Technical note: Plasma-sprayed ceramic thermal barrier coatings for smooth intermetallic alloys

A durable ceramic thermal barrier coating is applied directly to a smooth, highly oxidation resistant intermetallic alloy in two layers. The first layer of ceramic is applied by low pressure plasma spraying and the second layer is applied by conventional atmospheric pressure plasma spraying. This approach would allow the use of plasma sprayed ceramic coatings in applications where a metallic bond coat is not desirable.     

Influence of Plasma Instabilities in Ceramic Suspension Plasma Spraying

Direct current Suspension Plasma Spraying (SPS) allows depositing finely structured coatings. This article presents an analysis of the influence of plasma instabilities on the yttria-stabilized suspension drops fragmentation. A particular attention is paid to the treatment of suspension jet or drops according to the importance of voltage fluctuations (linked to those of the arc root) and depending on the different spray parameters such as the plasma forming gas mixture composition and mass flow rate and the suspension momentum. By observing the suspension drops injection with a fast shutter camera and a laser flash sheet triggered by a defined transient voltage level of the plasma torch, the influence of plasma fluctuations on jet or drops fragmentation is studied through the deviation and dispersion trajectories of droplets within the plasma jet. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

离心喷射沉积距离对TiAl基合金组织的影响

研究了γＴｉＡｌ基合金经离心喷射沉积成形时不同喷射距离对合金组织的影响。合金经等离子弧熔炼并重熔后，在真空条件下进行离心喷射沉积成形，喷射沉积距离分别为２００、３００、４００和５００ｍｍ。结果表明，经离心喷射沉积后的合金仍存在着孔隙，且随喷射距离的增加，孔隙率增加，孔隙越细密。成形后的组织结构为层片状组织，其形貌、层片大小也随成形距离的不同而变化     

Corrosion behavior of wire-arc-sprayed stainless steel coating on mild steel

The corrosion characteristics of a wire-are-sprayed stainless steel coating on mild steel have been investigated in regards to atomizing gases and sealing treatment. Salt spray test was performed. The corrosion behavior of the coating was observed under a microscope succesively through a cycling test of wetting and drying in a salt solution. The sealing-treated coating was found to rust faster compared with the non-sealing-treated coating; it protected the mild steel substrate against corrosion, but even it deteriorated the coating itself due to the interruption of the substrate as an anode. The air-atomized coating ruste more heavily than the nitrogen-atomized one. Four different phases were observed in the coating in regards to corrosion behavior; namely, chromium-based oxide, iron-based oxide, chromium-depleted metallic phase, and stainless steel matrix phase. It was found that the chromium-depleted metallic phase and the iron-based oxide are non-corrosion-resistant, whereas the chromium-based oxide and the stainless steel matrix phase are corrosion-resistant.     

纳米热喷涂技术的研究现状与展望

介绍了纳米热喷涂结构涂层的组装、涂层结构与性能等方面的研究现状，并展望了纳米热喷涂技术的发展前景。     

球形烧结态Cr3C2–25%NiCr复合粉末制备研究

试验通过添加高分子分散剂配制Cr₃C₂–25%NiCr料浆，采用喷雾干燥技术制备球形粉末，在保护气氛下进行液相烧结，气流粉碎分级后形成合适粒度粉末。实验研究了不同分散剂含量对喷雾干燥制备Cr₃C₂–25%NiCr复合粉末性能的影响，液相烧结工艺对Cr₃C₂与NiCr合金相之间冶金化结合状态的影响。研究结果表明：高分子分散剂能够很好的调解料浆性能，使喷雾干燥粉末具有良好的物性。采用SEM、XRD及化学成分分析表明粉末物理性能与国外粉末相当，超音速火焰喷涂涂层性能较好。     

TC4钛合金表面等离子喷涂Al2O3-13wt％TiO2涂层及激光重熔研究

采用等离子喷涂技术在TC4钛合金表面制备了常规Metco130陶瓷涂层及纳米结构Al2O3-13wt％TiO2涂层，并利用CO2激光器对涂层进行了激光重熔，采用X射线衍射分析（XRD）、扫描电镜分析（SEM）、微区成分分析（EDAX）及维氏硬度试验研究了激光重熔前后涂层的组织性能变化。结果表明，等离子喷涂涂层与基体形成了较好的机械结合，但涂层中存在孔隙，激光重熔后，重熔层与基体形成了良好的冶金结合，其组织结构更为均匀而致密。采用谢乐公式估算了重熔后涂层中各相的平均粒径，结果表明，等离子喷涂纳米结构的涂层在激光重熔后仍然处于纳米结构。另外，选择合理的激光工艺参数，涂层的硬度得到了较大提高。     

Rapid and Continuous Deposition of Porous Nanocrystalline SnO2 Coating with Interpenetrating Pores for Gas Sensor Applications

In this article, we proposed a rapid and continuous process for the production of nanoporous coatings for functional applications. Experiments following two statistical designs were implemented to screen and investigate the spraying parameters’ effects on coating crystallinity and porosity in order to gain a better understanding. The spraying standoff distance, solution flow rate and power were identified as having significant effects on coating porosity and crystallinity. The result yielded a peculiar microstructure comprised of interpenetrating pores and layered structures with embedded pores. A deposition mechanism was postulated to explain this microstructure. Ethanol gas sensors that are constructed from the coatings had comparable sensitivities to those reported in the literature for thick-film coatings and had a maximum sensitivity near 200 °C. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

7090/SiC_p复合材料的固溶工艺制度研究

研究了移动坩埚式喷射沉积制备的7090/SiCp复合材料的两种固溶热处理工艺对其组织和性能的影响。观察了材料挤压态、固溶态及时效后样品的微观组织及X射线衍射图谱。通过两种固溶制度的比较,表明经过挤压变形处理的移动坩埚式喷射沉积制备的7090/SiCp复合材料,经475℃×1h+120℃×24h处理后材料的最高抗拉强度仅有715MPa,而经450℃×3h+500℃×3h+120℃×18h热处理后复合材料达到峰时效,材料的最高抗拉强度可以达765MPa。     

军用计算平台机箱轻型化设计材料应用研究

为进一步解决军用计算平台产品轻型化问题,开展了使用塑料材料代替金属材料的应用研究,采用电镀工艺使塑料基材导电化,制定适宜的表面喷涂工艺,对实例产品进行试验验证,达到了国军标电磁兼容及三防技术要求,为塑料在军用产品上的应用提供了重要参考依据。