Additions of boron in modified titanium alloys and Ti-B composites result in the in situ formation during high temperature processing of TiB reinforcement phases that improve the mechanical properties and wear resistance of unreinforced titanium alloys, while still utilizing the high strength-to-weight ratio and excellent corrosion resistance of titanium. Several boron-modified titanium alloys and Ti-B composites in a Ti-6Al-4V matrix have been investigated to determine the effect of processing parameters on the TiB reinforcement phases and resultant microstructures and mechanical properties. Using optical microscopy, scanning electron microscopy, conventional characterization techniques, and newly developed methodologies for three-dimensional visualization, the microstructures of these Ti-B materials have been studied. Observations included a similar anisotropic whisker morphology with roughly hexagonal cross-sections among all TiB phases; alignment of all TiB phases with extrusion, with the extent of alignment affected by thermomechanical processing parameters; brittle fracture behavior of TiB whiskers, with fracture down the length of whiskers not aligned in the tensile direction and across the width of whiskers aligned in the tensile direction; and discoveries of the anisotropic morphologies of the coarse primary TiB phase and the sub-micron precipitated TiB phase. It has been observed that extruded boron-modified alloys with compositions in the hypoeutectic regime of the quaternary system of titanium, alloying elements aluminum and vanadium, and boron, containing a unimodal size distribution of eutectic TiB whiskers, significantly improve the strength and stiffness compared to unreinforced Ti-6Al-4V alloy while also demonstrating tensile elongation to failure within the fracture-critical limits required for aerospace structural applications. Materials design methodologies have been developed using Ti-B materials, and they show promise for predicting the effects of processing parameters and the resultant microstructures and mechanical properties for boron-modified titanium alloys and Ti-B composites optimized for a variety of commercial and industrial applications.

¡@In this study, the plastic deformation of (001) single crystal silicon at 900 oC is investigated by uniaxial compression along [001]. Using optical microscopy and scanning electron microscopy to observe the sample surface, and analysis the corresponding microstructure of different strain deformed silicon by transmission electron microscopy, particularly dislocation, slip systems and work hardening behaviour. ¡@Experimental temperature condition was chosen which over the BDT temperature range of silicon. We were found similar stages of work hardening described in metals and use the result of analysis dislocations and slip systems to suggest a hardening process of plastic deformation. ¡@The observations are similar to the feature in stage II (dislocation tangled) and stage III (dislocation cell structure). Partial dislocation and dipole are formed in less strained sample. We suggest a hardening process of plastic deformation from these results.

The composition dependent variation of ferroelectric domain structure in lead zirconate titanate (Pb(Zr0.52Ti0.48)O3) ceramics have been investigated within the morphotropic phase boundary (MPB). Tetragonal phase in sintered samples were identified via X-ray diffractometry (XRD). Representative microstructures of ferroelectric domains were examined using scanning electron microscopy (SEM). £\-boundaries, £_- boundaries, and £k-boundaries were analyzed from the contrast of extreme fringe patterns by transmission electron microscopy (TEM). Twin planes for 90o domains lie in {011) and for 180o domains lie in {100) and {220) were determined by selected area diffraction patterns (SADP). Traditional contrast analysis was adopted for determining displacement vectors (R). 90o domains with R = £`[011] and 180o domains with R = n[001]. Convergent beam electron diffraction (CBED) was performed to identify crystalline phases of different domain configurations. By examined the symmetry along the Z = [100], [110], and [111] zone axis, both £_-boundaries and £k-boundaries are tetragonal phase.

