Fuh-Sheng Shieu

Control of the mechanical properties of metal-ceramic interfaces through interfacial reactions

Abstract The use of interfacial reactions to control the structure and shear strength of metal-ceramic interfaces was studied in the NiO-Pt system. Interfaces were formed by hot1pressing together thin NiO single crystals and thick Pt polycrystalline films. Suitable choice of the annealing temperature, time and oxygen partial pressure allowed the introduction at the interface of a layer of either an intermetallic compound NiPt with thickness between 1 and 65 nm or a Ni-Pt solid solution.The shear strength of the NiO-Pt interface with and without the different interlayers present was measured by the periodic cracking method. Compared to its originally hot pressed state the shear strength of the NiO-Pt interface was increased by a factor of at least 4 by the presence of the NiPt and by ∼10 by the solid solution. The use of interfacial reactions to control interfacial strength may also be applicable in other metal-ceramic systems where the metal and the cation form intermetallic compounds, and where the oxidation potentials of the metal and the cation are significantly different.

Role of extrinsic atoms on the morphology and field emission properties of carbon nanotubes

Extrinsic atoms were doped into multiwalled carbon nanotubes (MWCNTs) using microwave plasma-enhanced chemical vapor deposition. Doped nitrogen atoms alter the original parallel graphenes into highly curved ones including some fullerene-like structures. Doped nitrogen atoms could replace carbon atoms in MWCNTs and therefore increase the electronic density that enhances the electron field emission properties. On the other hand, the incorporation of boron into the carbon network apparently increases the concentration of electron holes that become electron traps and eventually impedes the electron field emission properties. Fowler–Nordheim plots show two different slopes in the curve, indicating that the mechanism of field emission is changed from low to high bias voltages. β values could be increased by an amount of 42% under low bias voltages and 60% under high bias voltages in the N-doped MWCNTs, but decreased by an amount of 8% under low bias region and 68% under high bias voltage in the B-doped MWCNTs.

A formation mechanism for the macroparticles in arc ion-plated TiN films

Abstract Characterization of macroparticles in TiN films prepared by an arc ion-plating method on AISI 304 stainless steel was carried out by energy filtering transmission electron microscopy. The results show that most of the macroparticles have the shape of a bud, which has the equiaxial polycrystalline Ti metal located at the bottom center. The outerlayer consists of TiN 0.26 , α-TiN 0.3 and Ti 2 N, in addition to TiN, identified by selected area diffraction. On the basis of the analysis, a model describing the formation of macroparticles in the arc ion-plated TiN is proposed. Once emitted from the cathode, the liquid Ti droplets react with nitrogen during their migration to the substrate and form a thin layer of titanium nitrides on the surface of the droplets, resulting in a core-shell structure. As a result of the high-melting outshell, flattened torus voids are produced, upon impact on the substrate, beneath each particle which causes shadowing of the ion flux during deposition. Subsequent growth of TiN follows the orientation of the titanium nitride nuclei in the outshell to form a radial type structure, until coalescence with the regular TiN columns grown perpendicular to the substrate surface occurs.

Characterization and optoelectronic properties of p-type N-doped CuAlO2 films

This letter reports a technique for increasing the carrier concentration and the conductivity of the p-type CuAlO2 through doping the material with nitrogen. The x-ray photoelectron spectroscopy and the optical band gap analyses suggested that the nitrogen atoms occupying the interstitial sites of the delafossite structure provided the p-type CuAlO2 with an impurity energy level in the energy gap. It was also found that the N-doped CuAlO2 film had its optimum conduction properties when the dopant level reached 1.1at.%. Here, the carrier concentration was raised from 4.81×1016 in the undoped film to 2.13×1017cm−3 in the doped film, and the corresponding film’s conductivity was increased from 3.8×10−2to5.4×10−2(Ωcm)−1, as compared with the undoped CuAlO2 film.

Effects of Ti interlayer on the microstructure of ion-plated TiN coatings on AISI 304 stainless steel

Abstract The microstructure and chemistry of TiN coatings on AISI 304 stainless steel was analyzed by an energy filtering transmission electron microscope (TEM) equipped with an electron energy loss spectroscopy (EELS) detector. Two types of TiN-coated specimens, with and without a Ti interlayer, were prepared by a hollow cathode discharge ion plating coater. For the TiN directly coated on steel, it is found that the grain size, texture, and chemistry of the coating is thickness dependent. The large residual stresses in TiN caused the formation of dislocation networks and cell walls in the steel, and often resulted in early failure of the coating upon subsequent handling. Compared to the TiN–steel system, the introduction of a Ti interlayer between TiN and steel gives rise to the different results. The microstructure of TiN coatings with a Ti interlayer is mainly composed of columnar grains whose size is found to be relatively independent of coating thickness. Near the TiN–Ti interface, it is observed that many of the TiN grains grew out of the underlying Ti crystallites. Consequently, a very good epitaxial relation is established between TiN and Ti. The texture of the TiN coatings with a Ti interlayer, therefore, showed enhanced preferred orientation when approaching the TiN–Ti interface. From the calculation of the unrelaxed thermal stress based on a bilayer model, it is demonstrated that the presence of a Ti interlayer between TiN and steel can dramatically reduced the thermal stress in the TiN coating.

