Mechanical Properties and Thermal Shock Resistance of SrAl_(2)Si_(2)O_(8) Reinforced BN Ceramic Composites

Hexagonal boron nitride(h-BN)ceramics have become exceptional materials for heat-resistant components in hypersonic vehicles,owing to their superior thermal stability and excellent dielectric properties.However,their densification during sintering still poses challenges for researchers,and their mechanical properties are rather unsatisfactory.In this study,SrAl_(2)Si_(2)O_(8)(SAS),with low melting point and high strength,was introduced into the h-BN ceramics to facilitate the sintering and reinforce the strength and toughness.Then,BN-SAS ceramic composites were fabricated via hot press sintering using h-BN,SrCO_(3),Al_(2)O_(3),and SiO_(2) as raw materials,and effects of sintering pressure on their microstructure,mechanical property,and thermal property were investigated.The thermal shock resistance of BN-SAS ceramic composites was evaluated.Results show that phases of as-preparedBN-SAS ceramic composites are h-BN and h-SrAl_(2)Si_(2)O_(8).With the increase of sintering pressure,the composites’densities increase,and the mechanical properties shew a rising trend followed by a slight decline.At a sintering pressure of 20 MPa,their bending strength and fracture toughness are(138±4)MPa and(1.84±0.05)MPa·m^(1/2),respectively.Composites sintered at 10 MPa exhibit a low coefficient of thermal expansion,with an average of 2.96×10^(-6) K^(-1) in the temperature range from 200 to 1200℃.The BN-SAS ceramic composites prepared at 20 MPa display higher thermal conductivity from 12.42 to 28.42 W·m^(-1)·K^(-1) within the temperature range from room temperature to 1000℃.Notably,BN-SAS composites exhibit remarkable thermal shock resistance,with residual bending strength peaking and subsequently declining sharply under a thermal shock temperature difference ranging from 600 to 1400℃.The maximum residual bending strength is recorded at a temperature difference of 800℃,with a residual strength retention rate of 101%.As the thermal shock temperature difference increase,the degree of oxidation on the ceramic surface and cracks due to thermal stress are also increased gradually.

Effect of VC/Cr_3C_2 on microstructure and mechanical properties of Ti(C,N)-based cermets

Effects of VC/Cr3C2 on the microstructure and mechanical properties of Ti（C,N）-based cermets were studied. The microstructure was investigated by means of optical microscopy, X-ray diffractometry as well as scanning electron microscopy in combination with energy dispersive spectrometry. Mechanical properties, such as transverse rupture strength, hardness and fracture toughness, were measured. The results show that there are black core-grey rim structure and white core-grey rim structure in the microstructure. The grains become fine due to the VC/Cr3C2, and the grains of cermet added with 0.75VC/0.25Cr3C2 are refined most remarkably. The black core becomes finer with the increase of VC addition and rim phase becomes thicker with the decrease of Cr3C2 addition. The porosity increases with the increase of VC addition in VC/Cr3C2. Compared with the cermet free of VC/Cr3C2, the transverse rupture strength and hardness of cermets with VC/Cr3C2 are both improved, and the maximum values are both found for the cermet with 0.25VC/0.75Cr3C2. The fracture toughness can be effectively promoted by adding VC/Cr3C2 with an appropriate ratio of VC to Cr3C2, and the maximum value is found for the cermet with 0.5VC/0.5Cr3C2.

Effect of additives on properties of aluminium titanate ceramics

The influence of some additives on bulk density,phase composition,mechanical strength and thermal shock resistance of aluminium titanate （AT） ceramics was investigated.AT ceramics with different additives of MgO,SiO2 and Fe2O3 were prepared by reaction sintering.Properties of AT ceramics were tested by using Archimedes,three-point bending and thermal cycling tests.It was found that additives of MgO,SiO2 and Fe2O3 or their compound additives are favorable to reduce the porosities of AT,enhance mechanical strength and thermal shock resistance.The role of additives can be rationalized in terms of promotion of sintering process,formation of new phases and influence on lattice constant c of AT ceramics.

