SiCw—AlN复合材料工艺因素的研究

本文了工艺因素对ＳｉＣｗ－ＡｌＮ复合材料的影响。结果表明，１８５０℃是较合适的复合材料烧结温度，复合材料力学性能与添加剂组成和含量有密切关系。Ｙ２Ｏ３与ＳｉＯ２在烧结中起的作用下不同，Ｙ２Ｏ３与ＡｌＮ表面的Ａｌ２Ｏ３形成液相，是一种良好的烧结添加剂，而ＳｉＯ２由于与ＡｌＮ形成２７ＲＳｉａｌｏｎ多形体，反而阻碍材料致密化。     

热压烧结Cf/SiC复合材料的力学性能

以ＡｌＮ－Ｙ２Ｏ３为烧结助剂体系,采用先驱体转化－热压法制备出了Ｃｆ／ＳｉＣ复合材料。研究了烧结助剂及其用量和烧结温度对复合材料力学性能的影响。结果表明,由于ＡｌＮ－ＳｉＣ的固溶和液相烧结的作用;烧结温度为１８５０℃时,烧结助剂用量较少的复合材料具有很好的断裂韧性。随着烧结助剂用量的增加,虽然复合材料的抗弯强度不断提高,但由于晶界相和ＡｌＮ－ＳｉＣ固溶体量的增加,使纤维与基体的结合过程,从而导致纤     

AIN瓷TiN－Mo金属化方法研究

以Ｍｏ，ＴｉＮ为主要原料，采用金属粉末烧结法在ＡｌＭ瓷表面实现了金属化。探讨了金属化的工艺条件，运用ＸＰＳ，ＸＲＤ，ＳＥＭ等现代分析技术研究了界面现象及粘附机理。研究表明：液相的扩散、渗透，特别是ＡｌＮ瓷坯中的液相向金属化层的渗透是金属化层与ＡｌＮ瓷结合的主要原因。体积配比为７５％ＴｉＮ，２５％Ｍｏ及适量烧结助剂，烧结温度为１８００～１８５０℃，气氛为氮气（９０％）和氢气（１０％）的适宜条件下，获得了结合强度达４０ＭＰａ的良好金属化结合层。     

B_2O_3－Y_2O_3添加剂对AlN陶瓷显微结构及性能的影响

研究了以Ｂ_２Ｏ_３－Ｙ_２Ｏ_３作为助烧结剂的ＡｌＮ陶瓷的烧结特性及显微结构。结果表明，晶界处存在ＹＡｌＯ_３，Ｙ_４Ａｌ_２Ｏ_９及Ｙ_３Ａｌ_５Ｏ_（１２）等各种铝酸钇结晶物，Ｂ_２Ｏ_３可固溶到铝酸钇中形成固溶体。随烧结温度变化，第二相的种类、数量和分布不同，从而影响ＡｌＮ的热导率。在１８５０℃下，可获得热导率为１８９Ｗ／ｍ·Ｋ的ＡｌＮ陶瓷。     

碳化硅陶瓷的热等静压烧结

系统地研究了不同添加剂（如Ａｌ２Ｏ３，ＡｌＮ和Ｂ４Ｃ等）在热等静压（ＨＩＰ）烧结条件下对ＳｉＣ陶瓷之致密机理，显微结构以及力学性能的影响，结果表明：在ＨＩＰ烧结过程中，Ａｌ２Ｏ３可以与ＳｉＣ颗粒表面的ＳｉＯ２生成低共熔的铝硅酸盐玻璃相，并有效地促进ＳｉＣ陶瓷的致密化，当添加３％（以质量计）Ａｌ２Ｏ３时，采用ＨＩＰ烧结工艺，在１８５０℃温度和２００ＭＰａ压力下降结１ｈ，就可获得相对密度和抗弯强度分别     

