氧化气氛下热处理对SiC/h-BN复相可加工陶瓷性能的影响

采用热压烧结制备h-BN体积含量分别为30%和40%的可加工SiC/30%h-BN和SiC/40%h-BN复相陶瓷,并在不同温度和氧化气氛下对复相陶瓷样品进行热处理。测试了预制Vickers压痕的复相陶瓷样品在热处理前后的强度和表面硬度,并通过X射线衍射和扫描电子显微镜等研究了复相陶瓷表面成分和显微结构的变化。结果表明:氧化气氛下的热处理可恢复陶瓷在加工时由表面损伤降低的强度,1100℃热处理2h的陶瓷效果最佳。经1100℃热处理2h后,带压痕的SiC/40%h-BN复相陶瓷的强度恢复到389.81MPa,表面硬度从6.11GPa提高10.48GPa。SiC和h-BN的高温氧化行为是强度恢复和表面硬度升高的主要原因。     

YAG对TiCN陶瓷刀具材料力学性能及烧结工艺的影响

以钇铝石榴石(YAG)为添加相,采用热压烧结法制备YAG–TiCN复合陶瓷。研究了不同YAG添加量对复合陶瓷的物相、显微结构、力学性能的影响。结果表明:热压烧结过程中TiCN和YAG不发生反应;YAG第二相明显改善了TiCN的烧结性能,并有助于提高YAG–TiCN复合陶瓷的硬度、抗弯强度和断裂韧性;YAG含量在10%(质量分数)时复合陶瓷的致密度达到99.3%,并且Vickers硬度、断裂韧性、抗弯强度均达到最高,分别为:20.48GPa、7.27MPa·m1/2、570.36MPa,远远超过TiCN单相陶瓷的致密度以及力学性能:88.04%、9.33GPa、5MPa·m1/2、204.45MPa。YAG作为添加相可显著提高TiCN等难烧结陶瓷的致密度和力学性能。     

YAG对TiCN陶瓷刀具材料力学性能及烧结工艺的影响

以钇铝石榴石(YAG)为添加相,采用热压烧结法制备YAG–TiCN复合陶瓷。研究了不同YAG添加量对复合陶瓷的物相、显微结构、力学性能的影响。结果表明:热压烧结过程中TiCN和YAG不发生反应;YAG第二相明显改善了TiCN的烧结性能,并有助于提高YAG–TiCN复合陶瓷的硬度、抗弯强度和断裂韧性;YAG含量在10%(质量分数)时复合陶瓷的致密度达到99.3%,并且Vickers硬度、断裂韧性、抗弯强度均达到最高,分别为:20.48 GPa、7.27 MPa·m~(1/2)、570.36 MPa,远远超过TiCN单相陶瓷的致密度以及力学性能:88.04%、9.33 GPa、5 MPa·m~(1/2)、204.45 MPa。YAG作为添加相可显著提高TiCN等难烧结陶瓷的致密度和力学性能。     

YAG对TiCN陶瓷刀具材料力学性能及烧结工艺的影响

以钇铝石榴石(YAG)为添加相,采用热压烧结法制备YAG–TiCN复合陶瓷。研究了不同YAG添加量对复合陶瓷的物相、显微结构、力学性能的影响。结果表明:热压烧结过程中TiCN和YAG不发生反应;YAG第二相明显改善了TiCN的烧结性能,并有助于提高YAG–TiCN复合陶瓷的硬度、抗弯强度和断裂韧性;YAG含量在10%(质量分数)时复合陶瓷的致密度达到99.3%,并且Vickers硬度、断裂韧性、抗弯强度均达到最高,分别为:20.48GPa、7.27MPa·m1/2、570.36MPa,远远超过TiCN单相陶瓷的致密度以及力学性能:88.04%、9.33GPa、5MPa·m1/2、204.45MPa。YAG作为添加相可显著提高TiCN等难烧结陶瓷的致密度和力学性能。     