INTELLIGENT PRECISION CONTROL IN CNC GRINDING

The development of intelligent control techniques provides powerful means for the control of machine tools. In this paper, a intelligent control technique and an algorithm for precision control of CNC grinding of ceramic chips are introduced. In the process of ceramic chip CNC grinding, the dimension of the chips tends to get larger and the dimensional error to exceed the tolerance as the number of the chips increases which are machined on the same part program. There are many factors leading to the occurrence of the error and the law of error variation is very complicated. With the introduced intelligent self learning error compensation technique, the CNC system can improve the control strategy to compensate the error automatically. The simulational result is also given.

Thermodynamic analysis of interactions between Ti-Al alloys and oxide ceramics

The thermodynamics of interactions between various oxides（CaO,MgO,Al2O3 and Y2O3） and molten Ti and Ti alloys was investigated.The dissolution mechanism of oxides in molten Ti alloys was provided and the stability of oxides in molten Ti alloys was investigated and predicted by thermodynamic analysis.Interactions between oxides and Ti-Al melts were studied by oxide crucible melting experiments.By quantitative analysis,it is indicated that impurity contents in alloys are proportionally decreased with increasing the Al content in alloys and decreasing the melt temperature,which is in agreement with the results of the predicting thermodynamic stability.

Effect of sintering atmosphere on phase composition and mechanical properties of 5Ni/(10NiO-NiFe_2O_4)

5Ni/（10NiO-NiFe2O4） cermet materials were prepared by cold pressing sintering method in different atmospheres. The phase compositions were studied by XRD, microstructure was studied by SEM and mechanical properties were studied by three-point-bending strength and heat cycle. The results show that Ni/（NiO-NiFe2O4） cermet can be obtained by sintering in vacuum or atmospheres with oxygen content of 2×10-5, 2×10-4 and 2×10-3, respectively, but the phase composition of the ceramics varies greatly with oxygen content of the sintering atmosphere. The cermet tends to have a high content of NiO when sintered in vacuum. The content of NiFe2O4 and Ni in the cermet materials respectively increases and decreases with increasing oxygen in the sintering atmosphere. In the vacuum, cermet has an average grain size of 3.90 μm and bending strength of 138.59 MPa, which is able to withstand thermal shock tests 6.67 times in average.

Corrosion resistance of micro-arc oxidized ceramic coating on cast hypereutectic alloy

The corrosion resistance of the micro-arc oxidation(MAO) ceramic coating on a cast Al-13Si-5Cu alloy was investigated using various electrochemical methods including electrochemical impedance spectroscopy(EIS) and polarization curves.Microstructures of MAO ceramic coating were studied by SEM,and the influence of microscopic patterns on corrosion resistance was analyzed.The corrosion resistance of the aluminum alloy can be improved significantly by MAO process owing to increasing impedance and corrosion potential and decreasing corrosion current,and the ceramic coatings are composed of loose layer,compact layer and transition layer,which improve the corrosion resistance.The corrosin resistance is determined by the thickness of the compact layer and is not proportional to the total thickness of MAO,though the latter is one of the important factors influencing the corrosin resistance.

An investigation on crystallization property, thermodynamics and kinetics of wollastonite glass ceramics

