γ′ 相对高钨镍基高温合金拉伸和持久变形行为的影响

镍基高温合金在高温具有优异的力学和抗氧化腐蚀性能，是制造航空发动机和燃气轮机核心零部件的关键材料[1] 随着对航空发动机性能要求的提高，对其承温能力提出了更高的要求 高温合金中的难熔元素(W、Mo、Re等)能有效地提高其固溶强化水平，从而使其承温能力提高[2~5] 用W元素部分替代高温合金中的Re等稀贵金属元素，在提高其力学性能的同时还能降低制造成本[6] 因此，对高钨高温合金的研发受到国内外学者的极大关注[7, 8]

镍基高温合金中的析出相主要有A1型γ基体和L12型γ?有序相，皆为面心立方结构且有明显的共格关系[1] γ?相是镍基高温合金中最重要的强化相，其含量、形貌和尺寸都显著影响合金的高温力学性能[9, 10] 因此，在高温合金的变形过程中位错与γ?相的交互作用极为重要 Wang等[11] 的研究表明，在室温拉伸过程中位错以层错的形式切入γ?相并阻碍其他位错运动，使合金的屈服强度提高 Cui等[12]发现，M951G合金中的连续层错穿过γ?相，促进了合金的加工硬化 Zhou等[13]报道，在高钨高温合金的高温拉伸过程中析出的纳米γ?相颗粒有助于提高其高温强度 Xie等[14]指出，γ?相在蠕变过程中发生定向粗化，位错在γ-γ?界面形成密集的网状结构 这些研究结果表明，形貌和尺寸不同的γ?相在合金变形过程中与位错的作用机制也不同 虽然对γ?相与位错之间的关系研究得较多，但是在高温合金的服役过程中γ?相对位错迁移机制的影响仍不明确 研究表明，在单晶高温合金的超温蠕变过程中析出的二次γ?使其蠕变寿命降低[15] 而Guo等[16]发现，在K465合金的热循环蠕变过程中析出的二次γ?相有助于阻碍位错运动而使起抵抗蠕变变形的能力提高

K416B合金是典型的镍基高钨高温合金，其钨含量高达16%(质量分数)，使用温度超过1000℃ K416B是沉淀强化型高温合金，其中γ?相的体积分数可达60%~70%[17, 18] 因此，γ?相对K416B合金的性能至关重要 以往关于K416B合金的报道主要集中在长期时效和测试条件对其性能的影响[7, 19, 20]，对合金在高温下析出的二次γ?相与性能的关系研究较少 K416B合金在冷却过程中极易在γ通道中析出大量尺寸约为100 nm的细小二次γ?相，对合金的力学性能有重要的影响[21] 本文通过热处理调整合金中γ?相的尺寸及形貌，研究其对合金拉伸及持久性能的影响

1 实验方法

用VIM-F25型真空感应熔炼炉熔炼实验用K416B母合金锭，其主要化学成分(质量分数，%)为：C 0.1、Co 7.8、Cr 5.1、W 15.8、Al 5.8、Ti 0.8、Nb 1.7、Hf 1.1、Ni其余

将母合金锭浇铸成型，制备等轴晶试棒 从铸态K416B合金试棒上切取直径为3 mm、厚度为2.5 mm的圆柱形试样，使用STA449F3型差热分析仪进行差示扫描量热分析(DSC)，升降温速率为10℃/min

为了调整合金中析出相的形貌，将合金在1240℃固溶30 min后空冷，再在1160℃时效3 h后空冷，使K416B合金中保留部分大尺寸γ?相同时在γ相通道中析出细小的二次γ?相

将铸态和热处理态的K416B合金棒加工成标准拉伸(GB145-2001)和持久(GB/T 2039-2012)样品(图1) 标准拉伸样品的工作段长度为35 mm，直径为5 mm；标准持久样品的工作段长度为25 mm，直径为5 mm 用TSE504D型万能试验机进行拉伸测试 用F-25型蠕变/持久试验机进行持久测试，测试条件为975℃/235 MPa，用引伸计记录合金的变形

