Compressive strength and wear properties of SiC/Al6061 composites reinforced with high contents of SiC fabricated by pressure-assisted infiltration

Pressure-assisted infiltration was used to synthesize SiC/Al 6061 composites containing high weight percentages of SiC. A combination of PEG and glass water was used to fabricate SiC preforms and the effect of the presence of glass water on the microstructure and mechanical properties of the preforms was evaluated by performing compression tests on the preforms. Also, the compressive strength and the hardness of the SiC/Al composites were investigated. The results revealed that the glass water improved the compressive strength of the preforms by about five times. The microstructural characterization of the composites showed that the penetration of the aluminum melt into the preforms was completed and almost no porosity could be seen in the microstructures of the composites. Moreover, the composite containing 75 wt% SiC exhibited the highest compressive strength as well as the maximum hardness. The results of the wear tests showed that increasing the SiC content reduces the wear rate so that the Al-75 wt% SiC composite has a lower wear rate and a lower coefficient of friction than those of Al-67 wt% SiC composite. This indicated higher wear resistance in these composites than the Al alloy due to the formation of a tribological layer on the surface of the composites.     

高镁瓷工艺特性研究和应用

本文总结了ＭｇＯ－ＳｉＯ２－Ａｌ２Ｏ３系的高镁瓷配方、增塑及烧成工艺特性的研究过程与应用结果；介绍了适应大生产的高镁瓷制作工艺。     

Modeling Temperature in Coupled Electrical and Thermal Simulations of the Electroconsolidation® Process

Electroconsolidation® is a process for densifying complex-shaped parts by using electrically conductive particulate solids as a pressure-transmitting medium. The part is immersed in a bed of the particulate medium contained in a die chamber. Sintering temperature is achieved by resistive heating of the medium while applying compaction pressure. The process is capable of ultrahigh temperatures and short cycle times and offers the potential for low processing costs.

Control of the process and selection of process conditions require knowledge of the temperatures within the die. Temperature gradients exist because of the high heating rate and because of variations of density and electrical resistivity of the medium due to the presence of the part. Direct measurement of temperature with thermocouples or other conventional means is impractical because of the high temperatures, high currents, and high pressures that are involved. Therefore, a computer model was developed to predict temperature as a function of time and applied voltage for any location in the die. The computer model is composed of three parts: a geometrical model to approximate the density and resistivity variations in the medium, a finite-element model to calculate the rate of resistive heating within each element, and a finite-difference model to calculate the temperature distribution based on solution of the heat-transfer equations. Predicted temperatures have been shown to be in excellent agreement with measurements, and numerical simulation provided encouraging consistency and reasonably accurate predictions of temperature profiles within the die. The model demonstrated the feasibility of a new process to achieve simultaneous application of pressure and heat to powder densification in Electroconsolidation.     

差温无模预成形锻造的有限元模拟研究

利用热力耦合有限元方法 ,对AISI10 4 5钢圆柱体坯料在环形加热源局部加热下的差温无模预成形锻造过程进行了模拟研究。模拟结果表明 ,在坯料中获得和控制大梯度分布的不均匀温度场是实现无模预成形锻造的关键。复杂零件成形必须合理地组合加热源和冷却源 ,以便产生所需的温度梯度场。在快速变形条件下 ,变形过程中的持续加热对金属的流动影响甚微 ,变形前的温度分布基本上决定了金属的流动 ,但在慢速变形条件下 ,变形过程中的持续加热对金属的流动产生一定的影响 ,其影响程度视零件复杂程度而异。从该文研究结果可以预见 ,差温无模锻造可以发展成为一种无模锻造制坯新工艺     

SiC FIBER／ALUMINIUM PREFORM WIRES FABRICATEDBY ULTRASONIC LIQUID INFILTRATION PROCESS

ＳｉＣＦＩＢＥＲ／ＡＬＵＭＩＮＩＵＭＰＲＥＦＯＲＭＷＩＲＥＳＦＡＢＲＩＣＡＴＥＤＢＹＵＬＴＲＡＳＯＮＩＣＬＩＱＵＩＤＩＮＦＩＬＴＲＡＴＩＯＮＰＲＯＣＥＳＳＺｈａｎｇＣｈｅｎｇｅ；ＷａｎｇＬｉｎｇｓｅｎ（ＣｅｎｔｒａｌＳｏｕｔｈＵｎｉｖｅｒｓｉｔｙｏｆ...     