Wollastonite glass ceramics were prepared using the reactive crystallization sintering method by mixing waste glass powders with gehlenite.The crystallization property,thermodynamics,and kinetics of the prepared wollastonite glass ceramics were determined by X-ray diffraction analysis,scanning electron microscopy,energy-dispersive spectroscopy,high-resolution transmission electron microscopy,and differential thermal analysis.Results showed that crystals of wollastonite and alumina could be found in the gehlenite through its reaction with silicon dioxide.The wollastonite crystals showed a lath shape with a certain length-to-diameter ratio.The crystals exhibited excellent bridging and reinforcing effects.In the crystallization process,the aluminum ions in gehlenite diffused into the glass and the silicon ions in the glass diffused into gehlenite.Consequently,the three-dimensional frame structure of gehlenite was partially damaged to form a chain-like wollastonite.The results of crystallization thermodynamics and kinetics indicated that crystallization reaction could occur spontaneously under a low temperature(1173 K),with 20 wt%gehlenite added as the reactive crystallization promoter.The crystallization activation energy was evaluated as 261.99 kJ/mol by using the Kissinger method.The compression strength of the wollastonite glass ceramic samples(7.5 cm×7.5 cm)reached 251 MPa.

Sintering behavior and mechanical properties of sintered ceramics based on spodumene tailings

In this study,ceramics was prepared by slip casting(no pressure was used during shaping step)and atmospheric pressure sintering with low-melting point glass(LPG)powder as the binding material to facilitate the transformation of spodumene flotation tailings(SFTs)into ceramics at lower temperatures.The influence of sintering temperature and mass ratio of LPG on the mechanical properties(flexural strength and compressive strength)of ceramic materials was studied by orthogonal test.The results showed that when the mass ratio of LPG powder was higher than or equal to 20 wt%and the sintering temperature was higher than or equal to 550℃,mutual adhesion between the sample particles was realised and consequently the ceramic materials could be prepared with good mechanical properties(the maximum flexural strength=19.55 MPa,the maximum compressive strength=42.25 MPa,average porosity=24.52%,average apparent density=1.66 g/cm^(3),and average water absorption=14.79%).The sintered ceramics were characterized by XRF,XRD,optical microscopy analysis,SEM,TGA-DSC and FT-IR.The formation of liquid phase at high temperature may lead to the mutual bonding between particles,which might be the main reason for the improvement of mechanical properties of ceramic materials.Overall,SFTs were successfully sintered at low temperature to prepare ceramic materials with good mechanical properties,which are crucial for energy conservation and environmental preservation.

Effect of sintering atmosphere on composition and properties of NiFe_2O_4 ceramic

Ni Fe2O4 ceramics were prepared in different sintering atmospheres. The phase compositions, microstructures and mechanical properties were studied. The results show that the stoichiometric compound Ni Fe2O4 cannot be obtained in vacuum or atmospheres with oxygen contents of 2×10-5, 2×10-4 and 2×10-3, respectively. All the samples sintered in above-mentioned atmospheres contain phases of Ni Fe2O4 and Ni O. With increasing oxygen content, Ni Fe2O4 content in the ceramic increases, while Ni O content appears a contrary trend. In vacuum, Ni Fe2O4 ceramic has average grain size of 3.94 μm, and bending strength of85.12 MPa. The changes of the phase composition and mechanical properties of Ni Fe2O4 based cermets are mainly caused by the alteration of their properties of Ni Fe2O4 ceramic.

PREDICTION OF TEXTILE FABRIC REINFORCED COMPOSITE PROPERTIES BASED ON NODE INTERPOLATION CELL METHOD

Node interpolation cell method（NICM）is a micromechanics method employing the virtual displacement principle and the representative volume element（RVE）scheme to obtain the relationship between the global and the local strain.Mechanical properties of 2-D textile fabric reinforced ceramic matrix composites are predicted by NICM.Microstructures of 2-D woven and braided fabric reinforced composite are modeled by two kinds of RVE scheme.NICM is used to predict the macroscopic mechanical properties.The fill and warp yarns are simulated with cubic B-spline and their undulating forms are approximated by sinusoid.The effect of porosity on the fiber and matrix are considered as a reduction of elastic module.The connection of microstructure parameters and fiber volume fraction is modeled to investigate the reflection on the mechanical properties.The results predicted by NICM are compared with that by the finite element method（FEM）.The comparison shows that NICM is a valid and feasible method for predicting the mechanics properties of 2-D woven and braided fabric reinforced ceramic matrix composites.