YAG对TiCN陶瓷刀具材料力学性能及烧结工艺的影响

以钇铝石榴石(YAG)为添加相,采用热压烧结法制备YAG–TiCN复合陶瓷。研究了不同YAG添加量对复合陶瓷的物相、显微结构、力学性能的影响。结果表明:热压烧结过程中TiCN和YAG不发生反应;YAG第二相明显改善了TiCN的烧结性能,并有助于提高YAG–TiCN复合陶瓷的硬度、抗弯强度和断裂韧性;YAG含量在10%(质量分数)时复合陶瓷的致密度达到99.3%,并且Vickers硬度、断裂韧性、抗弯强度均达到最高,分别为:20.48GPa、7.27MPa·m1/2、570.36MPa,远远超过TiCN单相陶瓷的致密度以及力学性能:88.04%、9.33GPa、5MPa·m1/2、204.45MPa。YAG作为添加相可显著提高TiCN等难烧结陶瓷的致密度和力学性能。     

高温热循环对ADZ复相陶瓷性能的影响

以共沉淀法制备了钇稳定氧化锆溶胶,再与Al2O3微粉混合,通过干压成型和常压烧结工艺制备ADZ复相陶瓷。通过检测复相陶瓷的相对密度、硬度、常温抗弯强度和断裂韧性,研究1400℃热循环过程对ADZ复相陶瓷烧结性能、力学性能及微观结构的影响,并通过SEM方法对热循环后试样的微观结构进行表征。结果表明:随着1400℃热循环过程的增加,ADZ复相陶瓷的硬度、抗弯强度和断裂韧性均有不同程度的升高,最高值分别可达16.07 GPa,921 MPa和8.06 MPa·m1/2,提升幅度分别为3%、39%和10%,相对密度在98%以上。物相分析表明有34%的m-ZrO2向t-ZrO2转变,断口穿晶断裂增多。     

粉体合成工艺对TiB_2–TiC复相陶瓷微观组织及力学性能的影响

分别以直接法和间接法碳硼热还原工艺合成的TiB_2–TiC复合粉体为原料,采用热压烧结工艺制备了共晶成分的TiB_2–44%TiC(摩尔分数)复相陶瓷,研究了粉体合成工艺和烧结温度对TiB_2–TiC复相陶瓷显微组织和力学性能的影响。结果表明:以直接法合成粉末为原料烧结的TiB_2–TiC复相陶瓷中,TiB_2晶粒多呈棒状、组织细小均匀;而以间接法合成粉末为原料制备的复相陶瓷中TiB_2晶粒多呈等轴状。随着烧结温度的升高,复相陶瓷致密度提高,晶粒长大,但力学性能变化不明显。以直接法合成复合粉末为原料,在烧结温度为2 000℃、压力为30 MPa、保温时间为1 h工艺条件下制备的TiB_2–TiC复相陶瓷综合性能最佳,其致密度、弹性模量、Vickers硬度、抗弯强度和断裂韧性分别为99.9%、537 GPa、19.0 GPa、598 MPa、5.3 MPa·m~(1/2)(压痕法)和11.6 MPa·m1/2(单边切口梁法)。TiB_2–TiC复相陶瓷主要的增韧机制为裂纹偏转和分叉。     

热压烧结制备原位复合（TiB2+TiC）/Ti3SiC2复相陶瓷

采用热压烧结法制备了原位复合(TiB2+TiC)/Ti3SiC2复相陶瓷。采用X射线衍射、扫描电镜和透射电镜对材料的物相组成和显微结构进行了表征,研究了烧结温度对材料物相组成、烧结性能、显微结构与力学性能的影响。结果表明:烧结温度在1 350～1 500℃范围内,随着烧结温度的升高,合成反应进行逐渐完全,材料的密度、抗弯强度和断裂韧性显著提高。1 500℃烧结可得到致密的原位复合(TiB2+TiC)/Ti3SiC2复相陶瓷,材料晶粒发育较完善,层片状Ti3SiC2、柱状TiB2与等轴状TiC晶粒清晰可见,增强相晶粒细小,晶界干净,材料的抗弯强度、断裂韧性和Vickers硬度分别达到741 MPa,10.12 MPa.m1/2和9.65 GPa。烧结温度达到1 550℃时Ti3SiC2开始发生分解,材料的密度和力学性能又显著下降。     

