分散炭纤维对C/C-SiC复合材料压缩性能的影响

以短炭纤维为增强体,采用浸渍模压炭化增密工艺制备C/C多孔体,结合反应熔渗法制备C/C-SiC复合材料。采用电子万能试验机测定复合材料的压缩性能,利用扫描电镜观察该材料及其断口显微形貌;研究纤维分散性对C/C多孔体孔隙和C/C-SiC复合材料压缩性能的影响。结果表明:分散炭纤维制备的C/C多孔体中纤维分布更均匀,没有因纤维束搭桥而产生大孔隙等缺陷;分散纤维增强的C/C-SiC复合材料在平行方向和垂直方向均有较好的压缩性能,其压缩强度分别为100.6 MPa和76.2 MPa。     

短炭纤维增强C和SiC双基体材料的力学性能及破坏机理

以短炭纤维为增强纤维,以炭粉、Si粉和树脂为基体来源,采用温压—原位反应法制备C/C-SiC材料,研究该材料的力学性能及破坏机理。结果表明:C/C-SiC制动材料的纵向和横向抗弯强度分别为76 MPa和62 MPa,以韧性断裂为主,弯曲破坏表现为裂纹偏转、纤维桥接、纤维拔出和界面脱粘。纵向抗压强度达112 MPa,纵向压缩破坏表现为韧性断裂,以对角剪切破坏方式为主;横向抗压强度达84 MPa,横向压缩破坏主要表现为脆性断裂,以多层复合剪切破坏方式为主。材料的冲击韧性为3.1 kJ/m2。     

以不同酚醛树脂制备的C/C-SiC复合材料的力学性能

选用热固性酚醛树脂A和热塑性酚醛树脂B分别与短炭纤维、石墨粉、硅粉、碳化硅按一定比例混合后,采用温压-原位反应法,制得具有不同树脂炭基体的C／C-SiC复合材料的试样1和2,并对其力学性能进行研究,以期优化该复合材料的成分配方和进一步提高其技术性能。结果显示：试样1在垂直于纤维层方向的压缩载荷及弯曲载荷作用下,未出现纤维拔出、脱粘等现象,界面结合较强,呈现脆性断裂,压缩强度σ⊥=60．7MPa,弯曲强度σb=34．5MPa;而在平行于纤维层的压缩载荷作用下,纤维与基体存在剪切作用,出现纤维脱粘,呈现韧性断裂,σ∥=52．6MPa。试样2由于纤维的分散性不好,大量聚集在一起,在压缩和弯曲载荷作用下,均存在纤维的拔出和脱粘现象,界面结合较差,材料呈现韧性断裂,强度较低,σ⊥=45．8MPa,σ∥=19．4MPa,σb=16．1MPa。     

短碳纤维含量对温压-熔渗工艺制备C/C-SiC复合材料力学性能的影响

以短切碳纤维为增强体,采用温压–熔渗工艺(WP-LSI)制备纤维体积分数分别为20%、25%和30%的C/CSiC复合材料,研究纤维含量对C/C-SiC复合材料力学性能的影响,并与国外同类产品进行对比。结果表明:随碳纤维含量增加,复合材料的开孔率降低,抗弯强度和抗压强度均提高,纤维体积分数为30%的复合材料密度达2.00 g/cm3,开孔率仅2.88%,其抗弯和垂直抗压强度分别为104.63 MPa和167.99 MPa,比纤维体积分数为20%的材料分别提高86.04%和44.76%,比国外同类产品分别提高2.03%和11.99%;随碳纤维含量增加,复合材料的破坏形式由假塑性破坏向脆性破坏转变。     

化学镀镍(SCF-Ni)短炭纤维增强铝基复合材料的显微组织与力学性能

利用化学镀技术在短炭纤维(short carbon fiber, SCF)表面镀镍,制备镍层包覆的炭纤维(SCF-Ni)。采用湿混法将不同含量的镀镍短炭纤维(SCF-Ni)与铝硅合金粉(Al-Si)均匀混合,用放电等离子烧结技术(SPS)制备镀镍炭纤维增强铝基复合材料(SCF-Ni/Al-Si复合材料)。通过SEM观察炭纤维和复合材料的组织与形貌;用XRD分析复合材料界面物相,探究SCF-Ni质量分数对复合材料微观结构及力学性能的影响。结果表明,随SCF-Ni含量增加,SCF-Ni/Al-Si复合材料密度下降,硬度增加,室温抗拉强度先升高后降低,在SCF-Ni质量分数为9%时达到最大值152 MPa,较Al-Si基体的抗拉强度(90 MPa)提升了68%。     

