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1.
TiC/Si3N4 composites were prepared using the β-Si3N4 powder synthesized by self-propagating high-temperature synthesis (SHS) and 35 wt.% TiC by spark plasma sintering. Y2O3 and A12O3 were added as sintering additives. The almost full sintered density and the highest fracture toughness (8.48 MPa·m1/2) values of Si3N4-based ceramics could be achieved at 1550℃. No interfacial interactions were noticeable between TiC and Si3N4. The toughening mechanisms in TiC/Si3N4 composites were attributed to crack deflection, microcrack toughening, and crack impedance by the periodic compressive stress in the Si3N4 matrix. However, increasing microcracks easily led to excessive connection of microcracks, which would not be beneficial to the strength. 相似文献
2.
The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt.% TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference (ΔT) and number of thermal cycles (N) on fatigue crack growth (Δa). The mechanical properties and thermal fatigue resistance of TiC/Al2O3 composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al2O3 composites is due to a “true” cycling effect (thermal fatigue). Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites. 相似文献
3.
In this study, La2O3 was investigated as an additive to TiC/W composites. The composites were prepared by vacuum hot pressing, and the microstructure and mechanical properties of the composites were investigated. Experimental results show that the grain size of the TiC/W composites is reduced by TiC particles. When 0.5 wt.% La2O3 is added to the composites, the grain size is reduced further. According to TEM analysis, La2O3 can alleviate the aggregation of TiC particles. With La2O3 addition, the relative density of the TiC/W composites can be improved from 95.1% to 96.5%. The hardness and elastic modulus of the TiC/W + 0.5 wt.% La2O3 composite are little improved, but the flexural strength and the fracture toughness increase to 796 MPa and 10.07 MPa·m1/2 respectively, which are higher than those of the TiC/W composites. 相似文献
4.
The effect of different sintering additives on the high temperature oxidation and corrosion behaviour of silicon nitride based ceramics was investigated. Comparative tests were conducted at 1200 and 1500 °C in air, in water vapour, and with the highly corrosive gases HCl and SO2. Si3N4 was prepared with MgO, Al2O3, Y2O3 and Al2O3 + Y2O3 sintering additives. Hot pressed discs were tested for a total time of up to 128 h. The electrically conductive ceramic composites Si3N4 + TiN and Si3N4 + MoSi2 were also tested under the same conditions. The effects that the different corrosion environments have on the different ceramics are presented. SEM studies of the oxidised ceramics show the direct transformation of Si3N4 grains into SiO2 through a reaction interface layer. 相似文献
5.
Alfian NOVIYANTO Dang-Hyok YOON Kyungseok LEE Young Moon KIM Doo-In KIM Young-Keun JEONG Kwang Ho KIM Sehun KWON Young-Hwan HAN 《中国有色金属学会会刊》2013,23(2):420-425
Si3N4/SiC纳米复合材料由于具有优良的力学和热性能,广泛应用于涡轮发动机、热交换器和其他复杂情况中。然而,不添加添加剂很难制备出Si3N4/SiC复合材料。添加剂在烧结过程形成液相从而促进复合材料的致密化。然而,添加剂的存在降低了复合材料的高温力学性能。通常在不添加添加剂的情况下,采用电场辅助烧结,利用聚合物前体路线制备Si3N4/SiC复合材料。本研究中,在无添加剂、温度1700°C、真空50MPa条件下,热压烧结2h,利用非晶前体路线成功制备了六方-BN致密化的Si3N4/SiC复合材料。聚合物前驱体和BN的作用减少了的SiC含量。并对相变、致密化、微观组织和力学性能进行了讨论。 相似文献
6.