纳米莫来石的制备及其对氧化铝陶瓷性能的影响

以硝酸铝和硅溶胶为原料,采用溶胶-凝胶法合成了纳米莫来石粉体,进而探讨了纳米莫来石对氧化铝陶瓷烧结性能、抗弯强度以及抗热震性能的影响.结果发现,在1100 ℃煅烧硝酸铝与硅溶胶先驱体时仅有少量Al2O3生成,当将煅烧温度升高到1200 ℃时,获得了单一的莫来石晶相,粉体的平均粒径在50～60 nm之间;在氧化铝中添加2wt%～10wt%的纳米莫来石,可以有效促进陶瓷体的致密烧结,并获得良好的抗弯强度与抗热震性能;纳米莫来石含量为5wt%的陶瓷,在1650 ℃烧结后的抗弯强度为247.49 MPa,经过1200 ℃热震后的抗弯强度为218.52 MPa;当纳米莫来石的添加量超过10wt%时,将降低陶瓷的饱和体积密度,并恶化陶瓷的抗弯强度与抗热震性能.     

无机溶胶陶瓷结合剂的制备与研究

以硅溶胶、铝溶胶及化学纯H_3BO_3、NaNO_3、LiNO_3为原料,以溶胶凝胶法制备Al_2O_3-B_2O_3-SiO_2-R_2O体系无机溶胶陶瓷结合剂,并以金刚石为磨料,采用喷雾干燥法制备金刚石-陶瓷复合粉体,后经干燥、压制、烧结制得金刚石-陶瓷复合烧结体。利用X射线衍射仪、TG-DSC、扫描电镜、抗折试验机等表征手段对无机溶胶陶瓷结合剂的物相组成、显微形貌、复合烧结体断面形貌及抗弯强度等进行分析。结果表明,820℃/1h下进行烧结,以此配方制备的无机溶胶陶瓷结合剂结构均匀,且可熔融为液相并对金刚石进行较好地包覆。随着陶瓷结合剂含量的增加,金刚石-陶瓷复合烧结体的抗弯强度随之提高,而气孔率随之降低,且当结合剂含量为30wt%时,抗弯强度和气孔率分别为95.42MPa和34.36%。     

Texture,microstructures, and mechanical properties of AlN‐based ceramics with Si3N4–Y2O3 additives

Textured AlN‐based ceramics with improved mechanical properties were prepared by hot pressing using Si₃N₄ and Y₂O₃ as additives. The introduction of Si₃N₄–Y₂O₃ into AlN matrix led to the formation of secondary Y₃AlSi₂O₇N₂ and fiber‐like 2H^δ AlN‐polytypoid phases, the partial texture of all crystalline phases, and the fracture mode change from intergranular to transgranular. Consequently, Vickers hardness, fracture toughness and flexural strength of AlN‐based ceramics by the replacement of Y₂O₃ by Si₃N₄–Y₂O₃ increased significantly from 10.4±0.3 GPa, 2.4±0.3 MPa m^½ and 333.3±10.3 MPa to 14.2±0.4 GPa, 3.4±0.1 MPa m^½ and 389.5±45.5 MPa, respectively.     

烧结工艺对Si_3N_4/TiC纳米复合陶瓷材料微观结构及力学性能的影响

以La2O3和Y2O3作为复合烧结助剂,采用热压烧结法制备了Si3N4基复合陶瓷材料。研究了保温时间和烧结助剂含量对复合材料微观结构及力学性能的影响。研究表明:所制备的Si3N4/TiC陶瓷复合材料的微观结构呈现纵横交错、相互嵌套的结构,晶粒尺寸呈现明显的双峰分布特征,单位面积内晶粒数量与烧结助剂含量之间呈线性降低关系。当烧结助剂质量含量为8%时,该复合陶瓷材料具有最优的力学性能,其抗弯强度、断裂韧性和Vickers硬度分别达到943MPa,8.38MPa·m1/2和16.67GPa。     

A non-sintering fabrication method for porous Si3N4 ceramics via sol hydrothermal process

