关键词： sicf/sic   复合材料   显微结构   抗氧化性能  

摘要： 采用热梯度强制流动化学气相渗积(FCVI)工艺制备了连续SiC纤维增强SiC陶瓷基复合材料.渗积分两步进行,第一步先等温渗积裂解碳用为界面层.第二步热梯度强制流动渗积SiC.利用X射线衍射分析、电镜等手段研究了复合材料的显微结构,结果表明:FCVI制备的SiC基体为β-SiC,具有亚向微米级的晶粒结构,结晶度良好.测定了复合材料的强度和断裂韧性,研究了复合材料的抗氧化性能.结构表明:裂断碳界面层的氧化物是复合材料力学性能恶化循环化的主要原因.试样表面涂覆SiC涂层可以避免复合材料力学性能恶化.

关键词： 复合材料   本构方程   微观力学   纤维增强   铝基  

摘要： 运用随机介质微观力学的方法,对短纤维复合材料的弹性模量进行了分析,并给出了与微观性能相联系的计算公式。通过对铝基碳化硅增强短纤维复合材料的计算和试验。

关键词： 氮化硅   相组成   显微结构   力学性   粉末  

摘要： 研究了起始粉末中α/ β相组成的变化对所得氮化硅材料显微结构和力学性能的影响 .随着起始粉末中 β相含量的增加 ,显微结构明显细化 ,柱状颗粒数目增加而尺寸减小 ,从具有异常长大柱状颗粒的嵌套结构变为由小柱状颗粒组成的均匀结构 .结果说明可以通过改变起始粉末相组成来控制材料显微结构 .所得材料的力学性能随起始粉末中 β相含量的增加 ,在α/ β相体积比为 50∶50时 ,综合性能最好 .

关键词： 反应烧结   锆莫来石材料   显微结构  

摘要： 该文运用精细化工艺方法,选择适当的矿化剂,采用矾土生料(包括轻烧料)和锆英石砂合成锆莫来石基质料.通地运用XRD和SEM等测试手段,对烧后试样进行相组成和显微结构的研究,探索结构与性能之间的关系. 河南A级矾土生料与锆英石砂的配料易于烧结,主要原因是配料中引入较多的碱性氧化物.引入矿化剂或提高烧温度可以促进锆英石的分解,加速固相反和烧结的进行.具有以下显微结构特征的锆莫来石材料也具有良好的低温性能:主晶相莫来奋不顾身妻育成针柱状晶体,相互搭接成连续骨架,ZrO<,2> 的细小晶粒均匀分布于网络间隙,气孔小而匀,呈圆形存在.

关键词： 第二相粒子   固溶   增韧   补强   氮化硅陶瓷   结构  

摘要： 研究第二相粒子 (TiN ,TiB2 )的引入对氮化硅陶瓷材料性能和显微结构的影响 .结果发现 :TiN粒子的引入 ,对材料能起到协同增韧的作用 ;而TiB2 粒子由于与氮化硅颗粒表面的SiO2 发生反应 ,导致复合材料不致密 ,引起力学性能下降 .

关键词： 机械合金化   FeNi合金   纳米晶粉末   形貌   微结构  

摘要： 利用机械合金化方法制备了Fe1-xNix 合金纳米晶粉末 ,x分别为 0 .15、0 .45、0 .80 ,球磨时间为 2、4、8、16、40h。利用扫描电子显微镜和X射线分析仪观察和分析了样品的形貌和微结构。发现整个球磨过程可分为 3个阶段。开始阶段 ,由于冷焊 ,Fe、Ni混合粉末凝聚成一些粒径较大的颗粒 ;在中间阶段 ,内应力达到最大值 ,原先形成的大颗粒破碎 ,粒径分布变窄 ;最后阶段 ,FeNi粉完全合金化 ,粒度再次增大。至 40h时 ,可观察到层状结构。x =0 .15样品40h时形成了体心立方结构 ,而x =0 .45和 0 .80分别在 40h和 16h形成了面心立方结构。x =0 .45系列 40h以后晶粒平均粒径约为10nm ,内应力在 16h时有一极大值 0 .76 % ,在整个球磨过程中 ,测定的Ni含量偏离不超过 3 % (原子分数 )。

关键词： concretes   corrosion   durability   microstructure   reinforcing steel  

摘要： Corrosion of steel in concrete is a complex phenomenon. The corrosion performance of reinforcing steel embedded in concrete is dependent on many variables. These variables include differences in materials constituents, microstructure, processing procedures, concrete mixture proportions, structural design, construction methods, loadings, cracks, and environmental conditions. Reinforced concrete structures are often expected to have relatively long service lives under severe loading and exposure conditions. Often, the primary governing factor affecting the service life of the structure is the corrosion performance of the steel reinforcement. For many systems, concrete is often the only protective cover that prevents the ingress of aggressive ions and eventual corrosion of the reinforcing steel. Significant advances in state of the practice have been exhibited with the use of high-performance concrete materials. Due to the high cost associated with deteriorating reinforced concrete structures, however, other approaches need to be investigated to ensure long-term serviceability of these structures. A complementary approach to improving the quality and corrosion performance of reinforced concrete structures is to utilize reinforcement that has been microstructurally designed to resist corrosion. This approach can increase the redundancy of the protective system, decrease corrosion activity, and increase the service life of reinforced concrete structures. To properly evaluate the corrosion performance and to better predict the service life of reinforced concrete structures, it is necessary to evaluate the characteristics of the bulk concrete, the steel-concrete interface, the steel mill scale, the passive film, and the steel microstructure. This research program investigated the performance of microstructurally designed reinforcing steel for improved corrosion resistance when embedded in concrete and exposed to accelerated chloride environments. Reinforced concrete specim

关键词： microstructure-final   mechanical properties   abrasion   zirconia-flyash  

摘要： The addition of zirconia in different proportions to one type of Indian flyash has been studied. The study is concentrated on mechanical properties of the materials like MOR, MOE and hardness, the sand abrasion resistance and the microstructural investigation by scanning electron microscope. It is observed that MOR of the material increases upto 10 vol% of ZrO2 in flyash and then starts decreasing. On the other hand, both MOE and the Vickers hardness increase with the increase in ZrO2 content in the matrix. The abrasion volume loss of the material decreases upto 15 vol% ZrO2 in flyash which further increase with increase in ZrO2 content. It has been pointed out from the microstructural investigation that, with the increase in addition of ZrO2 in flyash, the needle shaped mullite phases are being replaced by the near spherical shaped zircon grains. This paper correlates these data along with the physical properties and phase identification studies, which were reported earlier. (C) 1999 Elsevier Science Ltd and Techna S.r.l. All rights reserved.

关键词： 纳米粉   添加剂   陶瓷   烧结性能   微结构  

关键词： 离子辐照   微结构   土壤结构