低温模压法制备的C/C-SiC复合材料的摩擦磨损性能

为深入了解低成本法制备的C/C-SiC复合材料的摩擦磨损规律,以短炭纤维、Si粉、炭粉和粘结剂为原料,通过均匀混合、模压成形、1 600℃反应烧结制备了C/C-SiC复合材料,研究了孔隙度、SiC含量及环境湿度对该复合材料摩擦磨损性能的影响,并用光学显微镜及X射线衍射仪对磨屑进行观测分析,对不同状况下的摩擦磨损机理进行研究。结果表明:C/C-SiC复合材料的致密度决定其磨损方式;SiC在摩擦过程中作为硬质支撑点,其含量对摩擦系数及其稳定性具有关键性影响;湿态时的摩擦系数与线磨损均略有下降,但仍能保持其良好的摩擦磨损性能。     

B_4C颗粒对C/C-SiC复合材料微观结构与力学性能的影响

采用浆料浸渗结合先驱体浸渍-裂解法制备B_4C颗粒改性C/C-SiC复合材料,研究B_4C颗粒对C/C-SiC复合材料力学行为的影响。结果表明,B_4C颗粒改性的C/C-SiC复合材料的抗弯强度和断裂韧性分别为250.41 MPa和13.56 MPa·m~(1/2),与C/C-SiC复合材料相比,其抗弯强度下降45.5%,而断裂韧性提高46.0%。B_4C颗粒可促进SiC基体的烧结,但由于大量闭孔和基体弱界面的形成,导致材料抗弯强度降低。B_4C颗粒改性的C/C-SiC复合材料断裂韧性提高的主要原因在于,B_4C颗粒与SiC基体中的弱界面使裂纹在SiC基体中得到有效偏转,增加了裂纹在基体中的扩展路径,使得材料的断裂韧性提高。     

炭化工艺对C/C-SiC制动材料摩擦磨损性能的影响

以短炭纤维、Si粉、炭粉和树脂为原料,通过均匀混合、温压成形,在1 500℃原位反应最终制得C/C-SiC复合材料.测试试样的开孔隙率、热扩散率及摩擦磨损性能,研究制备工艺过程中后续炭化对摩擦磨损性能的影响,并对摩擦表面及磨屑进行扫描电镜观察和X射线衍射分析.结果表明:采用树脂浸渍炭化工艺制备的C/C-SiC制动材料具有适中的摩擦因数和较低的磨损率;经后续炭化,树脂转变为树脂炭,以磨粒的形式增大摩擦力,同时有效地降低了磨损率.     

短纤维增强C/C-SiC复合材料的制备工艺

为缩短制备周期和降低成本, 采用水悬浮法制得含硅短炭纤维料饼, 经树脂模压成形和炭化后成为预制体, 再经浸渍/炭化增密和高温反应生成SiC, 制备了C/C SiC复合材料, 并对材料的显微组织、物相组成、石墨化度、力学性能和摩擦磨损性能进行了研究。结果表明制备的预制体密度为1.1 g·cm-3左右, 短炭纤维优先在摩擦面上交错排布, 部分在厚度方向上排布, 预制体中硅颗粒分布均匀; 最终石墨化处理后, 复合材料密度为1.75 g·cm-3左右, 组成相为炭和βSiC, 其中炭的石墨化度为54%左右; 复合材料的破坏形式为脆性断裂, 材料基本具有功能材料应具备的结构力学性能; 随炭纤维体积含量的增加, 材料的摩擦因素和磨损率均呈下降趋势,纤维体积含量为25%时具有适中的摩擦磨损性能, 摩擦因素为0.28, 磨损率为2.75 mm3·kJ-1。     

反应熔渗法制备C/C-SiC复合材料及其影响因素的研究进展

比较了C/C-SiC复合材料的3种主要制备方法,介绍了反应熔渗法制备工艺,以及液Si渗入C/C多孔体、液Si与固体C反应和C/C-SiC复合材料性能的主要影响因素,提出了尚待解决的关键问题。     

基体炭对反应熔渗法制备的C/C-SiC复合材料性能的影响

以炭纤维针刺整体毡为预制体,分别采用化学气相渗透(chemical vapor infiltration,CVI)法、浸渍炭化(Impregnation and carbonization,I/C)法以及CVI与I/C相结合(CVI＆I/C)的方法制备C/C坯体,坯体中的基体炭分别为热解炭,树脂炭,热解炭和树脂炭共存体...     

