The effects of copper and iron oxide additions on the sintering and properties of Y-TZP

Yttria-tetragonal zirconia polycrystals (Y-TZP) with a range of yttria contents were prepared from powders neutralized during processing with ammonium hydroxide and sintered at temperatures of 1300–1700 °C. Iron or copper oxide was ádded and studies made of body characteristics, mechanical properties and ageing resistance. Densification was aided by higher yttria concentrations. The effects of the oxide additives were dependent on amounts present and sintering conditions, including ramp rates and holding temperatures. Ageing resistance was significantly improved for both oxide additions fired to lower temperatures but rapid transformation to monoclinic phase was observed for materials with larger grain sizes associated with higher sintering temperatures.     

烧结方法对LiTaO3/Al2 O3复相陶瓷微观组织及力学性能的影响

为了研究铁电／压电陶瓷颗粒对结构陶瓷力学行为的影响规律及机理,分别采用真空热压烧结法和冷等静压成型无压烧结法制备了稳定共存的LiTaO3/Al2O3(LTA)复相陶瓷,对比研究了其微观组织与力学性能,结果表明,1500℃真空热压烧结制备的LTA复相陶瓷中,LiTaO3相熔化,冷却时分布在Al2O3基体晶界,基体晶粒粗化,力学性能较低,200MPa冷等静压成型,1300℃无压烧结制备的LTA复相陶瓷中,LiTaO3颗粒弥散分布,基体晶粒细小,ψ（LiTaO3)为5％的LTA复相陶瓷的力学性能显著改善,强韧化机理为细晶与压电效应和／或电畴运动耗散能量强韧化。     

Effect of sintering temperature on microstructure and electrical properties of ZVMCDN ceramics

The microstructure and electrical properties of ZnO-V₂O₅-MnO₂-Co₃O₄-Dy₂O₃-Nb₂O₅ (ZVMCDN) ceramics were investigated in accordance with sintering temperature (850-950 °C). The microstructure of the samples consisted of mainly ZnO grain as a main phase, and Zn₃(VO₄)₂, ZnV₂O₄, and DyVO₄ as the minor secondary phases. The sintered density decreased from 5.69 to 5.52 g/cm³ due to the volatility of V₂O₅ in accordance with increasing sintering temperature. The maximum nonlinear coefficient (57) was obtained at 925 °C. The donor concentration increased from 1.15 × 10¹⁸/cm³ to 11.1 × 10¹⁸/cm³ in accordance with increasing sintering temperature and the barrier height exhibited the maximum value (1.03 eV) at 925 °C.     

The effect of high energy mechanochemical processing on the microstructure, piezoelectric, ferroelectric and mechanical properties of PLZT ceramics

Lead lanthanum zirconate titanate (PLZT) ceramics were synthesized using a high energy mechanochemical processing technique, using tungsten carbide grinding vials and balls. The ceramic powders were prepared using the constituent oxide powders, which were subjected to high energy milling, without the use of any excess PbO in the starting composition. TEM studies revealed the formation of very fine particles of the order of 30?nm, due to the milling effect. Highly dense ceramics could be prepared via sintering which resulted in ultra-high strains in these piezoelectric samples of up to 0.25%, a value which has not been reported hitherto by any other known process. The effect of the reduction in particle size on the microstructure, mechanical and electrical properties of PLZT ceramics were studied and are discussed herein.     

Reactive sintering of B_4C-TaB_2 ceramics via carbide boronizing:Reaction process,microstructure and mechanical properties

Carbide boronizing is a promising approach to obtain fine grained boron carbide based ceramics with improved mechanical properties. In this work, reaction process, microstructural characteristics and mechanical properties of BxC-TaB_2(x = 3.7, 4.9, 7.1) ceramics were comprehensively investigated via this method. Dense BxC-TaB_2 ceramics with refined microstructure were obtained from submicro tantalum carbide and boron powder mixtures at 1800?C/50 MPa/5 min by spark plasma sintering. The stoichiometry of boron carbide was determined from lattice parameters and Raman shift. It was found that uniformly distributed TaB_2 grains in the BxC matrix is favor of the densification process and restricting grain growth.Besides, planar defects with high density were observed from the as-formed B7.1 C grains and transient stress was considered to contribute to the densification involved with plastic deformation. Microstructural observations indicate the dissolution of oxygen in the TaB_2 lattice and most of the B7.1 C/TaB_2 phase boundaries were clean. Owing to the highly faulted structure and finer grain size, as-obtained BxC-TaB_2 ceramics exhibit high Vickers hardness(33.3–34.4 GPa at 9.8 N) and relatively high flexural strength ranging from 440 to 502 MPa.     