AIN陶瓷基反在空气中的热氧化行为探讨

利用二次离子质谱（ＳＩＭＳ）并结合Ｘ射线衍射分析ＡｌＮ陶瓷基板在８５０－１１００℃空气中退火时的初始氧化行为。结果表明，未退火ＡｌＮ陶瓷基板表面区存在很薄的富氧层。在退火１０ｍｉｎ的条件下，随着退火温度的增加，富氧层迅速增厚。在１１００℃退火２０ｍｉｎ的条件下，ＡｌＮ陶瓷基板表面区有连续的氧化层生成。最后，结合化学热力学，探讨了ＡｌＮ陶瓷基板表面的初始氧化机理。     

冲击波对AlN粉体性能及低温烧结特性的影响

研究了冲击波对ＡｌＮ粉体性能的影响，并探索了以冲击波处理的ＡｌＮ粉体为原料，添加５％助烧结剂的低温结过程。结果表明，冲击波处理ＡｌＮ粉将使晶粒产生大量的晶格略变，从而活化了粉体。以冲击波处理的ＡｌＮ粉为原料，在１６１０℃下进行无压烧结，可得到密为３．３３ｇ／ｃｍ＾３的ＡｌＮ陶瓷。     

AlN陶瓷在空气中高温下的氧化行为

在空气中９００－１２００℃的高温下，研究了添加Ｙ２Ｏ３常压烧结ＡｌＮ陶瓷的氧化行为。用电光天平测量了氧化后ＡｌＮ陶瓷的相对质量变化△ｍ随氧化温度及时间的变化规律。运用扫描电镜（ＳＥＭ）、Ｘ射线衍射（ＸＲＤ）技术对氧化的ＡｌＮ陶瓷的表面形貌及生成的物相进行了分析。     

SiO2-AlN复合材料的制备及其性能研究

热压烧结制备了ＳｉＯ２－ＡｌＮ复合材料,研究了第二相ＡｌＮ的引入量和热压温度对ＳｉＯ２－ＡｌＮ复合材料力学性能、介电性能和热学的影响,结果说明,第二相ＡｌＮ的引入有利于ＳｉＯ２基复合材料力学性能的提高;３０％（体积分数）ＡｌＮ－ＳｉＯ２复合材料于１４００℃下烧结后抗弯强度和断裂韧性２００ＭＰａ和２．９６ＭＰａ·ｍ＾１／２,ＸＲＤ分析证实直至１４００℃ＡｌＮＳｉＯ２间未发生反应,两者有良好的化学相容     

AlN瓷TiN—Mo金属化方法研究

以Ｍｏ，ＴｉＮ为主要原料，采用金属粉末烧结法在ＡｌＮ瓷表面实现了金属化。探讨了金属化的工艺条件，运用ＸＰＳ，ＸＲＤ，ＳＥＭ等现代化分析技术研究了界面及粘附机理。研究表明，液相的扩散，渗透，特别是ＡｌＮ瓷坯中的液相向金属化层的渗透是金属化层与ＡｌＮ瓷结合的主要原因。     

Low-temperature hot-press sintering of AlN ceramics with MgO–CaO–Al2O3–SiO2 glass additives for ceramic heater applications

Aluminum nitride (AlN) is used a ceramic heater material for the semiconductor industry. Because extremely high temperatures are required to achieve dense AlN components, sintering aids such as Y₂O₃ are typically added to reduce the sintering temperature and time. To further reduce the sintering temperature, in this study, a low-melting-temperature glass (MgO–CaO–Al₂O₃–SiO₂; MCAS) was used as a sintering additive for AlN. With MCAS addition, fully dense AlN was obtained by hot-press sintering at 1500 °C for 3 h at 30 MPa. The mechanical properties, thermal conductivity, and volume resistance of the sintered AlN–MCAS sample were evaluated and compared with those of a reference sample (AlN prepared with 5 wt% Y2O3 sintering aid sintered at 1750 °C for 8 h at 10 MPa). The thermal conductivity of AlN prepared with 0.5 wt% MCAS was 91.2 W/m?K, which was 84.8 W/m?K lower than that of the reference sample at 25 °C; however, the difference in thermal conductivity between the samples was only 14.2 W/m?K at the ceramic-heater operating temperature of 500 °C. The flexural strength of AlN–MCAS was 550 MPa, which was higher than that of the reference sample (425 MPa); this was attributed to the smaller grain size achieved by low-temperature sintering. The volume resistance of AlN–MCAS was lower than that of the reference sample in the range of 200–400 °C. However, the resistivity of the proposed AlN–MCAS sample was higher than that of the reference sample (500 °C) owing to grain-boundary scattering of phonons. In summary, the proposed sintering strategy produces AlN materials for heater applications with low production cost, while achieving the properties required by the semiconductor industry.     

