G. J. Shen

Interface investigations of alumina and aluminosilicate short-fiber-reinforced aluminum-alloy composites

Abstract The interfacial microstructures of alumina (Al2O3) and aluminosilicate (Al2O3·SiO2) short-fiber-reinforced aluminum-alloy composites were studied by means of transmission electron microscopy (TEM). The experimental results showed that the SiO2 content in the fiber has a marked effect on the interface microstructures of the composites even though a silica binder is not used. The reaction product MgAl2O4 spinel oxide was formed at the interface of the aluminosilicate-fiber-reinforce aluminum-alloy composite, however, no spinel oxide was observed at the interface of alumina-fiber-reinforced composite. The alumina fiber could act as a heterogeneous nucleation substrate for the primary silicon phase as a result of the low disregistry (5.62%) between the (0001) of δ-Al2O3 and the (110) of silicon.

Interface and precipitate investigation of a TiB2 particle reinforced NiAl in-situ composite

Abstract The TiB2 particles reinforced NiAl alloy composite was fabricated by hot-pressing aided exothermic synthesis (HPES). The interface between TiB2 reinforcement and NiAl matrix and the precipitate in composite were studied by transmission electron microscopy (TEM). The experimental results show that there is no reaction product formation at the TiB2/NiAl interface and the relationships between TiB2 and NiAl have no specific orientations. In addition, a fcc phase with lattice constant a=1.05 nm precipitated in TiB2/NiAl composite. TEM energy dispersive X-ray spectroscopy analysis of this fcc phase indicated that it contains element Ni, Al and B with near atomic ratio 20:3:6, thus, this fcc phase is a boride, Ni20Al3B6.

SPACE GROUP ANALYSIS AND TRANSMISSION ELECTRON MICROSCOPE OBSERVATION OF DOMAIN STRUCTURE IN FERROELECTRIC SRBI2TA2O9 CERAMICS

Abstract Domain structure of the bismuth layered ferroelectric SrBi2Ta2O9 (SBT) ceramics has been studied by space group analysis and transmission electron microscope (TEM) observation. The space group analysis shows that there should exist five types of domain walls in SBT, namely: (1) antiphase boundary (APB); (2) 180°: (3) APB combined with 180°; (4) 90°; (5) APB combined with 90°. The 90° domain wall has been confirmed by TEM observation. Preliminary evidences for APB have also been obtained.

Identification of a cubic precipitate in γ-titanium aluminides

Abstract The microstructures of V and Nb doped TiAl-based alloys were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray (EDS) analysis. The experimental results show that there exists a cubic precipitate with lattice constant a =0.69 nm in Ti–54Al–5Nb and Ti–54Al–5V alloys, respectively. Further, EDS analysis indicates that this cubic particle is a Ti–Al–O ternary compound. However, in two-phase Ti–45Al–5Nb and Ti–45Al–5V alloys no such Ti–Al–O ternary compound was found because of the oxygen scavenging effect of the Ti 3 Al phase. It has been recognized that the cubic phase found in this paper is consistent with that found in the oxidation experiment of TiAl-based alloys.

Oxide precipitation in V-doped TiAl-based alloys

Abstract Oxide precipitation in V-doped TiAl-based alloys was studied by transmission electron microscopy (TEM). The experimental results showed that the interstitial oxygen in single-phase TiAl alloy precipitates in the form of oxide. A Ti–Al–O ternary oxide was observed and the structure of the precipitated oxide was determined. However, in two-phase TiAl/Ti 3 Al alloy no oxide was observed. The reasons responsible for the fact that oxide precipitates in TiAl-based alloys were discussed.

Transmission electron microscopy study of 180° domain structure in PbZrO3

Abstracts are not published in this journal

Crystal and domain structures in sputtered Ni-51.6 at% Ti shape memory alloy films

Abstract A new crystalline phase in sputtered Ni-51.6 at% Ti thin films crystallized at 550 deg;C for 0.5 h was discovered. Its crystal structure was determined by XRD and SAED patterns to be orthorhombic with a B-face centered cell. The lattice parameters are a = b = 4.250 A and c = 3.005 A and the structure belongs to space group Bmmm (D 2n 19 ). Its 90 ° domain structure was also established.

