SBIR Phase II: Chemical Vapor Deposition-SiC Coated Ceramic Valve Components of High Damage and Wear Resistance

*9800946 JUE这个小型企业创新研究第二阶段项目将证明，与采用烧结α-碳化硅组件的阀门相比，采用分级碳化硅(SIC)组件的阀门的耐腐蚀性、耐磨性和抗裂性以及使用寿命将有显著改善。碳化硅是一种低成本陶瓷，具有高硬度、良好的耐滑动磨损性能和优异的耐腐蚀性和抗氧化性。由于这些特性，它被用作汽车水泵的机械密封和截止阀中的球和阀座。然而，碳化硅的断裂韧性很低，这使得它在冲击和热冲击条件下容易断裂，在颗粒碰撞中容易受到表面损伤和侵蚀。在第一阶段，论证了增韧碳化硅的可行性。所采用的方法包括设计和制造一种功能梯度材料，其中外层是通过化学气相沉积(CVD)在由液态烧结的碳化硅-TiC颗粒复合材料制成的衬底上沉积的‘纯’β-碳化硅。设计的成分和热膨胀失配导致CVD-碳化硅涂层从沉积温度冷却时表面存在残余压缩。根据基材组成、涂层厚度和组件的几何形状，采用该方法可获得高达1.1 GPA的涂层压缩。梯度碳化硅的表面压缩使滚动接触疲劳寿命提高了100倍以上。第二阶段的研究将把这项技术应用到1.5英寸的球和座椅上。球阀由三期合作伙伴Valtek International制造和销售。开发制造碳化硅球体和阀座的陶瓷制造工艺、优化快速化学气相沉积/复合气相涂层(CVD/CVC)涂层工艺、低成本表面处理以及阀门部件的原型和现场试验是拟议研究的主要任务。二期研究项目旨在将表面压缩增韧碳化硅引入陶瓷球阀。1996年，这些阀门在北美的销售额为800万美元。该技术还可以应用于陶瓷轴承和汽车行业，例如凸轮从动件。***

*** 9800946 Jue This Small Business Innovation Research Phase II project will demonstrate significant improvements in resistance to corrosion, erosion and fracture and service lifetimes for valves with the graded silicon carbide (SiC) components to be developed relative to the valves with sintered alpha-SiC components. SiC is a low-cost ceramic that possesses high hardness, good sliding wear resistance, and excellent corrosion and oxidation resistance. Because of these attributes it is used as mechanical face seals for water pumps in automobiles and as balls and seats in shut-off valves. SiC, however, has a low fracture toughness that renders it susceptible to fracture under impact and thermal-shock conditions and to surface damage and erosion in particle impact. During Phase I, the feasibility of toughening SiC was demonstrated. The approach used consisted of designing and fabricating a functionally-graded material where the outer layer was 'pure' beta-SiC deposited by chemical-vapor deposition (CVD) on a substrate made of liquid-phase sintered SiC-TiC particulate composite. The designed composition and thermal-expansion mismatch led to a residual surface compression in the CVD-SiC coating on cooling from the deposition temperature. Coating compressions as high as 1.1 GPa were developed by this approach depending on the substrate composition, coating thickness, and the geometry of the component. Surface compression in the graded-SiC increased rolling-contact-fatigue life by greater than a factor of 100. The Phase II research will apply this technology to balls and seats in a 1.5 in. ball valve manufactured and marketed by Valtek International, the Phase III partner. Development of a ceramic manufacturing process for making SiC-TiC balls and seats, optimization of a rapid chemical-vapor deposition/composite vapor coating (CVD/CVC) coating process, low-cost surface finishing and prototype and field testing of the valve components are the major tasks in the proposed research. Th e Phase II research project is aimed at introducing surface-compression-toughened SiC in ceramic ball valves. These valves accounted for $ 8 million in sales in North America in 1996. The technology can also be implemented in the ceramic bearing and the automobile industries , e.g., cam followers. ***