基于BPNN的陶瓷材料抗弯强度预测

误差反向传播神经网络具有能够正确逼近非线性映射关系的优点，将其运用到复相结构陶瓷材料抗弯强度预测当中，克服了陶瓷材料研究中单因素实验法不能正确反映抗弯强度与添加组分多因素之间复杂的非线性关系的弱点，通过抗弯强度预测和试验验证，该方法可行有效，为快捷、经济地开发研制新的陶瓷材料提供新的思路和有效手段。     

陶瓷材料Knoop硬度测试中的能量平衡关系

借助于弹／塑性压痕模型，导出了一个用于描述陶瓷材料Ｋｎｏｏｐ压痕过程中能量平衡关系的表达式，并对由这一表达式所预测的压痕参数（Ｐ／ｄ）－ｄ之间存在的线性关系进行了实验验证，根据这一表达式，对陶瓷材料表现Ｋｎｏｏｐ硬度随荷载的变化关系进行了研究，指出：压痕过程中荷载所做功的额外消耗是导致表观硬度随荷载增大而降低的主要原因。     

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。     

人工晶体显微硬度的测量

用MeF_3 Vickers显微硬度计测定了近20种人工晶体的显微硬度(有些晶体是新近合成的,硬度未被测定过),并讨论了硬度与原子间键合力之间的关系。     

浸渍及热处理对常压烧结AlN/h-BN复相陶瓷微观结构及性能的影响

采用常压烧结方法在1 700℃保温2 h制备出AlN/20%(体积分数)h-BN复相陶瓷,对烧结后的样品分别采用A10铝溶胶和硅溶胶/酚醛树脂进行浸渍处理,随后在1 450℃氮气气氛下热处理2 h。对比研究了浸渍及热处理前后复相陶瓷的致密度、抗弯强度、Vickers硬度、微观结构和物相组成,并分析了复相陶瓷的强化机理。结果表明:A10铝溶胶浸渍处理后样品的抗弯强度和Vickers硬度略有提高;经过硅溶胶/酚醛树脂处理的样品抗弯强度和Vickers硬度大幅提高,抗弯强度和Vickers硬度分别从81.5MPa和1.99 GPa提高到130.1 MPa和3.58GPa;硅溶胶/酚醛树脂处理后的样品在孔隙界面处生成的碳化硅及氮氧化铝是样品抗弯强度和Vickers硬度显著提高的主要原因。     

陶瓷材料冲蚀磨损的研究

冲蚀磨损是现代工业生产中常见的一种磨损磨损形式，陶瓷材料由于其所具有的一些固有特性而在冲蚀环境下的应用越来越广。本文探讨了影响陶瓷材料冲蚀行为的因素。讨论了环境参数（如冲角，冲蚀速度，冲蚀时间和温度），磨粒性能（如硬度，粒度和形状），靶材性能（如硬度，断裂韧性和显微组织结构）等对冲蚀的影响规律。     

钛质陶瓷材料的研究

本文研究了较佳硬度、抗静电的钛质陶瓷材料;分析了影响材料硬度、体积电阻率的一些因素。     

陶瓷材料硬度表示方法的探讨

本文详细论述了陶瓷材料硬度的不同测试方法以及各种方法的优缺点,并对影响耐磨陶瓷材料硬度的因素进行了分析。以95氧化铝瓷为例,对其洛氏硬度进行了对比试验,发现A、C不同标尺之间的换算在一个特定范围存在相应误差。     

Al_2O_3–ZrO_2复相陶瓷的低温力学性能和热学性能

采用无压烧结法制备Al2O3–15%（质量分数）ZrO2（简称ZTA）复相陶瓷,研究了ZTA复相陶瓷在293～77K的力学性能以及300～5K的热学性能,分析了ZTA复相陶瓷在不同温度断裂时断面上ZrO2发生的相变量和相变区宽度。结果表明：ZTA复相陶瓷的抗弯强度、断裂韧性和Vickers硬度均随温度下降而逐渐提高;77K时抗弯强度、断裂韧性和Vickers硬度比293K时分别提高了10.8%、19.7%和10.4%;ZTA复相陶瓷的热导率随温度下降先增大,在97K时达到最大值,然后随温度下降而降低。低温环境增强了ZTA复相陶瓷中应力诱导t-ZrO2→m-ZrO2的相变增韧效应,提高了ZTA复相陶瓷的低温力学性能。ZTA复相陶瓷具有良好的低温力学性能和较小的低温热导率,是一种有广阔应用前景的低温结构陶瓷材料。     

