不同喷涂工艺下NiCoCrAlYTa涂层的显微结构和性能

为探索不同喷涂工艺对NiCoCrAlYTa涂层的显微结构和性能的影响规律,确定最优工艺,采用大气等离子、低压等离子、常规超音速火焰和低温超音速火焰4种工艺在镍基单晶高温合金表面制备了NiCoCrAlYTa涂层。采用X射线衍射(XRD)、扫描电镜(SEM)和显微硬度计等分析手段对喷涂态涂层的相组成、显微结构和显微硬度等进行了表征。结果表明,不同喷涂工艺下涂层的相组成均为γ′-Ni_3Al、β-NiAl和γ-Ni固溶体。低压等离子和超音速火焰喷涂的涂层致密且孔隙率低,其中超音速火焰喷涂的涂层孔隙率低于1%。低压等离子和低温超音速火焰喷涂的涂层氧含量很低,控制在0.3%~0.6%的范围。综合来说,低温超音速火焰喷涂工艺制备的涂层结构致密,孔隙率和氧含量很低。该工艺是沉积NiCoCrAlYTa涂层的首选。     

Ni包覆Al2O3粉体的RCVD法制备及机理研究

金属Ni包覆于陶瓷粉体的表面,可以促进其烧结、提高导电性或赋予新的功能性质.本文采用旋转化学气相沉积法(RCVD),利用二茂镍(NiCp_2)前驱体的热分解,借助载体氢气对反应的催化促进作用,在Al_2O_3粉体表面包覆了均匀分散的Ni纳米粒子,并研究了包覆温度和原料供应速率对反应产物物相、粒度和形貌的影响规律.研究表明,在包覆温度为450~550℃、前驱体二茂镍(NiCp_2)供给速率为(0.6~2.0)×10~(-6)kg/s条件下,通过对反应过程中镍纳米粒子的包覆温度和前驱体二茂镍(NiCp_2)供给速率调控可对镍纳米粒子的粒径大小和包覆层数进行调控.结合实验结果,分析了载体氢气对二茂镍反应的催化促进作用,阐述了旋转化学气相沉积条件下Ni纳米粒子在Al_2O_3粉体表面均匀包覆的过程与机制.通过调控包覆温度和原料供应速率,可以影响前驱体二茂镍的分解行为,从而调控镍纳米粒子在Al_2O_3粉体表面的包覆状态.     

LiNi0.8 Co0.15 A10.05 O2正极材料的表面包覆改性研究

LiNi_0.8 Co_0.15 A1_0.05 O₂正极材料具有容量高、价格低等优点,被认为是最具发展前景的锂离子电池正极材料之一.但LiNi 0.8Co 0.15A1 0.05O₂材料本身存在充放电过程中容量衰减较快、倍率性能差和储存性能差等缺陷,影响了其进一步发展.本文以 LiNi 0.8Co 0.15A1 0.05O₂为研究对象,采用共沉淀法制备氢氧化物前驱体,在前驱体的表面包覆一层Ni 1/3Co 1/3 Mn 1/3(OH)₂,制备成具有核壳结构的正极材料.通过XRD、SEM、EDX、电化学测试等分析手段,系统地研究了其结构、形貌以及电化学性能.分析表明:包覆改性后,LiNi 0.8Co 0.15Al 0.05O₂正极材料在0.1、0.2、0.5、1 C倍率下,材料的首次充放电比容量分别为167.6,160.1,0.4,8.5 mAhg -1.由0.1到1 C,包覆改性前后的正极材料的放电比容量衰减量由34.7 mAhg -1降为29.1 mAhg -1,容量衰减百分比由22.1%降低到17.4%.综合性能分析认为,包覆改性后电化学性能有一定的改善.     

Experimental investigation on chilled cast iron tappet manufacturing processes parameters

Chilled cast iron tappet has a tendency microstructure of white, mottled and gray iron. The exact composition and other casting parameters, like pouring temperature, inoculation and coating, need to be determined for achieving the desired thickness of the chilled layer. Chilled cast iron finds applications in areas where improved hardness and wear resistance are required. Mottled cast iron has very poor machinability and high brittleness due to the presence of secondary cementite. These constitute the limitations for its use. The influence of inoculation, pouring temperature, coating thickness and chill plate on chilled depth was investigated. Taguchi design-of-experiments (DOE) are used for generating an optimal set of casting parameters to obtain a satisfactory chilled depth. Analysis of the effects of all the parameters on chilled depth has been carried out through a microstructure study.     