Microstructure and corrosion resistance of a type 316L stainless steel

Abstract Characterization of the microstructure and chemistry of the oxide film of an air-oxidized type 316L stainless steel was carried out by an energy filtering transmission electron microscope equipped with an electron energy loss spectroscopy detector, and the corrosion resistance of the oxidized steel in a hot boiling sulfuric acid solution was evaluated by using an apparatus outlined by the International Standard Organization. It is demonstrated that the corrosion resistance of the steel in a 105°C, 30% sulfuric acid solution can be improved by an oxidation pretreatment of the steel in air at 500°C for 5 min, which produced an oxide film of ∼70 nm thick. The oxide film has a multilayered microstructure in which the topmost layer is composed of nanoscale γ -Fe 2 O 3 grains of size ∼4 nm, followed by a mixture of α -Fe 2 O 3 and Fe 3 O 4 phases of grain size ranging from 20 to 75 nm. Chemical analysis of the oxide film across thickness direction using electron energy loss spectroscopy revealed that the O content in the oxide film decreases from the oxide surface toward the oxide\steel interface. In addition, it is observed that an alloying depletion of Cr and Mn exists in the oxide film, compared with the alloying elements in the steel.

Experimental and theoretical studies of the dislocation structure of NiO-Pt interfaces

Abstract The dislocation structure of (001) NiO-Pt interfaces was studied using electron microscopy and electron diffraction techniques. Specimens were produced by hot pressing polycrystalline Pt films on to thin NiO single crystals, and bulk Pt single crystlas on to bulk NiO single crystals. The polycrystalline Pt specimens were used to determine the favored orientation relationships between the (001) NiO and Pt, while the bulk NiO-Pt specimens were used to study the detailed structur of interface. Three categories of orientation relationships were identified: exact epitaxy with (001) pt ∥ (001) NiO , [110] Pt ∥ [110] NiO ; small rotations away from exact epitaxy about the common [001] direction, and high index planes of Pt parallel to (001) of NiO. Theoretical calculations of the expected dislocation structures of interfaces with the first two orientation relationships, as well as others which are small perturbations away from these two, were made using a Bollmann-type analysis. The experimental observations and theoretical predictions were shown to be in generally good agreement, with some differences with respect to the detailed structure. The energies of the interfaces having the first two orientation relationships were shown to be similar which is believed to be the reason why they both occur.

Microstructure and coating properties of ion-plated TiN on type 304 stainless steel

Abstract The microstructure and chemistry of TiN coatings on type 304 stainless steel were characterized by using a Zeiss EM 902A energy filtering transmission electron microscope equipped with an electron energy loss spectroscopy (EELS) detector. Thin TiN films were produced by a hollow cathode discharge ion plating coater. It was found by plan-view transmission electron microscopy that the microstructure of the TiN coatings is thickness-dependent. The grain size of TiN ranges from 88 nm at the coating surface down to 9 nm near the TiN–steel interface. In addition, the TiN surface layer shows some degree of texture, but the sub-surface and internal TiN layers are mainly equiaxial and randomly oriented. Chemical analysis by EELS shows that the relative oxygen content increases approximately from the TiN surface to the TiN–steel interface, whereas the relative nitrogen content first decreases slowly and then drops rapidly near the interface. The presence of a Ti 2 N phase and the deficiency of nitrogen near the TiN–steel interface suggest that the early-deposited TiN is non-stoichiometric. By the periodic cracking method, the ultimate shear stress at the TiN/steel interface and the residual stress in the TiN thin film were estimated to be 2.2 and 12.8 GPa, respectively.

Low Temperature Sintering and Microwave Dielectric Properties of Ba2Ti9O20 Ceramics with 3ZnO–B2O3 Addition

Boron and zinc oxide (ZnBO) glass added in dielectric materials have drawn a great attention recently due to the low firing temperature. Microwave dielectric properties of the Ba2Ti9O20-based ceramics with ZnBO addition up to 3 wt% were investigated at the sintering temperatures ranging from 900 to 960°C. Effects of the ZnBO addition on the bulk density, microstructure, and dielectric properties of the Ba2Ti9O20-based ceramics at microwave frequency were elucidated. X-ray diffraction (XRD) results show the presence of five crystalline phases, Ba2Ti9O20, BaZr(BO3)2, BaTi3O7, BaZrO3 and Zn2SiO4 in the sintered ceramics, depending upon the amount of ZnBO addition. Optimum dielectric properties were obtained for the Ba2Ti9O20-based ceramic with 1 wt% ZnBO addition and sintered in air at 940°C for 2 h, having the dielectric properties: Q=1137 (Q×f=8300), er value=27.3, and τf=2.5 ppm/°C.

Microstructure and shear strength of a Au–In microjoint

Abstract Two types of Au–In microjoints, i.e. Au/In/Au in which In foil was used and Au/In, were prepared by either solid state interdiffusion (SSID) or solid–liquid interdiffusion (SLID) bonding for single lap tensile test. Deposition of the Au and In thin films was carried out by thermal evaporation on a polyethylene terephthalate (PET) substrate. It is found that the shear strength of the Au/In microjoints is higher than that of Au/In/Au using In foil. It is also observed that the fracture mode of Au–In microjoints depends on the types of In used. Failure of the Au/In microjoints appeared to be along the joint–substrate interface, whereas it occurred within the In foil for the other type of specimens. Examination of the Au/In microjoints by glancing angle X-ray diffraction reveals the presence of the two major constituent phases, Au 7 In 3 and Au, as well as other intermetallics AuIn 2 , Au 10 In 3 , and Au 9 In 4 in small amount. On the other hand, only the intermetallic AuIn 2 and pure In were observed in the Au/In/Au microjoints, where the total thickness of In is much higher than that of Au.