Dongdong Gu Yves-Christian HagedornWilhelm Meiners Konrad WissenbachReinhart Poprawe 《Surface & coatings technology》2011,205(10):3285-3292
A novel Selective Laser Melting (SLM) process was applied to prepare bulk-form TiC/Ti5Si3 in-situ composites starting from Ti/SiC powder system. The influence of the applied laser energy density on densification, microstructure, and mechanical performance of SLM-processed composite parts was studied. It showed that the uniformly dispersed TiC reinforcing phase having a unique network distribution and a submicron-scale dendritic morphology was formed as a laser energy density of 0.4 kJ/m was properly settled. The 96.9% dense SLM-processed TiC/Ti5Si3 composites had a high microhardness of 980.3HV0.2, showing more than a 3-fold increase upon that of the unreinforced Ti part. The dry sliding wear tests revealed that the TiC/Ti5Si3 composites possessed a considerably low friction coefficient of 0.2 and a reduced wear rate of 1.42 × 10− 4 mm3/Nm. The scanning electron microscope (SEM) characterization of the worn surface morphology indicated that the high wear resistance was due to the formation of adherent and strain-hardened tribolayer. The densification rate, microhardness, and wear performance generally decreased at a higher laser energy density of 0.8 kJ/m, due to the formation of thermal cracks and the significant coarsening of TiC dendritic reinforcing phase. 相似文献
7.
C. Santos K. Strecker S. A. Baldacim O. M. M. Silva C. R. M. da Silva 《International Journal of Refractory Metals and Hard Materials》2003,21(5-6):245-250
In the present work, the influence of the isothermal holding time on the physical (relative density and mass loss), chemical (α–β transformation and intergranular phase crystallization) and mechanical (hardness and fracture toughness) properties of Si3N4 ceramics with Al2O3 and CTR2O3 as additives has been studied. CTR2O3 is a natural rare earth oxide mixture, produced at DEMAR-FAENQUIL from the mineral xenotime, consisting mainly of Y2O3, Yb2O3, Er2O3 and Dy2O3. The increase in hardness and fracture toughness with increasing duration of isothermal sintering is discussed in regard of densification, α–β Si3N4 phase transformation and microstructure. The microstructural variations were decisive for the increase of fracture toughness, because larger grains (>4 μm) with higher aspect ratios (>6) developed during increased sinter periods, enhancing crack deflection and crack-bridging mechanism. In this way longer isothermal holding times contribute to the improvement of the physical and mechanical properties of silicon nitride based ceramics. 相似文献
8.
Porous preforms were fabricated by cold-pressing process using powder mixture of TiC, TiO2 and dextrin. After pyrolysis and sintering, Al melt was infiltrated into the porous preforms, leading to the formation of Ti3AlC2-Al2O3-TiAl3 composite. Effects of cold-pressing pressure of preforms on microstructures and mechanical properties of the composites were studied. Synthesis mechanism and toughening mechanism of composite were also analyzed. The results shows that TiO2 is reduced into Ti2O3 by carbon, the decomposition product of dextrin, which causes the spontaneous infiltration of Al melt into TiC/Ti2O3 preform. Then, Ti3AlC2-Al2O3-TiAl3 composite is in-situ formed from the simultaneous reaction of Al melt with TiC and Ti2O3. With the increase of cold-pressing pressure from 10 MPa to 40 MPa, the pore size distribution of the preforms becomes increasingly uniform after pre-sintering, which results in the reduction of defects, and the decrease of property discrepancy of composites. Nano-laminated Ti3AlC2 grains and Al2O3 particles make the fracture toughness of TiAl3 increase remarkably by various toughening mechanisms including stress-induced microcrack, crack deflection and crack bridging. 相似文献
9.
