In this paper, in order to improve the corrosion resistance of 316 stainless steel (316 SS) in molten chloride salt, an in situ grown Al 2 O 3 diffusion barrier is prepared through, first, electrodepositing an inner Ni-Al/NiO composite transition layer and an outer Ni layer through double-pulse composite electroplating technique, followed by annealing at 800°C for 12 h under Ar. The obtained Al 2 O 3 /Ni composite coating is dense and shows good adherence to the substrate. Then the corrosion resistance of Al 2 O 3 /Ni composite coating in molten 52MgCl 2 -48NaCl (wt%) is measured through electrochemical technique and immersion tests and the corrosion mechanism is also discussed. The results show that the 316 SS is effectively protected by the Al 2 O 3 /Ni composite coating from the corrosion of molten chloride salt.
To improve the oxidation resistance ability of carbon fiber (CF) in the high temperature environment, the composite electroplating method had been used to fabricate SiC-ZrO-MoSi 2 /Ni coating at the surface of CF. Both nanoparticles and Ni-matrix were plated onto CF successfully while the mechanical property of coated CF was only slightly weakened. The oxidation resistance performance of CF and the CF reinforced phenolic resin composites had been improved obviously. The microstructure of coatings was investigated by scanning electron microscope and X-ray diffraction analysis. Thermal gravimetric analysis was applied to test the anti-oxidation ability of coated CF. The mechanism of oxidation process had been discussed. It can be concluded that composite plating is an effective way to make composite coatings which can enhance the anti-oxidation ability of CF.
Qianqian Shen,Yu Zhang,Xuesha Li,Li Xiang,Chaoyin Nie
In order not to sacrifice nitrided layer thickness and reduce brittle compound layer thickness, Ni-coated pretreatment was carried out with electrodeposition on a pure iron surface, followed by gas nitriding. The brittle compound layer thickness of duplex surface treated samples was reduced, and the nitrided layer thickness increased to 320 μm. The microhardness was 4 times harder, and the wear loss was reduced by 68% compared with the original material. The results indicate that Ni-coated pretreatment could effectively improve microhardness and wear resistance and realize the controlled microstructure of a brittle compound layer of pure iron without compromising nitrided layer thickness. Ni coating plays an important role in ammonia adsorption and decomposition, and in the transfer of active nitrogen atoms during nitriding.
The purpose of this study is to prepare porous Zn-Ni coating with high infrared emissivity at a lower current density (1 A/cm 2 ) by using dynamic hydrogen bubble template (DHBT) method. Three types of ceramic micro-particles (Al 2 O 3 , SiO 2 and TiO 2 ) are introduced into the electrolyte to investigate their effects on the surface morphology and infrared emissivity of Zn-Ni coating. The results show that uniform porous coatings can be obtained when these micro-particles are added into the electrolyte. The suspended micro-particles in electrolyte can prevent the H 2 bubbles from rising up and escaping from the cathode, which is beneficial to the formation of porous structure, especially the insulating micro-particles, Al 2 O 3 and SiO 2 . The uniform porous structure containing ceramic micro-particles is beneficial to improve infrared emissivity. In addition, the infrared emissivity of porous composite coating is also significantly dependents on the type of ceramic particles inside pores. Among the three types of micro-particles, TiO 2 micro-particles have the greatest effect on the improvement of infrared emissivity which is increased from 0.83 to 0.91 when TiO 2 micro-particles are deposited into the Zn-Ni coating.
Bo Xu,Minxian Shi,Yanbing Wang,Fengyi Wang,Zhixiong Huang
Carbon fiber reinforced ceramizable phenolic resin composites (CF/CPR) have been widely used in the field of thermal protection materials. However, the industrial application of the CF/CPR is restricted by its easy oxidation failure at oxidizing environment. In this work, a series of Ni-coated carbon fiber reinforced ceramizable composites modified with AlB 2 and SiC were prepared. The thermal stability, phase evolution and anti-oxidation mechanism of the composites were investigated. The flexural strength and residual weight yield of obtained ceramizable composite after 15 min' static ablation at 1400 °C was 62.3 MPa and 84.0 %, increased by 154.2 % and 51.0 % compared to those of the composite without ceramic fillers. The excellent oxidation resistance and high temperature bearing capacity of the composites can be attributed to the synergistic effect of the multiphase ceramic protective layer and catalytic graphitization of the Ni phase. This work may provide great application prospects in thermal protection materials for hypersonic vehicles under harsh environments.
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