Thermal decomposition and mechanical properties of hydroxyapatite ceramic

Pure hydroxyapatite（HAP）ceramic and HAP composite ceramic with B2O3 were prepared by isostatic press forming and pressureless sintering.The relationships between thermal decomposition ratio and mechanical properties for pure HAP ceramic and the composite ceramic were investigated by means of FTIR,X-ray diffraction and three-point bending method.The results indicate that the decomposition ratio of pure HAP ceramic increases with ascending the sintering temperature and nearly reaches 80%at 1 350？殆or the HAP composite ceramic,the thermal decomposition is inhibited obviously due to the addition of B2O3.The added B atoms incorporate into the crystal lattice of HAP to form solid solution,resulting in an enlargement in the crystal spacing and an improvement in the binding strength of HAP crystal cell.Thermal decomposition ratio of HAP decreases but bending strength and fracture toughness are enhanced for HAP composite ceramics.However,when the added B2O3 is more than 5%（mass fraction）,HAP decomposition is promoted and a steady？-TCP is formed due to the fact that when B atoms with higher negative electricity are combined with O,sp2 and a full-air p are formed,and those voids have a strong trend to intake of the outer electrons.So,it is very possible to occupy the place where HAP loses OH - or PO4 3- .

Dielectric properties and point defect behavior of antimony oxide doped Ti deficient barium strontium titanate ceramics

The microstructures and dielectric properties of Sb2O3-doped Ti deficient barium strontium titanate ceramics prepared by solid state method were investigated with non-stoichiometric level and Sb2O3content by SEM,XRD and LCR measure system.It is found that with the increase ofδ,(Ba0.75Sr0.25)Ti1-δO3-2δceramics transform from single phase solid solutions with typical cubic perovskite structure to multiphase compounds while(Ba0.75Sr0.25)Ti0.998O2.996ceramics remain to be single-phase with the increasing Sb2O3content.The distortion of the ABO3perovskite lattice caused by VTi″″and VO..induces the drop of Curie temperature and the rise of relative dielectric constant in(Ba0.75Sr0.25)Ti1-δO3-2δceramics with increasingδvalue.The orientation of VO??elastic dipoles results in the domain-wall pinning and thus the reduction of the dielectric loss.With increasing Sb2O3content,the relative dielectric constant,dielectric constant maximum and Curie temperature of(Ba0.75Sr0.25)Ti0.998O2.996ceramics decrease dramatically while the dielectric loss increases.

Studies on rock magnetic and paleointensity of some archaeological artifacts from Tamilnadu,India

This study investigates the magnetic mineralogy and paleointensity values of a collection of archaeological artifacts(pottery) . The actual magnetic carriers and their domain states present in the archaeological pottery were obtained using the low field susceptibility,thermomagnetic curves and acquisition of isothermal remanence. The magnetic mineralogy of all the samples was dominated by ferrimagnetic mineral(magnetite/magnetite with low titanium content) ,which was suitable for paleointensity measurements. The geomagnetic paleointensity value obtained by subjecting them to modified Thellier and Thellier method,is found to be(48.81±0.15) μT.

Enhancing microstructural properties of alumina ceramics via binary sintering aids

Alumina ceramics are widely used in many fields such as cutting tools,laser shock materials,roadbed board and refractory.Herein,Al_(2)O_(3)ceramics are prepared by a low-cost pressureless sintering technology,using the binary sintering aids of MgO and SiO_(2).The effects of sintering temperature and the ratio of binary sintering aids on the mechanical properties and microstructure of Al_(2)O_(3)ceramics are investigated.A spinel second phase(MgAl_(2)O_(4))is found out by the analysis of the results of XRD and EDS when MgO and SiO_(2)are introduced in the samples.The optimum properties are found when MgO content is 20 wt.%based on the total sintering aids and the sintering temperature is 1550℃.The bending strength and the bulk density reach a maximum value of 314 MPa and 3.73 g/cm^(3),respectively.The addition of appropriate amount of SiO_(2)makes the formation of liquid phase sintering and the removal of large pores.Meanwhile,a small amount of magnesium oxide doping has an effect on the grain refinement from the microstructure of the sample.Therefore,it is believed that MgO and SiO_(2)are the ideal sintering aids for promoting the densification and property of alumina ceramics.