混料方式对氮化硅陶瓷力学性能和显微结构的影响

借助扫描电镜、透射电镜、高分辨电镜、能量分散X射线等分析手段,研究了无压烧结氮化硅陶瓷材料的力学性能和显微结构,着重比较了粉料混合方式对材料力学性能和显微结构的影响。研究结果表明:行星式球磨机强化球磨混料可以有效地改善陶瓷粉料的混和效果,使烧结助剂均匀分布,抑制了晶粒的异常长大,有利于均匀结构的形成,力学性能也有不同程度的提高,而采用普通球磨混料方式制备的材料在局部区域产生晶粒异常长大情况。强化球磨混料制备氮化硅陶瓷的弯曲强度高达1.06GPa,Rockwell硬度达92,Vickers硬度达14.2GPa,断裂韧性达6.6MPa·m1/2。     

传统陶瓷工艺制备玻璃陶瓷/SiC晶须复合材料

针对传统陶瓷工艺难以直接用于制备玻璃陶瓷/SiC晶须复合材料问题,本文以白云鄂博尾矿基透辉石系玻璃粉和商用SiC晶须为主要原料,在石墨粉包埋条件下,采用传统陶瓷工艺成功制备出透辉石玻璃陶瓷/SiC晶须复合材料.在此基础上,研究了填加0～40wt％SiC晶须对所制备复合样品显微结构及性能的影响.结果证明了所制备复合材料样...     

烧结温度对氮化硅陶瓷球显微结构和力学性能的影响

以α-Si3N4粉为原料,纳米级Y2O3和Al2O3为烧结助剂,采用气压烧结工艺制备氮化硅陶瓷球,研究了烧结温度对陶瓷球显微结构及力学性能的影响.结果表明,随着烧结温度的升高,陶瓷球的维氏硬度和压碎强度先提高后降低,断裂韧性不断提高.烧结温度为1780℃的陶瓷球综合力学性能最佳,其相对密度达到了99％,维氏硬度、断裂韧...     

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.     

Wear resistance characteristics of micro-sized ceramic beads in a vertical bead mill

To investigate the wear resistance characteristics of micro-sized ceramic beads, wear tests reflecting real milling conditions were performed on yttrium-stabilized zirconia beads with diameters of approximately 100 μm. And a novel method for monitoring of wear state is proposed to obtain the wear rate of micro-sized beads using the change in size of beads with time. A vertical bead mill was employed to simulate the milling environment of the beads. The size change of the ceramic beads as a function of milling time was monitored using a particle size analyzer and plotted to determine their wear rate. The wear rate of each ceramic bead was derived from the slope obtained through linear regression analysis: 0.0215 μm/h, 0.0058 μm/h, and 0.0075 μm/h for Beads #1, #2, and #3, respectively. The Vickers hardness, phase fraction, and grain size of the ceramic beads were analyzed and compared to find out the cause of the difference in the wear rate. Vickers hardness was measured in the central, intermediate, and outer regions of the cross-sections of the ceramic beads. The wear rate of the ceramic beads was largely dependent on the hardness of the outer region, rather than those of the central and intermediate regions. Bead #2, which had the lowest wear rate, exhibited the highest hardness of 1371 HV (measured in the outer region). Bead #2 had more tetragonal phase and smaller grain sizes than those of Beads #1 and #3.     

ZCAS-assisting low-temperature hot-press sintering of SiC ceramic for immobilizing simulated radioactive graphite

The safe treatment and disposal of high-level radioactive graphite is an essential challenge in the governance of irradiated graphite. SiC has an insurmountable defect in densification sintering at low temperatures, although it is an ideal host material for immobilizing high-level radioactive graphite. To solve this issue, we employ ZCAS (short for ZnO–CaO–Al₂O₃–SiO₂ glass) as a sintering aid to prepare SiC-ZCAS composite ceramic with the relative density up to 98% by vacuum hot-press sintering. For investigating the optimum formula and technological conditions of (1-x) SiC-x ZCAS composite ceramic, the effects of synthesis and sintering process on preparation (1-x) SiC-x ZCAS (x = 25-40 wt%) composites were investigated in detail. The results show that the SiC-ZCAS composite powder with x = 25-40 wt% can be synthesized at 1350 °C for 2 h when the Si/C mole ratio is 1.05:1. The relative density, Vickers hardness, and thermal conductivity of SiC-ZCAS composites ceramic increase rapidly by increasing sintering temperature and pressure. However, these properties will display different effects from the increase in the content of ZCAS, such as continuous elevation of the relative density and dramatic depression of thermal conductivity. the Vickers hardness starts to decline when the content of ZCAS is 30 wt%. Considering the above mentioned, we can conclude that the 0.7SiC-0.3ZCAS composite ceramic has choiceness comprehensive properties when sintered at 1550 °C and 60 MPa for 1 h, with the relative density, Vickers hardness and thermal conductivity of 95.5%, 1084 (HV 10) and 7.104 W/m·k, respectively.     

