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1.
采用铸造法制备原位自生亚共晶Al-10Mg2Si复合材料,研究Cu和T6热处理对该复合材料组织与力学性能的影响。结果表明:适量Cu的添加能显著减小共晶Mg2Si相晶粒尺寸,使其晶体结构由粗大的长条状和汉字状转变为细小的条状和纤维状;同时使针状的β-Al5Fe Si相转变为细小的不规则富Cu颗粒。经T6热处理后,质量分数为1.5%的Cu复合材料中的共晶Mg2Si相完全球化。质量分数为1.5%的Cu添加同时提高了材料铸态下的抗拉强度(Rm)、屈服强度(Rp0.2)和伸长率(A),达317、169 MPa和2.3%,比未添加Cu提高了42.2%、24.3%和53.3%;经T6热处理的Rm和Rp0.2值分别增至332、181 MPa,而A值保持不变。同时,材料由脆性断裂完全转变为韧性断裂。  相似文献   
2.
基于COMSOL平台开发了一套基于多物理场全耦合的燃料性能分析程序,并通过径向功率分布模型对比验证了该程序的正确性与准确性;然后进一步分析了U3Si2燃料与双层SiC包壳组合、U3Si2燃料与锆合金包壳组合在反应堆正常运行工况下的性能,并与UO2燃料与锆合金的组合进行了对比分析。计算结果发现U3Si2燃料与锆合金包壳组合相比UO2燃料与锆合金的组合具有更低的燃料中心温度、裂变气体释放量及内压,但气隙闭合时间会提前;而U3Si2燃料与双层SiC包壳的组合相比U3Si2燃料与锆合金的组合具有更高的燃料中心温度、更大的裂变气体释放量及内压,且随着燃耗的增加,其燃料中心温度大幅增加,与锆合金包壳相比,双层SiC包壳能够有效延迟气隙闭合,缓解燃料与包壳的力学相互作用。   相似文献   
3.
为解决基于机器视觉的传统单一图像去噪算法对混合噪声信号处理效果不佳,导致不能有效地检测识别航空发动机中应用的Si3N4圆柱滚子表面缺陷问题,提出一种基于改进的耦合去噪算法与多尺度阈值分割算法相结合的视觉检测方法。通过优化的小波阈值去噪算法与改进的中值滤波算法相耦合方法对Si3N4圆柱滚子的表面缺陷图像进行去噪处理,采用多尺度阈值分割算法对缺陷图像进行图像分割,识别提取Si3N4圆柱滚子表面缺陷。实验结果表明:Si3N4圆柱滚子表面缺陷图像经过改进的耦合去噪算法进行去噪后,信噪比>24.5%,多尺度阈值分割算法对Si3N4圆柱滚子表面缺陷图像的检测识别准确率>94%;该视觉检测方法具有良好的图像去噪效果,为进一步图像的缺陷识别打下基础,并且具有一定的通用性。  相似文献   
4.
目的 研究Si含量对CoCrFeNi高熵合金激光熔覆涂层的组织及性能的影响.方法 利用激光熔覆技术在45#钢基材上制备CoCrFeNiSix(x=0.0,0.5,1.0,1.5,2.0)高熵合金涂层,通过扫描电镜(SEM)、X射线衍射仪(XRD)、显微硬度计、摩擦磨损试样机,对单道和多道熔覆层的宏观形貌、微观组织、显微硬度及摩擦磨损性能进行观察和测试.结果 高熵合金涂层与基体形成良好的冶金结合,添加适量的Si可以提高熔覆层的表面成形性,随着Si的添加,合金的稀释率先增后减,且润湿角逐渐减小.涂层的微观组织随Si含量的升高由等轴晶变为树枝晶,后又变为等轴晶,晶粒结构尺寸减小,涂层致密度提高.涂层由fcc结构变为bcc结构.涂层的显微硬度随Si含量的增加而增加,在x=2.0时,硬度达到600HV0.5左右,约为基体3倍.磨损方式由粘着磨损变为磨粒磨损,当Si含量最高时,磨损量达到最少,摩擦因数也最低,约为0.49.结论 在CoCrFeNi基高熵合金中添加Si可以降低合金的熔点,提高润湿能力;Si还可以增加涂层的形核率,起到细化晶粒的作用;Si作为添加元素还提高了涂层硬度,改善了涂层的耐磨减摩作用.  相似文献   
5.
Given the superior thermal stability and electromagnetic features, continuous Si–B–(C)–N ceramic fibers have displayed great potential to fulfill the increasing demand for the high-temperature structural and functional materials. Manufacture of such ceramic fibers depends heavily upon the design of processable polymer precursors. Herein, a class of polyborosilazanes (PBSZs) with high spinnability were created through a facile one-pot synthesis. The trade-off between spinnability and ceramic yield of PBSZs was overcome by using heptamethyldisilazane and hexamethyldisilazane as the co-condensing agents to polymerize silicon and boron chloride monomers. The optimal PBSZs can fabricate continuous Si–B–C–N fibers with homogeneous diameter of 7.9 ± 0.5 μm and high ceramic yield of 80 wt%. Experimental characterization and quantum chemical computation revealed the mechanistic pictures of the impact of pendant groups on the polycondensation, melt spinning, and pyrolyzing process. These insights improve our understanding of spinnable pre-ceramic polymers for exploiting high-performance nitride ceramic fibers.  相似文献   
6.
