Key Engineering Materials Vols. 368-372

Abstract: Polycrystalline cubic boron nitride (PCBN) is formed by sintering cubic boron nitride particles (cBN) at high temperature and high pressure. In this process, a network of cBN particles is formed by intergrowth and bridging between the particle phases. The response of the aggregate to applied stresses in process such as hard machining, will therefore principally involve the deformation of this skeletal structure. In this work, the microstructure and hot hardness and adhesion properties of three high-density PCBN aggregates were comparatively studied. The results were correlated to their cutting performance and wear modes in machining a carbide-based hardfacing material.

Abstract: Ultra-high temperature ceramics (UHTCs) have attracted increasing attention of material scientists and engineers due to their promising application in reactive atmospheres such as monatomic oxygen at high temperatures over 1600°C. However, the mechanical properties of this kind of ceramics at ultra-high temperature are difficult to measure because of the temperature limits of the furnace and fixture. In this work, an innovative measuring approach, trace analysis method, is presented for estimating the ultra-high temperature mechanical properties. Various material parameters, including elastic modulus, hardness, recovery deformation and energy dissipation capacity at ultra-high temperature could be determined via a residual indent trace that was induced by a fast impact of a ceramic conical indenter on the local area at high temperature.

Abstract: This paper reports some new progresses on layered and graded coatings for plasma facing materials in fusion devices in Laboratory of Special Ceramics and Powder Metallurgy (LSCPM), University of Science and Technology Beijing (USTB), China. They included tungsten coatings made be various particle sizes of initial feedstock and interlayers and boron carbide graded coatings. All the coatings were fabricated on the oxygen free copper by plasma spraying. The microstructures and properties were investigated for PFM. Water quenching and high heat loading experiments were also carried out to estimate the thermal performance of these coatings.

Abstract: Tape casting and hot-press sintering were used to fabricate an Al2O3/3Y-TZP laminated composite. In order to investigate the deformation properties, the as-prepared material was deep drawn at high temperatures. It was found that the microstructure of the material sintered at 1550°C was fine and no significant pores were detected from SEM observations at the interfaces between the two types of layers. The superplastic forming experiment shown that, when the strain rate was constant, temperature had a great influence on the superplasticity of the Al2O3/3Y-TZP laminated composite. A hat-like part with the largest deformation height was obtained at 1500°C.

Abstract: For enhanced mechanical properties of ceramics for structural application, a great deal of attention has concentrated on preparation of layered composites. In this study, numerical simulation technique, which is applicable for the evaluation of mechanical performance for layered composite material, was developed. A generalized material constitutive equation coupled with material damage model based on the continuum damage mechanics approach was proposed and has been implemented to an in-house type finite element analysis code. The material behaviors for each component of layered composites can be simulated by the pre-defined material model on the simulation. A series of finite element analyses was carried out in order to elucidate the effect of fabrication related residual stress on the structural capacity of the layered composites.

Abstract: In this paper, the transient heat conduction and transient thermal stresses in an infinite plate with double-sided functionally graded coatings (FGM coatings) under the convective boundary condition are investigated. The thermo-physical properties of the two symmetrical FGM coatings are assumed to have distributions of power forms along the thickness direction of the plate, the effects of which on the thermal shock resistance of the FGM coated plate are analyzed via numerical calculations. And consequently some design rules for the double-sided FGM coatings are put forward, which provide a guidance for the development of FGM coated cutting tools.

Abstract: (001)-, (1110), and (105)- oriented SrBi4Ti4O15 films with its c-axis tilted 0, 45 and 55o from the surface normal were epitaxially grown by metal organic chemical vapor deposition and the temperature dependency of the dielectric constant was systematically investigated. Relative dielectric constant, εr, and its temperature dependency increased when the tilting angle of the c-axis from the substrate surface normal increased. Temperature dependency of εr was positive in case of the (105) and (1110) orientation, which is in good agreement with the conventional ferroelectric materials. On the other hand, it became negative for (001) orientation. This shows the orientation dependency of εr in SrBi4Ti4O15.

Abstract: {0.75SrBi2Ta2O9-0.25Bi3TiTaO9}(SBT-BTT) thin films were prepared by the modified metalorganic solution deposition (MOSD) technique. The microstructure and ferroelectric properties of SBTBTT thin films were studied. The SBT-BTT thin films were produced at 750°C. The grain size and surface roughness of SBT-BTT films showed significant enhancement with an increase in annealing temperatures. It is found that SBT-BTT thin films have good ferroelectric properties. The measured remanent polarization values for SBT-BTT, SBT and BTT capacitors were 15, 7.5 and 4.8μC/cm2, respectively. The coercive field for SBT-BTT capacitors was 50kV/cm. More importantly, the polarization of SBT-BTT capacitors only decreased 5% after 1011 switching cycles at a frequency of 1MHz.

Abstract: LixTixNi1-2xO (x =0, 10 and 20 at. %) thin films with 200 nm in thickness were deposited on Pt/Ti/SiO2/Si (100) by a sol-gel spin-coating method. All samples have a uniform microstructure. The grain sizes grew from 100 nm to 300 nm by co-doping Li and Ti. The LiTiNiO thin films consist of NiO, NiTiO3 and Li2NiO2, while the Li-free thin films consist of NiO, NiTiO3 and NiTi0.99O3. The dielectric properties of the LiTiNiO thin films improved obviously by co-doping Li and Ti, but excess Li increases the amount of Li2NiO2 phase and decreases the dielectric properties. The dielectric constants at 100 Hz for the Li0.1Ti0.1Ni0.8O and Li0.2Ti0.2Ni0.6O thin films are 506 and 388 respectively. Appropriate co-doping contents of Li and Ti are important to obtain a high dielectric property.

Abstract: Mg-Al, Zn-Al, and Mg-Fe layered double hydroxides (LDHs) have been synthesized through a stepwise control route. In the stepwise control route, we controlled the state of Al or Fe composition as Al or Fe hydroxyl aqueous complexes in aqueous solution first, then dropwise Mg2+ or Zn2+ and OH - and keep procedure at constant pH value simultaneously at room temperature. The textural and structure properties of the resulting samples were characterized by XRD and TG-DTG. The results showed that products obtained by the stepwise control route were pure and highly crystalline LDHs. The particle size and size distribution was measured by DLLS.