Correlation of hardness with MFFT and CPVC of latex/ceramic coatings

Hardness, porosity, and microstructure of film-forming in polyvinyl acetate/alumina coatings from aqueous suspensions were investigated with a minimum film formation temperature (MFFT) bar, Vickers hardness tester, and scanning electron microscopy (SEM). The hardness of opaque composite coatings (alumina:latex=1:2 by volume) increased abruptly at the MFFT of the latex, suggesting that the alumina particles did not change the latex film formation behavior and that the hardness measurement is an alterative to the optical criterion. Studies of coatings from latex particles that were smaller or larger than a common size of ceramic particles indicated that the composition of maximum hardness, called critical Vickers hardness concentration (CVHC), matched conventional critical pigment volume concentration (CPVC). More efficient polymer binding in the coatings from the smaller latex gave them higher peak hardness and CPVC. Department of Chemical Engineering & Materials Science, 421 Washington Ave., SE, Minneapolis, MN 55455-0132.     

Quantitative relationship between microstructure and mechanical properties in Nd: YAG transparent ceramics

In this work, stereology and fractals were applied to identify the quantitative relation between stereology parameters, fractal dimension, and mechanical properties of Nd: YAG transparent ceramics sintered at 1750 °C for 8–50 h. Mechanical properties and microstructure of the samples were investigated by using universal testing machine, micro-hardness tester, and scanning electron microscopy (SEM), respectively. When the ceramics were sintered at 1750 °C for 50 h, the compressive strength, flexural strength, and Vickers hardness reached 381.6 ± 5.2 MPa, 275.0 ± 5.5 MPa, and 1330.4 ± 18.5 MPa, respectively. Besides, the fracture toughness of ceramic samples was calculated by Vickers hardness. Micrographs of the sample surface and frequency distribution of crystal grains were analyzed by using metallographic image analyzer software. Findings suggest that compressive strength, flexural strength, and Vickers hardness linearly increase upon an increase in equivalent sphere diameter (D_3S). However, compressive strength, flexural strength, and Vickers hardness decrease as a function of specific surface area per unit volume of the grains (S_V) and discrete grains (S_VP) and mean free distance (λ). Perimeter and area of crystal grains were obtained by using Image-Pro Plus image analysis software. The relationship between the fractal dimension of grain boundary and mechanical properties was analyzed based on the area-perimeter (small-island) method. When the grain boundary fractal dimension is close to 1.0, the geometry of ceramic grains tends to be regular, and mechanical properties of ceramic samples increases.     

Ti3AlC2的制备与性能研究进展

综合介绍了新型陶瓷Ti3AlC2的研究进展。三元碳化物Ti3AlC2属于六方晶系，其晶体为层状结构。它同时兼有金属和陶瓷的优良性能，具有良好的导电和导热能力、高弹性模量和低维氏硬度、良好的抗破坏能力；能在室温下进行切削加工，在高温下能产生塑性变形；它还具有良好的高温稳定性和抗氧化性能。应用SHS、HIP、HP等方法可制备出高纯、致密的Ti3AlC2材料。     

Reliability prediction of a microwave sintered Si3N4-based composite ceramic tool

The wear life reliability prediction model of microwave sintered Si₃N₄/(W,Ti)C/Y₂O₃/MgO/Al₂O₃ composite ceramic tools based on the random distribution characteristics of hardness and fracture toughness of ceramic tool material was established. It showed that the Vickers hardness of ceramic tool materials followed a normal distribution and the fracture toughness followed a lognormal distribution. Distribution law of wear life can be determined by the joint distribution of hardness and fracture toughness. Experimental research on tool reliability of continuous dry cutting quenched high quality carbon steel T10A was carried out and the applicability of the tool reliability prediction model was verified. The results showed that the error between the theoretical reliable life and the actual life of the ceramic tool was less than 5% under the same reliability when the reliability was above 0.5.     

Spark Plasma Sintering of Nanocrystalline Niobium Nitride Powders

Nanocrystalline niobium nitride (NbN) powders were sintered by spark plasma sintering under a nitrogen atmosphere at temperatures from 1040° to 1230°C. Fully dense bulk NbN ceramic with grain sizes of 0.5–1.0 μm was obtained at 1130°C. The effects of sintering temperature on the density, phase content, electrical conductivity, Vickers hardness, and microstructure of the NbN ceramic were discussed.