反应自生Al_3Ni－Al_2O_3－Al复合材料

通过热力学计算，选择Ｎｉ_２Ｏ_３粉末作原材料，采用反应挤压铸造方法实现了Ａｌ与Ｎｉ２Ｏ３直接压铸反应合成Ａｌ３Ｎｉ－Ａｌ２Ｏ３－Ａｌ原位复合材料。研究了压铸工艺参数和预制块中纯Ａｌ粉的含量对反应合成复合材料过程的影响，并对反应机理做了较深入的分析。结果表明，Ｎｉ２Ｏ３与Ａｌ的反应是为高放热反应，反应是爆发式的，通过调整预制块中Ａｌ粉的体积分数控制了反应的剧烈程度，并能获得不同组成和基体含量的复合材料。对反应机理的分析表明，在Ａｌ足量的情况下，Ｎｉ２Ｏ３与Ａｌ反应合成复合材料分为两个过程，一是反应过程，即Ｎｉ２Ｏ３＋Ａｌ→Ａｌ２Ｏ３＋［Ｎｉ］；二是凝固过程，即反应后多余的Ａｌ与反应生成的［Ｎｉ］在随后冷却中的凝固过程，最终形成Ａｌ３Ｎｉ＋α－Ａｌ２Ｏ３＋Ａｌ复合材料。     

内生TiC颗粒增强NiAl基复合材料的初步研究

用ＨＰＥＳ工艺合成了２０ｖ．％ＴｉＣ颗粒增强的ＮｉＡｌ基复合材料，其维氏硬度、压缩屈服强度都比单相ＮｉＡｌ有大幅度提高。特别是室温和１０００℃以上，屈服强度比基体提高近二倍，室温塑性也优于单相ＮｉＡｌ。     

反应自生Al3Ni—Al2O3—Al复合材料

通过热力学计算，选择Ｎｉ２Ｏ３粉末作原材料，采用反庆挤压铸造方法实现了Ａｌ与Ｎｉ２Ｏ３直接压铸反应合成Ａｌ３Ｎｉ－Ａｌ２Ｏ３－Ａｌ原位复合材料，研究了压铸工艺数和预制块中纯Ａｌ粉的含量对反应合成复合材料过程扣影响，并对反应机理做了较深入的分析。结果表明，Ｎｉ２Ｏ３与Ａｌ的反应是为高放热反应，反应是爆发式的，通过调整预制块中Ａｌ粉的体积分数控制了反应的剧烈程度，并能获得不必基体含量的复合材料，对反应     

r—Al2O3,莫来石纤维增强Al—Si复合材料拉伸过程原位SEM研究

用扫描电镜观察了莫来石、ｒ－Ａｌ２Ｏ３两种短纤维增强Ａｌ－１２％Ｓｉ复合材料的拉伸变形和断裂过程，结果表明：对莫来石纤维增强Ａｌ－１２％Ｓｉ复合材料，与外加载荷方向成小角度的纤维是裂纹优先萌生的地方；ｒ－Ａｌ２Ｏ３纤维增强Ａｌ－１２％Ｓｉ事材料抵抗断裂能力小于晨来石纤维增强Ａｌ－１２％Ｓｉ复合材料；提出了莫来石纤维增强Ａｌ－１２％Ｓｉ复合材料的断裂模式。     

高压原位合成Al3Ni晶须增强AI基复合材料

在１－６ＧＰａ范围内原位合成Ａｌ３Ｎｉ晶须增强Ａｌ基复合材料。原位合成的Ａｌ２Ｎｉ晶须尺寸小，在高致密度的复合中分布弥散；并研究了对Ａｌ３Ｎｉ昌须尺寸及晶发布取向的影响。     

SiCw／Al－Ni复合材料的组织结构和拉伸性能

研究了挤压铸造法制备的ＳｉＣｗ／Ａｌ－Ｎｉ复合材料的组织结构和拉伸性能．研究结果指出。该种复合材料的显微组织由ＳｉＣ晶须、颗粒状的金属间化合物Ａｌ３Ｎｉ及α－Ａｌ组成。金属间化合物Ａｌ３Ｎｉ对位错运动有明显的钉扎作用。ＳｉＣｗ／Ａｌ－Ｎｉ复合材料具有较好的常温拉伸性能和优异的高温拉伸性能。     

NiAl／TiB2纳米复合材料的机械合金化合成

ＮｉＡｌ／ＴｉＢ２纳米复合材料可以通过室温球磨元素粉末而合成。其反应生成机理属于爆炸反应生成模式，并包含着两个独立的化学反应，即Ｎｉ＋Ａｌ→ＮｉＡｌ，Ｔｉ＋２Ｂ→ＴｉＢ２。巨大的生成热是反应进行的驱动力。     

