A novel ultra-high-temperature oxidation protective MoSi2-TaSi2 ceramic coating for tantalum substrate

To protect refractory metal against oxidation at ultra-high temperatures, a MoSi₂-TaSi₂ ceramic coating was prepared on a pure tantalum (Ta) substrate using a novel three-step process, which included dip-coating with a molybdenum slurry, vacuum sintering, and halide-activated pack cementation (HAPC). The original coating had a MoSi₂-TaSi₂ double-layer structure from the surface to the substrate. After oxidation at 1700°C for 8 h in air, the coating exhibited a complex multi-layer structure composed of SiO₂-Mo₅Si₃-MoSi₂-(Mo,Ta)₅Si₃-TaSi₂-Ta₅Si₃ from the outer layer to the inner layer, due to the high-temperature phase transition and diffusion of Si and O. The coating effectively protected the Ta substrate at 1700°C for 12 h without failure, thereby demonstrating great improvement to its service life in an ultra-high-temperature aerobic environment. The protective effect was attributed to the integrity of the ceramic coating and the formation of a dense, uniform SiO₂ film that effectively lowered the inward oxygen diffusion rate.     

Preparation of a tantalum-based MoSi2-Mo coating resistant to ultra-high-temperature thermal shock by a new two-step process

To develop an ultra-high-temperature resistant coating for a reusable thermal protection system,the preparation of a tantalum-based MoSi2-Mo coating by a new two-step process of multi-arc ion plating and halide activated pack cementation is presented.The coating has a dense structure and is well compatible with the tantalum substrate,which can be thermally shocked from room temperature to 1750℃ for 360 cycles without failure.The mechanism of the coating's excellent resistance to high-temperature thermal shocks is that a strong-binding gradient interface and a dense SiO2 oxide scale with good oxygen resistance are formed by the high-temperature self-diffusion of Si.     

Comparison of microstructure and oxidation behavior of La-Mo-Si coatings deposited by two approaches

To investigate the effect of preparation methods on the La-Mo-Si (LMS) coatings, we developed a new LMS coating system using pack cementation (PC) and supersonic atmospheric plasma spraying (SAPS). Microstructure analysis showed that the SAPS-LMS coating possessed a higher porosity than that of the PC-LMS coating. Higher porosity can provide more channels to the oxidative and corrosive gasses to permeate the SAPS-LMS ceramic top-coat. After static oxidation for 150 h under 1773 K, the mass loss of SAPS-LMS coating (3.12 wt%) was much higher than that of the PC-LMS coating (0.05 wt%), and the parabolic rate constants presented faster oxidation kinetic in SAPS-LMS coating with respect to the PC-LMS coating. These results revealed that the protection effectiveness of SAPS-LMS coating was inferior to PC-LMS coating. Compared with SAPS-LMS coating, microscopic pores and cracks appeared in the PC-LMS coating with a thicker oxide film, which benefits from the formed La-Si-O-Al glass oxide with an excellent ability for crack healing. The reasons for poor antioxidant performance of SAPS-LMS coating are the higher volatility of La-Si-O glass containing Mo₅Si₃ and a weak interfacial interaction between coatings and substrate.     

Entwicklung von Diffusionsschichten auf Nickelbasiswerkstoffen für den Einsatz in chlorhaltigen Hochtemperaturprozessen

Development of diffusion coatings on nickel base alloys for the use in chlorine‐containing high temperature processes To open up the possibility of using sewage sludge ashes as fertilizers the removal of their heavy metal contents is obligatory. A process newly developed at the BAM Berlin executes this separation in highly chlorine‐containing atmospheres at temperatures of up to 1000 °C [1]. Unfortunately there are no materials available which can withstand such conditions over longer periods of time. This project deals with the development of materials that allow the operation in highly corrosive environments. The corrosion resistance of nickel base alloys against chlorine‐induced high‐temperature corrosion will be optimized by application of aluminum‐ and/or silicon‐containing diffusion coatings. As coating method the pack cementation process was selected. In this process, the metal to be coated is embedded in a powder, consisting of the coating metal, a halogen‐distributor (e.g. ammonium chloride) and aluminum oxide as filler material. During an annealing process of several hours at temperatures of 800 to 1000 °C, gaseous metal halides form. They diffuse through the powder pack and decompose at the substrate surface, thereby depositing the coating metal. Subsequent solid phase diffusion results in the formation of a protective diffusion layer. From the thermodynamic point of view, materials with a high content of aluminum and silicon show best prerequisites to build up slow‐growing, stable oxide layers with a high potential to protect the material against corrosive attacks. The actual performance of the materials will be examined in long‐time tests under simulated field conditions (high temperatures and chlorine‐containing atmospheres).     