图1



图1拉伸试样和持久试样的加工示意图

Fig.1Schematic diagram of mechanical test samples (a) tensile (b) durable (unit: mm)

将铸态、热处理态及其断裂后的纵剖面样品机械研磨、抛光后，用腐蚀剂5 g CuSO4+25 mL HCl+20 mL H2O进行化学腐蚀 用Stemi 508型光学显微镜(OM)和ZEISS MERLIN Compact场发射扫描电镜(SEM)观察不同状态合金样品的组织形貌 在距离断口5 mm处横向切取500 μm厚的透射电镜样品薄片，将其双面机械研磨至50 μm以下后进行冲孔得到直径为3 mm的圆片 将透射样品在-25℃进行双喷电解减薄，双喷液是体积分数为10%高氯酸乙醇溶液 用Tecnai G220透射电镜进行组织观察和位错分析

2 实验结果2.1 铸态合金的组织

图2给出了铸态K416B合金的晶粒和共晶组织的形貌 可以看出，合金的晶粒尺寸较大，平均尺寸约为3.5 mm 如图2b中的箭头所示，合金的枝晶间有大量的γ/γ?共晶，是其在凝固过程中元素偏析所致 γ/γ?共晶是高温合金中的非平衡组织，对其高温力学性能有不利的影响 图3给出了K416B合金的升温和降温过程DSC曲线 升温曲线上的四个特征温度分别对应合金中γ?相的溶解温度，γ/γ?共晶熔化温度，碳化物回溶温度和合金完全熔化温度(图3a) 在冷却曲线上出现了五个特征温度(图3b)，在1147℃出现一个微弱的放热峰，是二次γ?相的生成温度[21] 二次γ?相，是在高温合金连续冷却过程中γ?相在基体中多批次形核析出的 二次γ?相属于后析出的γ?相，析出温度较低，在γ通道中形核但是难以长大，因此其尺寸比初生γ?相的小[22] 按照图4给出的合金固溶和时效热处理理制度，得到不同于铸态组织的、具有两种γ?尺寸的K416B合金组织(图5) 从图5a可见，铸态K416B合金中γ?相在枝晶干分布均匀，呈立方状，平均尺寸约为200 nm 图5b给出了K416B合金热处理后组织形貌，可见γ?相尺寸迅速增大到1 μm左右，且其形状由立方状转变为长条状 另外，γ基体通道明显粗化，细小的二次γ?相在γ基体通道中均匀析出

图2



图2铸态K416B合金的OM图像

Fig.2OM micrographs of as-cast K416B alloy (a) low magnification, (b) high magnification

图3



图3铸态K416B合金的DSC曲线

Fig.3DSC results of as-cast K416B (a) heating, (b) cooling

图4



图4热处理过程

Fig.4Heat treatment process

图5



图5铸态和热处理态K416B合金中γ?相的组织形貌

Fig.5Morphologies of γ? phase in K416B (a) as-cast state, (b) heat treatment

2.2 K416B合金的拉伸性能

图6给出了铸态和热处理态K416B合金的应力-应变曲线，表1列出了两组合金的典型性能参数 可以看出，与铸态合金相比，热处理态K416B合金的屈服强度明显地由936 MPa下降到775 MPa，但是其拉伸强度没有明显的变化，延伸率和断面收缩率均有所增大 相比之下，热处理态K416B合金的塑性优于铸态

Table 1

表1

表1K416B合金拉伸性能

Table 1Tensile properties of K416B alloy

	Rp0.2 /MPa	Rm/MPa	A/%	Z/%
As-cast	936	1054	4.0	10.0
Heat-treatment	775	1040	6.5	11.0

图6



图6γ?结构不同的K416B合金的应力-应变曲线

Fig.6Stress-strain curves of K416B alloy with different microstructures of γ?