基于西门子S7-300PLC的光纤预制棒温度控制系统的设计

针对光纤制造行业预制棒加热系统温度控制要求,介绍基于西门子S7-300PLC的光纤预制棒温度控制系统的硬件配置、软件流程、人机画面等。     

Sensitivity analysis based preform die shape design using the finite element method

This paper uses a finite element-based sensitivity analysis method to design the preform die shape for metal forming processes. The sensitivity analysis was developed using the rigid visco-plastic finite element method. The preform die shapes are represented by cubic B-spline curves. The control points or coefficients of the B-spline are used as the design variables. The optimization problem is to minimize the difference between the realized and the desired final forging shapes. The sensitivity analysis includes the sensitivities of the objective function, nodal coordinates, and nodal velocities with respect to the design variables. The remeshing procedure and the interpolation/transfer of the history/dependent parameters are considered. An adjustment of the volume loss resulting from the finite element analysis is used to make the workpiece volume consistent in each optimization iteration and improve the optimization convergence. In addition, a technique for dealing with fold-over defects during the forming simulation is employed in order to continue the optimization procedures of the preform die shape design. The method developed in this paper is used to design the preform die shape for both plane strain and axisymmetric deformations with shaped cavities. The analysis shows that satisfactory final forging shapes are obtained using the optimized preform die shapes.     

骨架结构对SiC/Al双连续相复合材料的影响

用挤压铸造法制备了不同结构的SiC泡沫增强ZL109双连续相复合材料,研究了增强体骨架结构(筋的结构、泡沫孔和体积分数)对复合材料压缩性能和弯曲性能的影响。结果表明:SiC泡沫增强体的筋的结构影响了界面的结合,影响了材料的压缩性能;当筋具有三明治结构时,复合材料的强度最大;当筋具有双层结构时,复合材料的强度最低;随着SiC泡沫孔径的增大,复合材料的压缩强度、弹性模量和屈服强度都有所提高,材料的屈服应变减小,弯曲强度先升高后降低,弯曲强度在泡沫孔径为1.5 mm时达到最大值;复合材料的压缩强度随着增强体体积分数的增大而提高,屈服应变随着体积分数的增大而减小。     

电子封装SiCp/Al复合材料的制备与性能

研究了无压渗透法制备电子封装SiCp/Al复合材料过程中,烧结工艺对SiC预制件开孔率、抗压强度的影响,以及渗透工艺对Al液渗透形成复合材料的影响,并对所制备的复合材料热物理性能和表面涂覆进行了评价。结果表明,经1100℃分段烧结的SiC预制件开孔率、抗压强度较好;Al液浇铸温度、保温温度分别在750～850℃、800～900℃的范围时,SiC预制件的渗透效果较好;所制备的55%SiCp/Al复合材料相对密度为98.3%,热膨胀系数在（7.23～9.97）×10-6K^-1之间变化,热导率为146.5～172.3W/（m.K）,复合材料表面涂覆性能可行性好。     

三维编织复合材料预制件表面图象计算机分析系统

介绍了三维编织复合材料预制件表面图像检测与纹理分析的 基本原理。该系统以CCD为传感器,与微型计算机连接,进行三维编织复合材料预制件表面 编织角的检测。本系统对改善三维编织复合材料预制件的加工工艺具有指导作用,同时也为 纺织复合材料新的性能指标建立提供了有利条件,为纺织复合材料在各个领域的广泛应用提 供理论基础。