A. Nevarez-Rascon A. Aguilar-Elguezabal E. Orrantia M.H. Bocanegra-Bernal 《International Journal of Refractory Metals and Hard Materials》2009,27(6):962-970
In this work the influence of pressureless sintering on the Vickers hardness and fracture toughness of ZrO2 reinforced with Al2O3 particles (ATZ) and Al2O3 reinforced with ZrO2 particles (ZTA) has been investigated. The ceramic composites were produced by means of uniaxial compacting at 50 MPa and the green compacts were heated to 1250 °C using a heating rate of 10 °C min−1, then to 1500 °C at 6 °C min−1 and maintained at this temperature during 2 h. After sintering, relative density over 94%, hardness values between 9.5 and 21.9 GPa, and fracture toughness as high as 3.6 MPa m1/2 were obtained. The presence of TZ-3Y particles on the grain boundaries suggests that they inhibit notably the alumina grain growth. The grain sizes of pure Al2O3 and TZ-3Y as well as Al2O3 and TZ-3Y in the 20 wt% Al2O3+80 wt% TZ-3Y composite were 1.27 ± 0.51 μm, 0.57 ± 0.12 μm, 0.65 ± 0.19 μm and 0.41 ± 0.14 μm, respectively. The 20 wt% Al2O3 + 80 wt% ZrO2 + 3 mol% Y2O3 (TZ-3Y) composite showed a hardness of 16.05 GPa and the maximum fracture toughness (7.44 MPa m1/2) with an average grain size of 0.53 ± 0.17 μm. On the other side, the submicron grain size and residual porosity seem to be responsible for the high hardness and fracture toughness obtained. The reported values were higher than those obtained by other authors and are in concordance with international standards that could be suitable for dental applications. 相似文献
10.
Jun Zhao Xunliang Yuan Yonghui Zhou 《International Journal of Refractory Metals and Hard Materials》2010
An Al2O3-based composite ceramic tool material reinforced with WC microparticles and TiC nanoparticles was fabricated by using hot-pressing technique. The cutting performance, failure modes and mechanisms of the Al2O3/WC/TiC ceramic tool were investigated via continuous and intermittent turning of hardened AISI 1045 steel in comparison with those of an Al2O3/(W, Ti)C ceramic tool SG-4 and a cemented carbide tool YS8. Worn and fractured surfaces of the cutting tools were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results of continuous turning revealed that tool lifetime of the Al2O3/WC/TiC ceramic tool was higher than that of the SG-4 and YS8 tools at all the tested cutting speeds. As for the intermittent turning, tool life of the Al2O3/WC/TiC ceramic tool was equivalent to that of YS8, but shorter than that of the SG-4 at lower cutting speed (110 m/min). However, tool life of the Al2O3/WC/TiC ceramic tool increased when the cutting speed increased to 170 m/min, becoming much longer than that of the SG-4 and YS8 tools. The longer tool life of the Al2O3/WC/TiC composite ceramic tool was attributed to its synergistic strengthening/toughening mechanisms induced by the WC microparticles and TiC nanoparticles. 相似文献
11.
《Acta Materialia》2007,55(12):4193-4202
Si3N4/Si3N4w/TiN nanocomposites were fabricated by a hot-pressing technology with different sintering processes. The effect of nanoscale TiN and Si3N4w on the mechanical properties was investigated. The microstructure and indention cracks were observed by scanning electron microscopy, transmission electron microscopy and energy-dispersive spectrometry investigations. The research results showed that Si3N4/Si3N4w20/TiN5 nanocomposites containing 5 vol.% of nanoscale TiN and 20 vol.% of nanoscale Si3N4w, which were sintered under a pressure of 30 MPa at a temperature of 1650 °C for 40 min, had optimum mechanical properties. The addition of both nanoscale TiN and nanoscale Si3N4w contributed to the microstructural evolution and an improvement of the mechanical properties. The toughening and strengthening mechanisms are discussed for Si3N4/Si3N4w20/TiN5 nanocomposites. 相似文献
12.
B. Zou C.Z. Huang H.L. Liu M. Chen 《Journal of Materials Processing Technology》2009,209(9):4595-4600
Si3N4/TiN nanocomposites ceramic tool materials were sintered under 30 MPa at 1650 °C for 40 min. The effects of nano-scale TiN on the mechanical properties and microstructure were investigated. The strengthening and toughening mechanisms of Si3N4/TiN nanocomposites were studied by observing the fracture surfaces, samples for TEM and cracks. The oxidation resistance of Si3N4/TiN nanocomposites was also discussed based on the observation of microstructure. The results showed that the elongated Si3N4 grains which were pulled out from the fracture surfaces were reduced with the increase of the addition of nano-scale TiN, and many intragranular TiN grains were observed in Si3N4/TiN nanocomposites. The greater crack deflection and microcrack provided the contributions to the strengthening and toughening mechanisms for Si3N4/1 vol%TiN nanocomposite. However, Si3N4/TiN nanocomposites were oxidized strongly at higher temperature. 相似文献
13.