WC／Ni3Al基复合材料的研制

通过机械合金化，将ＮｉＡｌ粉、Ｎｉ粉和ＷＣ粉机械混合，制坯，半烧结，再堆焊形成以Ｎｉ３Ａｌ为基，ＷＣ颗粒强化的复合材料。在烧过程中，形成部分Ｎｉ３Ａｌ相，在堆焊过程中形成Ｎｉ３Ａｌ基体，并有少量ＷＣ分解溶入基体。在８５０℃以下组成相稳定，颗粒均匀分布和基体具有良好的润滑性能。该复合材料硬度高，具有很高的耐磨性能。     

Al_2O_3 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。     

富Ni的NiAl退火组织和室温力学性能

快速凝固Ｎｉ－３４．６ａ．％Ａｌ薄带经１５２３Ｋ退火２ｈ并以较快速度冷却扣形成以ＮｉＡｌ马氏体为基体，γ－Ｎｉ３Ａｌ沿晶界网状分布和少量残β－ＮｉＡｌ的组织，退火，室温弯曲延性良好。     

TiB2-TiN复合陶瓷刀具材料的显微结构和力学性能研究

热压烧结制备了不同TiN含量的复合陶瓷刀具材料TiB2-TiN-(Ni, Mo),对其性能测试表明,随着TiN含量的增加,材料的抗弯强度和断裂韧度逐渐提高,但是材料的硬度在TiN的含量达到40%(体积分数)时却大幅度降低.利用X衍射(XRD)、扫描电镜(SEM)和能谱(EDAX)分析了复合材料的物相和显微组织,结果表明,烧结过程中生成了MoNi相;随TiN含量增加,材料从以沿晶断裂为主转变为同时有沿晶断裂和穿晶断裂的断裂模式;裂纹扩展过程中有金属颗粒桥连现象.分析认为,材料的主要增韧机制是延性相颗粒桥连和裂纹偏转.     

A method for testing interlaminar dynamic fracture toughness of polymeric composites

Static and dynamic Mode I delamination fracture in two polymeric fiber composites was studied using a WIF test method. The dynamic test was conducted on a Split Hopkinson Pressure Bar apparatus. Crack speeds up to 1000 m/s were achieved. Dynamic fracture and crack propagation were modeled by the finite element method. Dynamic initiation fracture toughness of S2/8552 and IM7/977-3 composites were obtained. The dynamic fracture toughness of IM7/977-3 associated with the high speed propagating crack was extracted from the finite element simulation based on the measured data. It was found that the dynamic fracture toughness of the delamination crack propagating at a speed up to 1000 m/s approximately equals the static fracture toughness.     

Dynamic delamination fracture toughness in unidirectional polymeric composites

A modified end-notched flexure (ENF) specimen was used to determine Mode-II-dominated dynamic delamination fracture toughness of fiber composites at high crack propagation speeds. A strip of FM-73 adhesive film was placed at the tip of the interlaminar crack created during laminate lay-up. This adhesive film with its greater toughness delayed the onset of crack extension and produced crack propagation at high speeds. Dynamic delamination experiments were performed on these ENF specimens made of unidirectional S2/8553 glass/epoxy and AS4/3501-6 carbon/epoxy composites. Crack speed was measured by means of conductive aluminum lines created by the vapor deposition technique. A finite-element numerical simulation based on the measured crack speed history was performed and the dynamic energy release rate calculated. The results showed that the dynamic fracture toughness is basically equal to the static fracture toughness and is not significantly affected by crack speeds up to 1100 m/s.     

Hydrogen effect on fracture toughness of thin film/substrate interfaces

The effect of hydrogen on the interface fracture toughness of two nano-film/substrate structures, Ni/Si and Cu/Si, were evaluated using four-point bend specimens with and without hydrogen charging. Hydrogen typically decreases the fracture toughness of materials. However, we found in this study that the interfacial toughness between the Ni film and the Si substrate increased due to the presence of hydrogen, while that of Cu/Si decreased. Nanoindentation experiments for the Ni and Cu films revealed that local plasticity in the Ni and Cu films is promoted by the charged hydrogen. The critical stress intensity at the Ni/Si interface crack considering the plasticity of Ni, namely the true fracture toughness, is scarcely influenced by the existence of hydrogen. The apparent increase in fracture toughness of the Ni/Si interface is due to the large stress relaxation near the crack tip caused by softening due to the presence of hydrogen. Although the promotion of plastic deformation of Cu relaxes the stress intensity at the Cu/Si interface crack, the apparent interfacial toughness still decreases because of the significant decrease in the true toughness due to the presence of hydrogen.     

