Reaction Sintering and Properties of AlON-AlN Composite Ceramics
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AlON-AlN composite ceramics were prepared with Y2O3 as sintering additive by pressureless reaction sintering in nitrogen atmosphere.The phase compositions and microstructure of AlON-AlN composite ceramics were characterized by XRD and SEM.The effects of sintering temperature and Al2O3 and Y2O3 content on sintering performance,mechanical properties and thermal conductivity were studied.The results show that the AlON-AlN composite ceramics could be fabricated at 1 650-1 800 ℃.As the temperature increased,the bend strength and thermal conductivity both increased first and then decreased,and the maximum values(378 MPa,38 W·m-1·K-1) were gained respectively at 1 750 ℃ and 1 700 ℃.As the Al2O3 content increased,the bend strength of the sample increased till Al2O3 content up to 30%,and then decreased.The thermal conductivity decreased obviously with the increase of Al2O3 content.The bend strength increased remarkably as the Y2O3 content increased while the maximum of thermal conductivity appeared when the Y2O3 content was 3%.Cite
Atmospheric temperature range
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Liquid phase
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Pressureless sintering of the SiC-AlN system with Y2O3 as a sintering aid was carried out. Composites with<50vol% SiC were densified to above 98% of the theoretical density in N2 atmosphere of 0.1MPa at temperatures below 1900°C using commercial SiC and AlN powders. The densification behavior was investigated and analyzed on the basis of microstructural observation. The strength and deformation of the densely pressureless-sintered AlN and SiC-AlN composites were measured from room temperature to 1500°C by small punch testing. The sintered AlN and SiC-AlN composites showed no strength decrease at temperatures below 1200°C, whereas the SiC-AlN composites showed higher strength at room temperature and retained them to higher temperature. At 1500°C, plastic-like deformation was observed in the SiC-50 and 70vol% AlN composites. The microstructural observation suggested that the fine microstructure with a uniform and fine grain size in the SiC-AlN composites was a dominant factor responsible for the plastic-like deformation at high temperature.
Pressureless sintering
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Using MnO2 as sintering aids,the influence of MnO2 content and sintering process on sintering ability and properties of 8YSZ were investigated.Archimedes principle,hardness-testing devices and universal-testing machine was employed to measure the relative density,hardness and bending strength of the sintered bulk.XRD and SEM were also used to analyze the crystallographic phase,microstructure of the sintered bulk.The results show that the relative density of the sintered bulk increases with the increase of the proportion of MnO2.The best sintering ability is obtained when 3%MnO2 is doped.The relative density of the sintered bulk also increases as the temperature rises.The relative density reaches 98.59%,and the hardness and flexural strength reach 1830.21(HV) and 235.46 MPa respectively,when the sintering temperature is 1 300 ℃ and soaking time is 4 h.
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Reaction sintering B 4 C/SiC ceramics with high density were manufactured. The effect of the carbon content in green bodies on the microstructure and mechanical properties of the ceramics has been studied. Results showed that the carbon content and the value of carbon relative density (ρ CRD ) in the green bodies were the major factors affected the composition, that is, the free silicon and carbon contents and mechanical behaviors of sintered specimens. The optimal value of ρ CRD was gotten at 0.85 g/cm 3 . The fracture toughness, flexural strength, and hardness of the composites increased with increasing carbon content up to 20 wt.%. The maximum values of fracture toughness of 3.8 MPa∙m 1/2 , flexural strength of 475 MPa, and hardness of 32.0 GPa were obtained under the following process parameters: value of ρ CRD in the green bodies was about 0.85 g/cm 3 ; carbon, B 4 C and SiC contents in green bodies were 20 wt.%, 30 wt.% and 50 wt.%, respectively; compact pressure was 75 MPa and sintering temperature was 1600°C.