A non-sintering fabrication method for porous Si₃N₄ ceramics with high porosity and high mechanical strength was proposed. Strength of the porous ceramics can be obtained by silica sol mass transfer process in hydrothermal conditions rather than a traditionally controlled high temperature sintering process. Under hydrothermal circumstances, silica sol is continuously transferred to the necks of Si₄N₃ powder compact, depositing there and thus consolidating the ceramic skeleton. The key of the method to obtain homogeneous microstructure and mechanical strength is how to keep the silica sol from gelatin during hydrothermal procedure. The stabilization of silica sol and its affecting factors were studied. The results indicated that ultrasonic treatment makes alkali-catalyzed silica sol remain stable even in 200?℃ hydrothermal condition, which insures consecutive silica transportation. The effect of hydrothermal time on open porosity/mechanical strength of the porous Si₄N₃ ceramics were also thoroughly investigated. The porous Si₄N₃ ceramics with open porosity above 42% and flexural strength of 45?MPa were obtained without any high temperature sintering process. This method can be widely employed for the preparation of other porous ceramics as well.     

Preparation and study of the mechanical and optical properties of infrared transparent Y2O3–MgO composite ceramics

In this study, fine Y₂O₃–MgO composite nanopowders were synthesized via the sol–gel method. Dense Y₂O₃–MgO composite ceramics were fabricated by pre-sintering the green body in air at different temperatures for 1 h and then subjecting the sintered bodies to hot isostatic pressing at 1300°C for 1 h. The effects of pre-sintering temperature on the microstructural, mechanical, and optical properties of the resulting ceramics were studied. The average grain size of the ceramics was increased, whereas their hardness and fracture toughness were decreased with increasing pre-sintering temperature. A maximum fracture toughness of 1.42 MPa·m^1/2 and Vickers hardness of 10.4 GPa were obtained. The average flexural strength of the ceramics was 411 MPa at room temperature and reached 361 MPa at 600°C. A transmittance of 84% in the 3–5 µm region was obtained when the composite ceramics were sintered at 1400°C. Moreover, a transmittance of 76% in the 3–5 µm region was obtained at 500°C.     

Preparation of high-strength lightweight alumina with plant-derived pore using corn stalk as pore-forming agent

To improve the mechanical and thermal insulation properties of lightweight alumina, which was prepared by using pore-forming agent from biological sources, the silica sol-infiltrated corn stalk was utilized. Spring back and hygroscopicity of corn stalk powder as well as cold compressive strength, thermal conductivity, microstructure, and pore size distribution of lightweight alumina were characterized. The results indicate that impregnation of silica sol leads to different degrees of decrease in spring back height due to achieving better mesh by silica gel between the corn stalk powders, and then improves the formability, although at the same time the large number of hydrophilic groups results in an increase in hygroscopicity. Furthermore, sol impregnated pore-forming agent optimizes the microstructure of the lightweight alumina pores. Lightweight alumina with a cold compressive strength up to 48.64 MPa was produced, and with the silica sol concentration of 3 wt%, lower thermal conductivity values at all test temperatures were obtained. Hence, the use of corn stalk impregnated with the appropriate concentration of silica sol as pore-forming agent could enhance the mechanical and thermal insulation properties of lightweight alumina for the spheroidization of pore shape, randomization of pore distribution as well as miniaturization of pore size.     

In situ synthesis,mechanical properties,and microstructure of reactively hot pressed WB4 ceramic with Ni as a sintering additive

