Zirconia-alumina multiphase ceramic fibers with exceptional thermal stability by melt-spinning from solid ceramic precursor

Zirconia-alumina multiphase ceramic fibers with 80 wt% (Z80A20 fiber) and 10 wt% (Z10A90 fiber) proportions of zirconia were prepared via melt-spinning and calcination from solid ceramic precursors synthesized by controllable hydrolysis of metallorganics. The zirconia-alumina multiphase fibers had a diameter of about 10 µm and were evenly distributed with alumina and zirconia grains. The Z80A20 and Z10A90 ceramic fibers had the highest filament tensile strength of 1.78 GPa and 1.87 GPa, respectively, with a peak value of 2.62 GPa and 2.71 GPa. The Z80A20 ceramic fiber has superior thermal stability compared to the Z10A90 ceramic fiber and a higher rate of filament strength retention due to the stability in grain size. After heat treatment at 1100 °C, 1200 °C, and 1300 °C for 1 h respectively, the filament tensile strength retention rate of Z80A20 ceramic fibers was 87 %, 80 %, and 40 %. While Z10A90 ceramic fiber was fragile after being heated at 1300 °C. The results showed that the high zirconia content facilitated the fiber's thermal stability.     

Local microstructure of Ge layers buried in a silicon crystal studied by extended X-ray absorption fine structure

The local structure of Si-capped Ge quantum dots formed in Stranski–Krastanov growth mode on a (001) Si substrate was probed by X-ray absorption at the Ge K-edge. Analysis by extended X-ray absorption fine structure (EXAFS) was performed under the assumption of a solid solution model of the Si distribution inside the quantum dots (QDs) and taking into account polarization effects. It was found that QDs formed for 8 ML are strained and the Ge–Ge and Ge–Si bond lengths vary with direction. The Si content inside the QDs was found to be at a level of ∼25 at.% for strained (8 ML sample) QDs and ∼12 at.% for unstrained (10 ML sample) QDs. This work demonstrates the usefulness of EXAFS analysis for the determination of the local atomic structure in covered low-dimensional structures.     

Structural stabilization of EBC with thermal energy reflection at high temperatures

Structural stability of an environmental barrier coating (EBC) with thermal energy reflection function that has a periodic layered structure consisting of Y₂Ti₂O₇ (YT) and Al₂O₃ is essential to maintenance of the EBC performance at high temperatures. The effect of adding Al to YT layer on the structural stability was investigated using model samples in which Al₂O₃ layer was formed on both the YT and Al-doped YT (AYT) substrate by aerosol deposition (AD). Exposure to heat selectively dissipated the Al₂O₃ layer on the YT substrate near the interface between the layer and the grain boundaries of the substrate. In contrast, the Al₂O₃ layer on the AYT substrate remained intact upon heating when Al was added at the solid solution limit. The Al₂O₃ layer was found to exhibit a pronounced degree of (0001) basal plane texture. An increase in the impact velocity of particles during AD effectively developed the basal fiber texture.     

悬浮液等离子喷涂高效制备TiO2涂层及其光催化性能

目的 解决TiO2粉末催化剂在污水净化过程中易沉降和难回收问题,同时提高TiO2在可见光条件下降解有机污染物的速率。方法 采用悬浮液等离子喷涂(SPS)技术,以H2为辅助气体制备TiO2涂层,借助H2将高温等离子体焰流中熔融态TiO2中的Ti⁴⁺还原成Ti³⁺。通过场发射扫描电子显微镜、X射线衍射仪、X射线光电子能谱光谱仪、紫外-可见光谱仪等对TiO2粉末以及所制备涂层的结构形貌、物相组成、元素价态、光学特性进行分析。以亚甲基蓝为目标污染物,使用光化学反应仪测试粉末和涂层的光催化性能。结果 TiO2涂层表面呈现由熔融和半熔融颗粒组成的“喀斯特”微观形貌,表面粗糙度为2.94 µm,孔隙率为10.2%。TiO2粉末物相为纯锐钛矿,涂层物相由锐钛矿、金红石相及TiO2－x相组成。TiO2涂层中Ti³⁺的存在使其带间隙减小0.6 eV。在紫外光条件下,TiO2粉末的催化速率为0.003 48,而涂层的催化速率为0.003 45。在可见光条件下,粉末的催化速率与亚甲基蓝的光解速率相近,涂层的催化速率是0.003 07。结论 通过SPS技术成功制备了TiO2光催化涂层,其在可见光条件下的催化性能较粉末有显著提升。     

