大型GH4169D环形锻件组织与性能研究

对航空发动机用大型GH4169D合金环形锻件的组织和性能进行了研究,介绍了锻造加热温度、加热火次、棒材原始晶粒组织等对GH4169D合金环形锻件晶粒组织的影响,以及不同晶粒组织对其性能的影响。研究结果表明,在标准热处理状态下,减少锻造加热火次、降低锻造加热温度、使用组织更细小均匀的棒材均能细化锻件组织,采用低温模锻制坯+少火次环轧工艺可显著细化锻件最终的晶粒组织;当锻件晶粒度细化到9.5~11级时,可显著提升锻件的拉伸强度及低周疲劳性能。

Microstructure and homogenization process of as-cast GH4169D alloy for novel turbine disk

To investigate the microstructure, segregation, and suitable homogenization process of as-cast GH4169D alloy, the microstructure, elements segregation, and precipitates of cast GH4169D ingots prepared by vacuum induction melting (VIM) and vacuum arc remelting (VAR) were observed by optical microscopy (OM), scanning electron microscopy, and energy-dispersive X-ray spectroscopy (EDS). According to the residual segregation model and simulation results of DICTRA thermodynamic software, the homogenization temperature and time range were set as 1120–1170°C and 5–20 h, respectively. The experimental results showed that microscopic dendrite and element segregation occurred in the interior of ingots and the main segregation elements were Nb and Ti. In addition, the precipitates were mainly distributed in interdendritic regions and were composed of NbC, Laves,γ′, and δ phases. The homogenization process suggested that the interdendritic detrimental precipitated Laves phase can be eliminated or redissolved after homogenization at 1150°C for 20 h, suggesting it was the most suitable homogenization treatment. Thermal compression test results showed that the GH4169D alloys after homogenization treatment had no cracks and dynamic recrystallization occurred, with recrystallization volume fraction increasing with temperature, indicating a good working plasticity at temperatures from 1050 to 1200°C.

电弧微铸锻复合增材制造GH4169D高温合金的显微组织与力学性能

GH4169D合金作为一种新型的高力学性能和高稳定性的镍基高温合金,在用于制造高性能复杂结构零件方面具有巨大应用价值,但该合金在电弧增材制造中表现出柱状晶粗大、力学性能各向异性等问题。本工作采用电弧微铸锻复合增材制造(hybrid arc and micro-rolling additive manufacturing,HARAM)技术成形GH4169D高温合金试块,并制定多种热处理制度对所成形的试块进行热处理。运用OM、SEM、EBSD、EDS、XRD、TEM等手段以及室温拉伸实验对合金的微观组织和力学性能进行观测和分析,并与常规电弧熔丝增材制造(wire and arc additive manufacturing,WAAM)方法成形的GH4169D合金进行对比。结果表明,HARAM技术中同步轧制的“微锻”作用能有效地使合金原本粗大的柱状晶发生“破碎”。与常规WAAM方法相比,采用HARAM技术所成形合金的室温抗拉强度提高(X向提高48 MPa,Z向提高90 MPa),力学性能的各向异性得到有效抑制。均匀化+固溶+双时效热处理有效消除了HARAM技术成形合金中的Laves偏析相,并促进受“微锻”作用的合金组织发生再结晶,使晶粒比未热处理时更为细小均匀,合金的综合力学性能达到最优(抗拉强度和断后延伸率X向为1366 MPa和25.0%,Z向为1354 MPa和24.6%)。

GH4169D高温合金锻件持久寿命的影响因素研究

对航空发动机GH4169D高温合金前置扩压器锻件的高温持久寿命和显微组织进行了评定,通过分析锻件本体和试环的力学性能与显微组织,研究了GH4169D高温合金锻件持久寿命的影响因素。结果表明,锻件的晶粒组织、热处理制度及析出相均为影响因素,且析出相η相的含量为主要影响因素,锻件中析出过多的η相会导致强化相γ′相析出不足,从而降低锻件的持久寿命。提高固溶热处理温度和固溶冷却速度,可在一定程度上抑制η相的析出,从而提高锻件的持久寿命。此外,锻造过程中应尽可能保证锻件晶粒组织均匀,避免出现混晶组织,否则也易导致锻件持久寿命不合格。

GH4169D合金电子束焊接接头显微组织和持久断裂特征

采用金相显微镜和扫描电镜分析了GH4169D合金电子束焊接接头的显微组织,利用显微硬度计测试了母材、热影响区和焊缝的显微硬度,采用体式显微镜和扫描电镜研究了焊接接头持久断裂特征。结果表明,GH4169D母材中的主要析出相为1~20μm长的片层状晶界η相、30~80 nm的颗粒状γ′相和少量的碳氮化物。热影响区中的主要析出相为10~20 nm的颗粒状γ′相,几乎没有晶界η相。焊缝中为枝晶组织,枝晶间存在含有共晶组织的白色析出相,析出相尺寸为2~6μm,枝晶杆中含有10 nm以下的细小颗粒状γ′相。母材的显微硬度低于热影响区和焊缝,不同区域的显微硬度主要受γ′相尺寸的影响。焊接接头的持久断裂过程包括蠕变裂纹扩展、快速扩展和瞬断3个阶段,蠕变裂纹扩展区中为沿晶断裂,快速扩展区中为沿晶和穿晶混合断裂,瞬断区为穿晶断裂。蠕变裂纹扩展起始于试样表面的热影响区,热影响区中晶界η相含量低和裂纹尖端晶界氧化是导致焊接接头持久性能低于母材的主要原因。