片状Al2O3对Al2O3/FEP复合材料热导率的影响

通过混炼工艺制备了片状Al₂O₃填充聚全氟乙丙烯(FEP)复合材料,以颗粒状Al₂O₃为对比样品,研究了片状Al₂O₃形状和尺寸对 FEP基复合材料热导率的影响,利用SEM观察了FEP基复合材料的微观形貌。结果表明：在低填充量下,Al₂O₃颗粒在FEP基体中呈“海岛”状分布,没有形成连续的导热网链,但其热导率明显提高;复合材料拉伸强度与断裂伸长率随Al₂O₃含量的增加而减小;低填充量时复合材料热导率的提高主要来自Al₂O₃的微细片状结构,这种微细片状结构一方面提高了有效导热路径,另一方面增加了颗粒与基体之间接触面积,因此有利于热导率的提高。     

氧化铝体积分数对Al2O3f+Cf/ZL109混杂复合材料干滑动摩擦磨损行为的影响

利用挤压铸造法制备了Al₂O_3f+C_f/ZL109短纤维混杂金属基复合材料,并探讨了Al₂O₃纤维对该混杂复合材料干滑动摩擦磨损行为的影响。结果表明:混杂复合材料的摩擦系数以及从轻微磨损到急剧磨损转变的临界载荷均随着Al₂O₃体积分数的增加不断增大。在轻微磨损阶段,复合材料的主要磨损机制为犁沟磨损和层离,且Al₂O₃体积分数为12%时混杂复合材料的磨损率最低。发生严重磨损时,基体和复合材料的磨损机制均为严重的粘着磨损。     

Al2O3-SiO2纤维增强ZL108合金复合材料的强度特性

用低成本的Al₂O₃-SiO₂系纤维作为增强相,通过加压铸造法制作ZL108合金复合材料,并对该复合材料和ZL108合金进行不同温度下的时效处理和压缩试验。通过DSC、EPMA和TEM分析认为:经488K、0.5h时效处理(T6处理)的V_f 20%的复合材料在573K以下的压缩屈服强度低于ZL108合金,是由于基体中的Mg与Al₂O₃-SiO₂纤维在加压铸造过程中起化学反应而生成MgAl₂O₄,损耗了基体中的大量Mg,导致基体铝合金时效硬化效果很差,所以压缩屈服强度低下。623K、720h保温后的V_f 20%的复合材料的压缩屈服强度比ZL108合金要高得多,是由于在这种温度环境下对ZL108合金来说是过时效,所以纤维的增强怍用显得明显。在高温(673K)下V_f 20%的复合材料的屈服强度比ZL108台金高一倍左右。不论在什么温度场合下V_f5%的复合材料的屈服强度比V_f 20%的复合材料都低。     

SiO2玻璃原位反应合成Al/Al2O3复合材料

利用SiO₂玻璃具有易近成型、致密及各向同性的特点,通过SiO₂玻璃与铝熔体间的反应合成了Al/Al₂O₃复合材料,克服长期以来在合成Al/Al₂O₃复合材料时均采用颗粒反应物的局限。反应产物是一种组织均匀致密的Al 与Al₂O₃互为网络的Al/Al₂O₃陶瓷基复合材料。反应温度升高,整个反应产物中的Al的体积分数上升。Al/Al₂O₃复合组织在三维空间的真实形态中存在着Al相被Al₂O₃完全包围的形态,证明了网络状Al₂O₃组织形成的烧结机理。与合成Al/Al₂O₃的其它工艺相比,本工艺可在1000℃的较低温度进行,并具有反应速度快、断裂韧性和抗弯强度值高的特点。     

Lanxide Al/Al2O3陶瓷基复合材料的显微结构研究

本文利用XRD、EPMA,SEM等分析方法对Lanxide技术制备的Al/Al₂O₃复合材料的显微结构进行了研究。结果表明,Lanxide Al/Al₂O₃材料是以三维连通骨架状α-Al₂O₃为基体的陶瓷基复合材料,网状或点块状金属相(Al、Si)和孔洞相分布于Al₂O₃晶间或晶粒内。改变工艺对材料的组织和性能有较大影响。     

Al2O3短纤维/Al-5.5Zn复合材料裂纹形核及扩展的TEM动态拉伸观察

利用透射电镜(TEM)动态拉伸技术研究了外力作用下Al₂O₃短纤维增强Al-5.5Zn基复合材料的细观力学行为。结果表明,该材料中裂纹形核及扩展主要是在基体中或纤维/基体界面处进行。导致这一结果的原因在于纤维、基体之间强度差异太大。实验中还发现,卸载时,微裂纹有闭合现象。     

