喷射成形镍基高温合金热变形特性及微观组织变化

采用Gleeble-1500D热力模拟试验机对喷射成形 热等静压制备的镍基高温合金,在变形温度1050-1140 ℃,应变速率0.01-10.0 s-1,工程应变量50%的条件下进行了热压缩实验.利用实验数据建立了合金的热加工图和热激活能图,对变形过程中组织演化进行了研究.结果表明,热等静压并没有使喷射成形高温合金晶粒尺寸明显长大.真应力-应变曲线出现了屈服降落现象;合金热加工图失稳区出现在温度区间1050-1110 ℃,应变速率0.01 s-1处;在1110-1140 ℃,应变速率1.0-10.0 s-1区间功率耗散值(η)出现最大值;在1140 ℃,应变速率1.0-10.0 s-1区间激活能出现一个小平台区.在变形温度1110-1140 ℃、应变速率1.0-10.0 s-1、变形量50%的条件下,可得到完全再结晶组织,该变形条件与热加工图中功率耗散最大值所在区间和激活能图中小平台区所在区间相对应.     

基于数值模拟的镍基高温合金电渣重熔工艺优化

利用MeltFlow软件对镍基高温合金电渣重熔过程进行数值模拟计算,探究了电渣重熔过程中温度场、流场、熔池形貌及微观组织的分布特点,通过工业试验验证模拟的准确性,定量分析熔速对熔炼过程的影响规律,提出了一种改善铸锭凝固质量的工艺优化方法。结果表明,渣池内的温度相对较高且分布均匀,熔池形貌近似“V”型。铸锭一次枝晶间距从中心到边缘沿径向逐渐减小,而二次枝晶间距没有明显差别。对比试验数据,数值模拟结果误差较小,可以准确预测镍基高温合金电渣重熔过程中的熔池形貌和枝晶间距。随着熔化速率的减小,金属熔池深度降低,ESR铸锭二次枝晶间距逐渐减小,且宏观偏析程度得到改善,黑斑产生概率逐渐降低。控制熔化速率由0.47 kg/min降低至0.45 kg/min,有利于获得凝固质量较好的镍基高温合金电渣重熔铸锭。     

Precipitate coarsening and its effects on the hot deformation behavior of the recently developedγ’-strengthened superalloys

Recently,theγ’-strengthened superalloys are of great interests in high temperature applications due to their excellent high temperature strength which is derived from theγ’strengthening phase.For theseγ’-strengthened superalloys,the changes in morphology,size and distribution ofγ’precipitates due to coarsening during thermal exposure have a significant impact on the properties of alloys.This article briefly summarizes the recent advances on the coarsening behavior of gamma prime precipitates in the recently-developedγ’-strengthened superalloys and its effects on the hot deformation behavior of superalloys,drawing specific examples on Allvac^■718 Plus TM and Ni3 Al-based intermetallic superalloys.It is found that the particle size plays an important role in morphological evolution ofγ’precipitates.For instance,the morphology ofγ’precipitates evolves from cuboidal to strip-like or other complex structures in Ni3 Al-based intermetallic alloys,while theγ’precipitates in Allvac^■718 Plus alloy always present nearspherical morphology due to the relatively small initial particle size.The Lifshitz-Slyozof-Wagner(LSW)theory and its modifications,as well as Trans-Interface Diffusion Controlled(TIDC)theory have been applied to describing the coarsening kinetics ofγ’precipitates.Additionally,the hot deformation behavior ofγ’-strengthened superalloy is found to be greatly influenced by the coarsening ofγ’precipitates.     

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.

     

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.     

一种镍基单晶高温合金中碳化物热稳定性研究

利用SEM、TEM研究了一种镍基单晶高温合金中碳化物在950℃时效不同时间的退化规律。固溶处理过程中形成的MC碳化物随时效时间的增加而逐渐退化为M6 C和M23 C6碳化物。同时,由于在时效处理过程中Re元素进入M6 C碳化物中,破坏了其结构稳定性,促使M6 C碳化物也可以退化为M23 C6碳化物。至时效3000 h时,没有观察到碳化物退化的逆反应。本研究可以为高温合金高温下服役的稳定性提供实验参考。     

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。     

近平衡与亚快速凝固条件下K424高温合金组织演化规律研究

采用差示扫描量热仪与铜模喷铸技术,研究了较宽冷速(0.17~100 K/s)范围内K424镍基高温合金的近平衡与亚快速凝固行为。利用光学显微镜、扫描电镜及能谱分析仪对不同冷速作用下K424合金γ基体相、γ′沉淀相、MC碳化物及共晶组织进行了表征,并对平均二次枝晶间距进行了定量分析。结果表明：冷速的提高有效细化了初生γ相,二次枝晶间距由0.17 K/s时的84 μm显著下降到100 K/s时的5 μm, 同时导致γ′沉淀相的析出时间缩短,平均晶粒尺寸下降。亚快速凝固条件下所形成的过饱和固溶体在后续加热过程中发生沉淀相析出。枝晶组织的细化与溶质截留的发生,降低了凝固过程中成分偏析,有利于γ+γ′共晶相及碳化物尺寸的下降。