高品质镍基合金大尺寸电极残余应力形成机制和控制方法

High quality large size electrode is the premise for the fabricating high quality large size high temperature nickel-base superalloys, which is a key point for producing of high-grade equipment needs. While the residual stress in the alloy-electrode seriously restricted preparation. Based on this background, the purpose of present application is focus on this problem, by using the electromagnetic field fine grains technology and mechanical vibration fine grains of complementary advantages, combined with ProCAST, MAXCDI, FDM numerical simulation of solidification process of the electrode temperature field and stress/strain field calculation. According to the system analysis of effects of electromagnetic field and mechanical vibration on dendritic characteristics (including size, alloying elements segregation, etc.), the evolution mechanism of residual stress in alloy-electrode will be understood. Combining the FEM and FDM numerical simulation with TMA and DSC experimental determinations for temperature changing and phase transformation during the process, analysis, thermal stress and phase transformation stress changing of alloy-electrode during the cooling process will be clarified, and both residual stresses will be controlled by suitable cooling of alloy-electrode, and the physical nature of the residual stress evolution changing will be revealed. Through the interaction of electromagnetic field and mechanical vibration on alloy-electrode solidification, combined with cold cracking countermeasures of cooling controlling, then optimization controlling parameters, residual stress of large size nickel-base superalloy electrode will be effectively controlled, the production bottleneck of high-quality large size nickel-base superalloys can be broken through.

高品质镍基高温合金大尺寸电极，是制造高端装备急需的高品质大尺寸镍基高温合金材料的前提。而合金电极制备中的残余应力严重制约了现实生产，为此本申请借助电磁场细化晶粒技术与机械振动细化晶粒技术的优势互补，结合ProCAST、MAXCDI 、FDM数值模拟对电极凝固过程温度场、应力/应变场的计算，系统解析电磁场与机械振动复合作用下电极残余应力与合金枝晶特征（包括尺寸、合金元素偏析等）演变的微观机制；利用FEM与FDM数值模拟方法，结合实验测定凝固过程中温度及相变（TMA、DSC）分析，解析合金电极冷却中热应力及相变应力变化规律，揭示控制合金电极冷却与残余应力演化的物理本质；通过电磁场与机械振动复合作用的电极凝固组织控制与优化，结合控制合金电极冷却中的温差与相变残余应力对策，实现有效地控制镍基高温合金大尺寸电极残余应力，突破高端装备用高品质大尺寸镍基高温合金材料生产瓶颈。

高品质镍基高温合金大尺寸电极，是制造高端装备急需的高品质大尺寸镍基高温合金材料的前提。而合金电极制备中的残余应力严重制约了现实生产，为此解析合金电极冷却中热应力及相变应力变化规律，揭示控制合金电极残余应力的物理本质；结合理论研究与现场实际研发有效地控制镍基高温合金大尺寸电极残余应力的方法，突破高端装备用高品质大尺寸镍基高温合金生产瓶颈迫在眉睫。.系统分析了大尺寸镍基高温合金电极裂纹与枝晶组织、微观成分偏析的定量关系。研究揭示，合金电极二次枝晶臂间距尺寸超过某临界值（约80-120m，合金不同略有差异）、主要合金元素偏析系数小于0.5时电极开裂倾向增大，这两条可作为镍基高温合金电极开裂的判据。研究发现，采用合金凝固过程中施加外场（旋转永磁场、低频脉冲电磁场）可有效地控制镍基高温合金电极的凝固过程，减小枝晶尺寸和降低合金元素偏析程度、细化合金凝固组织，降低电极开裂倾向。其细化机制为：其一，外场搅拌使得熔池温度低于液相线温度，增加形核数；其二，外场使合金熔体的强迫对流，打断枝晶臂、加速熔断，从而细化合金组织。研究揭示了时效强化型镍基高温合金的时效析出与内应力的相关变化规律，且经轮廓法残余应力表征，大尺寸镍基高温合金电极残余应力的实际检测得到了验证。基于镍基高温合金电极凝固、时效析出与合金内应力的研究结果，结合现场实际优化设计了新型电极模、电极时效去应力退火工艺，实现了抑制合金电极开裂、制备出了高品质大尺寸镍基高温合金棒材。.项目的主要创新点在于澄清了大尺寸镍基高温合金电极残余应力的形成机制，建立了有效控制大尺寸镍基高温合金电极凝固组织、合金偏析、残余应力及开裂的一体化技术。项目研究成果为解决高品质大尺寸镍基高温合金电极制备提供了理论基础与技术支撑