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This paper presents the investigation of the effect of sintering temperature on mechanical properties of Al/SiC composites. The composites were produced via conventional powder metallurgy processing. The particle size of Al and SiC powders are 63 µm and 37 µm respectively. The sintering temperatures exerted on the samples were 550, 570, 590, 610, 630 and 650oC at a fixed time of 1 h. The compressive, hardness and impact tests were performed on the sintered samples to characterize their mechanical properties. It was found that as the sintering temperature increase, the mechanical properties of the samples were also increased at earlier temperature and show a decrease trend thereafter. Similarly, this trend was also observed in the density test. Furthermore, microscopic observations showed that the porosity level decrease as the sintering temperature increase excluding at the temperature of 650oC.
Powder Metallurgy
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The mullite/SiC-Si3N4multiphase ceramics were fabricated by pressureless sintering. The multiphase ceramics were analyzed by the X-ray diffraction and environmental scanning electron microscopy; meanwhile the bulk density,apparent porosity, linear shrinkage and mechanical properties of the obtained ceramics were also characterized. The results show that the main phase of the obtained ceramics is mullite after sintering at different temperatures. With increasing sintering temperature, the grain size increases, the ceramics form more close porosity, the bulk density and linear shrinkage increase, the apparent porosity decreases, the microhardness decreases significantly, the bending strength and compressive strength are improved obviously with the maximum values of 110 MPa and 193 MPa, respectively. For the ceramic sintered at 1 600 ℃, with the composition of the molar ratio increasing by the order of n(Al2O3):n(SiO2)=1:1,11:9, 3:2, the bulk density, microhardness and compressive strength increase, the pore size decreases.
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TiB whisker reinforced Ti-4.5Al-6.8Mo-1.5Fe titanium matrix composite was fabricated by mechanically mixing the elemental powders of titanium,aluminum,molybdenum,iron,lanthanum hexaboride as well as titanium diboride,and then followed by high-velocity compaction and vacuum sintering at 1 150,1 250 and 1 350 ℃,respectively.The phase composition and microstructure were characterized by X-ray diffractometry(XRD),optical microscopy(OM) and scanning electron microscopy(SEM),and the mechanical properties were also tested.The effect of sintering temperature on microstructure and mechanical properties of the samples were discussed.The results show that the relative density of the sintered samples increases with increasing sintering temperature,and the maximum value reaches 98.9% at 1 350 ℃.While the ratio of length to diameter of the TiB whisker decreases remarkedly with increasing sintering temperature.The mechanical properties such as the Vickers hardness(HV2.0) and tensile strength increase firstly and then decrease with increasing sintering temperature,and the maximum values of 399 HV and 1 179 MPa,respectively are obtained sintered at 1 250 ℃.
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Stereolithography
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Alumina ceramic
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Electrical discharge machining can be used easily for the materials which has good conductivity. In order to improve conductivity of Si3N4 based ceramics, TiN/Si3N4 composite was sintered by adding TiN into Si3N4 powder. In the present research, influence of sintering temperature (1535-1925°C, 8 temperatures) on properties and microstructure of the TiN/Si3N4 composite were investigated with La2O3, AlN as sintering additives, liquid phase pressure less sintering used. Densities of the sintered sample were measured. Bending strength, hardness, fracture toughness and electrical resistively of the sample were tested. Phase composition and microstructure of the samples were analyzed by XRD, SEM and EDX. The results showed that the density and fracture toughness of the sintered bodies reached maximum at temperature of 1760°C (relative density of 97.9%; fracture toughness of 8.5 MPa•m1/2) in the sintering temperature range of 1535~1925°C. With increasing of temperature, the bending strength and hardness of the samples kept raising, reached maximum at temperature of 1925°C (bending strength of 634MPa and Vickers hardness of 1869). But the weight lost at the highest temperature was the severe. Microstructure and EDX showed that crystals of the Si3N4 transferred into complete β phase from α + β both phases. The grain of Si3N4 grew up into long columnar from equiaxial fine particles. The fine grain of TiN grew up also. The comprehensive performances of the samples are better at sintering temperature of 1760°C. The long columnar β-Si3N4 grains interweaved with conductive TiN particles, formed conductive nets through sintering. At this sintering temperature, the bending strength of TiN/Si3N4 sintered body was 560MPa，Vickers hardness 1708MPa. The conductivity of the sintered bodies was irregular with the difference of temperature. The minimum of the conductivity is 20Ω.
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