Investigation of TiAlN coated roller burnishing on Al-(B4C)p MMC workpiece material

Burnishing avoids the need for super finishing operations after the conventional turning process, to enhance the surface quality. This paper deals with the surface modifications of Al(B₄C)_p Metal Matrix Composites (MMC) workpiece material after burnishing with a TiAlN coated WC roller. The burnishing speed, lubrication type, burnishing passes, and coating were the input parameters. Surface hardness and roughness after the burnishing were studied. It was found that the coating on the WC roller had enhanced the hardness in the workpiece after burnishing in the case of Al-5?wt.% (B₄C)_p, under all conditions. The effect of the coating on the work piece surface hardness was not significant with Al-10?wt.% (B₄C)_p. While burnishing Al-5?wt.% (B₄C)_p, the minimum surface roughness combined with maximum surface hardness was obtained, during the third pass under dry condition using uncoated rollers. The number of passes to achieve the desired surface conditions reduced, on using coated rollers with kerosene as the lubricant.     

Characteristic study of N07718 superalloy surface prepared by cold spray

For better performance in erosive–corrosive, wear and other extreme environmental conditions surface properties of metals and alloys are usually altered by different techniques. Amongst the various surface coating techniques cold spraying is a relatively new and less reported method. Coating formation at energy lower than the melting stage of materials brings novelty to this process. In this study surface of UNS No. - N07718 alloy is altered by cold spraying chromium-carbide (nickel-chromium) layer. The microstructure properties of this cold sprayed surface are observed by various characterization techniques and the results are used to study mechanism of coating layer formation by cold spray process. This newly developed cold sprayed surface is found to be eligible for further testing in wear and erosive-corrosive environmental conditions.     

Magnetic Properties of Thermal Sprayed Tungsten Carbide–Cobalt Coatings

In the information age, the storage and accessibility of data is of vital importance. There are several possibilities to fulfill this task. Magnetic storage of data is a well‐established method and the range of materials used is continuously extended. In this study, the magnetic remanence of thermally sprayed tungsten carbide–cobalt (WCCo)‐coatings in dependence of their thickness is examined. Two magnetic fields differing in value and geometry are imprinted into the coatings and the resulting remanence field is measured. It is found that there are two effects, which in combination determine the effective value of the magnetic remanence usable for magnetic data storage.

     

Mechanical and thermal properties of RE4Hf3O12 (RE=Ho,Er, Tm) ceramics with defect fluorite structure

The thermal and environmental barrier coatings (T/EBC) are technologically important for advanced propulsion engine system. In this study, RE₄Hf₃O₁₂ (RE=Ho, Er, Tm) with defect fluorite structure was investigated for potential use as top TBC layer. Dense pellets were fabricated via a hot pressing method and the mechanical and thermal properties were characterized. RE₄Hf₃O₁₂ (RE=Ho, Er, Tm) possessed a high Vickers hardness of 11 GPa. The material retained high elastic modulus at elevated temperatures up to 1773 K, which made it attractive for high temperature application. The coefficient of thermal expansion (CTE) of RE₄Hf₃O₁₂ (RE = Ho, Er, Tm) laid in the range between 7 × 10⁻⁶ K⁻¹ to 10 × 10⁻⁶ K⁻¹ from 473 K to 1673 K. In addition, the rare earth hafnates exhibited lower thermal conductivity which rendered it a good candidate material for thermal barrier applications.     

喷雾干燥法制备富锂正极材料及其电化学性能

用喷雾干燥法制备Li_1.2Mn_0.54Ni_0.13Co_0.13O₂富锂正极材料并表征其结构、形貌以及电化学性能,研究了烧结温度对材料电化学性能的影响。结果表明：这种正极材料具有良好的层状结构,一次颗粒粒径为100 nm左右且分布均匀,样品的首次放电比容量为220.2 mAh/g,库伦效率为72.5%,18个循环后容量保持率为96.8%。电化学阻抗和循环伏安特性的测试结果表明,这种正极材料具有良好的电化学性能。