The success in fabrication of various nano-sized powders, wires or tubes has arisen the new possibility in modifying the existing commercial materials in terms of their functional or structural characteristics. In this study, the AZ61 Mg alloy is adopted as the matrix, and nano-sized SiO2 particulates are introduced into the alloy by means of casting, powder metallurgy, or spray forming processes to fabricate a high performance Mg matrix composite. The strengthening mechanisms, fracture toughness and bending toughness of the AZ61 Mg based composites are examined. The composites were prepared either by spray forming, ingot metallurgy, or powder metallurgy, followed by severe hot extrusion. The spray formed composites exhibit the best nano particle distribution and toughness, but the volume fraction of the nano particles that can be inserted is limited. The nano composites fabricated through the powder metallurgy method possess the highest strength due to the extra strengthening effect from the MgO phase. Strengthening analysis based on the Orowan strengthening mechanism can predict well the composite strength provided that the nano particles are in reasonably uniform dispersion. For composites containing higher nano particle volume fractions greater than 3%, the experimental strength data fall well below the theoretical predictions, suggesting poor dispersion of the reinforcement. The creep properties of the composites are also explored. The specimens are subjected to tensile loading at temperatures 200 to 400oC and strain rates 1x10-3 to 1x10-1. The creep mechanism is identified as dislocation creep controlled with the rate controlling diffusion step being the magnesium lattice diffusion at low strain rates and grain boundary diffusion at high strain rates.

FOUR 6061 AL SYSTEMS WERE PREPARED, INCLUDING THE CAST 6061 ALLOY BY TMT OR ECAP, THE PM 6061 ALLOY, AND THE MODIFIED PM 6061 ALLOY ADDED WITH 1 VOL% NANO-SIO2. THE MODIFIED 6061/1%NANO-SIO2 ALLOY POSSESSED A GRAIN SIZE~0.5 UM AND MAINTAINED FINE GRAIN SIZE UPON LOADING AT HIGH TEMPERATURE, RESULTING IN HSRS OVER 300% AT 550-590 OC AND 1-5X10-1 S-1. THE GRAIN BOUNDARY MISORIENTATION DISTRIBUTION IN THE MODIFIED 6061/1%NANO-SIO2 ALLOY WAS ALSO MOST RANDOM COMPARED WITH OTHER THREE UNMODIFIED 6061 ALLOYS. THE CURRENT RESULTS SUGGEST THAT THE ADDITION OF A SMALL AMOUNT OF CHEAPER SIO2 OR AL2O3 NANO-PARTICLES INTO COMMERCIAL AL ALLOYS CAN EFFECTIVELY SUPPRESS GRAIN GROWTH AT HIGH TEMPERATURES AND ENHANCE HSRS, SIMILAR TO THE EFFECTS BY ADDING 15-25VOL% MICRO-SIZED SIC OR SI3N4 REINFORCING PARTICULATES OR WHISKERS.

Abstract Recently Cu has been used as a replacement of Al in microelectronics industry to its lower electrical resistivity and higher electromigration resistance than aluminum. It is essential to have high performance diffusion barrier to suppress the diffusion between Cu and Si . In this experiment ZrN was investigated as a possible diffusion barrier. All coatings were deposited by RF magnetron reactive sputtering system. The growth of ZrN has been evaluted at different vacuum condition¡BRF power¡Bgrowth time¡BN2 flow rate Ar flow rate and Zr or ZrN target. The thin films were then annealed at temperatures from 450 ¢J to 700 ¢J for 30 min to study its durability. In this work XRD was used to study the thin film structure, SEM and TEM study the microstructures and AFM to study the surface roughness . The film¡¦s resistivity was measured as a function of N2 flow rate and annealing temperature by four point probe . For pure Zr film Cu3Si phase has formed after annealing at 550 ¢J for 30 min . As to ZrN film, only CuZr2 is present after annealing at 650 ¢J for 30 min indicating the diffusion barrier is still effective. After annealing at 700 ¢J for 30 min, Cu3Si was detected indicating the failure of the diffusion barrier. Results up to now suggest that ZrN layer can be a successful candidate as a diffusion barrier between Cu and Si.