Effects of excessive magnesium oxide and sintering regime on microstructure and dielectric properties of forsterite ceramics for millimeterwave dielectrics

Journal of Materials Science: Materials in Electronics - forsterite (Mg2SiO4) ceramic is an important millimeterwave dielectric ceramic with the advantages of low dielectric constant, high quality...     

Effects of sintering aids on the microstructure and mechanical properties of laminated Si3N4/BN ceramics

Laminated Si₃N₄/BN ceramics with two types of sintering aids, MgO–Y₂O₃–Al₂O₃ (MYA) and La₂O₃–Y₂O₃–Al₂O₃ (LYA), were fabricated through roll compaction and hot-pressing. Sintering aids influence evidently the microstructure and mechanical properties of laminated Si₃N₄/BN ceramics. In comparison with La₂O₃–Y₂O₃–Al₂O₃, MgO–Y₂O₃–Al₂O₃ sintering aid is easier to form a glassy phase with lower viscosity and lower eutectic temperature, which is much easier to migrate into BN interlayers. This results in the denser interlayer microstructure and good bending strength of laminated Si₃N₄/BN ceramics at room temperature, but poor work of fracture (WOF) at room temperature, low strength and work of fracture at elevated temperature. In addition, the LYA sintering aid is good for forming elongated and interlocked β-Si₃N₄ grains and beneficial to the mechanical properties of the laminated Si₃N₄/BN ceramics.     

Effect of sintering condition on microstructure and dielectric properties of BSTN composite ceramics

The effect of sintering condition on the phase composition, microstructure and dielectric properties of barium strontium titanate niobate (BSTN) composite ceramics, in which the perovskite phase and the tungsten bronze phase coexisted, was investigated by XRD, SEM and LCZ Meter. The results show that more Sr²⁺ ions dissolved from the grain boundaries into the crystal lattice of the pervoskite phase and the tungsten bronze phase, especially, into the lattice of the pervoskite phase with the increasing of sintering temperature and sintering time, respectively. So the Curie temperature point decreases with the increasing of sintering temperature. The crystal growth rate of the tungsten bronze phase is higher than that of the perovskite phase in BSTN composite ceramics as the sintering temperature increases. The reasonable sintering temperature is about 1275 °C for BSTN composite ceramics. The activation energy to setting up polarization in BSTN composite ceramics increases with the increase of the applied frequency.     

The effect of Si additions on the sintering and sintered microstructure and mechanical properties of Ti-3Ni alloy

Thermodynamic predictions suggest that silicon has the potential to be a potent sintering aid for Ti-Ni alloys because small additions of Si lower the solidus of Ti-Ni alloys appreciably (>200 °C by 1 wt.% Si). A systematic study has been made of the effect of Si on the sintering of a Ti-3Ni alloy at 1300 °C. The sintered density increased from 91.8% theoretical density (TD) to 99.2%TD with increasing Si from 0% to 2%. Microstructural examination reveals that coarse particles and/or continuous networks of Ti₅Si₃ form along grain boundaries when the addition of Si exceeds 1%. The grain boundary Ti₅Si₃ phase leads to predominantly intergranular fracture and therefore a sharp decrease in ductility concomitant with increased tensile strengths. The optimum addition of Si is proposed to be ≤1%. Dilatometry experiments reveal different shrinkage behaviours with respect to different Si contents. Interrupted differential scanning calorimetry (DSC) experiments and corresponding X-ray diffraction (XRD) analyses clarify the sequence of phase formation during heating. The results provide a useful basis for powder metallurgy (PM) Ti alloy design with Si.     

烧结温度对WZV材料力学性能和显微结构的影响

为了开发一种新型刀具材料,以WC、ZrO2和VC为原料,利用热压烧结工艺,分别在1500、1550、1600℃和1650℃烧结温度下制备了4种相同成分的WC/ZrO2/VC(WZV)复合材料.分析了烧结温度与刀具材料相对密度、硬度、抗弯强度和断裂韧性之间的关系,研究了烧结温度对刀具材料力学性能和显微结构的影响,确定了该材料合理的烧结温度为1550℃.试验结果表明,ZrO2质量分数为10%的WZV复合粉末经过48 h的高能球磨,在1550℃、30 MPa的热压烧结条件下,可获得相对密度为99.2%,维氏硬度为17.6 GPa,抗弯强度为786 MPa,断裂韧性为11.51 MPa.m1/2的优异性能.此外,通过对材料显微结构和断裂方式的分析,发现烧结温度对材料的断裂方式具有重要影响.     