2.3 拉伸断裂后的组织形貌

图7给出了铸态和热处理态K416B合金拉伸断口的SEM形貌 由图7a可以看出，铸态K416B合金的断口宏观上较为平整，在断口的中央可见明显的河流状花样 由此可以推断，铸态K416B合金的室温拉伸断裂机制是以解理断裂为主的脆性断裂 在高倍数SEM照片(图7b)中清晰可见台阶状的解理小平面，还能观察到沿枝晶断裂的迹象(图7b) 而热处理态K416B合金的断口整体凹凸不平，呈现出海绵状特征(图7c) 图7d表明，在断口中不仅出现解理小平面，还出现了少量微孔和由微孔聚集成的扩展裂纹 这表明，热处理态K416B合金的断裂方式主要是解理和微孔聚集，表现为混合断裂

图7



图7γ?结构不同的K416B合金的拉伸断口形貌

Fig.7Fracture morphologies of K416B alloy with different microstructures of γ? (a, b) as-cast state; (c, d) heat treatment

图8给出了K416B合金断裂后的纵截面形貌，可见合金拉伸断裂的二次裂纹均位于枝晶间区域 铸态K416B合金的裂纹主要沿着枝晶间γ/γ?共晶边缘扩展，γ?强化相的阻碍使裂纹不能进入枝晶干区域(图8a) 而图8b显示，热处理态K416B合金的二次裂纹存在于大块γ?，与铸态相比热处理态的二次裂纹尺寸较大，表明大块γ?相难以阻碍裂纹的扩展

图8



图8γ?相形貌不同的K416B合金拉伸断裂后的SEM照片

Fig.8SEM images of K416B alloy with different microstructures of γ? after fracture (a) as-cast state, (b) heat treatment

图9给出了铸态K416B合金拉伸断裂后的TEM明场像 可以看出，室温拉伸断裂后位错在外力作用下形成了位错环(图9a) 另外，部分位错以位错对的形式切割γ?相 图9b表明，部分切入γ?的<110>超位错分解为层错 图10给出了热处理态K416B合金γ?相的STEM-EDS图像，可见初生γ?尺寸约为500 nm，细小的二次γ?相在γ基体中析出 图10表明，Cr和Co元素偏析于γ基体，Al元素富集于γ?相，而W元素在γ基体和γ?相中等量分布 图11给出了热处理态K416B合金拉伸断裂后的TEM图像 由图11a可见，在室温拉伸期间合金基体中出现了位错塞积 大量全位错切入初生γ?相，降低了合金的屈服强度 从TEM暗场相可观察到弯曲的位错组态(图11b)，表明在合金变形过程中位错以Orowan机制绕过二次γ?，并留下相应的位错环

图9



图9铸态K416B合金拉伸断裂后的TEM图像

Fig.9TEM images of as-cast K416B alloy after tensile fracture

图10



图10热处理态K416B合金的STEM-EDS图像

Fig.10STEM-EDS images of heat-treatment K416B alloy

图11



图11热处理态K416B合金拉伸断裂后的TEM图像

Fig.11TEM images of heat-treatment K416B alloy after tensile fracture

2.4 K416B合金的持久性能

图12给出了在975℃/235 MPa条件下铸态和热处理态K416B合金的持久曲线 与铸态K416B相比，热处理态合金的持久寿命和延伸率均有所降低 从图12可见，合金热处理后其持久变形第二阶段的速率明显提高、时间缩短，持久寿命取决于稳定变形阶段 铸态K416B合金的持久寿命为89 h，断后伸长率约为3.40% 稳态阶段应变速率约为3.48×10-4 h-1 而热处理态合金的持久寿命仅为28 h，断后伸长率约为2.40%，稳态阶段应变速率提高到7.63×10-4 h-1