疲劳氧化环境中3D SiCf/SiC复合材料损伤演变

研究了疲劳氧化环境中3D SiC_f/SiC复合材料损伤演变,并对该环境中SiC_f/SiC复合材料的失效机制进行了分析。结果表明,疲劳氧化环境中3D SiC_f/SiC复合材料的损伤主要为：基体开裂;热解碳界面相脱粘、氧化及取向性排列;纤维断裂、氧化及其结构的改变。这些损伤使氧化性气体通过基体开裂形成的裂纹不断氧化复合材料内部;界面相脱粘和取向性排列使纤维更容易拔出;纤维的氧化、纤维中无定形碳的增多以及SiC晶粒的长大导致纤维强度降低。     

两种Al2O3短纤维增强纯Al复合材料拉伸断裂过程与强化机理研究

选用国产Al₂O₄纤维与英国Saffil纤维怍为增强体,工业纯Al作为基体制成复合材料。在扫描电镜下,进行了微观断裂过程动态观察,并结合强度测定及断口分析探讨了不同情况下的断裂机理。     

Al2O3颗粒增强纯铝基复合材料的研究

本文探讨了用粉末冶金法,采用常规的冶金加工设备和工艺,制造Al₂O₃颗粒增强纯铝基复合材料的可行性。研究了不同Al₂O₃体积含量复合材料的显微组织及力学性能。初步试验了二次热挤压变形对颗粒分布和对基体强化的影响。结果表明,Al₂O₃颗粒与纯铝粉混合,加压烧结制备的复合材料,组织致密,颗粒分布均匀,随Al₂O₃含量增加,复合材料强度、硬度及弹性模量大大提高,Al₂O₃含量小于10%时,塑性不降低。二次热挤压有助于提高颗粒分布的均匀性;并使基体显著强化。     

Al2O3短纤维/Al-12Si复合材料启裂特征的TEM原位观察研究

利用挤压铸造法制备了Al₂O₃(15%)/Al-12Si复合材料,并采用透射电镜动态拉伸技术对复合材料的裂纹形成及微观断裂过程进行了原位观察,发现该复合材料的纤维/基体界面是破坏路径之一,并发现了纤维中裂纹形成及扩展至完全破坏的现象.     

反应热压(Al2O3+TiB2+Al3Ti)/Al复合材料的低周疲劳行为

采用反应热压法以Al、B₂O₃、TiO₂粉和Al、B、TiO₂粉为原料制备了两种(Al₂O₃+TiB₂+Al₃Ti)/Al复合材料。后一种原料粉制备的复合材料从基体中析出了细小的Al₃Ti相。研究了应变控制原位生成复合材料的室温低周疲劳行为。结果表明,在应变幅较小时(ε_</em>t≤0.3%),不含Al₃Ti析出相的材料表现为循环稳定;而在应变幅较大时(ε_</em>t≥0.4%), 则表现为第一周的循环硬化和随后的循环软化。在所采用的应变幅下,含Al₃Ti析出相的材料均表现为循环稳定。疲劳裂纹萌生部位为Al₃Ti相断裂、Al₃Ti相与基体的界面开裂和基体中微裂纹。疲劳裂纹穿过基体,绕过Al₂O₃、TiB₂质点扩展。两种复合材料的疲劳寿命均符合Coffin-Manson公式。      

High-cycle fatigue behaviour and mechanism analysis of a forged TiZr-based alloy

Fatigue resistance, particularly the endurance limit, is an important design consideration in engineering applications for TiZr-based alloys. The investigated Ti–20Zr–6Al–4?V (wt-%) alloy exhibited a high fatigue endurance limit of 775?MPa. Results showed that severe local stress concentration due to extensive dislocation pile-up at α/β interfaces was responsible for the crack initiation. A transition from a tensile mode to a shear mode crack was observed during crack propagation. Many striations as well as some micro-cracks which can improve the resistance to crack propagation exist in the stable crack-propagation region. A localised deviation between the crack-growth direction was also found, and this outcome combined with micro-cracks and tear ridge may be attributed to varied crystallographic orientations between different phases.     