烧结温度对多孔TiNi合金微观结构和力学性能的影响

采用Ti、Ni纯元素混合粉末真空烧结技术制备了孔隙分布均匀且力学性能优良的多孔TiNi形状记忆合金(SMA),并利用X射线衍射仪、金相显微镜、扫描电子显微镜及电子万能试验机研究对比了900、950、1000、1050、1100和1150℃6个不同烧结温度对合金微观结构和力学性能等的影响。结果表明,烧结温度是影响多孔TiNi合金性能的决定性因素,通过调节烧结温度可有效调节合金的相组成、孔隙特征和力学性能。随着烧结温度的升高,合金的次生相逐渐减少,相组成成分更加均一;致密度不断提高,由59%上升到62%,孔隙分布愈加均匀且孔隙形貌由多尖角形趋于球形化;抗拉强度由72.43MPa增加到160.12MPa,弹性模量从1.08GPa增加到1.32GPa。     

Microstructures and electrical properties of copper oxide doped terbium oxide ceramics

The effects of copper oxide (CuO) on the microstructure and electric properties of nonstoichiometric compound terbium dioxide (Tb₄O₇) ceramics were investigated. Results included a reduction in the sintering temperature to 1,100 °C, a grain size of 4.2 μm, and a density of 96.2 %, which are larger than the values in previous investigation for Tb₄O₇ ceramics (grain sizes between 0.4 and 1.0 µm). Among the sintered ceramics, the sample doped with 10.0 wt% CuO showed the maximum nonlinear coefficient α = 43.5, which is obviously greater than α = 3.03 of the pure sample. Doping with 10.0 wt% CuO also exhibited nonlinearity α = 2.14 even at 1,123 K. In addition, the impedance spectra of the sample doped with 5.0 mol% CuO showed the largest grain boundary semicircle; 0 and 20 % samples showed both inductive and capacitive reactance.     

Effects of sintering temperature on the microstructure and dielectric properties of titanium dioxide ceramics

Nanostructured (~200 nm grain size) titanium dioxide (TiO₂) ceramics were densified at temperature as low as 800 °C by pressureless sintering in a pure oxygen atmosphere. Phase transition and microstructural development of sintered samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Dielectric properties including d.c. conductivity, dielectric constant, loss tangent, and dielectric breakdown strength (BDS) were determined for samples sintered at various temperatures. The influence of sintering temperature on the microstructural development, defect chemistry, and dielectric properties of TiO₂ is discussed. Nanostructured TiO₂ ceramics with high sintering density (>98%) lead to improved dielectric properties; high BDS (~1800 kV/cm), low electrical conductivity (~5 × 10⁻¹⁵ S/cm), high dielectric constant (~130), and low loss tangent (~0.09% at 1 kHz), which is promising for application in high energy density capacitors.     

The effect of aluminium on the electrical and mechanical properties of BaTiO3 ceramics as a function of sintering temperature

The effect of aluminium additions on the mechanical behaviour of BaTiO₃ positive temperature coefficient of resistance ceramics sintered in air at temperatures ranging between 1220 and 1400° C has been investigated. Tensile strength has been measured indirectly by the diametral compression of lapped discs using concave loading anvils. Values of ∼ 85 and ∼ 110 MPa for samples fired near their optimum sintering temperature were determined for two batches of material, the latter of which contained additions of Al₂O₃ (0.55 mol%). Strength did not vary systematically with grain size and appeared to be controlled by near surface defects. The size of these cavities, which were generally crescent shaped, was consistent with the material having a bulk fracture toughness of ∼1.3 MPam^1/2. The higher mechanical strength of samples which contained Al₂O₃ additions was attributed to the enhanced “healing up” of these cavities by the liquid phase giving a smaller inherent critical defect size rather than by increasing the bulk toughness of the ceramic.     