图12



图12不同组织的K416B合金在975℃/235 MPa条件下的持久曲线

Fig.12Durable rupture curves of K416B alloys with different morphologies under the condition of 975℃/235 MPa

2.5 持久断裂组织的形貌

图13给出了在975℃/235 MPa条件下铸态和热处理态K416B合金持久断裂后的显微组织 图13a、b给出了铸态K416B合金的断口纵剖面组织形貌，可见持久裂纹在枝晶间萌生并垂直于应力方向 图13b给出了合金断口处γ?相的形貌 可以看出，γ?相在持久过程中完全筏化并出现了拓扑倒置现象，如图中箭头所示 铸态K416B合金的筏形结构连续性差，分布不均匀 图13c、d给出了热处理态K416B合金断口的纵剖面组织形貌 与铸态相比，热处理态合金的枝晶间裂纹更加宽大(图13c) 这表明，合金热处理后裂纹易于在枝晶间扩展 图13d给出了合金断口处γ?相的形貌，可见γ?筏形的完整度高于铸态，在γ-γ?界面还析出了碳化物颗粒

图13



图13铸态和热处理态合金在975℃/235 MPa条件下断口纵剖面的组织

Fig.13Cross-sectional view of the alloys under the condition of 975℃/235 MPa (a, b) as-cast state; (c, d) heat treatment

图14给出了K416B合金持久断裂后的TEM图像 在持久变形过程中，位错在γ基体中沿不同方向滑移并塞积在碳化物附近(图14a) 随着持久变形的进行基体中的位错密度逐渐提高，沿不同方向滑移的位错在γ-γ?界面相互作用形成网状位错缠结(图14b) 位错堆积在γ基体和γ?相界面产生应力集中，使部分位错切入γ?相并在γ?相中缠结，如图14b中的箭头所示

图14



图14K416B合金在975℃/235 MPa条件下断裂后的位错组态

Fig.14Dislocation structures of K416B after rupture under 975℃/235 MPa

图15给出了K416B合金持久断裂后的STEM-EDS图像 从图15a可见，在K416B合金的持久变形过程中大量纳米级碳化物颗粒在基体通道内析出，在图的右下角可见少量碳化物出现在γ?相中 图15b给出了EDS面扫结果，可见在碳化物中富集W元素，由此判定碳化物为M6C型 还可以看出，大量碳化物在两相界面析出，延缓了γ?相的筏化速度，使局部γ?相仍能维持一定的立方度

图15



图15K416B合金在975℃/235 MPa条件下蠕变断裂后的STEM明场相和对应的能谱

Fig.15STEM bright field image (a) and corresponding elemental mapping (b) of K416B after creep rupture under 975℃/235 MPa

3 讨论3.1 γ? 相对K416B合金拉伸性能的影响

K416B合金中γ?相，对合金的拉伸断裂方式有重要的影响 在合金的室温拉伸过程中，应力倾向于集中在枝晶间区域 枝晶间的碳化物其强度较高，在拉伸过程中破碎产生裂纹[23] 随后，裂纹在相邻的共晶中扩展 与大块γ?相不同，γ/γ?共晶中的γ通道能改变裂纹扩展方向，使裂纹沿共晶边缘生长[24] 因此，铸态K416B合金发生脆性断裂 而热处理后共晶中的γ相溶解，大块γ?相发生更大的塑性变形，裂纹在枝晶间区域的扩展加快 随着拉应力的增大，裂纹在大块γ?相中形成的微孔洞聚集连接并沿晶界扩展 合金热处理后枝晶间的γ/γ?共晶转变为γ?相，是合金发生混合断裂的主要原因

