Key Engineering Materials Vol. 591

Abstract: Ni₃Al based alloy IC10 has been developed for turbine blades and vanes of advanced aero-engines and other high temperature structural components. Conventional two-layered structure thermal barrier coatings (TBCs) were produced by EB-PVD onto Ni-based superalloy. The thickness of bond coat and top coat was approximately 60μm and 120μm, respectively. After thermal barrier coatings were produced, it was heated at 1523K for 2hs, 6hs, 14hs and 20hs under 1×10^-2Pa, respectively. After heat treatment was done, the thermal cyclic test was carried out by exposure to air at 1373K for 0.5h, and then cooled to room temperature within 5 minutes by forced air cooling. Scanning electron microscopy (SEM) was employed to study the microstructure of the coatings. After thermal cycled in air at 1373K for TBCs without heat treatment at 1523K, its lifetime is about 810 hours. After 760hs thermal cycles, the spallation occurred on the TBCs that the heat treatment was treated at 1523K for 2hs. The lifetime of TBCs, which the heat treatment was treated at 1523K for 6hs, was 710hs. The lifetime of TBCs, which the heat treatment was treated at 1523K for 14hs and 20hs, was 600hs and 560hs, respectively. The results showed that, with the increasing of the time of heat treatment, the weight gain increased evidently during thermal cycled. The results showed that heat treatment at 1523K affect the lifetime of TBCs during thermal cyclic evidently.

Abstract: CrN coatings were fabricated by Closed Filed Unbalanced Magnetron Sputtering (CFUMS). The effect of substrate temperature (T_S) on phase components, morphologies and mechanical properties of CrN coatings were studied. The results show that the phase in coatings, which has little to do with T_S, was the coexistence of Cr, Cr₂N and CrN. The grain shape of the columnar crystal CrN coating was the coexistence of pyramidal and plane topography. The hardness and adhension of CrN coating first increased with the rise of temperature, then decreased when the values of both them were constant ones. It has the highest hardness and bonding strength simultaneously at 300°C.

Abstract: Sr₂KNb₅O₁₅ ceramic powders have been synthesized by molten salt method, ceramics were sintered via a pressureless sintering method. The effect of calcining temperature on the phase composition and microstructure of ceramic powders were investigated by XRD and SEM analysis. The results show that microstructure of ceramic powders changed from acicular to platy, and the average size of ceramic powders become bigger with the calcining temperature increased. The optimal calcining temperature was 1200°C, and the length and diameter of ceramic powders was about 1-5 mm and 0.2-1 mm, thus the aspect ratio of ceramic powders was about 1-5. The influence of sintering temperature on density, microstructure and electrical properties of the ceramics were systematically analyzed. The results indicate that density and electrical properties of the ceramics first increased then decreased with increasing the sintering temperature. When the sintering temperature was 1400°C, the ceramics show optimized relative density and electrical properties (d₃₃=40 pC/N, e_r=616, tand=0.029, E_c=9.83 kV/cm, P_r=32.50 mC/cm²).

Abstract: Ce-doped bismuth titanate (Bi_4-xCe_xTi₃O₁₂: BCT) and pure Bi₄Ti₃O₁₂ (BIT) thin films with random orientation were fabricated on Pt/Ti/SiO2/Si substrates by pulsed laser deposition technique. These samples had polycrystalline Bi-layered perovskite structure without preferred orientation, and consisted of well developed rod-like grains with random orientation. The experimental results indicated that Ce doping into BIT result in a remarkable improvement in ferroelectric propertis. The Pr and the Ec values of the BCT film with x=0.75 were 23 μC/cm2 and 80 kV/cm, respectively.

Abstract: Y-doped bismuth titanate (Bi_4-xY_xTi₃O₁₂: BYT) and pure Bi₄Ti₃O₁₂ (BIT) ceramics with random orientation were fabricated by a conventional electroceramic technique. These samples had polycrystalline Bi-layered perovskite structure without preferred orientation, and consisted of well developed plate-like grains with random orientation. Y-doping into BIT caused a large shift of the Curie temperature ( TC ) from 675 °C to lower temperature and a improvement in dielectric property. The experimental results indicated that Y doping into BIT also result in a remarkable improvement in ferroelectric property. The Pr and the Ec values of the BYT ceramic with x=0.75 were 20 μC/cm2 and 85 kV/cm, respectively.

Abstract: Y₂O₃-doped bismuth titanate (Bi_4-xY_xTi₃O₁₂: BYT) and pure Bi₄Ti₃O₁₂ (BIT) thin films with random orientation were fabricated on Pt/Ti/SiO₂/Si substrates by rf magnetron sputtering technique. These samples had polycrystalline Bi-layered perovskite structure without preferred orientation, and consisted of well developed rod-like grains with random orientation. Y-doping into BIT caused a large shift of the Curie temperature ( TC ) from 675 °C to lower temperature and a improvement in dielectric property. The experimental results indicated that Y doping into BIT also result in a remarkable improvement in ferroelectric property. The Pr and the Ec values of the BYT film with x=0.75 were 28 μC/cm2 and 65 kV/cm, respectively.

Abstract: The electrical properties of Yb-doped bismuth titanate,Bi_4-xYb_xTi₃O₁₂ (BYbT) ceramics prepared by a conventional electroceramic technique were investigated. XRD analyses revealed Bi-layered perovskite structure in all samples. SEM micrographs showed randomly oriented and plate-like morphology. For the samples with x=0.25 and 1.0 the current-voltage characteristics exhibited negative differential resistance behaviors and their P-V hysteresis loops were characterized by large leakage current, whereas for the samples with x=0.5 and 0.75 the current-voltage characteristics showed simple ohmic behaviors and their P-E hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( P_r ) and coercive field (E_c) of the BYbT ceramic with x=0.75 were above 16μC/cm² and 75KV/cm , respectively.

Abstract: Yb-doped bismuth titanate and random oriented Bi_4-xYb_xTi₃O₁₂ (BYbT) thin films were fabricated on Pt/Ti/SiO₂/Si substrate with pulsed laser deposition method. The structures and ferroelectric properties of the BYbT films were investigated. Yb doping resulted in a marked improvement in remanent polarization (P_r) and coercive field (E_c). At an applied electric field of 120kV/cm, the P_r and (E_c) of the BYbT (x=0.8) films annealed at 650°C were 20 μC/cm² and 85 KV/cm, respectively.

Abstract: The electrical properties of Er₂O₃-doped bismuth titanate,Bi_4-xEr_xTi₃O₁₂ (BET) ceramics prepared by a conventional electroceramic technique were investigated. XRD analyses revealed Bi-layered perovskite structure in all samples. SEM micrographs showed randomly oriented and plate-like morphology. For the samples with x=0.4 and 1.0 P-E hysteresis loops were characterized by large leakage current, whereas for the samples with x=0.6 and 0.8 P-E hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( P_r ) and coercive field (E_c) of the BET ceramic with x=0.8 were above 20μC/cm² and 65KV/cm , respectively.

Abstract: The electrical properties of Pm₂O₃-doped bismuth titanate,Bi_4-xPm_xTi₃O₁₂ (BPT) ceramics prepared by a conventional electroceramic technique were investigated. XRD analyses revealed Bi-layered perovskite structure in all samples. SEM micrographs showed randomly oriented and plate-like morphology. For the samples with x=0.4 and 1.0 P-E hysteresis loops were characterized by large leakage current, whereas for the samples with x=0.6 and 0.8 P-E hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( P_r ) and coercive field (E_c) of the BPT ceramic with x=0.8 were above 18μC/cm² and 75KV/cm , respectively.