铸造镍基高温合金增材修复技术的研究现状

铸造镍基高温合金广泛用于燃气轮机与航空发动机叶片等高温部件,长时间运行过程中经常发生叶片局部损伤失效,其维修或更换成本极高。通过增材修复来恢复局部损伤叶片的性能,将极大地降低制造成本、缩短制造周期、节约资源,具有极大的社会效益和市场价值。本文针对燃气轮机与航空发动机用铸造镍基高温合金部件的服役工况与失效形式,结合铸造镍基高温合金的成分、组织与性能特点,系统分析了增材修复时出现裂纹的类型、特点及形成机理,阐述了各类裂纹的主要影响因素,从增材工艺和材料两方面分类综述了减少或避免裂纹的增材修复工艺与技术现状,分析了不同增材修复方法的优缺点与未来可能的研究热点。     

超瞬态凝固增材制造梯度整体涡轮叶盘用高温合金粉末特性研究Ⅱ：叶片用合金粉末

本文针对超瞬态凝固增材制造梯度整体涡轮叶盘高温合金叶片用合金粉末特性开展研究。根据合金的承温能力和JMatPro相平衡计算结果,选用DZ4125作为叶片材料,K418作为叶盘轮缘部位材料。采用真空感应熔炼氩气雾化制粉(VIGA)制备DZ4125高温合金粉末,筛分至53-105μm粒度范围,采用采用差示扫描量热分析（DSC）、场发射扫描电镜（FESEM）和能谱（EDS）、激光粒度仪、动态图像粒度粒形分析仪以及综合粉体性能测试仪对DZ4125高温合金粉末的相变温度、显微组织、析出相成分、元素偏析行为、粒度、粒形、松装密度、振实密度和流动性进行系统表征。结果表明：DZ4125比K418合金的固液凝固温度范围宽,过渡区DZ4125+K418混合成分合金其液相线温度和MC碳化物开始析出温度介于两种合金之间,γ′开始析出温度与两种合金相当。DZ4125合金粉末形貌主要为球形和近球形,表面和截面显微组织主要呈树枝晶结构。所含元素中偏析倾向较强的元素有Hf、Ta、Ti、Mo和W,而偏析倾向弱的元素包括Ni、Co、Cr和Al。粉末内部枝晶间区分布有细小的MC碳化物,尺寸约为200nm。激光衍射和动态图像分析法测得的DZ4125粉末粒度值接近,中位径D50分别为70.2μm和72.8μm。动态图像法测得DZ4125合金粉末具有较好的球形度,SPHT和b/l均值分别为0.91和0.86。所选DZ4125高温合金粉末具有较好的松装密度、振实密度和流动性,其松装和振实密度分别达到合金理论密度的52%和63%,压缩度为17.7%,且粉末具有较好的流动性（20.79 s?(50 g)-1）。     

Room temperature tensile deformation behavior of a Ni-based superalloy with high W content

K416B Ni-based superalloy with high W content has good high temperature properties and low cost, which has a great development potential. To investigate the room temperature tensile property and the deformation feature of K416B superalloy, tensile testing at room temperature was carried out, and optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the deformation and damage mechanisms. Results show that the main room temperature tensile deformation features of the K416B nickel-based superalloy are dislocations slipping in the matrix and shearing into γ′ phase. The <110> super-dislocations shearing into γ′ phase can form the anti-phase boundary two coupled (a/2)<110> partial-dislocations or decompose into the configuration of two (a/3)<112> partial dislocations plus stacking fault. In the later stage of tensile testing, the slip-lines with different orientations are activated in the grain, causing the stress concentration in the regions of block carbide or the porosity, and cracks initiate and propagate along these regions.

     

热力耦合对一种第四代镍基单晶高温合金1100℃蠕变组织演变的影响

以一种第四代镍基单晶高温合金为研究对象,采用变截面蠕变试样,在1100℃、43~96 MPa条件下进行200 h蠕变中断实验,利用SEM和TEM观察了微观组织演变规律,利用同步辐射高能XRD和EPMA分析了高温低应力条件下镍基单晶高温合金的蠕变组织演变。结果表明:随着应力的增大,镍基单晶高温合金的γ′相体积分数降低,筏化程度增大且筏排厚度下降,同时,γ相通道宽度逐渐增大,而γ/γ’两相界面位错网间距逐渐减小。固溶强化元素Re、Mo和Cr等在γ相中的富集导致γ/γ’两相错配度绝对值增大。蠕变过程中γ’相体积分数降低和γ’相筏排厚度减小显著降低了合金的强度。另外,位错在γ′相溶解所导致的弯曲相界处的塞积,使位错易于切入γ′相,也是镍基单晶高温合金室温硬度下降的重要原因。     

Effect of strain rate on microstructure evolution of a nickel-based superalloy during hot deformation