在含有高体积分数沉淀强化相的高温合金中，位错切过γ?的临界应力小于Orowan绕过应力 研究表明，在奥氏体高温合金中位错通过γ?的方式与γ?尺寸相关[25] 在临界尺寸以下，位错以位错对的形式切入γ?相 屈服强度位于刃型位错对和螺型位错对切割γ?的理论强度之间，并随着γ?相尺寸的增大而提高 γ?相的尺寸超过临界尺寸后位错以Orowan机制绕过γ?强化相，随着γ?相之间距离的增大屈服强度的提高缓慢 本文的实验结果表明，在铸态K416B合金拉伸期间形变位错在基体通道中滑移，γ?强化相有效阻碍了位错运动 位错塞积在γ-γ?界面导致应力集中，少量位错以位错对的形式切入γ?相 此外，K416B合金中W元素的含量较高使合金中γ?相的层错能降低，<110>超位错在γ?相中分解形成层错(图9b) 热处理后K416B合金的初生γ?迅速粗化 与铸态K416B合金相比，在热处理态合金的拉伸变形过程中更多位错切入γ?，使合金产生更大的塑性变形 这表明，γ?相的强度随着其尺寸的增大而降低，阻碍位错运动的能力减弱 因此，热处理后K416B合金强度降低而延伸率提高

值得注意的是，与先前研究中具有大尺寸γ?相的K416B合金(710 MPa/5.0%)相比[19, 20]，本文通过热处理制备的K416B合金(775 MPa/6.5%)其屈服强度和延伸率更高 其原因是，在热处理态K416B合金中除了初生γ?相，在基体中还析出了大量二次γ?相 二次γ?相的生成降低了γ通道的宽度，增大了位错切割γ?的临界切应力，使变形过程中位错以Orowan机制绕过小尺寸二次γ?相 这表明，二次γ?反向畴界能较高、硬度较大，位错难以通过切割的方式进入γ?相

3.2 γ? 相对K416B合金持久变形的影响

在持久变形过程中，合金中的位错密度逐渐提高 由于γ?相的强度高于γ基体，基体的塑性变形量高于γ?相，使γ基体和γ?强化相界面处产生应力集中并出现密集的位错网络(图14) 在持久变形期间，合金中的γ?相发生粗化 铸态K416B合金中的γ?相在基体中均匀分布，发生筏化所需的时间更长，位错通过γ?相需要更多的能量，因此铸态K416B合金的持久寿命可达90 h 与之相比，热处理态K416B合金的持久寿命仅为30 h，其大幅度下降可归因于：1)热处理后γ?相的尺寸增大，γ基体通道的宽度也随之增大 在γ通道中析出了细小的二次γ?相和元素扩散距离减小，使γ?的筏化速率提高和合金抵抗变形的能力减弱 2)热处理后初生γ?相尺寸的增大促进位错切入初生γ?相，并提高了持久应变速率(图11) 因此可以观察到，热处理态K416B合金持久断裂后γ?筏形更加完整(图13d) 形变位错切入初生γ?相诱导颗粒状W6C在γ?相中弥散析出(图15)消耗了大量的W元素，使γ-γ?两相错配度减小，降低了合金的强化水平，导致持久寿命大幅度降低[26~28]

4 结论

(1) K416B合金中γ?相尺寸的增大使其屈服强度降低和延伸率提高 小尺寸二次γ?相有助于提高合金的屈服强度，大尺寸初生γ?相使其塑性提高 K416B合金的持久寿命随γ?相尺寸的增大而下降

(2) 在K416B合金的拉伸过程中产生的裂纹主要萌生于枝晶间区域 在铸态K416B合金的拉伸变形期间基体中形成高密度位错缠结，单根位错切入γ?相并分解为层错，另有部分位错以位错对的形式切入γ?相 在热处理态K416B合金中，在基体通道内滑移的位错受到二次γ?的阻碍，位错以位错对或全位错的形式切入大尺寸γ?相，以Orowan机制绕过二次γ?相

(3) 在热处理后的K416B合金中初生γ?相的尺寸增大，使持久变形期间更多的位错切入γ?相并促进颗粒状W6C析出 在γ通道中析出的二次γ?相提高了合金的筏化速率，使热处理态K416B合金的持久寿命低于铸态

参考文献

View Option 原文顺序文献年度倒序文中引用次数倒序被引期刊影响因子

[1]

Reed R C. The Superalloys: Fundamentals and Applications [M].