AlN陶瓷低温烧结制备与性能研究

采用两组复合烧结助剂Y2O3-CaF2,Y2O3-CaF2-Li2CO3在1600℃烧结AlN陶瓷,对AlN陶瓷烧结密度,热性能和电性能进行了测试,并分析了AlN陶瓷物相变化和微观结构。结果表明,复合烧结助剂在低温下能明显促进AlN陶瓷致密化及晶粒生长发育,尤其是添加3wt%Y2O3-2wt%CaF2作烧结助剂,1600℃常压烧结4h制备了结晶良好,相对密度为98.4%,热导率为133.62W/m.K,同时具有较低相对介电常数的AlN陶瓷。在低温常压条件下制备出性能较高的AlN陶瓷。     

Thermal conductivity of AlN ceramics sintered with CaF2 and YF3

Dense AlN ceramics with a thermal conductivity of 180W/m·K were obtained at the sintering temperature of 1750 °C using CaF₂ and YF₃ as additives. At temperatures below 1650 °C, the shrinkage of AlN ceramics is promoted by liquid (Ca,Y)F₂ and Ca₁₂Al₁₄O₃₂F₂. Liquid CaYAlO₄ mainly improves the densification of the sample when the sintering temperature increases to 1750 °C. The formation of liquid (Ca,Y)F₂ at a relatively low temperature results in homogeneous YF₃ distribution around the AlN particles, which benefits the removal of oxygen impurity in the AlN lattice, and thus a higher thermal conductivity.     

Thermal conductivities and mechanical properties of AlN ceramics fabricated by three dimensional printing

AlN ceramics were successfully fabricated through a joint process of digital light processing (DLP) 3D printing technology and heat treatment at 1780 °C∼1845 °C. DLP is an addictive manufacturing process, enabling the near net shape fabrication. The AlN grains in this work developed well and there were small amounts of grain-boundary phases at the three-grain junctions. The particle size of AlN became larger and the densification increased with increasing sintering temperature. The pores of AlN ceramics also decreased, which led to the increase of thermal conductivity and flexural strength. The optimal thermal conductivity and flexural strength of AlN ceramic reached 155 W/(m·K) and 265 ± 20 MPa when sintered at 1845 °C.     

Ion-Exchange Loading of Yttrium Acetate as a Sintering Aid on Aluminum Nitride Powder via Aqueous Processing

A novel fabrication process of AlN ceramics via aqueous colloidal processing and pressureless sintering has been presented. The chemical stability of AlN powder in water was improved by the surface chemical modification with sebacic acid, while maintaining a hydrophilic surface. The treatment of the sebacic acid-modified powder with yttrium acetate tetrahydrate resulted in strong immobilization of Y³⁺ ions, as a sintering aid, at a highly dispersive level on the AlN powder surface through ion exchange with the free carboxyl groups of the sebacic acid molecules attached to the AlN surface. By selecting slip compositions for a well-deflocculated condition and firing conditions to burn out organic components in the slip cast compacts, a thermal conductivity of about 250 W/(m·K) could be attained by the pressureless sintering at 1900°C for 5 h.     