Effects of PbO content on the sintering behavior, microstructure, and properties of La-doped PZST antiferroelectric ceramics

Effects of PbO content, from 4 mol % deficiency to 4 mol % excess, in the original lanthanum-doped lead zirconate titanate stannate powder compositions (PLZST) on the sintering behavior, microstructure, and properties of the antiferroelectric ceramics were investigated. PbO-deficient samples undergo solid-state sintering at temperatures above 1000 °C, which results in smaller pores but higher porosity in the materials, while PbO excess introduces an additional liquid-phase sintering mechanism and a fast densification at rather low temperatures, down to 700 °C, but leads to larger pores and exaggerated grain growth within the ceramics. It is indicated by the dilatometry data that the maximum solid-state sintering rate and corresponding temperature decrease with rising PbO content. The main fracture mode of the material changes from transgranular to intergranular with PbO content going from deficiency to excess. PbO content also influences the final density, the lattice parameters of the perovskite structure, and Youngs modulus of the specimens. Altogether, the electric field for the transition from the antiferroelectric to the ferroelectric state decreases slightly with PbO content, while the back transition field exhibits the opposite trend. Thus, the hysteresis of the field-induced strain loop is found to decrease with an increase in the PbO content; the linear strain at the antiferroelectric to ferroelectric transition field, however, remains at about 0.2%, independent of the PbO content.     

Thermal effects on the microstructure and mechanical properties of ion implanted ceramics

The effects of varying the substrate temperature on the implantation-induced structures and surface mechanical properties of single crystal sapphire and MgO have been investigated for a range of 300 keV implanted ions. As the implantation temperature is lowered, the dose at which amorphization occurs is reduced and thus, for the same doses, more amorphous material is produced at lower temperatures. Quantitative modelling shows that the activation energy for annealing of the amorphous material during implantation is very much lower than might be expected for post-implantation thermal annealing of the same material. Also, as the implantation temperature increases there is a small amount of damage annealing in the damaged-but-crystalline material.Both the microhardness and implantation-induced stresses depend critically on the presence of amorphous material since this is relatively soft and can support only small stresses. However, while the hardness behaviour in the damaged-but-crystalline material is dominated by radiation hardening, the substitutionality, ionic misfit and charge state of the implanted ions have also been found to contribute to the further solid solution component of the hardening produced by ion implantation. These effects are also observed to be temperature dependent. Crazing of the implanted layers has also been reappraised. It has been established that the formation and configuration of crazes is a sensitive function of implantation temperature, and it is now proposed that crazes form in response to the stresses generated as a result of the thermal expansion mismatch between the amorphous layer and the substrate.     

The effects of pressurization on the microstructure and mechanical properties of magnesium oxide

Changes in microstructure in single crystals of MgO, containing elastic discontinuities, which result from pressurization treatments in the range 0.2 to 2 GN m^–2 have been studied using an etch-pitting technique. Complex dislocation arrays have been observed around cubical and spherical cavities and precipitates. The observations are discussed in terms of stress and strain criteria. Production of {100} and {110} cracks at high pressure is also described. Following a 1 GN m^–2 pressurization the flow stress was observed to decrease by < 10% and this has been related to the induced dislocation density. In polycrystalline MgO the fracture strength was unaltered by pressurization but the critical temperature difference of thermal shock,T _C, was increased by 55K. This has similarly been attributed to the movement of pressurization-induced dislocations.     

Annealing effects on microstructure and mechanical properties of chromium oxide coatings

Reactive radio frequency magnetron sputter-deposited chromium oxide coatings were annealed at different temperatures and times. The influence of annealing temperature on the microstructure, surface morphology and mechanical properties was examined by X-ray diffraction, nanoindentation, pin-on-disc wear and scratch tests, respectively. X-ray results show that the chromium oxide sputtered at room temperature in low oxygen flux is primarily amorphous. Annealing below 400 °C did not cause much change, while annealing at higher temperature of 500 °C caused a significant change in microstructure and mechanical properties. Hardness increased from 12.3 GPa to 26 GPa, and the wearability improved with higher annealing temperature due to the formation of crystalline Cr₂O₃ phase, which occurs at 470 °C. Annealing time had little effect on mechanical properties and microstructure, although coating surface roughness increased with a longer annealing time. Coating adhesion was improved by annealing, due to residual stress relief and possible interfacial interdiffusion.     

Effect of additives on the microstructure and mechanical properties of commercial alumina ceramics

The effect of impurities or additives on the microstructure of some commercial alumina ceramic samples have been characterized by scanning electron microscope-energy dispersive x-ray spectrometer and the mechanical properties investigated. Both the hardness and the toughness have been found to increase as the SiO₂ content decreases, and the theoretical density is reached in these materials. Grain size and distribution seem to be important factors in the mechanical properties of alumina ceramics. If the additives are controlled carefully, finer grain size and distribution can be obtained, together with a high relative density in terms of pore distribution characteristics and consequently enhanced mechanical properties.