浸渗时间对无压浸渗制备Al/SiCp陶瓷基复合材料的影响

本文采用无压浸渗法,研究浸渗时间对Al/SiCp陶瓷基复合材料组织、致密度、硬度的影响。浸渗保温时间1h,能浸透,但致密度差,硬度低。保温时间3h,发生粉化现象。结果表明浸渗保温时间2h是无压浸渗较好的工艺参数。     

无压浸渗工艺制备铝基复合材料的研究现状和机理探讨

无压浸渗法是一类先进的金属基复合材料制备方法.总结了无压浸渗方法制备陶瓷增强金属基复合材料的工艺特点及国内外的研究现状,分析了影响无压漫渗工艺的主要因素及存在的问题,探讨了该工艺的可能机理,并指出了该工艺存在的问题和今后的研究重点.     

高体分铝基复合材料无压浸渗近净形制备

目的 研究高体分铝基复合材料无压浸渗近净形制备的可行性,分析近净形复合材料的微观组织和力学性能。方法 分别采用74 μm的碳化硅颗粒和5%(质量分数)的聚乙烯醇溶液作为增强相和黏结剂,通过模具冷压获得立方体陶瓷生坯,经干燥后加工成异形预制体,再经高温烧结脱胶处理,采用无压浸渗法制备高体分铝基复合材料近净形样品,并采用颗粒自然堆积方案制备复合材料对比样品。采用扫描电子显微镜、三点弯曲测试等手段对比分析复合材料的微观组织、力学性能和断口形貌。结果 基于无压浸渗法成功制备出具有特定外形结构的铝基复合材料,复合材料密度为2.93 g/cm³,弯曲强度为327 MPa,弹性模量为205 GPa,可达到自然堆积型复合材料弯曲强度的86.7%。碳化硅颗粒均为脆性解理断裂,说明颗粒和基体合金结合良好。结论 采用模压和烧结通用方法制备的异形陶瓷预制体可以实现特定外形结构铝基复合材料的无压浸渗近净形制备,近净形复合材料的弯曲强度可满足电子元器件的性能要求。     

无压浸渗法制备Al/70vol%Sip复合材料

采用无压浸渗工艺,成功制备出Al/70vol%Sip复合材料,对Al-Si体系进行了自发浸渗的热力学及动力学分析,并分析了组织中残留微细孔隙的形成机理.研究表明:由于存在冶金润湿,在毛细压力作用下,Al合金液能较好浸渗Si多孔预制体,浸渗深度与时间成抛物线关系;采用饱和成分的Al合金浸渗,可有效抑制对Si预制体的溶解浸蚀;对复合材料浸渗组织观察表明,Si颗粒发生钝化,相邻颗粒融合连接,呈连续三维网状.     

无压浸渗法制备氧化态SiC颗粒增强铝基复合材料

研究了SiC颗粒在1000~1200℃的氧化行为, 其氧化增重率与保温时间符合抛物线规律, 氧化增重受扩散过程控制, 氧化激活能为219 kJ/mol. 采用预氧化处理的SiC颗粒为增强体, 含Si、Mg的铝合金为基体, 通过无压浸渗方法制备了SiC_p/Al复合材料, 分析了复合材料的微观组织与界面形貌, 探讨了无压浸渗机理. 复合材料中颗粒分布均匀, 无偏聚现象. 材料制备过程中存在界面反应, SiC颗粒表面的氧化层与铝合金中的Mg、Al反应形成了一定数量的MgAl₂O₄. 界面反应的存在提高了润湿性, 促进了无压自发浸渗.     

挤压浸渗金属基短纤维复合材料浸渗压的理论分析及应用

本文根据Laplace方程及流体力学的基本原理建立了挤压浸渗法制备金属基复合材料的浸渗压模型,应用该模型对ZA22/Al₂O₃复合材料的浸渗过程进行了理论分析.以此为指导制出了性能优良的ZA22/Al₂O₃复合材料.      

融盐自发浸渗用微米级多孔陶瓷预制体的烧制

探索以SiO2为骨料,选择合适的助剂、烧成制度、成型压力和颗粒粒度,烧制成三维连通网格状多孔陶瓷预制体的工艺制度,用于自发浸渗熔融无机盐相变材料以制备无机盐/陶瓷基复合相变储能材料.讨论了制备工艺与预制体的显气孔率、孔结构以及显微组成之间的关系,烧制出的石英质多孔陶瓷具有40%～45%的显气孔率和5～40μm的孔径大小,完全符合自发熔融浸渗工艺的要求.     

