静电场同/异步加载对Inconel718合金多层夹芯结构的Laves相转变、组 织转变、力学性能的影响规律及内在机理研究

The multi-sheet sandwich structure of Inconel 718 superalloy will be widely used in vehicles as heat resisting and heat shielding structure due to its lightweight, high strength and stiffness. There are the residual Laves phase in the multi-sheet sandwich structure fabricated by laser welding and superplastic forming technology. Laves phase can be eliminated by high temperature solid solution+double aging treatment. But in the condition of this heat treatment, the grains of multi-sheet sandwich structure grows and reduces the mechanical properties of the structure. In order to solve this problem, the novel idea of this program is presented to use the electrostatic field in the processing of multi-sheet sandwich structure. By using the electrostatic field, temperature field and stress field in the different steps of the processing of multi-sheet sandwich structure of Inconel718 superalloy, the Laves phase can be eliminated, the grain size can be suppressed, and the mechanical properties of the structure can be improved. This program will explore the effects of the electrostatic field loading sequence on phase transition of Laves, the evolution of microstructure and mechanical properties, clear the relationship between the sequence of electrostatic field loading and Laves phase transition, the evolution of microstructure and mechanical properties; reveal the mechanism of Laves phase transition, the weld deformation mechanism, the refinement mechanism under the conditions of the electrostatic field, establish the Laves dissolution model in the multi-field conditions.

Inconel718合金多层夹芯结构具有高强度、高刚度、轻量化等特点，在航空航天耐热及防热方面具有广阔的应用前景。采用激光连接+超塑成形技术制造的多层夹芯结构焊缝中存在残余Laves相，采用高温固溶+双时效处理消除该相会导致晶粒长大而使结构力学性能降低。针对这一难题，本项目首次提出将静电场用于Inconel718合金多层夹芯结构制造过程中。通过在制造的不同步骤综合运用静电场、温度场、应力场拟消除Laves相，抑制晶粒长大，提高结构力学性能。多场作用下Laves相回溶机制，晶粒长大抑制机理是需要明确的科学问题。研究将探索静电场加载顺序对Laves相转变，组织演变及力学性能的影响规律；明确静电场顺序加载与Laves相转变，组织演变及力学性能之间的关系；揭示静电场条件下Laves相变机理，δ相析出及回溶规律与机制，焊缝变形机理，组织细化机理。

针对GH4169高温合金焊缝有害相Laves相消除时会使母材晶粒长大，导致强度下降的问题。研究了电场同异步加载对GH4169高温合金激光焊缝微观组织及性能的影响规律。研究结果表明，电场的引入能够加速Laves向δ相转化，但在1000℃以下未能完全使Laves相溶回溶，但与相同变形条件下，未加载电场相比，电场加载Laves相转变速度要快于未加载电场，并且转变体积分数均要高于未加载电场的情况，在相同条件下，平均转变体积分数高218.2%。在加载顺序方面，发现同步加载对于Laves相消除效果好于异步加载；在同步加载下，Laves相转化为δ相体积分数最高达到92.7%，虽然在实验条件下无法完全消除Laves相，但能够降低后处理温度和缩短后处理时间，所有经过电场处理的焊缝后仅需要在1020℃进行5min退火即可，这种条件抑制了晶粒长大，提高了母材强度达到18.3%，电场的加载有利于焊缝中Laves相中Nb元素的扩散，提高合金多层结构的抗压强度和抗弯强度，平均提高幅度分别达到21.6%，22.5%，同时建立了多场加载情况下的回溶模型。