复杂藕状氧化钙陶瓷型芯微喷射粘结成形及性能调控机理研究

The new type high-speed railway and aviation castings are developed toward to integration, hollow thin-wall and complication. The silicon and aluminum based ceramic cores and their forming and leaching processes are difficult to meet casting requirements of the new castings. The micro-jetting and bonding forming technology with low cost and highly flexible can be used to prepare complex calcium oxide ceramic core with high collapsibility, which can realize green and low cost rapid casting of any complex structure casting. However, calcium oxide is easy to absorb moisture and easy expand with heat, and the precision and strength of calcium oxide ceramic core formed by micro-jetting and bonding forming technology are low, the sintering shrinkage is large and the surface is rough. These problems seriously hinder its industrial application. This project uses mixed solution with the oxide nanoparticle dispersion solution as the binder, through adjust the amount of binder in different part of the forming contour, spray blocked layer on the particles surface of outside contour, and use the structure of lotus-type micro through hole in ceramic core to solve the problems of micro-jetting and bonding formed calcium oxide ceramic core. Concrete study the distribution characteristics and formation mechanism of nano-particles dispersion binder in powder layer, study the characteristics and mechanism of interface bonding between binder and powder particles outside of the outline, study the influence mechanism and regulation method of the sintering properties of lotus-type microporous structure, study the mechanics characteristic of ceramic core in pouring process and collapse mechanism of ceramic core in leaching process. The results of this project have a large value for theory and application.

新型高铁和航空铸件向整体化、空心薄壁化、复杂化方向发展，硅基和铝基陶瓷型芯及其成形和脱芯工艺难以满足其精密铸造需求。采用低成本、高柔性化的微喷射粘结成形技术制备氧化钙等易溃散复杂陶瓷型芯，可实现任意复杂铸件绿色低成本快速铸造成形。但氧化钙陶瓷型芯易吸湿且易受热膨胀，经微喷射粘结成形的精度和强度低、烧结收缩大、表面粗糙，这些难题严重阻碍其工业应用。本项目采用氧化物纳米粉末与粘结剂混合后喷射填充粉层轮廓孔隙，通过调节成形轮廓内部不同部位粘结剂喷射量、轮廓外侧粉体表面喷射纳米阻隔层、型芯内部采用藕状微通孔结构等措施解决微喷射粘结成形氧化钙陶瓷型芯上述难题。具体研究纳米分散液粘结剂在粉层中的分布特征及形成机制，研究粉层轮廓外侧粘结剂与粉末颗粒界面结合特征及机理，研究藕状氧化钙陶瓷型芯烧结性能的影响机理及调控方法，研究型芯浇注过程受力特征和脱芯过程溃散机理。本项目研究成果具有较大的理论和应用价值。

为解决微喷射粘结成形复杂氧化钙陶瓷型芯坯体精度和致密度低、烧结收缩率大、表面质量和抗吸湿性能差等难题，分析了微喷射粘结成形过程中氧化钙陶瓷型芯坯体质量的影响因素及机理，提出了以纳米氧化物分散液作为喷射溶液粘结成形氧化钙陶瓷型芯坯体的新方法。研究了纳米氧化物粉末在粘结剂溶液中的分散机制；建立了粘结剂喷射溶液与粉层间力的关系模型，揭示了纳米氧化物分散液在粉层中的渗透行为及其对粉层内部结构的影响机理；开展了喷射粘结剂在粉层轮廓外侧的分布规律及机理研究，分析了轮廓外侧粘结桥的形貌特征及形成机制；研究了烧结过程中不同工艺参数对氧化钙陶瓷型芯烧结性能的影响规律及机理；分析了氧化钙陶瓷型芯在浇注过程受到的热应力；探索了氧化钙陶瓷型芯在脱芯过程中的溃散机理。研究结果表明：通过调节分散剂加入量使纳米氧化锆颗粒在粘结剂溶液中的zeta电位达到最小值，可制备固相含量高达20%的可喷射纳米氧化锆无水乙醇分散液；纳米氧化锆分散液在粉层中的铺展渗透行为与粉层孔隙尺寸、孔隙率、分散液的密度、分散液粘度、固化速率等主要因素有关，纳米氧化锆分散液随溶剂渗透后均匀分布在氧化钙颗粒表面和孔隙中，从而改善坯体致密度和表面粗糙度，采用20%纳米氧化锆分散液成形的氧化钙陶瓷型芯坯体致密度提升了13.6%，粗糙度减小了69.3%；分散液向轮廓外侧的渗透距离与渗透动力成正比，而渗透动力与粘结剂粘度成反比，分散液固相含量越高，成形的氧化钙尺寸精度越高，采用20%纳米氧化锆分散液成形的氧化钙长条试样，其X轴向尺寸精度提升了62.5%，Y轴向尺寸精度提升了88.5%；烧结过程中，纳米氧化锆颗粒与氧化钙在高温下形成CaZrO3而包裹氧化钙颗粒，拟制氧化钙晶粒长大，并有效阻隔氧化钙与空气的接触，提高烧结强度和抗吸湿性能；采用纳米氧化锆分散液成形的氧化钙陶瓷型芯可在水溶液中溃散，溃散时间与纳米氧化锆加入量成正比。本项目的研究成果较适合复杂金属零件的低成本快速铸造，具有重要的理论和实际意义。