c = 1.20 nm. High-resolution images show that the interface between the precipitates and the matrix is semicoherent.