Onset of selective laser flash sintering of AlN

Flash sintering uses a combination of heating and electric fields to rapidly densify ceramics. Previously, it has been shown that a scanning laser can be used to initiate flash sintering in localized regions on an yttria-stabilized zirconia (YSZ) sample in a process known as selective laser flash sintering (SLFS). In this work, we show using a combination of measurements of electric current flowing through the sample and observations of necks formed between powder particles that aluminum nitride (AlN) can also undergo SLFS. Scan conditions required to initiate SLFS are characterized over a range of laser powers and laser scan speeds in a dry nitrogen environment. It is shown that initiation of SLFS in AlN is governed by both the local input energy density per scan and heat dissipation and a numerical model is developed to predict temperatures during SLFS. Assuming the minimum temperature along the conductive path determines the onset of SLFS, the minimum temperature and time required is 450–670 K in 2–0.25 s for the pressed AlN pellets used in this study for laser scan speeds of 33–300 m/s, laser powers of 10–30 W, and an applied electric field of 3000 V/cm.     

Effect of hot-pressing sintering on thermal and electrical properties of AlN ceramics with impedance spectroscopy and dielectric relaxations analysis

The effects of hot-pressing sintering on the phase composition, microstructure, thermal and electrical properties of AlN ceramics with CeO₂–CeF₃ additives were studied. During hot-pressing sintering, high pressure reduced the grain boundary phase CeAlO₃ and decreased the concentration of oxygen in AlN ceramics. The hot-pressing sintered AlN samples had a much higher thermal conductivity of 191.9 W/m·K than pressureless sintered ones because of the great reduction of grain boundary phases and oxygen impurities in AlN ceramic. As the carbon content in hot-pressing sintered sample was very high, carbon contamination led to the decrease in electrical resistivity and changes in polarization mechanisms for AlN ceramics. The relaxation peak in the dielectric temperature spectrum with an activation energy of 0.64 eV for hot-pressing sintered samples was caused by electrons from free carbon at low temperature. Overall, hot-pressing sintering can effectively increase the thermal conductivity and change the electrical properties of AlN ceramics.     

添加Y2O3的AlN陶瓷材料的烧结过程

本研究以先进的进口热膨胀仪为主要手段，探讨了ＡｌＮ材料的烧结过程。用Ｘ射线衍射仪对ＡｌＮ烧结后试样进行了相分析。用最小二乘法回归分析实验数据，依据现有的烧结理论后表明，添加Ｙ２Ｏ３的ＡｌＮ材料的中后期烧结机理为相界反应速率控制的溶解－淀析过程。     

Densification and properties of AlN ceramic bonded carbon

To obtain light and tough materials with high thermal conductivity, AlN ceramic bonded carbon (AlN/CBC) composites were fabricated at temperatures from 1600 to 1900 °C in a short period of 5 min by the spark plasma sintering technique. All AlN/CBCs (20 vol% AlN) have unique microstructures containing carbon particles of 15 μm in average size and continuous AlN boundary layers of 0.5-3 μm in thickness. With an increase in sintering temperature, AlN grains grow and anchor into carbon particles, resulting in the formation of a tight bonding layer. The AlN/CBC sintered at 1900 °C exhibited a light weight (2.34 g/cm³), high bending strength (100 MPa), and high thermal conductivity (170 W/mK).     

Fabrication and thermal conductivity of AlN/BN ceramics by spark plasma sintering

Aluminum nitride/boron nitride (AlN/BN) ceramics with 15–30 vol.% BN as secondary phase were fabricated by spark plasma sintering (SPS), using Yttrium oxide (Y₂O₃) as sintering aid. Effects of Y₂O₃ content and the SPS temperature on the density, phase composition, microstructure and thermal conductivity of the ceramics were investigated. The results revealed that with increasing the amount of starting Y₂O₃ in AlN/BN, Yttrium-contained compounds were significantly removed after SPS process, which caused decreasing of the residual grain boundary phase in the sintered samples. As a result, thermal conductivity of AlN/BN ceramics was remarkably improved. By addition of Y₂O₃ content from 3 wt.% to 8 wt.% into AlN/15 vol.% BN ceramics, the thermal conductivity increased from 110 W/m K to 141 W/m K.