Fatigue damage evolution in SiC fiber-reinforced Ti-15-3 alloy matrix composite

Tension-tension fatigue damage behavior of an unnotched SiC (SCS-6) fiber-reinforced Ti-15-3 alloy matrix composite at room temperature was examined, applying maximum stresses of 450, 670 and 880 MPa with R = 0.1. The change in stress-strain hysteresis curves was measured. Fiber fracture behavior and matrix cracking behavior were observed in situ and the results were compared with the change of unloading modulus obtained from the hysteresis curves. The fiber fracture behavior inside the specimen was also determined by dissolving the Ti alloy matrix. The results showed abrupt reductions in the unloading modulus of the composite at stresses of 450, 670 and 880 MPa; the normalized unloading modulus decreased by 8%, 12% and 17%, respectively, in the initial stage (N 10 cycles). This reduction was caused by the multiple fiber fragmentation. Thereafter, the unloading modulus maintained a nearly constant value; and non-propagating matrix cracks were initiated adjacent to the end of fractured fiber. The propagation of the matrix crack again led to a rapid reduction of the unloading modulus, and the composite then failed. With higher applied stress, the fatigue life was reduced. The fracture behavior of the composite was discussed with special attention to the fiber fracture behavior and its effect on the modulus of the composite.     

Interlaminar fatigue crack propagation in continuous glass fiber/polypropylene composites

The mode II interlaminar fatigue crack propagation behavior of unidirectional continuous glass fiber (GF) composites with a polypropylene (PP) matrix obtained under three different molding conditions has been studied with the use of the end-notch flexure (ENF) geometry. The microstructure and mechanical performance, especially the interlaminar fatigue crack propagation, are strongly affected by the molding conditions. Comparative results reveal a major influence of the fiber–matrix interface and the matrix morphology on the crack propagation resistance. The distribution of the ductile amorphous PP phase in the semi-crystalline PP matrix appears to be the controlling parameter determining the fatigue crack propagation resistance of the PP/GF composite. Fractographic observations clearly showed the role of this phase.     

Creep behavior of SiC fiber-reinforced hot-pressed Si3N4 composites

The creep response of SiC fiber-reinforced Si₃N₄ composites has been measured using four-point flexural loading at temperatures of 1200–1450°C and stress levels ranging from 250 to 350 MPa. Parameters characterizing the stress and temperature dependence of flexural creep strain rates were determined. A numerical analysis was also performed to estimate the power-law creep parameters for tensile and compressive creep from the bend test data. The incorpoporation of SiC fiber into Si₃N₄ resulted in substantial improvements in creep resistance even at very high stresses. The steady-state creep deformation mechanism, determined to be subcritical crack growth in the unreinforced matrix, changed to a mechanism in the composites of repeated matrix stress relaxation-fiber rupture-load dispersion by the matrix. Multiple fiber fracture rather than multiple matrix cracking resulted. The tertiary creep in the composite resulted from the rapid growth of the microcracks which initiated from the fiber rupture sites. Fiber strength, matrix cracking stress and interfacial shear strength have been identified as the key microstructural parameters controlling the creep behavior of the composite.     

基体合金对连续M40石墨纤维/Al复合材料纤维损伤及断裂机制的影响

选用M40石墨纤维为增强体,采用真空气压浸渗法制备了纤维体积分数为40%,基体合金分别为ZL102、ZL114A、ZL205A及ZL301合金的连续M40/Al复合材料,并用NaOH溶液萃取出M40纤维,研究了基体合金对连续M40/Al复合材料纤维损伤和断裂机制的影响。结果表明:不同的基体合金对M40纤维造成的损伤差异较大,从M40/ZL301复合材料中萃取的纤维拉伸强度最高,其拉伸强度为1 686 MPa,约为纤维原丝拉伸强度的38.3%;而从M40/ZL102复合材料中萃取的纤维拉伸强度最低,其拉伸强度仅为687 MPa,且纤维表面粗糙程度不一。不同M40/Al复合材料的断裂机制存在明显差别,M40/ZL102和M40/ZL114A复合材料断裂时无纤维拔出及界面脱粘,裂纹横向穿过纤维导致复合材料在低应力下失效;M40/ZL205A复合材料则表现为少量纤维拔出,界面轻微脱粘;同时,M40/ZL301复合材料表现为大量纤维拔出,裂纹沿界面纵向扩展,界面脱粘明显,纤维充分发挥其承载作用,复合材料的拉伸强度最高,达到了670.2 MPa。      