Flexible scintillating fiber plays an important role in X-ray radiation monitoring and high-resolution medical imaging, while construction of scintillating fiber derived from the commercial material system meet with limited success. Here, we report the design and successful fabrication of the Ce-activated lutetium aluminum silicate glass, nanostructured glass, and fiber, and explore their scintillating properties. The scintillating glass with optimized composition and optical properties is determined. The crystallization behavior of lutetium aluminum silicate glass is studied and the nanostructured glass embedded with orthorhombic Lu2Si2O7 phase is successfully constructed for the first time. Importantly, the crystalline layer thickness of the nanostructured glass can be finely tuned and ~172.89% enhancement in the scintillating performance can be achieved. Furthermore, the fiber with large sized core is fabricated and its radiation response properties are tested. The results show that it exhibits high sensitivity and its scintillating emission is lineally dependent on the X-ray power, indicating the potential application for radiation detection.  相似文献   
7.
《Ceramics International》2022,48(21):31203-31210
Ti–Si–Fe alloys extracted from high-titanium blast furnace slag were utilized to replace part of the silicon powders, and then nitride/oxynitride bonded SiC ceramics were prepared by reactive sintering in graphite bed. Ti–Si–Fe alloys could react with CO/N2 at a low temperature (1200 °C), and the addition of Ti–Si–Fe alloys could reduce the nitriding temperature of Si. Density functional theory calculations suggested that Ti–Si–Fe alloys enhanced reaction activity via weakening the strength of CO and NN bonds. The regional equilibrium phase diagrams of Si–C–N–O and Ti–Si–C–N–O under CO/N2 atmosphere were calculated by thermodynamics. The change of whiskers morphology was observed by scanning electron microscope. Furthermore, the bulk density, the cold modulus of rupture, and the cold compressive strength improved with Ti–Si–Fe alloys content. The results showed that the addition of Ti–Si–Fe alloys not only significantly promoted nitriding of Si and formation of Si3N4 whiskers, but also improved the mechanical properties of the samples.  相似文献   
8.
《Ceramics International》2021,47(23):33353-33362
High thermal conductivity Si3N4 ceramics were fabricated using a one-step method consisting of reaction-bonded Si3N4 (RBSN) and post-sintering. The influence of Si content on nitridation rate, β/(α+β) phase rate, thermal conductivity and mechanical properties was investigated in this work. It is of special interest to note that the thermal conductivity showed a tendency to increase first and then decrease with increasing Si content. This experimental result shows that the optimal thermal conductivity and fracture toughness were obtained to be 66 W (m K)-1 and 12.0 MPa m1/2, respectively. As a comparison, the nitridation rate and β/(α+β) phase rate in a static pressure nitriding system, i.e., 97% (MS10), 97% (MS15), 97% (MS20) and 8.3% (MS10), 8.3% (MS15), 8.9% (MS20), respectively, have obvious advantages over those in a flowing nitriding system, i.e., 91% (MS10), 91% (MS15), 93% (MS20) and 3.1% (MS10), 3.3% (MS15), 3.3% (MS20), respectively. Moreover, high lattice integrity of the β-Si3N4 phase was observed, which can effectively confine O atoms into the β-Si3N4 lattice using MgO as a sintering additive. This result indicates that one-step sintering can provide a new route to prepare Si3N4 ceramics with a good combination of thermal conductivity and mechanical properties.  相似文献   
9.
The aim of this study was to determine the influence of severe plastic deformation processing and the changes in microstructure resulting therefrom on the corrosion resistance of an Al–Mg–Si alloy. The alloy was processed using incremental equal channel angular pressing, which caused a reduction in grain size from 15 to 0.9 µm. The grain refinement was accompanied by an increase in the number of grain boundaries and dislocations, and by changes in grain orientation. However, there was no change in the size and number of intermetallic particles, which presumably resulted in a constant number of galvanic couplings. Electrochemical experiments revealed only slight differences between the samples before and after processing. Higher potential transients/oscillations upon immersion and increased corrosion currents in the vicinity of corrosion potential point to slightly higher reactivity of the most refined material. This indicates that intermetallic particles are the most crucial microstructural elements in terms of corrosion resistance. Their impact exceeds that of grain boundaries, in particular, at the stage of corrosion initiation. The development of corrosion attack is controlled more by the microstructure of the matrix as the grain refinement resulted in a less pronounced corrosion attack in comparison with the coarse-grained sample.  相似文献   
10.
高硅铝合金由于硅含量很高,故切削加工性较差,切削刀具极易磨损且已加工表面存在大量缺陷。为进一步研究材料加工损伤,采用化学气相沉积法制备了金刚石涂层铣刀,开展70%Si/Al(70%指质量分数)合金材料铣削试验。试验研究了铣削力、刀具磨损及加工损伤机理,并与常用TiN涂层铣刀进行了对比。结果表明:铣削过程中由于初晶硅硬质颗粒的冲击和刻划,金刚石涂层刀具的失效形式主要是涂层剥落和磨粒磨损;在金刚石涂层铣刀的正常磨损阶段,铣削力稳定在43.57~48.95 N,而相同切削用量下TiN涂层铣刀的铣削力更大、刀具寿命更短;加工表面存在凹坑、划痕和颗粒破碎等损伤,在保证刃口强度的前提下适当减小切削刃圆弧半径可明显减小加工损伤;铣刀刃口圆弧半径r=12 μm的已加工表面粗糙度(Sa=2.3 μm)远低于r=156 μm时加工的表面粗糙度(Sa=6.7 μm)。  相似文献   
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