非平衡雾化过程的协同降熵破碎机制研究

There is a huge material market demand of the narrow and fine powder, which can be applied to the 3D printing and cold spraying. The gas atomization is an important powder preparation technology, which has a wide powder size distribution leading to the issue that the production efficiency is relatively low. This is not meet the requirement that the development and utilization efficiency of energy and resources increase substantially which is proposed by 13th Five Year Plan. The powder size distribution is mainly affected by the nonequilibrium melt breakup process in the gas atomization, including primary and secondary breakup. However, considering the complex gas flow field in the atomization tower, the unique breakup mechanism of gas atomization is still not clear, which restricts the gas atomization to step from technology to science. In this work, the primary and secondary breakup process is analyzed by numerical simulation and visualization test system, in order to understand the influence factors of metal droplet size and its control technology in the primary and secondary breakup process respectively. In addition, the standard deviation of the particle size normal distribution is defined as the entropy in the gas atomization, and both Synergy and Law of Entropy are introduced in breakup theory of gas atomization. Based on the above results, the synergistic and reducing entropy break-up mechanism of nonequilibrium gas atomization is proposed. Thus it will improve the breakup theory of gas atomization and provide scientific guidance for reducing cost and improving efficiency.

可应用于3D打印、冷气体动力喷涂等领域的高性能窄细粒径粉末材料市场需求空间巨大，其主要制备技术为气雾化工艺。但是，该工艺制备的粉末粒度分布宽泛，导致生产效率低，这与“十三五规划”提出的“能源资源开发利用效率大幅提高”极为不符。调控粉末粒度分布的核心就是明确气雾化熔体非平衡破碎过程，包括初始破碎和二次破碎。然而，由于气雾化复杂的气体流场结构，使得仍未明晰其独特的破碎机制这一科学问题，进而阻碍了其由工艺走向科学。本申请项目拟采用数值模拟和可视化试验系统考察初始破碎和二次破碎历程，并分别明确两个破碎历程中金属液滴粒径的影响因素及控制技术；在此基础上，创造性地将粉末粒度正态分布的标准差定义为气雾化制粉过程中的熵，并将“协同论”和“熵增定律”共同引入气雾化破碎理论中。在肯定协同作用、明确降熵导向的条件下，提出非平衡雾化协同降熵破碎机制，从而补充气雾化破碎理论，为气雾化工艺的“降本增效”提供科学指导。

可应用于增材制造、表面强化等高端领域的高性能窄细粒径粉末材料市场需求空间巨大，其主要制备技术为气雾化工艺。但是，该工艺制备的粉末粒度分布宽泛，导致生产效率低。调控粉末粒度分布的核心就是明确气雾化熔体非平衡破碎过程，包括初始破碎和二次破碎。然而，由于气雾化复杂的气体流场结构，使得仍未明晰其独特的破碎机制这一科学问题，进而阻碍了其由工艺走向科学。本项目综合运用粉末冶金学、冶金物理化学、传输原理等理论方法，采用了数值模拟计算、可视化模拟试验等多种研究手段，探讨了雾化气体流场特征，剖析了金属液流初始破碎和金属液滴二次破碎历程。研究明确了窄粒径合金粉末生产工艺参数区间：雾化气体压力为28-44atm，雾化气体温度为450-500K，金属液流速率为5-10kg/min，金属液滴过热度为200-300K。在此基础上，创造性地将粉末粒度正态分布的标准差定义为气雾化制粉过程中的熵，并将“协同论”和“熵增定律”共同引入气雾化破碎理论中。在肯定协同作用、明确降熵导向的条件下，提出非平衡雾化协同降熵破碎机制，为粉末粒度的合理调控提供科学判据，补充完善了气雾化基础理论，为气雾化工艺的“降本节能”提供了科学指导。以此工艺为基础，本项目研究团队进一步试制了高性能窄粒径不锈钢和镍基合金粉末，满足了增材制造、表面强化等高端领域使用需求。