硅酸铝纤维增强铝基复合材料的疲劳断裂特征

采用压力铸造法, 制得Al₂O₃?SiO₂短纤维增强的铝合金复合材料, 对其弯曲疲劳性能进行了测试, 并详细观察了疲劳裂纹的形成及扩展方式。结果表明: Al₂O₃?SiO₂f/ ZL 108复合材料存在 多种疲劳源; 疲劳裂纹的扩展是通过主裂纹与裂尖前方孔洞的相互联接而进行的, 是不连续的, 沿着纤维及渣球密集的路径扩展; 疲劳过程中主裂纹的形成消耗了大部分的疲劳寿命, 一旦主裂纹形成就快速扩展瞬间断裂。该复合材料的断裂宏观上是脆性的, 但微观上显示出塑性的特征。     

Effect of carbon fibres on the static and fatigue mechanical properties of fibre metal laminates

It is crucial to understand the characteristic fatigue crack initiation and its growth mechanisms, as well as the relationship between the mechanical properties and the fatigue damage evolution in fibre metal laminates (FMLs). Two types of FML were studied in this work: a polyacrylonitrile‐based carbon fibre epoxy matrix composite sandwiched by Ti‐6Al‐4V (Ti‐alloy) sheets (IMS60‐Ti) and a pitch‐based carbon fibre epoxy matrix composite sandwiched by Ti‐alloy sheets (K13D‐Ti). The static and fatigue mechanical properties of IMS60‐Ti and K13D‐Ti were investigated. The increased failure strain of the FML was greater than that of carbon fibre‐reinforced polymer (CFRP) matrix composites. The fatigue life of IMS60‐Ti was much longer than that of K13D‐Ti. The fatigue damage process in IMS60‐Ti was related to the fatigue creep behaviour of the Ti‐alloy face sheet and mode II cracking at the CFRP/Ti‐alloy interface, and the damage in K13D‐Ti was related to the K13D CFRP laminate.     

Effect of water on the fatigue behaviour of a pa66/glass fibers composite material

The aim of this study is to evaluate the effect of the humidity on the long term behaviour of glass fiber reinforced thermoplastic in fatigue. Two sets of samples were studied, one set contained 0.2 wt% of water, the second 3.5 wt%. The fatigue tests are performed at a 10 Hz frequency, at room temperature and two various relative humidity ratios, 50% RH and 96% RH. The S–N curve of dried samples (0.2%) is above the one of humid samples (3.5%), the endurance limit at 10⁷ cycles for dried samples is equal to 40 MPa against 35 MPa for the second set. For a given strain, the fatigue life is higher for humid samples because the induced stress is much lower due to the plasticizing effect of water. Though the tests are carried out at room temperature (23 °C), the sample temperature at the surface reaches values higher than Tg and whatever the applied strain, the matrix is in a rubbery state when the fracture occurs. On the basis of S.E.M. examinations, the following scenario is proposed: crack initiation at the fiber end, crack propagation along the fiber sides going with debonding, then crack propagation in the rubbery matrix.     

层状Ti3SiC2陶瓷的组织结构及力学性能

利用热压烧结TiH₂,Si和C粉获得了致密度大于98%的层状Ti₃SiC₂陶瓷。利用压痕法,在不同的载荷下测定了材料的维氏硬度, 发现其硬度值随载荷的增加而降低,在最大载荷30kg时,硬度值为4GPa。压痕对角线没有发现径向裂纹的出现。 这归因于多重能量吸收机制——颗粒的层裂、裂纹的扩展、颗粒的变形等。利用三点弯曲法和单边切口梁法测定了材料的强度和韧性分别为270MPa和6.8MPa·m1/2。Ti₃SiC₂材料的断口表现出明显的层状性质,大颗粒易于发生层裂和穿晶断裂,小颗粒易被拔出。当裂纹沿平行于Ti₃SiC₂基面的方向扩展造成颗粒的层裂,当裂纹沿垂直于基面的方向扩展时,裂纹穿过颗粒的同时,在颗粒内部发生偏转,使裂纹的扩展路径增加。裂纹的扩展路径类似人们根据仿生结构设计的层状复合材料。裂纹在颗粒内的多次偏转、裂纹钉扎以及颗粒的层裂和拔出等是材料韧性提高的主要原因。此外,在室温下得到的荷载-位移曲线,说明Ti₃SiC₂材料不象其它陶瓷材料的脆性断裂,而是具有金属一样的塑性。