使役环境涡轮叶片EB-PVD热障涂层失效机制

运用场发射扫描电镜、能量色散光谱仪和金相显微镜等测试表征手段,详细检查退役高温发动机涡轮叶片表面涂层残存状况,发现带气膜孔的高温发动机涡轮叶片经服役2000 h后,表面各部位EB-PVD涂层承受CMAS攻击、硬质物撞击和冷热应力冲击程度各异,导致退役叶片表面共存多种损伤.通过对这些损伤现象的分析,了解使役环境下叶片各部位的失效模式和失效机理.研究结果表明:叶棱为受CMAS攻击最严重处,同时也是受硬质点撞击最密集处,存在大面积涂层脱落;气膜孔周围的TBCs涂层受CMAS攻击发生本质性固化,受交变热应力和机械应力共同作用而呈规律性脱落;叶棱周围气膜孔表面(无论是叶背或是叶盆)均存在硬质物碾压划过叶片表面而压实CMAS,引起表面TBCs脱落的现象,同时在气膜孔内发现飞落的TBCs柱和CMAS块,从侧面反应对叶片表面造成实质性伤害的硬质物可能为脱落的TBCs柱或固化的CMAS块.     

尖端结构对PS-PVD YSZ涂层沉积的影响

采用等离子喷涂-物理气相沉积(PS-PVD)技术在设计的尖端结构试样表面制备了YSZ涂层,研究了YSZ涂层在尖端不同区域的形貌、厚度、孔隙率和微区力学性能的差异.结果表明:尖端部位各区域涂层呈现羽柱状结构,在涂层生长过程中柱状晶之间会因生长的空间受限而存在“挤压”竞争效应,尖端边角的几何特性会削弱“挤压”竞争效应,因此其涂层厚度远高于尖端其他区域;此外,尖端尖角附近的涂层羽柱状结构呈放射状,并沿基体表面法线方向向上生长;纳米压痕表明涂层硬度由顶部至底部呈现逐渐下降趋势,这与涂层结构和残余应力相关;尖端结构的尖角区域涂层微区硬度,显著高于尖端两侧区域;结合数值模拟分析结果发现,半封闭型面会导致等离子射流紊乱度上升,由于不同方向等离子体存在“卷流”和“冲击”现象,其对应沉积的涂层厚度下降,孔隙率上升.     

大气等离子喷涂制备锰钴尖晶石涂层及其电导率

采用大气等离子喷涂(APS)工艺制备了Mn-Co尖晶石涂层,同时研究了不同载气和喷距对涂层形貌及电导率的影响.采用直流四电极法测量涂层的电导率,利用SEM,XRD和XPS等表征手段对涂层微观形貌、组成等进行表征.结果表明,所制备的涂层致密、孔洞较少、与基体结合良好,表面呈现液态沉积与微熔颗粒堆积相混合的状态.800℃时,载气量为2 SLPM下涂层的电导率是18 S/cm,而其余载气量下涂层电导率仅有8 S/cm,低载气量制备的Mn-Co涂层具有良好的导电性;800℃下只有喷距为130 mm的涂层电导率超过了10 S/cm,增加喷距对电导率影响较小,各涂层电导率分布较为接近.测试态涂层表面形成了各种取向的金字塔状尖晶石晶体结构,其尖晶石相衍射峰强度显著提高;高电导率涂层中2价和3价元素比例更接近1∶2,为典型的尖晶石结构,其表现出较高的电导率.因此,适当的载气流量和喷涂距离可使涂层中含有更多的高电导率尖晶石相.     

