Formation Of Transient Liquid Phase Research Articles

Fabrication of multi-layered structures for proton conducting ceramic cells

We show manufacturing of 25 cm2 BZCY half-cells by tape-casting of assemblies with electrolyte thickness 10–20 μm. BaY2NiO5 transient liquid phase formation is analysed and proton conductivity with values of σ = 0.003 S cm−1 at 600 °C is shown.

Formation of bulk titanium boride (TiB) nano‐ceramic with Fe–Mo addition by electric‐field‐activated‐sintering

AbstractThe present work is focused on optimization of Fe–Mo content, which is essential for transient liquid phase formation and densification, during in‐situ reaction sintering of nanostructured titanium boride (TiB) in the bulk form. The principle objective is to develop a systematic understanding of how the Fe–Mo additions affect the densification, microstructure, and hardness of the TiB nano‐ceramic. Various TiB ceramic compositions, with varying Fe–Mo content and retaining a high‐volume fraction of TiB in the final microstructure, were made by the electric‐field‐activated‐sintering (EFAS) technique. An increase in Fe–Mo content is found to decrease the beginning point of densification temperature/time during the consolidation process through transient liquid phase formation. It is shown that at the optimum level of Fe–Mo, which is around 1.5 wt%, the density and hardness reach maximum levels with a least amount of spatial segregation of Fe within the ceramic. Interestingly, it has been found that Mo is uniformly incorporated within the orthorhombic lattice of the boride, while Fe is largely segregated to β‐Ti phase. At the optimal Fe–Mo content (1.5 wt%), a relative density of 99.7% and a Vickers hardness of 2050 ± 40 kg/mm2 were achieved. From microstructural and X‐ray diffraction analyses, it is found that a high proportion of TiB (>99 vol%), with a least amount of metallic ductile phase, is formed in this composition.

Low temperature sintering and nonlinear dielectric properties of Li2O doped Ba0.6Sr0.4TiO3 ceramics derived from the citrate method

A nominal composition of Ba0.6Sr0.4TiO3 + 0.5 wt. % Li2O ceramic specimen was prepared from the citrate method. The addition of Li2O was found to be effective to reduce the sintering temperature of Ba0.6Sr0.4TiO3 ceramics, which was attributed to the formation of transient liquid phase. The ceramic specimen sintered at 900 °C showed a fine-grained microstructure with considerable densification and attained the relative density of 97%. The diffusion of Li2O into Ba0.6Sr0.4TiO3 lattice was found to have an evident effect on the dielectric properties of the ceramics. The specimen exhibited a dielectric constant of 1997 and a dielectric loss 0.67% at 10 kHz and zero bias-field together with a tenability of 27.8% and a FOM of 41 at 10 kHz and 30 kV/cm.

THE INFLUENCE OF NI-TI RATIO ON THE REVERSIBLE AUSTENITE-MARTENSITE TRANSFORMATION AND MECHANICAL PROPERTIES PRODUCED BY METAL INJECTION MOULDING

This paper highlights the influence of Ni-Ti ratio on the phase constituents, the reversible austenite-martensite transformation and mechanical properties produced by metal injection molding (MIM). The binder system used was mainly palm stearin with minor fraction of polyethylene. Injection moulding was done successfully at 130˚C to form tensile shape samples. It was followed by solvent extraction, thermal debinding at 500oC and subsequently sintered in high vacuum at 1100˚C. The result showed that as the Ni content increased, the fraction of austenite phase also increased owing to greater fraction of transient liquid phase formation during the sintering, thus improved the mechanical tensile properties. However, the reversible austenite to martensite phase transformation temperatures (PTTs) seemed to be broadened with increased Ni content due to formation of metastable R-phase.

Addition of rare earth and diopside to improve performances of alumina matrix ceramic materials

In the present work, mixed rare earth and diopside were simultaneously introduced in alumina matrix ceramic materials. Composites were fabricated by hot press sintering, during which liquid phase, leading to interface reactions between alumina matrix and additives, was formed. Hardness, fracture toughness and bending strength of the composites were measured. Microstructure observations on fracture surfaces of alumina matrix ceramic materials were analysed. Results showed that diopside, as a sintering assistant, could prompt the formation of transient liquid phase as well as carbides and nitrides of rare earth elements and thus contributed to improve the mechanical properties of alumina matrix ceramic materials.

Conversion behavior comparison of TFA–MOD and non-fluorine solution-deposited YBCO films

The densification behavior during conversion of YBa 2Cu 3O 7− x (YBCO) films formed by the trifluoroacetate (TFA)-based metal–organic deposition (MOD) technique was compared to a non-fluorine oxycarbonate-based MOD process and nitrate-based polymer-assisted deposition (PAD). The critical current densities obtained in all processes exceeded 10 6 A/cm 2 in films at least 300 nm thick. Rapid densification of films was observed in all processes, beginning at 700 °C in the TFA and PAD processes and 650 °C in the oxycarbonate process. YBCO nucleation occurred shortly after densification began in all processes. Residual carbon measurements were performed using wavelength dispersive spectroscopy (WDS). Carbon persisted in films from all processes until after densification began, but it was reduced to background levels soon after YBCO nucleation. Film density and second phase morphology were controlled through adjustments to the ambient oxygen partial pressure. Morphological evidence of extensive transient liquid phase formation was observed in PAD films and is consistent with the densification and nucleation behavior. The common behavior between the PAD, oxycarbonate–MOD, and TFA–MOD processes suggests that a melt forms in all systems, but the extent of this melt varies.