熔融自发浸渗制备多孔陶瓷复合相变储能材料

研究了融盐Na2SO4与石英质多孔陶瓷预制体的自发熔融浸渗制备工艺,成功地制备出无机盐/陶瓷基(Na2SO4/SiO2)复合相变储能材料,观察和分析了该材料的物相组成与显微结构特征,对该材料的各项热物理性能和机械性能进行了测量.结果表明:自发熔融浸渗工艺比混合烧结工艺更适合于制备无机盐陶瓷基复合相变储能材料.     

Fe高温浸渗法制备防静电3Y-TZP陶瓷及其性能研究

以3Y-TZP陶瓷为基体, 采用还原Fe粉包埋、高温浸渗的表面改性方法, 制备防静电性能与力学性能兼备的ZrO₂陶瓷。研究了浸渗时间、浸渗温度对ZrO₂陶瓷表面电阻率及硬度的影响, 结果表明：随着浸渗时间延长, 浸渗温度升高, 表面电阻率降低, 硬度下降。在1000℃浸渗4 h, ZrO₂防静电陶瓷表面电阻率由10¹⁴ ?/□以上降低至8.3×10⁷ ?/□, 硬度由12.7 GPa降低至11.23 GPa。采用XRD、SEM、XPS等方法对防静电ZrO₂陶瓷的显微结构、化学组成及防静电机理进行了分析。结果表明, 浸渗过程中, 发生由t-ZrO₂转变为m-ZrO₂相变; Fe元素以Fe₃O₄、FeO、单质Fe的形式存在晶界处, 从而使ZrO₂陶瓷具备了防静电性能。     

浸渗掺杂技术在制备半透明氧化铝陶瓷中的应用

实验证实了可以使用液相前驱体浸渗技术来均匀引入添加剂和制备半透明氧化铝陶瓷。首先在不同的浸渗条件下使用硝酸钇的水溶液浸渗了预烧的氧化铝坯体。通过线扫描表征了沿坯体厚度方向上的钇元素分布情况, 发现当试样厚度更小, 溶液浓度更低时, 钇元素分布更加均匀, 而且引入量的调控也更为精确。通过假设气孔被溶液完全填充, 提出了预测浸渗引入理论量的公式。最后使用浸渗方法制备了透明氧化铝陶瓷, 发现与球磨制备的样品相比, 浸渗制备的材料显微组织更为均匀, 透光性能也更好。     

Nicalon-fibre-reinforced silicon-carbide composites via polymer solution infiltration and chemical vapour infiltration

A new, faster process was developed for the fabrication of Nicalon-fibre-reinforced SiC composites by combining polymer solution infiltration (PSI) and chemical vapour infiltration (CVI). The process led to the near-net-shape fabrication of fibre-reinforced ceramic-matrix composites and reduced infiltration time. Typical flexural strength and fracture toughness of these composites were 296 MPa and 10.9 MPa m^1/2 at room temperature (RT) and 252 MPa and 9.6 MPa m^1/2 at 1000 °C, respectively. The composites exhibited load-carrying capability after crack initiation.     

Fabrication of SiCf/SiC composites by chemical vapor infiltration and vapor silicon infiltration

Three-dimensional (3D) silicon carbide fiber reinforced silicon carbide matrix (SiC_f/SiC) composites, employing KD-1 SiC fibers (from National University of Defense Technology, China) as reinforcements, were fabricated by a combining chemical vapor infiltration (CVI) and vapor silicon infiltration (VSI) process. The microstructure and properties of the as prepared SiC_f/SiC composites were studied. The results show that the density and open porosity of the as prepared SiC_f/SiC composites are 2.1 g/cm³ and 7.7%, respectively. The SiC fibers are not severely damaged during the VSI process. And the SiC fibers adhere to the matrix with a weak interface, therefore the SiC_f/SiC composites exhibit non-catastrophic failure behavior with the flexural strength of 270 MPa, fracture toughness of 11.4 MPa·m^1/2 and shear strength of 25.7 MPa at ambient conditions. Moreover, the flexural strength decreases sharply at the temperature higher than 1200 °C. In addition, the thermal conductivity is 10.6 W/mk at room temperature.     