Chunyan Tian Hai JiangNing Liu 《International Journal of Refractory Metals and Hard Materials》2011,29(1):14-20
Si3N4-TiN nano-composites were fabricated by hot press sintering nano-sized Si3N4 and TiN powders. The microstructure, mechanical properties and thermal shock behavior of Si3N4-TiN nano-composites were investigated. The addition of proper amount TiN particles can significantly increase the flexural strength and the fracture toughness. Si3N4-TiN nano-composites showed both higher critical temperature difference and higher residual strength compared with those of monolithic silicon nitride nano-ceramic when the amount of TiN is less than 15 wt.%. But a further increase in the amount of TiN leaded to a decrease in the thermal shock resistance. 相似文献
14.
In this study, fully dense β-SiAlON/TiN composites were produced by Spark Plasma Sintering (SPS) method. Si3N4, Al2O3, AlN and TiO2 powders were used as precursors. Starting powders were mixed with high energy ball milling and then were sintered by SPS method (at 1750 °C under pressure of 30 MPa for 12 min.). The milled powders had an average particle size of below ~ 155 nm. The XRD patterns of SPS-ed composites showed that the entire β-SiAlON phase constituent was in the form of Si4Al2O2N6 phase and cubic TiN phase can be formed by the phase transformation of TiO2 in relation with other precursors. FESEM micrographs confirmed that TiN particles were distributed homogeneously throughout β-SiAlON matrix. Mechanical properties evaluation revealed that by adding micro sized TiO2, optimal mechanical properties with a hardness ~ 14.6 GPa and a fracture toughness ~ 6.3 MPa m1/2 were obtained. The improvement in the fracture toughness was attributed to the presence of the crack deflection as the dominant toughening mechanism in the SPS-ed β–SiAlON/TiN composites. 相似文献
15.
V. Medri 《Corrosion Science》2003,45(11):2525-2539
The corrosion behaviour of an electroconductive Si3N4-35 vol% TiN composite, hot pressed with the addition of Al2O3 and Y2O3 as sintering aids, was studied in 1.8 M sulphuric acid aqueous solution at RT, 40 and 70 °C up to 400 h. The corrosion follows linear kinetics at RT and at 40 °C, involving only the progressive chemical dissolution of grain boundary phases, in the system Al-Y-Si-Ti-O-N. Chemical attack of TiN occurs at 70 °C, while Si3N4 is not affected by the selected corrosive environment.The effect of the corrosion on flexural strength, fracture toughness and electrical resistivity were investigated. Very high strength levels are maintained after corrosion for 400 h at room temperature, while the strength decreases of about 10% and 16% after the treatment at 40 and 70 °C, respectively. The electrical resistivity rises after corrosion at 40 and 70 °C, in line with the progressive chemical dissolution of the conductive TiN particles. 相似文献
16.
《Acta Materialia》2007,55(9):3245-3251
The heat treatment of silicon nitride ceramics with only CeO2 as a sintering additive was carried out at different temperatures. Large residual stress was induced only by the non-relaxed volume changes and not by the relaxed volume changes (i.e. the crystallized phases with cavities or microcracks). The fact that the liquid formation temperature of the Si–Ce–O–N system (∼1470 °C) is much lower than that of the Si–Yb–O–N system (∼1650 °C) is the reason why the residual stress is comparable almost to each other in CeO2-doped Si3N4, but increases steadily with heat-treatment temperature in Yb2O3-doped Si3N4. The large residual stress and the induced cavities and microcracks are the dominant factors for the reduction in room-temperature strength of the heat-treated samples. The defects in β-Si3N4 grains of heat-treated samples were caused by the large residual stress, and may lead to the reduction of both room- and high-temperature strengths. These results significantly extends our previous study (Guo GF, Li JB, Yang XZ, Lin H, Liang L, He MS, Tong XG, Yang J. Acta Mater 2006;54:2311) on heat-treated Si3N4 ceramics with only Yb2O3 (one of the heavier lanthanide oxides) as a sintering additive. 相似文献
17.