The hot deformation behavior of a nickel-based superalloy was investigated by means of isothermal compression tests in the strain rate range of 0.001–10 s⁻¹ at 1110 °C. Transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) technique were used to study the effect of strain rate on the microstructure evolution of the alloy during hot deformation. The results revealed that the dynamic recrystallization (DRX) process was stimulated at high strain rates ($\dot{\epsilon }⩾5{\text{s}}^{-1}$) due to the high dislocation density and adiabatic temperature rise. Meanwhile, high nucleation of DRX and low grain growth led to the fine DRX grains. In the strain rate rage of 0.001–1 s⁻¹, the volume fraction of DRX grains increased with the decreasing strain rate, and the grain growth gradually governed the DRX process. Moreover, the strain rate has an important effect on DDRX and CDRX during hot deformation. On the other hand, particular attention was also paid to the evolution of twin boundaries during hot deformation. It was found that there was a lower fraction of Σ3 boundaries at the intermediate strain rate of 1 s⁻¹, while the fractions of Σ3 boundaries were much higher at both the lower strain rates ($\dot{\epsilon }⩽0.1{\text{s}}^{-1}$) and higher strain rates ($\dot{\epsilon }⩾5{\text{s}}^{-1}$).     

A quantitative metallographic assessment of the evolution of porosity during processing and creep in single crystal Ni‐base super alloys

The present work reviews previous research on the evolution of porosity. It presents new results from a detailed study on the evolution of porosity during casting, heat treatment and creep of a single crystal Ni‐base superalloy subjected to uniaxial tensile creep at 1050 °C and 160 MPa in [001] and [110] directions. A quantitative metallographic study was performed on carefully polished metallographic cross sections, monitoring sampling fields of 4500 × 1000 µm² using the back scatter contrast of an analytical scanning electron microscope; evolutions of pore sizes and pore form factors were analyzed and all important details which were previously revealed in a synchrotron study could be reproduced. In addition, it was observed that micro cracks form at larger cast pores. They interlink and thus initiate final rupture. The [110] tensile creep tests showed lower rupture strains than the [001] experiments. In agreement with earlier work, this can be rationalized on the basis of aligned porosity along primary dendrites.     

航空难加工材料切削刀具磨损与剩余寿命预测研究进展

航空制造领域因轻量化、强度等特殊的应用需求,大量使用钛合金、镍基合金等难切削材料,刀具磨损速率快,刀具过度磨损会影响产品质量,在保证产品质量的前提下,为了充分发挥刀具使用价值,亟需监测刀具磨损状态和预测刀具剩余寿命。针对刀具剩余寿命预测的定义、分类和主要预测方法进行了阐述,同时,刀具磨损监测作为刀具寿命预测的基础和先决条件,简述了其重要的流程和常见模型。刀具剩余寿命预测模型主要包括基于物理模型的预测、基于数据驱动的预测和混合预测三大类,对不同预测方法的优缺点和适用场景进行总结,并讨论了刀具剩余寿命预测的未来研究方向。     

不同温度时效后Ni-20Cr-18W-1Mo合金晶界偏聚及力学性能研究

采用扫描电镜(SEM)、透射电镜(TEM)、电子探针(EPMA)和高温力学试验机等手段,研究了不同时效温度(200-800 °C)对Ni-20Cr-18W-1Mo高温合金的元素晶界偏聚和力学性能的影响。结果表明,硫、磷元素的晶界偏聚临界时间随时效温度升高而降低;时效温度对元素在晶界和晶内的成分分布有显著的影响;实验合金的抗拉强度和延伸率随时效温度升高而降低。分析发现,硫、磷元素在晶界中的含量随时效温度升高而增大直至两者分别在650和400 °C时达到峰值,是合金在200-600 °C区间内力学性能降低的重要原因。     

FGH96高温合金的再结晶组织特征

FGH96高温合金的再结晶主要包括孕育期、形核期和晶核长大期。再结晶形核与长大对温度非常敏感:当变形量较小时,在1050℃充分形核,在1080℃再结晶晶核等轴化过程稳定,能够得到均匀细小的等轴晶,而当温度高于1110℃时,再结晶等轴晶粒显著长大;随着变形量的增大,获得细晶粒的温度由1110℃降低到1080℃左右。促进形核、抑制晶粒长大均有利于晶粒细化。另外,再结晶优先在原始颗粒边界发生,当变形不充分时,内部残留未再结晶区,得到不完全再结晶组织,即"项链"组织。同时,这种组织也是粉末冶金材料晶粒细化过程中必然存在的中间态特征组织,随着变形方向的增加、累积变形量的增大,原始颗粒中心区域能够发生再结晶,"项链"组织也逐渐转化成等轴细晶组织。     

型壳中央散热对一种单晶高温合金凝固组织与持久性能的影响

单晶凝固过程中温度场均匀性控制对单晶制备过程特别重要。本文以国内广泛应用的第二代单晶高温合金DD6为研究对象,研究型壳中央散热对其凝固组织与持久性能的影响。结果表明,与合金中柱型壳相比,石墨中柱型壳能有效地改善单晶凝固过程中温度场的均匀性,提高温度梯度,有利于保持单晶凝固过程中热流方向的平直。因此,石墨中柱型壳有利于降低一次枝晶间距,细化γ-γ’共晶相,减少单晶生长方向与[001]方向的角度差,使单晶高温合金获得较高的持久寿命。