The status of the large grain niobium cavity R&D in Asia and the future scope are presented. Recently KEK has received CBMM and NingXia large grain niobium sheets through collaborations. KEK has fabricated 1.3 GHz single cell cavities using these materials and measured the cavity performance. Those results are presented in this paper.

In this paper, we report on glancing-incidence X-ray analysis (GIXA) of ZnO thin films, ZnO/ZnMgO and ZnO/Au heterostructures grown by laser molecular beam epitaxy (L-MBE) on c-plane Al2O3 substrates. The surface and interface sensitivity of X-ray reflectivity (XRR) has been exploited to evaluate the surfaces and interfaces of ZnO-based structures. The presence of smooth interfaces is responsible for the observation of intensity oscillation in XRR, which is well correlated to the clear Pendellosung fringes in high-resolution X-ray diffraction (HRXRD) measurements. In addition, the simulation of XRR data yields reliable and precise information of the layer thickness, the surface and interface roughness of each layer. The correlation of a smooth surface and high optical and structural quality is substantiated by time-integrated photoluminescence (TIPL) and XRD measurements of ZnO/ZnMgO heterostructure and ZnO thin films. The intense exciton-related emission, in contrast to a negligible deep-level radiation and the high c-axis orientation of ZnO films, indicates good optical and structural properties due to the superior surface and interface quality of our samples.

The microstructures of three alloys of nominal compositions of Ti–60 at.% Al, Ti–62.5at.% Al and Ti–64 at.% Al were studied by transmission electron microscopy after the alloys were annealed at 1200, 1000, 800 and 600°C. Four phases based on the face-centered cubic lattice, designated as TiAl, Ti3Al5, TiAl2S (S for short period) and TiAl2L (L for long period) were confirmed. Their crystallographic orientation relationships (ORs) were studied in detail. The stability ranges of these phases are briefly outlined as well. It is found that the observed ORs are independent of the annealing procedures and can approximately be regarded as ‘cubic-to-cubic’ relationships. The structural connection for the observed ORs is that the planes containing pure Al layers are parallel to each other. The possible mechanisms leading to these ORs are discussed with a consideration of atomic tiling of the AlnTim planes.

An alloy of the nominal composition of Ti-62.5at.% Al was annealed at 1000 degrees C. Transmission electron microscopy (TEM) was performed to study the microstructure. Two types of crystallographic orientation relationships (ORs) between Ti3Al5 and TiAl2L (L for long period) were found. They respectively correspond to different phase interfaces. Most of the observed interfaces correspond to an OR of aTi(3)Al(5) // aTiAl(2)(L), cTi(3)Al(5) // cTiAl(2)(L). Such a type of (001) interfaces contains dislocation networks with orthogonal Burgers vectors along [110] and [110]. (101) interfaces containing ledges can occasionally be observed. The corresponding OR slightly deviates from bTi(3)Al(5) // bTiAl(2)(L), aTi(3)Al(5) // cTiAl(2)(L). The different interfaces are accounted for misfit between Ti3Al5 and TiAl2L, and might result from different phase transition procedures.

The TiAl based alloy is one of the most promising candidate materials for high temperature applications in the next decade. However, its low-temperature brittleness hinders its wide usage. In the last twenty years the deformation mechanisms of TiAl alloys have been intensively investigated. It is well known that the extremely common feature of deformation microstructures at room temperature is the existence of numerous stacking faults surrounded by 1/6 partials. Further investigations by Hug et al showed that these planar faults were extrinsic faulted dislocation dipoles which were produced by the rearrangement of the core structure of a pinned 1/2 superdislocation. In their previous paper, the authors reported an experimental observation of a new type of faulted dipoles. The surrounding partials of these faulted dipoles have a Burgers vector of 1/3 rather than 1/6 . This is striking. One could argue that it seems impossible to identify unambiguously the Burgers vector of partial dislocations bounding a stacking fault by extinction rules only because the contrast of partial dislocations is often affected significantly by that of the bounded stacking faults. In order to check the previously reported result, image simulation has been performed and is presented in this note.

Two phase {gamma}-TiAl-based alloys composed of ({gamma} + {alpha}{sub 2}-Ti{sub 3}Al) are currently under extensive investigation because their mechanical properties are superior to either single phase {alpha}{sub 2} or {gamma} alloys. The alloys usually have a duplex microstructure consisting of equiaxed {gamma}-grains with various volume fractions of lamellar colonies in them. The lamellar colony, which consists of alternating layers of ordered {gamma} and {alpha}{sub 2} plates with the orientation relationship {l_brace}111{r_brace}{sub {gamma}}//{l_brace}0001{r_brace}{sub {alpha}{sub 2}}, {gamma}// {sub {alpha}{sub 2}}, is formed either by a phase transformation {alpha} {r_arrow} {alpha}{sub 2} and then {gamma} precipitates from the {alpha}{sub 2} matrix, or by {alpha} {r_arrow} {alpha}/{gamma} {r_arrow} {alpha}{sub 2}/{gamma} upon cooling. The microstructure of the colony has been studied in detail by many investigators. It has been suggested that the precipitation of the {gamma} phase essentially involves a HCP {r_arrow} FCC structure change together with long-range transport of atoms to obtain the composition of the two phases. The structure change can be brought about if a/3 Shockley partials travel on alternate basal planes of the HCP phase. Thus, the {gamma} nuclei are essentially basal stacking faults in the {alpha}{sub 2} phase. This means that gliding of a/3 partial appears tomore » play an important role in the transformation. If it is so, it would be expected that an external stress would probably enhance the process. More recently, Gao et al. have claimed that stress-induced phase transformation may occur in two-phase TiAl-based alloys during deformation at room temperature, which is related to a stage on stress-strain curves. In this note, the authors are briefly reporting on evidence of the stress-induced {alpha}{sub 2} {r_arrow} {gamma} transformation in a {gamma}-TiAl-based alloy.« less