激光增材制造高Co-Ni二次硬化超高强度钢的氢陷阱及环境氢脆机制

In marine atmosphere environment, main load-bearing components of high Co-Ni secondary hardening ultra-high strength steel (UHSS) for carrier-based aircraft are exposed to high risk of hydrogen environment embrittlement (HEE) fracture. Due to non-equilibrium rapid solidification and cyclic solid phase transformation, laser additive manufactured (LAM) high Co-Ni secondary hardening UHSS has apparently different macro/micro multi-scale microstructure characteristics compared to forged one. Based on microstructure design, main types and related parameters of hydrogen traps in alloy were firstly revealed by hydrogen thermal desorption tests and electrochemical hydrogen permeation, and influence of microstructure evolution on hydrogen trapping states and hydrogen diffusion behaviors was understood; furthermore, hydrogen-induced plasticity loss of alloy was achieved by a slow strain rate tensile test, and the influence of microstructure and strength on HEE sensitivity of the alloy was evaluated; finally, crack initiation sites and growth behaviors of hydrogen assisted delayed cracking was studied, and HEE mechanism of LAM high Co-Ni secondary hardening UHSS was further proposed with combined understanding of hydrogen trapping and diffusion effects. The results of this project will play a theoretical foundation for safety assessment of LAM UHSS components in carrier-based aircraft, and provide an optimization method of anti-hydrogen embrittlement performance for LAM UHSS by microstructure control. Thus, it has important scientific meaning and significance engineering application value.

在海洋性大气环境中，舰载机用高Co-Ni二次硬化超高强度钢主承力构件面临的环境氢脆断裂失效风险高。受非平衡快速凝固和后续循环固态相变影响，激光增材制造（LAM）高Co-Ni二次硬化超高强度钢具有（区别于锻件）显著的宏/微观多尺度组织特征。基于合金组织设计，本项目首先通过氢热脱附试验和电化学氢渗透试验揭示合金中主要氢陷阱类型和相关氢陷阱参数，掌握组织演化对合金中氢陷阱和氢扩散行为的影响机制；然后通过慢应变速率拉伸试验测试合金氢致塑性损失，评价组织和强度对合金环境氢脆敏感性的影响；最后研究合金氢致滞后开裂裂纹的萌生位置和扩展行为，并结合氢陷阱和氢扩散规律，掌握合金环境氢脆机制。项目成果将为LAM超高强度钢构件在舰载机中服役的安全评定奠定理论基础，并可为组织调控影响下的合金抗氢脆性能优化提供参考，具有重要的科学意义和工程实用价值。

海洋性大气环境中舰载机用大型复杂结构高Co-Ni二次硬化超高强度钢主承力构件面临的环境氢脆断裂失效风险高。本项目针对激光增材制造AerMet100超高强度钢非平衡快速凝固组织，通过后续热处理调控，设计了三类等轴状细晶组织试样。利用氢热脱附和电化学氢渗透等试验手段研究了增材制造合金钢氢陷阱状态和扩散行为，掌握了氢-金属交互作用机制。增材制造合金钢中至少存在三类氢陷阱位置，低温氢脱附峰对应的可逆氢陷阱状态与纳米尺度碳化物（沉积状态组织M3C碳化物、回火状态组织M2C碳化物）的演化行为密切相关，中温氢脱附峰对应氢陷阱受逆转变奥氏体的形成影响较大，高温氢脱附峰对应氢陷阱主要与晶粒内基体相的高角晶界相关。热处理前后，合金可逆氢陷阱脱陷激活能变化不大；相比沉积态较低可逆氢陷阱密度（~1019 cm3），回火状态合金钢中氢陷阱密度呈现先升高后降低且在482oC附近达到峰值（约3.4×1020 cm-3）。增材制造合金钢的氢扩散行为不但与其氢陷阱状态相关，而且与奥氏体相特征（形貌、尺寸、分布和含量）有关。相比沉积状态组织较高的表观氢扩散系数DH,eff（9.3×10-9cm2/s）, 不同热处理组织的DH,eff值较低（482oC对应2.4×10-9cm2/s）并随着回火温度的升高具有增高趋势。.采用慢应变速率拉伸和裂纹扩展试验研究了不同组织合金钢试样在氢环境中的性能和断裂行为，建立了工艺-组织-氢脆阻力/裂纹扩展速率间的关联关系，阐明了合金钢的环境氢脆机制。在增材制造合金钢不同时效状态组织中，过时效状态组织的环境氢脆阻力较优异，氢致滞后开裂主要沿晶粒内基体相高角界面，回火状态组织临界氢浓度值较沉积状态约高1个数量级。完成了不同载荷条件下增材制造合金钢氢致开裂裂纹扩展速率和断裂特征的评价研究，掌握了不同组织状态下合金钢的应力强度因子（幅值）-裂纹扩展速率关联关系。本项目为激光增材制造高Co-Ni二次硬化超高强度钢氢脆阻力提高提供组织设计方面的科学基础。