In this study, tungsten tetraboride (WB₄) ceramics were synthesized in situ from powder mixtures of W and amorphous B with Ni as a sintering aid by reactive hot pressing method. The as-synthesized ceramics exhibited porosity as low as 0.375% and ultra-high Vickers hardness (H_v), as much as 49.808?±?1.683?GPa (for the low load of 0.49?N). It was seen that the addition of Ni greatly improved the sinterability of WB₄ ceramic. Besides, the flexural strength and fracture toughness of WB₄ ceramic were measured for the first time to be 332.857?±?36.763?MPa and 4.136?±?0.259?MPa?m^1/2, respectively, suggesting that the ceramic has good mechanical properties. The effects of sintering temperature and holding time on the densification, Vickers hardness, and mechanical properties of WB₄ ceramics were also investigated systematically as part of our study. The results indicated that increasing the sintering temperature can obviously improve the densification and mechanical properties of the ceramics. The bulk density and Vickers hardness of WB₄ ceramic sintered at 1650?°C for 60?min under 30?MPa revealed the highest values of 6.366?g?cm^?3 and 27.948?±?0.686?GPa (for the high load of 9.8?N), respectively. The flexural strength increased to the highest value of 332.857?±?36.763?MPa for sintering temperature up to 1550?°C, but decreased slightly as the sintering temperature further increased to 1650?°C. On the other hand, the fracture toughness increased gradually with increasing temperature. It was also found that Vickers hardness showed a similar trend as the densification of the samples with increasing temperature and holding time. Besides, no obvious improvements in the densification, mechanical properties, and Vickers hardness of the samples with sintering time were observed in this study. The microstructure and fracture behaviours of the as-synthesized WB₄ ceramic were also revealed, and the toughening mechanism has been discussed.     

High-strength Ti2AlN ceramics prepared by pulse electric current sintering based on powders synthesized by molten salt method

Ti₂AlN powders were synthesized through molten salt method and re-calcination process using TiH₂, Al and TiN powders as raw materials at 1100 ℃. The composition of final composite was directly influenced by the initial Al and TiH₂ content in the starting mixture. The purity of the synthesized Ti₂AlN powder could reach 97.1 wt% when the Al molar ratio was 1.05. Then high strength Ti₂AlN ceramics were successfully prepared in different modes, including two forms of pulse electric current sintering (PECS/SPS) and hot-pressing sintering (HP). A record-high flexural strength of 719 MPa was obtained for the PECS/SPS with an electrical insulating die (PECS/SPS II) sintered sample, based on the synthesized powder in which the initial molar ratio of Al was 1.1. The sintering behaviors in various modes were analyzed, confirming the shrinkage of particles starting at lower temperature in PECS/SPS II. The density, microstructure, Vickers hardness and elastic modulus of sintered ceramics were also investigated. Therefore, the present work provided the new methods about powder preparation and ceramic sintering of Ti₂AlN, making it possible to be used as high strength structural ceramics.     

无助剂AlN陶瓷的高压烧结制备及热导率

以碳热还原法生产的AlN粉体为原料,用国产六面顶压机,在5.0GPa,1 300～1 800℃,在无烧结助剂的情况下,高压烧结制备了AlN陶瓷.用X射线衍射、扫描电镜对高压烧结AlN陶瓷微观结构进行了表征.结果表明:经1 300℃烧结50 min制备的AlN陶瓷的相对密度达94.8%.经1 400℃烧结50min制备的AlN陶瓷的断裂模式为穿晶断裂.经1 800℃烧结50min制备的AlN陶瓷由单相多晶等轴晶粒组成,该样品的热导率达115.0W/(m·K).高压烧结制备的AlN陶瓷的晶格常数比AlN粉体的略有减小.高压烧结温度的提高和烧结时间的延长有助于提高AlN陶瓷的热导率.     

A novel approach to fabricate porous alumina ceramics with excellent properties via pore-forming agent combined with sol impregnation technique

An innovative approach for fabricating porous alumina ceramics (PACs) with improved mechanical and thermal properties using walnut shell powders as pore-forming agent combined with alumina sol impregnation is reported in the present work. It is demonstrated that uniform distribution of spherical pores can be observed in as-prepared PACs by using above technical route. The decrease of walnut shell powder sizes significantly promotes the enhancement of crushing strength and reduction of thermal conductivity of the PACs. Meanwhile, the impregnated alumina sol is favoring for the formation of spherical micro-pores, then further improves their mechanical and thermal insulation performances. The lowest thermal conductivity and highest crushing strength of resulting sample reach 0.16?W/m?K and 29.2?MPa, respectively. This novel method offers new possibilities to fabricate high-quality PACs.