Research on toughening mechanisms of alumina matrix ceramic composite materials improved by rare earth additive

Mixed rare earth elements were incorporated into alumina ceramic materials. Hot-pressing was used to fabricate alumina matrix composites in nitrogen atmosphere protection. Microstructures and mechanical properties of the composites were tested. It was indicated that the bending strength and fracture toughness of alumina matrix ceramic composites sintered at 1550 °C and 28 MPa for 30 min were improved evidently. Besides mixed rare earth elements acting as a toughening phase, AlTiC master alloys were also added in as sintering assistants, which could prompt the formation of transient liquid phase, and thus nitrides of rare earth elements were produced. All of the above were beneficial for improving the mechanical properties of alumina matrix ceramic composites.

PZT thick films for sensor and actuator applications

PZT thick films with thicknesses between 5 and 150 μm are of great interest for microsystems applications where direct coating onto microelectronic substrates and high electromechanical performance are required. Dense PZT thick films have been obtained by combining a PZT-PMN powder with a low melting point glass and the eutectic forming oxides Bi 2O 3 and ZnO. Densification is due to transient liquid phase formation with additional incorporation of cations into the growing PZT grains during sintering. PZT thick films prepared by this method show excellent dielectric, ferroelectric and piezoelectric properties. They have been applied on various substrates, like Al 2O 3, ZrO 2, Low Temperature Cofired Ceramics (LTCC) and silicon wafers which are basis materials for microsystems technology. The influence of the substrate material on the PZT thick film properties and the role of buffer layers will be discussed.

Sintering behaviour of Ti–2Ni and Ti–5Ni elemental powders

The effect of nickel powder additions (2 and 5 at.%) on the sintering behaviour of titanium powder has been investigated through the dilatometric sintering study. The sintering of titanium powder was found to be enhanced significantly and the activation energies were decreased with increasing nickel content. The sintering of Ti–2 at.% Ni system at lower temperature was found to be controlled by Ti–Ti and Ti–Ni solid state sintering, whereas inter-diffusion dominates in Ti–5 at.% Ni sintering. At higher temperatures, sintering was found to be controlled by mixed mechanisms, i.e. inter-diffusion, chemical reaction and transient liquid phase formation.

Mechanical properties of injection molded Fe-6% Ni-0.4% C steels with varying Mo contents of 0.5 to 2%

In our previous studies, sintered and heat-treated alloy steels (Fe−6Ni−0.5Mo−0.4C (mass%)) produced by a MIM process showed excellent mechanical properties of 2000 MPa tensile strength and 5% elongation. This was attributed to the solid solution strengthening and the mezzo-heterogenous microstruture, which consisted of martensite or retained austenite (Ni and Mo rich phases) surrounded by a network of tempered martensite. This study has been performed to clarify the effect of Mo on the mezzo-heterogeneous microstructure and the mechanical properties of MIM processed and sintered alloy steels (Fe−6Ni−0.4C) with varying Mo content (0.5–2 mass%). The tensile properties of the heat-treated steels with added 2 mass% Mo were lower than those of the steels with added 0.5 mass% Mo. The reduction in the tensile properties, particularly the appearance of large pores formed at the original location of Mo power through the transient liquid phase formation and the low hardness of the matrix, was due to the low sintered density. By using mechanically milled fine Ni and Mo powders, the heat-treated steel (Fe−6Ni−2Mo−0.4C) showed excellent properties, including tensile strength of 1800 MPa and ductility of 2.2% elongation.

Transient liquid phase diffusion bonding of 8090 Al-Li alloy using copper interlayer

Transient liquid phase (TLP) diffusion bonded (DB) joints have been produced in 8090 aluminium alloy (of nominal composition (wt-%) Al-2.5Li-1.3Cu-0.8Mg-0.12Zr-0.1Fe-0.05Si) using copper interlayers. Transient liquid phase formation and melt solidification were controlled by solid state diffusion of copper along Al-Li alloy grain boundaries. The shear strengths of the TLP DB joints were comparable with the shear strengths of solid state DB joints and greater than 90% of that of the base metal.

Solid Solubility and Diffusivity in an Alumina/Zirconia System

ABSTRACTPolycrystalline zirconia-coated single crystal sapphire fiber displays reconstruction of the sapphire surface in regions of contact with zirconia grains. This is a concern where ZrO2 -coated sapphire fiber is desired for reinforcement of ceramic matrices. Previous work has demonstrated pitting is partially attributed to impurity-induced transient liquid phase formation with local dissolution of alumina; however, the extent of reconstruction witnessed via microscopy suggests that other mechanisms are active. The present study has addressed the issue of solid solubility and interdiffusivity to more thoroughly understand the solid state mechanisms contributing to pitting. Single crystal sapphire and zirconia were ion implanted with zirconium and yttrium, and aluminum, respectively, and then subjected to diffusion anneals at 1200° - 1600°C to study redistribution of implanted cations. Secondary Ion Mass Spectroscopy (SIMS) was used to profile the redistribution of implanted ions for measurement of diffusion coefficients and solubility limits after heat treatments. The results will offer a significant set of data on interface stability in the alumina/zirconia system.