化学气相渗积压力对渗积速率和热解炭组织结构的影响(英文)

采用天然气为前躯体在不同压力下使用化学气相渗积法制备炭/炭复合材料。利用甲烷分解热力学与沉积动力学研究了渗积压力对渗积速率和热解炭组织结构的影响。采用偏光显微镜观察热解炭的组织结构。结果表明:随着渗积压力的增加,初始渗积速率增大;但在渗积后期,渗积速率随着渗积压力的增大而降低,导致在高渗积压力下相同时间制备样品的最终密度降低。热解炭组织结构对渗积压力具有很强的依赖性。在低压(1 kPa)下渗积得到的热解炭基体全部为粗糙层结构。在适中的压力(3kPa,5 kPa,10 kPa)下,以炭纤维为圆心由内到外依次得到各向同性和粗糙层热解炭,整个基体以粗糙层为主。在15 kPa下,得到的热解炭组织结构为各向同性和光滑层组织。     

Fabrication and infiltration kinetics analysis of Ti-coated diamond/copper composites with near-net-shape by pressureless infiltration

The Ti-coated diamond/copper composites with near-net-shape are manufactured by pressurelessly infiltrating liquid copper into porous Ti-coated diamond preforms. The contact angle between diamond and copper, relative density, thermal conductivity (TC), coefficient of thermal expansion (CTE), leak rate and microstructure are evaluated and characterized. In addition, the numerical analysis of the pressureless infiltration kinetics is also discussed. The results indicate that the relative density, TC and CTE of composites are 99.3%, 385 Wm⁻¹ k⁻¹ and 3–8 × 10⁻⁶ K⁻¹, respectively. It can meet heat-sink package requirement of high-power electronic devices as LED, insulated gate bipolar transistor (IGBT), etc. The liquid copper exhibits a turbulent flow with the Reynolds number in the range of 27.83–49.7. The porosity ? and the pressure drop Δp are the main influence factors controlling the velocity of liquid copper. Moreover, under vacuum condition of 8.7 × 10⁻³ Pa, the maximum theoretical infiltration length L_max of Ti-coated diamond/copper composites is found to be 552 mm.     

Pressure-assisted infiltration of molten aluminium into open cell ceramic foams: Experimental observations and infiltration modelling

Partial infiltration of molten Al into three different open cell ceramic foams has been effected using pressure-assisted vacuum investment casting equipment. For the maximum pressure difference (only 0.25 MPa) up to 90% of the open porosity could be filled, but since the ceramic foams were found to contain closed pores, the resulting composite densities were low. A simple modelling approach accurately predicts the infiltration behaviour and enables the processing conditions and architecture of the preforms to be optimised in respect of the maximum infiltration pressure available from the processing equipment.     

Carbon fibre-reinforced CMCs by PCS infiltration

C/SiC-based composites were produced by infiltration of a woven carbon fabric preform with a polycarbosilane (PCS) solution. Progress of the infiltration process up to eight infiltrations was followed by density measurements, microscopy and mechanical testing. After six infiltration cycles, the density increase tended to a plateau. Dense deposition of the matrix on the outer surface sealed off the core of the composite, which hindered successive infiltrations. With further re-infiltration cycles, the development of the matrix and the degree of bonding between the fibre and matrix increased. There was also a transition in the failure mode of the composite, when tested in 3-point bending, from shear to plain brittle tensile failure, as the number of infiltrations increased.     

Optical, mechanical properties and infiltration rate of spinel/zirconia-glass dental composites prepared by melt infiltration

Spinel/zirconia-glass dental composites were prepared by melt infiltration to investigate the effect of zirconia addition on mechanical, optical properties and infiltration rate of the composites. The glass infiltration rate decreased with raising the zirconia content having a parabolic dependence of infiltration distance on time described by the Washburn equation due to the reduction in pore size. Although the optimum strength (308 MPa) of the spinel/zirconia-glass dental composite was observed when 20 wt% of zirconia was added, transmittance decreased with further increase in the zirconia content.     

真空脉冲渗氮研究

为提高真空热处理技术的应用，我所进行真空脉冲渗氮设备的研制及真空脉冲工艺的研究，研究表明，利用真空热处理技术，进行脉冲渗氮，使渗氮后工件表面脆性小，渗氮层均匀，而且无公害，同时模具的寿命提高1－2倍，并取得一定的经济效益。