化学镀碳纤维增强羟基磷灰石复合材料的性能

通过化学镀方法,在碳纤维表面分别镀上Ni和Cu+Ni镀层,以这种表面改性碳纤维与羟基磷灰石陶瓷复合,制备表面改性碳纤维增韧增强羟基磷灰石复合材料,研究各种碳纤维的含量对复合材料的抗弯强度、断裂韧度、尺寸变化率和孔隙率的影响。结果表明,表面改性碳纤维可以显著提高材料的性能,尤其是铜镍复合镀碳纤维的效果更好,其断裂韧度可达基体断裂韧度的2.5倍,抗弯强度可达基体抗弯强度的3.4倍,增韧增强后的复合材料的尺寸和孔隙率变化不大。     

Hybridization Effect on the Mechanical Behavior of Monophase Reinforced PA66/Teflon Blend Based Hybrid Thermoplastic Composites

The Monophase reinforced hybrid thermoplastic composites are the materials for the superior mechanical behavior. This article deals with the effect of single reinforcing phase (Fiber) in hybrid mode on the mechanical behavior of PA66/Teflon blend. Two hybrid material systems were selected: 10 wt% short glass fibers (SGF) and 10 wt% short carbon fibers reinforced 80 wt% PA66/20 wt% Teflon (PA66/PTFE) blend (GB) and 10 wt% SGF and 10 wt% short basalt fibers reinforced 80 wt% PA66/20 wt% Teflon (PA66/PTFE) blend(GB). These hybrid composite materials were prepared by melt mixing method by using twin screw extruder followed by injection molding. The experimentally determined mechanical properties were tensile behavior, flexural behavior and impact behavior. Experimental results revealed that addition of hybrid short fibers into the blend greatly enhanced the mechanical behavior of PA66/PTFE composites. Increase in tensile strength by 46 and 33%, flexural strength by 45 and 57% for GC and GB composites respectively were observed. The GC composites had the better impact strength than GB composites. The peak load obtained was 36 and 48% higher than that of neat blend for GC and GB composites respectively were observed. The strain rate of the hybrid composites deteriorated due to the hybrid effect. The synergistic effect between the fibers and the matrix blend improved the mechanical behavior. The hybrid effect increased the size of the voids and also the number of aggregates of the short fibers. This would weaken the reinforcement effect simultaneously building the strong bridge for the development of internal crack. Fractured surfaces were observed through Scanning Electron Microscopy photographs.     

原位合成TiB2对B4C/2024Al合金复合材料组织与力学性能的影响

在B4C粉末中加入5%高纯TiO2,经过压制和烧结制备B4C-TiB2陶瓷预制体,然后在氩气气氛中1 200℃下浸渗2024铝合金制得B4C-TiB2/Al合金复合材料。对该复合材料进行力学性能测试、X射线衍射分析、显微组织观察和断口分析。结果表明:该复合材料主要由B4C,Al,Al3BC和AlB2相组成,原位合成的TiB2使B4C/Al合金复合材料的抗弯强度和断裂韧性显著提高,分别达到361 MPa和7.49 MPa m1/2,增幅分别为14.6%和11.5%,但密度变化很小。原位合成TiB2使B4C/Al合金复合材料的抗弯强度和断裂韧性提高主要来源于金属铝塑性变形的裂纹桥接机制、TiB2细化晶粒及微裂纹引起的主裂纹偏转分叉机制。     

浸渍工艺对炭/炭复合材料力学性能的影响

通过对浸渍前后C/C复合材料抗弯性能、剪切性能和耐压性能的比较,分析了浸渍工艺过程对C/C复合材料力学性能的影响.浸渍工艺使C/C复合材料力学性能有明显改善:抗弯强度由浸渍前的101MPa提高到浸渍后的159 MPa,剪切强度由浸渍前的8.6 MPa提高到浸渍后的12.1MP,抗压强度由浸渍前的82 MPa提高到浸渍后的136 MPa.浸渍前后C/C复合材料断口的扫描电镜照片分析可得出浸渍工艺的炭生长层有与CVD工艺类似的微现结构的结论.     