Preparation of porous silicon carbide by combustion synthesis

Porous silicon carbide ceramics were prepared by combustion synthesis technique. SiC/TiC composite was gained by combustion reaction of Si, C and Ti. Thermodynamics analysis of Si-C-Ti system indicates that the content of TiC in products should be larger than 30%. The experimental results show that the content of Ti+C should be larger than 25% to achieve a complete combustion reaction. The X-ray diffractometry results show that the final products with a relative density of 45%64% are composed of α-SiC, β-SiC, TiC and a small quantity of Si. The images of scanning electron microscopy show that the structures of grain in SiC based porous ceramics consist of particles with a few microns in size.

Impact of Letian Pottery Workshop for the Students of Fine Arts Department of Jingdezhen Ceramic Institute

＂Jingdezhen is a very spiritual place, and a lot of people want to engage in pottery complacent here＂. It is no exaggeration to say that Pottery Workshop chooses Jingdezhen, which has long history of ceramics and profound culture, and the local development is promising. It is not only young artists and students to communicate with the creation of the stage, like a pottery family. Someone said that it was the ＂798＂ of Jingdezhen, not only because it is a gathering place for foreign potters, the bigger reason is that it is becoming a ceramic culture and a model of the market economy model. Here not only can give you a display space, more importantly, you can gain practical experience and recognition for their work.

Microstructure and mechanical properties of WC-Co,WC-Co-Cr_3C_2 and WC-Co-TaC cermets fabricated by spark plasma sintering

Spark plasma sintering was successfully used to produce WC-Co cermets with the addition of Cr3C2and TaC grain growth inhibitors. The spark plasma sintered compacts were investigated by scanning electron microscopy, X-ray diffraction analysis, density measurements, hardness tests, fracture toughness tests and elastic modulus tests. The results were comparedwithan inhibitor-free WC-Co cermet consolidated under the same process parameters. By using Cr3C2and TaC additives, it is possible to improve the hardness and fracture toughness of WC-Co cermets, but Cr3C2has better grain growth inhibition propertythan that of TaC. The best combination of hardness （HV30（2105±38）） and fracture toughness （（8.3±0.2）MPa·m^1/2） was obtained by the WC-5Co-2Cr3C2 cermet.

THICKNESS RESPONSE OF β DOSE-RATE IN TL DATING OF POTTERY FRAGMENTS

Generally, the walls of ceramic ware are thin and the sample to be used for TL dating has to be collected from 1￣2mm under the surface.This call introduce significant error into the dating method.Therefore,the results of a series of simulated experiments are reported on the build-up effect of the internal β dose response in different thicknesses of pottery fragments (involving tile and brick).Correction factors,corresponding to different thicknesses,and correction 'depths' are proposed in terms of the experimental findings which may be incorporatd into the dating methods.

Preparation and properties of nano-composite ceramic coating by thermo chemical reaction method

Nano-composite ceramic coating was fabricated on Q235 steel through thermo chemical reaction method. Structure of the coating was analyzed and the properties were tested. The results show that a few of new ceramic phases, such as MgAI2O4, ZnAI2O4, AI2SiO5, Ni3Fe and Fe3AI, are formed on the coating during the process of solidifying at 600 ℃. The ceramic coating is dense and the high bonding strength is obtained. The average bonding strength between the coating and matrix could be 14.22 MPa. The acid resistance of the coating increase by 8.8 times, the alkali resistance by 4.1 times, the salt resistance bv 10.3 times, and the wear resistance bv 2.39 times.