激光工艺参数对H13钢粉末单道成形特性的影响

为了解激光工艺参数对H13钢表面再制造成型H13粉末层几何特征的影响规律,设计研究了工艺参数(激光功率、光斑直径)对单道成形层几何特征(成形层高度、宽度、基体熔化深度与宽度)影响的实验,根据实验结果归纳了工艺参数对成形层几何特征的影响规律,并采用极差分析了各几何特征的主要影响因素,同时利用了激光再制造形成层几何特征模型对实验结果进行了分析。结果表明光斑尺寸对熔覆层宽度、基体熔化区宽度、深度影响更明显,而激光功率、光斑尺寸对熔覆层高度的影响无显著差别;此外,粉末综合利用率随辐照激光能量密度的增大先增大后维持基本不变。     

Electrodes modified with Ni electrodeposition decrease hexavalent chromium generation in an alkaline electrolysis process

Alkaline water electrolysis is one of the easiest methods used to produce hydrogen, offering the advantages of simplicity and low cost. The challenges for the widespread use of water electrolysis are to reduce energy consumption, cost and maintenance and to increase the reliability, durability and safety of the process. The alkaline electrolysis of water has been used for many years to obtain H₂ and O₂; however, less expensive, more active, endurable and efficient electrodes must be designed. Stainless steel (SS) is considered one of the least expensive electrode materials for alkaline electrolysers, since it is relatively chemically stable and has a low overpotential. Nevertheless, SS anodes do not withstand high concentration alkaline solutions because they undergo a corrosion process. If the electrolyser operates at a voltage of up to 1.6 V, it can generate Fe₃O₄ and hazardous hexavalent chromium (Cr⁶⁺) at the anode. Hexavalent chromium is generated when the chromium-containing stainless steel electrodes undergo an electro-oxidation process. In this work, a low power alkaline electrolyser was designed. In the first step, six electrodes were manufactured of stainless steel. In the second step, a nickel layer with matte or opaque finish was deposited on the SS surfaces to improve their resistance to corrosion and wear. Then, the performance curves and the production of hexavalent chromium were determined. The performance curve after 70 h of operation with nickel-plated electrodes showed an overpotential of 0.5 V at 10 A compared with stainless steel electrodes. Cr⁶⁺ was detected in the electrolyte and bubbler water of the system using SS electrodes at values that exceeded the standard (>0.5–1 mg L⁻¹). If the electrolyser used Ni-electrodeposited electrodes, Cr⁶⁺ was observed in quantities within the normal range (<0.1 mg L⁻¹). It is very important to prepare modified anodes with nickel electro-deposited, this process prevents the generation of hexavalent chromium, contamination of the electrolyte and reduces maintenance times. The above compensates the slight increase in electrodes cost and energy consumed by the electrolyser.     

冷喷涂IN718涂层组织及性能研究

目的 针对Ti6Al4V耐磨性能较差的问题,利用高压冷喷涂技术在Ti6Al4V基体表面以不同的工艺参数制备了IN718涂层,为在Ti6Al4V基体表面制备高性能IN718涂层提供基础理论依据。方法 采用光学显微镜和扫描电子显微镜对涂层组织、断口形貌进行观察分析,以便更好地了解不同的工艺参数和工作气体类型(He/N2)对IN718涂层组织形貌、力学性能和摩擦磨损性能的影响。结果 以N2为推进气体制备的IN718涂层,其结合强度为115 MPa,硬度为557HV0.3,孔隙率约为0.24%,涂层磨损率为5.34×10^–4 mm³/(N.m);以He为推进气体制备的IN718涂层,其结合强度可高达256 MPa,是以N2为推进气体制备涂层的2倍多,硬度为602HV0.3,明显高于以N2为推进气体制备的涂层,涂层孔隙率和缺陷明显减少,孔隙率测试结果约为0.1%,涂层更加耐磨,磨损率为3.51×10^–4 mm³/(N.m)。结论 相较于以N2为推进气体制备的IN718涂层,以He为工作气体制备的IN718涂层的组织更致密、涂层孔隙率更小,硬度和结合强度更高,耐磨性能更好,所以采用He可以制备出性能更加优异的IN718涂层。