Strength degradation of SiC fiber during manufacture of titanium matrix composites by plasma spraying and hot pressing

Titanium matrix composites (TMCs) reinforced with Sigma 1140+ SiC fiber have been manufactured by a combination of low pressure plasma spraying (LPPS spray/wind) and simultaneous fiber winding, followed by vacuum hot pressing (VHP). Fiber damage during TMC manufacture has been evaluated by measuring fiber tensile strength after fiber extraction from the TMCs at various processing stages, followed by fitting of these data to a Weibull distribution function. The LPPS spray/wind processing caused a decrease in mean fiber strength and Weibull modulus in comparison with as-received fibers. A number of fiber surface flaws, primarily in the outer C layer of the fiber, formed as a result of mechanical impact of poorly melted particles from the plasma spray. Coarse feedstock powders promoted an increase in the population of fiber surface flaws, leading to significant reduction in fiber strength. The VHP consolidation promoted further development of fiber surface flaws by fiber bending and stress localization because of nonuniform matrix shrinkage, resulting in further degradation in fiber strength. In the extreme case of fibers touching, the stress concentration on the fibers was sufficient to cause fiber cracking. Fractographic studies revealed that low strength fibers failed by surface flaw induced failure and contained a large fracture mirror zone. Compared with the more widely investigated foil-fiber-foil route to manufacture TMCs, LPPS/VHP resulted in less degradation in fiber strength for Sigma 1140+ fiber. Preliminary results for Textron SCS-6 fiber indicated a much greater tolerance to LPPS/VHP damage.     

Synthesis of Al2O3/TiCN-0.2%Y2O3 Composite by Hot Pressing

Al2O3/TiCN composites were synthesized by hot pressing.The influences of components and HP temperature on mechanical properties,such as bending strength,breaking tenacity and Vickers hardness were investigated.The results showed that the mechanical properties of Al2O3/TiCN composite increased with temperature when hot pressing temperature is below 1650 ℃.The mechanical properties reached their maximums when the composites were sintered at 1650 ℃ for 30 min under hot pressing pressure of 35 MPa,the value of bending strength,breaking tenacity and Vickers hardness was 1015 MPa,6.89 MPa·m1/2,and 20.82 MPa,respectively.When hot pressing temperature was above 1650 ℃,density decreased because of decomposition with increased temperature,and mechanical properties dropped because of rapid growth of grains in size at high temperature.Microstructure analysis showed that the addition of Y2O3 led to the formation of YAG phase so as to inhibit the growth of crystals.This helped to improve breaking tenacity of the composites.TiCN particles with diameters of 1 μm dispersed at Al2O3 grain boundaries,inhibited grain growth and enhanced mechanical properties of the composites.SEM study of the propagation of indentation cracks showed that the bridge linking behavior between matrix and strengthening phase might lead to the formation of the coexisted field of crack deflection,branching and bridge linking.The mechanism of this phenomenon was that the addition of Y2O3 improved the dispersion of TiCN particles so as to enhance the tenacity of the composites.The breaking tenacity was changed from 5.94 to 6.89 MPa·m1/2.     

Fibridization Effect on the Mechanical Behavior of PA66/PTFE Blend Based Fibrous Composites

The use of natural fiber along with the glass fiber in polymer composites is one of the present material combinations for automotive industries. This article deals with the hybrid effect of 10 wt% short glass fibers (SGF) and 10 wt% short basalt fibers (SBF) on the mechanical behavior of 80 wt% PA66/20 wt% Teflon (PA66/PTFE) blend. These composite materials were prepared by melt mixing method, by using twin screw extruder followed by injection molding. The mechanical performance of the composite materials was tested as per ASTM method. The experimentally determined mechanical properties were tensile behavior, flexural behavior and impact behavior. Hardness and density of the blended composites were also studied. Experimental results revealed that the effect of hybrid short fibers on the blend greatly enhanced the mechanical behavior. Increase in tensile strength and flexural strength by 33% and 57% respectively and 6% reduction in elongation was exhibited by the blend due to the hybrid effect of fibers. The synergistic effect between the fibers and the matrix blend improved the mechanical behavior. The strain rate of the hybrid composites was deteriorated due to the hybrid effect. The enhancement of load carrying capacity by 17.35, 8.5 and 36% was exhibited by SGF, SBF and hybrid fiber filled PA66/PTFE blend composites respectively. The impact strength of the hybrid composites was reduced due to the brittle nature of the hybrid filled composites. Fiber fracture, fiber pull out and fiber misalignment were the certain mechanisms observed during mechanical performance. The fractured surfaces were analyzed through Scanning Electron Microscopy photographs.