DZ17G定向凝固高温合金微激光冲击强化方法与疲劳试验研究

Reseach on micro-scale laser shock peening method and fatigue experiment of DZ17G directional-solidified superalloy

摘要:

针对航空发动机定向凝固涡轮叶片疲劳断裂故障,对DZ17G合金模拟叶片进行激光冲击处理,为了防止剧烈塑性变形导致粗大柱状晶发生晶粒细化,提出基于微激光冲击强化系统的水下无吸收保护层高频冲击方法,采用短脉宽、微尺度激光降低塑性变形程度和深度,采用无吸收保护层的高频冲击方式获得均匀形变强化层。试验结果表明：DZ17G模拟叶片微激光冲击后浅表层内仅形成了高密度位错和位错缠结等组织结构,未发生晶粒细化,而且位错密度随深度快速降低；高密度位错集聚缠结使表面硬度提高达30%,但硬化层深度仅为180 μm。DZ17G模拟叶片疲劳强度由257.00 MPa提高到302.00 MPa,提高幅度达17.5%,而且800℃下保温2h后仍有11.7%的提高,其中高密度位错和位错缠结是疲劳性能提高的内在原因。

Abstract:

Aim at the fatigue fracture fault of aero-engine directional solidified turbine blade, laser shock peening was suggested to be conducted on the DZ17G superalloy simulated blades to improve fatigue performance. However, in order to avoid the occurrence of grain refinement in the columnar crystals,a special laser shock treatment method, high frequency shock without ablation coating underwater based on micro-scale laser shock peening, was proposed. In this method, short laser pulse width micro-scale laser beam was conducted to decrease the plastically degree and affected depth, and high frequency shock without ablation coating was conducted to form a uniform plastically strengthening layer. The experiment results indicate that there are high density disloactions and dislocation tangles generated in the shallow layer of DZ17G superalloy simulated blade, but no grain refinement, and the density of dislocations decrease with the depth sharply. High density disloactions and dislocation tangles result in a high improvement of hardness, increased by 30%. However, There is a 180 thick hardened layer generated. The fatigue strength of DZ17G superalloy simulated blades is improved form 257.00 MPa to 302.00 MPa, increased by 17.5%. There is still a improvement of 11.7% on fatigue strength after thermal insulation for 2h under 800℃. High density disloactions and dislocation tangles are the immanent cause of fatigue performance improvement.