Effect of compressive transverse normal stress on mode II fracture toughness in polymeric composites

Effect of transverse normal stress on mode II fracture toughness of unidirectional fiber reinforced composites was studied experimentally in conjunction with finite element analyses. Mode II fracture tests were conducted on the S2/8552 glass/epoxy composite using off-axis specimens with a through thickness crack. The finite element method was employed to perform stress analyses from which mode II fracture toughness was extracted. In the analysis, crack surface contact friction effect was considered. It was found that the transverse normal compressive stress has significant effect on mode II fracture toughness of the composite. Moreover, the fracture toughness measured using the off-axis specimen was found to be quite different from that evaluated using the conventional end notched flexural (ENF) specimen in three-point bending. It was found that mode II fracture toughness cannot be characterized by the crack tip singular shear stress alone; nonsingular stresses ahead of the crack tip appear to have substantial influence on the apparent mode II fracture toughness of the composite.     

Studies of the effect of metal particles on the fracture toughness of ceramic matrix composites

The purpose of this study was to describe the influence of metal particles on the fracture toughness of ceramic matrix composites. Here, alumina matrix composites with molybdenum particles have been investigated. The results presented show that the change of fracture toughness of a ceramic–metal composite can be controlled by the volume fraction of metallic phase and size of metal particles.

The model proposed in this paper describes the change of crack length and as a consequence, the change of K_IC value. The results of modelling calculations have been compared with experimentally measured K_IC values. This model is useful for simulation of crack length changes in the composites and to design a material with an optimum fracture toughness.     

Fracture surface roughness and toughness of Al2O3-platelet reinforced glass matrix composites

The correlation between fracture surface roughness and fracture toughness of alumina platelet reinforced borosilicate glass matrix composites was investigated. With increasing volume fraction of platelets both fracture toughness and fracture surface roughness increase. The fracture roughness parameter Ra was determined by the profilometric technique. A linear correlation was found between the fracture toughness and the Ra values of the composites. Scanning electron microscopy observation of fracture surfaces confirmed that surface roughness is related to a crack deflection process. Crack deflection is thus one of the toughening mechanisms acting in these composites.     

Combined effect of fiber content and microstructure on the fracture toughness of SGF and SCF reinforced polypropylene composites

Composites of polypropylene (PP) reinforced with short glass fibers (SGF) and short carbon fibers (SCF) were prepared with extrusion compounding and injection moulding techniques. The fracture behavior of the two types of composites was studied. The fracture toughness (K _c of the composites was measured in the T-direction [main crack transverse to mould flow direction (MFD)] and in the L-direction (main crack parallel to the MFD) using compact tension (CT) specimens made from the plaques manufactured. The study was focused on the combined effect of fiber volume fraction and microstructure (fiber length and alignment) on the fracture toughness of short fiber composites. It was observed that the addition of fibers effectively enhanced the fracture toughness for both SGF/PP and SCF/PP systems in the T-direction but only improved the composite toughness in the L-direction for the case of a low fiber volume fraction (8%). The composite fracture toughness kept almost unchanged in the T-direction and decreased in the L-direction with increasing fiber volume fraction. These were explained using the combined effect of fiber volume fraction and microstructure.     

Effect of nano-metal particles on the fracture toughness of metal–ceramic composite

A theoretical model is proposed to study the influence of nano-metal particles (NMPs) on the fracture toughness of metal–ceramic composites (MCC). In the framework of the model, the crack tip intersects the grain boundary of the NMPs. Stress concentration at crack tip initiates edge dislocations which makes a shielding effect on the crack and leads to fracture toughness of the MCC. The dependence of critical crack intensity factors on grain size of the NMPs was calculated. The calculation suggested that the existence of the NMPs lead to an increase of critical crack intensity factors by 14%.     

Effect of Layers Position on Fracture Toughness of Functionally Graded Steels in Crack Divider Configuration

In the present study, fracture toughness of functionally graded steels in crack divider configuration has been modeled. By utilizing plain carbon and austenitic stainless steels slices with various thicknesses and arrange- ments as electroslag remelting electrodes, functionally graded steels were produced. The fracture toughness of the functionally graded steels in crack divider configuration has been found to depend on the composites’ type together with the volume fraction and the position of the containing phases. According to the area under stress-strain curve of each layer in the functionally graded steels, a mathematical model has been presented for predicting fracture toughness of composites by using the rule of mixtures. The fracture toughness of each layer has been modified according to the position of that layer where for the edge layers, net plane stress condition was supposed and for the central layers, net plane strain condition was presumed. There is a good agreement between experimental results and those acquired from the analytical model.