Transmission electron microscopy study of precipitates in a NiAl–TiB2 composite

Abstract A TiB2 particle-reinforced NiAl alloy composite was fabricated by hot-pressing aided exothermic synthesis. The microstructures of the composite were investigated by transmission electron microscopy (TEM). The experimental results show that a fcc phase with lattice constant a=1.05 nm precipitated in the TiB2/NiAl composite. TEM energy dispersive X-ray (EDX) spectroscopy (Philips, CM200 FEG, spot size: 5 nm) analysis on this fcc phase indicated that it contains the elements Ni, Al and B with near atomic ratio 20:3:6, thus, this fcc phase is a boride, Ni20Al3B6.

Transmission electron microscopic observations of ferroelectric domains in potassium tantalate niobate crystals

Abstract By transmission electron microscopy and electron diffraction methods, thin single crystals of potassium tantalate niobate are studied in detail. The 90° and 180° ferroelectric domains in analogy to the known results in BaTiO3 1 have been revealed. Under electron radiation, the nucleation and growth of a-c 90° domains and motion of ferroelectric 180° domain boundaries are observed and some novelties associated with it have been found. In addition, the interactions between different types of domains and domains induced by dislocations are observed in this material.

The twinning orientation relationship between A and B martensite variants in a Cu-Zn-Al shape memory alloy

It is known that in the Cu-Zn-Al shape memory alloy, the variants of thermoelastic martensites which are transformed from parent phase appear as a collection of the plate groups, each consisting of three fundamental combinations A : B, A : C and A : D type pairs [1–3]. All three of these combinations involve a twin orientation. Since their twin boundaries are mobile under applied stress, they are also regarded as deformation twin [4–6]. The A : C and A : D type pairs of plates which have intervariant boundary plane 1 2 8 and 1 0 1 0 respectively as a mirror reflection plane are classified as type I reflection twins [7]. However, the A : B type pair of plate which has no such boundary plane as a mirror reflection plane has been regarded as type II twin orientation in which two variants are related by a rotation of π about [10 9 1]β ′ 1 [8]. For type II twin, it can be deduced that plane (1 2 8)A and (1 0 1 0)A, which are perpendicular to [10 9 1]β ′ 1 , should be parallel to (1 2 8)B and (1 0 1 0)B exactly. That is, (1 2 8)A and (1 2 8)B spots should superimpose in the electron diffraction pattern. The twinning orientation relationship between A : B type pair, as well as A : C and A : D, is essential feature of martensites in shape memory alloys. Thus, an understanding of such relations is vital to further understanding of mechanism of self-accommodation between martensite plate variants and shape memory behavior. In this paper, direct evidence which shows that the A and B martensite variants are not related by a rotation of π about [10 9 1]β ′ 1 is provided. The orientation relationship between A and B martensite variants has been verified as secondary twin. The alloy studied in this work has a composition of 67.6 at % Cu, 22.1 at % Zn and 10.1 at % Al. The alloy was annealed for 1 h at 600 ◦C and cold-rolled from 2.0 mm to 1.1 mm strip. After mechanically thinning to 0.1 mm, the strip was punched into 3 mm diameter discs. The discs were jet-electropolished with a solution of H2NO3 : CH3OH= 2 : 1 at −30 to −50 ◦C; the resulting specimen was examined in a JEOL-2000 EX transmission electron microscope equipped with a doubletilt holder and operating at 160 kV. Lattice parameters of M18R martensite used for indexing of diffraction patterns and calculation of twins are a= 0.4553 nm, b= 0.5432 nm, c= 3.8977 nm and β = 87.5◦ [9]. Fig. 1a is an electron micrograph showing A and B martensite variant pair in Cu-Zn-Al shape memory alloy. The composite diffraction pattern taken from this area is shown in Fig. 1b. The orientation relationship derived from this diffraction pattern is [2 1 0]A//[2 9 2]B : (1 2 8)A//(1 2 8)B. It can be seen that 1 2 8 reflection spots from both component diffraction patterns do not overlap. One may argue this “splitting” might originate in long period stacking sequence or other source. In order to clarify this point, we have tilted the specimen about 50◦ to [8 0 1] zone where two variants A and B are in symmetry. Fig. 2 is its composite diffraction pattern in [8 0 1] zone. It is clear that two 1 2 8 spots are separated. This separation can be verified by observing 2 4 16 spots. The angle these two spots subtend is 3.5◦. From the fact that (1 2 8)A and (1 2 8)B spots do not superimpose, we can believe that A : B type pair is not type II twin. In this instance, we suggested that A : B type pair might be a secondary twin relationship. It is known that for reflection twin, the indices of a plane, (h k l), and a direction, [u v w], in the twin may be determined in terms of matrix by [10–14] h T kT lT  = T hk l  (1)