Hot Corrosion Behavior of a Cr-Modified Aluminide Coating on a Ni-Based Superalloy

A Cr-modified aluminide coating is prepared on a Ni-based superalloy using arc ion plating and subsequent pack cementation aluminizing.Hot corrosion behavior of the Cr-modified aluminide coating exposed to molten Na2SO4/K2SO4(3:1) or Na2SO4/NaCl(3:1) salts at 900 °C in static air are evaluated as well as the aluminide coating.The results indicate that compared with the aluminide coating,the anti-corrosion properties of the Cr-modified aluminide coating in the both salts are improved,which should be attributed to the beneficial effect of the Cr in the coating.The corrosion mechanism of the Cr-modified aluminide coating,especially the role of Cr in the mixture salt corrosion,is discussed.     

Boride coatings obtained by pack cementation deposited on powder metallurgy and wrought Ti and Ti-6Al-4V

Wear resistance of Ti alloys needs to be improved, and an effective way to achieve this is through surface treatment. Boronizing is a surface treatment in which boron diffuses into the surface of Ti leading to the formation of hard and wear-resistant Ti borides. Boronizing of wrought and/or cast Ti alloys by pack cementation has been studied, while similar coatings on Ti alloys produced by powder metallurgy (PM) have not been reported. Also critical process parameters for boronizing Ti alloys, such as pack cementation powder composition and the process temperature have not been systematically studied and analysed. The present work reports on the surface modification of PM Ti and PM Ti-6Al-4V by boronizing, and presents some important thermodynamic aspects of the process comparing it with similar coatings applied to wrought Ti-6Al-4V. The coatings were characterised using scanning electron microscopy and X-ray diffraction. For both Ti and Ti-6Al-4V alloys the use of amorphous B as a B element supplier in the boriding powder pack led to the formation of a uniform external boride layer, while the use of B₄C as a B element supplier in the pack and under the same boronizing conditions, led to the formation of an external TiN layer and an internal layer containing B. The thermodynamic calculations performed proved successful in determining the appropriate conditions for boride coating deposition and estimating the phases likely to be formed. Finally the effect of surface roughness on the coating quality is discussed.     

Corrosion Behavior of Fe–Al Coatings Fabricated by Pack Aluminizing Method

In this study,the two kinds of Fe–Al coatings were fabricated by pack aluminizing on low-carbon steel at different temperatures.The corrosion behavior of the Fe–Al coatings in artificial seawater was investigated by the electrochemical and weight loss techniques.Results show that the thickness of coating layer increases with increasing aluminizing temperature.The coatings exhibit high micro-hardness and good metallurgical bonding with the substrate.In comparison with the steel substrate,the corrosion current density Icorrof the Fe–Al coatings is always lower than that of substrate,about 1/38 or 1/33 after 2 h immersion,and 1/3 or 1/6 for 720 h immersion.As can be seen from the weight loss curve,the Fe–Al coatings show less loss than that of the substrate within 30-day immersion.The corrosion products formed on the surface of the coatings include oxides of Al,Mg,Fe and Ca,and pitting defect has also been found.The Fe–Al coating with higher content of Fe_2Al_5 has better corrosion resistance.     

涤纶仿真丝对纺丝组件的工艺要求

本文结合我厂的实际生产情况，从纺丝组件的清洗和纺丝组件各部件的选型等方面，去探讨纺丝组件怎样才能满足仿真丝的工艺要求，并且以事例说明纺丝组件对生产的影响及解决的方法．     

新型卷烟条包缺包检测器

针对GD包装机现有的3种(称重型缺包检测、CT处烟包堆叠检测和CH再生料斗后端光电检测)条包缺包检测器产生漏检和误检的原因进行了分析,介绍了透射式电涡流缺包检测的工作原理及特点。透射式电涡流缺包检测利用电涡流传感器,通过检测条包包装材料中的金属含量来判断条包是否缺包。该检测器弥补了现有3种条包缺包检测的各种不足,可以杜绝缺包问题的产生。     

新型绿色缓冲包装材料及生产设备的研究

研究了新型缓冲包装材料－充气纸垫及其生产工艺、设备,同时对新型缓冲气垫的缓冲性能进行了试验研究,研究结果表明,新型缓冲充气纸垫缓冲性能良好,能满足多种工业品的缓冲包装要求,同时具有环保特性,因而具有广阔的市场前景。