FeSi/Si3N4 ceramic composite was fabricated by hot pressing technique, using α-Si3N4 and Fe3Al. The toughening effect of Fe3Al on the Si3N4 matrix is explained on the basis of microstructural characterizations and schematic representations. Results indicate that the reaction between α-Si3N4 and Fe3Al results in the formation of FeSi and sialon phases at the interface. Both phases effectively restrain coalescence and movement of the gaseous reaction product, N2, retaining it in situ to form small separated pores. The dominant toughening effect of these pores reduces the interface bonding strength, consumes the crack propagation energy, and decreases the stress-concentration at the crack tip, thereby improving the fracture toughness of the matrix. 相似文献
18.
Shou-ren Wang Hao-ran Geng Lin-hai Hui Ying-zi Wang 《Journal of Materials Engineering and Performance》2007,16(1):113-118
A multiphase reticulated porous ceramic (RPC) as Si3N4–Al2O3–SiO2 was fabricated by replication techniques. Proper volumes of additives and twice sinter- twice immerse process endow the RPC
an excellent crack healing and submerging property. The compressive strength and fracture toughness improved owing to the
crack bridging behavior. The existence of pores in struts in RPC blunt the crack tip and increased the external force needed
to propagate the crack. The mechanisms play a beneficial role in enhancing the compressive strength and fracture strength.
Si3N4 RPC with additives of 5%Al and 5% Al2O3 yielded the compressive strength of 9.8 MPa and fracture toughness of 0.3 MPa m1/2. 相似文献
19.
Cristina Della Pina Michele Rossi Anna Maria Ferretti Alessandro Ponti Massimiliano Lo Faro Ermelinda Falletta 《Synthetic Metals》2012
Polyaniline/Fe3O4 nanocomposites were prepared by a one-pot synthesis using N-(4-aminophenyl)aniline as the reagent, molecular oxygen or hydrogen peroxide as the oxidizing agents in the presence of Fe3O4 nanoparticles (NPs) in powder and ferrofluid form. Both magnetic NPs in powder and ferrofluid form showed similar catalytic behaviour. The catalytic effect is particularly evident when molecular oxygen was used as the oxidizing agent. However, concerning the morphological aspects, only the composites prepared in the presence of ferrofluid-type Fe3O4 NPs showed a preferential morphology of nanorods (between 30 and 110 nm in diameter). All the composites are superparamagnetic at room temperature but at low temperature they are in a blocked state. Inter-particle interactions significantly affect the magnetic properties of the composites. The electrical conductivity of the composites is about 10−2 S cm−1, in agreement with the values obtained for polyaniline prepared by chemical route. A mechanism of the nanorods formation is proposed. 相似文献
20.
Bulk WC-Al2O3 composites prepared by spark plasma sintering 总被引:1,自引:0,他引:1
Donghai ZhengXiaoqiang Li Xuan AiChao Yang Yuanyuan Li 《International Journal of Refractory Metals and Hard Materials》2012,30(1):51-56
WC and WC-Al2O3 materials without metallic binder addition were densified by spark plasma sintering in the range of 1800-1900 °C. The densification behavior, phase constitution, microstructure and mechanical properties of pure WC and WC-Al2O3 composite were investigated. The addition of Al2O3 facilitates sintering and increases the fracture toughness of the composites to a certain extent. An interesting phenomenon is found that a proper content of Al2O3 additive helps to limit the formation of W2C phase in sintered WC materials. The pure WC specimen possesses a hardness (HV10) of 25.71 GPa, fracture toughness of 4.54 MPa·m1/2, and transverse fracture strength of 862 MPa, while those of WC-6.8 vol.% Al2O3 composites are 24.48 GPa, 6.01 MPa·m1/2, and 1245 MPa respectively. The higher fracture toughness and transverse fracture strength of WC-6.8 vol.% Al2O3 are thought to result from the reduction of W2C phase, the crack-bridging by Al2O3 particles and the local change in fracture mode from intergranular to transgranular. 相似文献