AlN thin films grown on GaN/Sapphire substrate by RF magnetron sputtering technique with AlN target has been studied. Simple MIS capacitor was fabricated in order to evaluate the electrical properties of AlN films that played as a insulator. Various microstructures of AlN thin films can be obtained by controlling the growth parameters, such as sputtering powers, sputtering distances and working pressure. The microstructures of the AlN films were examined by X-ray diffraction. The observation of the surface morphology ,the distribution of defects and the interface of AlN/GaN were performed by transmission electron microscopy. The results showed that the amorphous AlN thin films were obtained with a 21cm long sputtering working distance and under the 100W sputtering power and 8mtorr working pressure conditions. The results of the C-V measurement indicated that the MIS device demonstrated a capacitor behavior, however a large leak current showed up in the end. The quality of the AlN films and the process procedures of MIS device still need be improved further.

This research is based on ¡§GTAW¡¨ mode, toweld the premixedferrite, molybdenum, and carbon powders on SC45 carbon steel substrate. Learning from the previous experiments, a wear test under a high temperature of 450¢J, was employed to get the Ring-disk coefficients of sliding friction about 0.3, the depletion amounts to 0.67 mg Nm per million, that exhibited a better hardness and anti-wear property than the substrate. The welding layer¡¦s solidification structure was examined by XRD,SEM, EPMA and TEM. The experimental results revealed that in the layer welded with GTAW, primary dendritic arms are of eutectic solidification structures. In X sample, £]-Mo2C is located in the dendrite closed to the un-melted zone. We can see that £^ phase (dispersed phase) with the rod shape solidified in the dendrite. And then £b-Fe3Mo3C (continuous phase) solidified between the rod spacing. In Z sample, £b-Fe3Mo3C solidified as dendrite first, and then the £^ phase solidified between the inter-dendrite. The solidification path is ¡§£\ + L ¡÷ £\ + £^ + L ¡÷ £\ + £^ + L+ £b ¡÷ £^ + £b¡¨. £^ phase and £b-Fe3Mo3C are both FCC structures in an ordered phase, and the coherence of lattice is good, with a perfect orientation relationship.

The metal hydride used as hydrogen storage material has come into public notice. It is very important to understand the crystal structure and the permutation of hydrogen and the metal crystal structure of hydride for developing industrial hydrogen storage material. The tetrahedral formation of the atom intervals of titanium/zirconium alloys benefits the absorbing of hydrogen atoms. Especially under high temperature, the titanium/zirconium alloys have high affinity on hydrogen, and hydrogen atoms help to absorb within the titanium/zirconium alloys can spread and enter materials fast on the surface, this way will get uniform saturation solid solution. Therefore, we use hydrogen gas in the high-temperature gaseous phase to melt the titanium/zirconium alloys and observe the crystal structure and morphology of hydride precipitates with transmission electron microscopy. The research contents are as follows: (1) In Ti-H system, ageing of quenched specimens which contained the hydrides are found to have a face-centered tetragonal structure (£^-titanium hydride). Ageing of furnace-cooled specimens which contained the hydrides are found to have a face-centered cubic structure (£_-titanium hydride). (2) In Zr-H system, ageing of quenched specimens which contained the hydrides are found to have a face-centered tetragonal structure (£^-zirconium hydride). Ageing of furnace-cooled specimens which contained the grain-boundary hydrides are found to have a face-centered cubic structure (£_-zirconium hydride).

Producing more reaction regions on the PEMFC cathode using cavities with micro structures can be used to add more reaction points on the electrode. The original ladder type cavity is limited by the laser diffraction in its manufacture. The flat electrode has its performance improved for 58%. The energy density is increased from 462 mW/cm2 to 720mW/cm2. Pressure required in the micro-structure imprinting is reduced, so as the fuel transportation blocked by mold releasing. The total catalyst amount is cut from 0.5mg/cm2 to 0.25mg/cm2. No obvious performance drop can be found. This shows that most of the reactions happen in the region between catalyst layer and micro hole layer. Limited by the pattern of micro-structure, the electrospray does not perform as expected. In the future, this issue should be considered in making micro-structure.