高熵合金涡轮叶片激光直接3D制造机理研究

The manufacture of high-performance turbine blade is always one of the core technologies for the national strategic development. The range of thrust-weight ratios of the international 5th aero engines is up to 15-20. The combustor temperature is near 1900℃, which highly exceeds the superalloy melt point. Then the thermal endurance and high-temperature property of the blade material should meet the more harsh serving conditions in the combustor. Therefore, the complicated air cooling structure inner the blade is designed to increase the serving temperature, however it lead to great challenge to the traditional blade manufacturing technology. High-entropy alloy (HEA) has excellent properties, such as heat tolerance, high strength to weight ratio, creep resistance etc., which will be an important blade material in future. However, the melt point of HEA is so high (over 2500℃) that composition segregation and casting residual stress are severe, which is hard to cast. In this project, the HEA turbine blade fabricated based on laser direct 3D manufacturing was proposed. The heat transfer of molten bath will be studied during the laser forming process, as well as liquid metal flow and solidifying morphology. The equal molar ratio control of different elements will be focused with the process of solute uniform diffusion. The solidification mechanism of the HEA micro molten ratio will be discussed. The important influence of atoms cluster deposition behavior on the microstructure growth, density and continuity of molten ratio will be studied and explained. The promoting effect of laser direct forming to the HEA lattice distortion and automatic sluggish diffusion will be analyzed, which will improve the final combination property. The mechanism of laser direct 3D manufacturing HEA hollow blade will be revealed, and the experimental data and theories are prepared and provided for the manufacture of high-performance blade.

高性能叶片制造技术一直是国家发展的战略核心。国际第五代航空发动机推重比高达15-20，其使用温度逼近1900℃，远超现有高温合金的熔点，从而对叶片材料的耐温性和高温性能提出了更苛刻的要求。为此，叶片的冷却结构极其复杂，给传统制造技术带来巨大挑战。而高熵合金具有优异的耐温、高比强等性能，是未来叶片材料的发展方向；但其熔化温度极高(2500℃以上)且偏析及残余应力严重，难以铸造成形。本项目提出基于激光直接3D制造技术成形高熵合金叶片，重点研究金属粉末熔化过程中，激光高能冲击对熔池传热、流动和形态的影响，考虑溶质均匀化扩散强调不同元素的等摩尔比控制；深入探讨高熵合金微熔池的凝固机理，解释原子团簇沉积对组织生长、致密度和熔池连续性的影响；分析激光直接成形对高熵合金晶格畸变及原子迟滞扩散的促进从而对综合性能的积极作用。揭示激光直接3D制造高熵合金空心叶片机理，为高性能叶片制造提供实验数据和理论支持。

高性能叶片制造技术一直是国家发展的战略核心。目前国际先进航空发动机涡轮进口温度接近1900℃，高性能涡轮叶片的材料耐温更高、结构更复杂，因此涡轮叶片的材料和成形工艺即为亟待解决的关键问题。本项目提出基于激光增材制造的新型高熵合金涡轮叶片制造研究。高熔点高熵合金熔点高达2800℃以上，通过高熔点原子固溶及置换使晶格发生畸变，从而具有的高温强度、抗腐蚀性等性能均优于现有镍基高温合金和常见超级钢材料；目前该合金主要采用真空电弧熔炼方式加工，形成简单柱坯形状，采用常规加工手段无法成形复杂构件，同时存在宏观偏析、局部原子团簇，影响性能等问题。.本项目以高熔点高熵合金激光直接3D成形为依托，形成了WNbMoTa高熔点高熵合金材料体系，提出了高熔点高熵合金激光直接3D成形机理，实现了混粉、冶金与成形同步完成的高熔点高熵合金成形思路，获得了组织均匀、性能优异的高熵合金激光直接成形样件；提出了塑性元素添加的方法，改善了成形件开裂和空隙缺陷，进一步提高了成形件高温力学性能。高熔点高熵合金激光直接成形的材料和加工工艺实验成本较高，本项目针对性提出激光直接成形过程的计算机数值模拟仿真。采用移动的嵌套网格技术大幅降低了激光连续制造过程计算量巨大的科学难题，真正实现了连续过程的温度场模拟，进而耦合有限差分-有限元方法（FD-FE）方法实现了激光增材制造过程的应力应变模拟，判断了翘曲发生位置。结合实验及模拟辅助工艺优化研究，提出了激光直接成形WNbMoTa系高熔点高熵合金的成套方案，并初步实现了具有复杂结构的涡轮叶片试验件制造。获得的高熵合金样件在1000℃条件下具有803MPa的高温强度，大幅提高了航空发动机涡轮叶片服役温度，并可简化复杂内腔结构设计，简化传统叶片制造工艺。该技术预期能够用于航空/燃气涡轮发动机叶片、高超声速飞行器鼻锥、核岛支撑裙等关键部件等高端装备制造。