Cambridge:

Cambridge University Press, 2006: 19

[本文引用: 2]

[2]

Su X L, Xu Q Y, Wang R N, et al.

Microstructural evolution and compositional homogenization of a low Re-bearing Ni-based single crystal superalloy during through progression of heat treatment

[J]. Mater Des., 2018, 141: 296

DOIURL [本文引用: 1]

[3]

Long H B, Mao S C, Liu Y N, et al.

Microstructural and compositional design of Ni-based single crystalline superalloys―A review

[J]. J. Alloys Compd., 2018, 743: 203

DOIURL

[4]

Gong L, Chen B, Du Z H, et al.

Investigation of solidification and segregation characteristics of cast Ni-base superalloy K417G

[J]. J. Mater. Sci. Technol., 2018, 34(3): 541

DOI " />

As-cast Ni-based superalloys with high W content are used extensively in the turbine vane of aero-engine due to their good heat resistance and temperature capability. During high temperature service, the creep deformations and microstructure evolution are occurred in the using materials, and the creep behavior mainly depends on their chemical composition and microstructure, such as size, distribution and morphology of g ' phase and carbides. Thereinto, the mophologies of carbide phases are closely related to creep resistance of the alloy. Generally, the carbide particles displaying dispersive distribution may enhance the creep resistance of the alloy, while the carbide with continuous morphologies distributed in the boundaries, they may provide easy paths for crack propagation and degrade the mechanical properties of the alloy. Besides the creep life of the alloy also depends on the microstructure evolution under high temperature. But the evolution mechanism of carbides in K416B superalloy during creep is still unclear up to now. For this reason, by means of creep property measurement and microstructure observation, the evolution behavior of precipitates in K416B Ni-based superalloy with high W content during high temperature creep has been investigated. The results show that the size of g ' phase is inhomogeneous in the as-cast alloy, and the stripe MC-carbide distribute in the inter-dendrite regions displaying Chinese structures. During high temperature creep applied stress, fine M6C carbide discontinuously precipitate in the deformed g matrix. The thermodynamics analysis indicates that the carbon element segregates in the regions of stress concentration and combines with carbide-forming elements W etc, which promoted the fine M6C carbide to precipitate from the g matrix. At the same time, the grooves are formed on the surface of stripe MC carbide, and then gradually decomposed and transformed into M6C particles. Thereinto, the additional press formed in the surface of stripe MC carbide is the main factor to promote the MC phase continuous dissolution and spheroidizing.

谢 君, 于金江, 孙晓峰 等.

高钨K416B铸造镍基合金高温蠕变期间碳化物演化行为

[J]. 金属学报, 2015, 51(4): 458

[本文引用: 2]

[8]

Zhou T J, Feng W, Zhao H B, et al.

Coupling effects of tungsten and molybdenum on microstructure and stress-rupture properties of a nickel-base cast superalloy

[J]. Prog. Nat. Sci.: Mater. Int., 2018, 28: 45

DOIURL [本文引用: 1]

[9]

Roebuck B, Cox D, Reed R.

The temperature dependence of γ′ volume fraction in a Ni-based single crystal superalloy from resistivity measurements

[J]. Scripta Mater., 2001, 44: 917

DOIURL [本文引用: 1]

[10]

Harte A, Atkinson M, Smith A, et al.

The effect of solid solution and gamma prime on the deformation modes in Ni-based superalloys

[J]. Acta Mater., 2020, 194: 257

DOIURL [本文引用: 1]

[11]

Wang X G, Liu J L, Jin T, et al.

Tensile behaviors and deformation mechanisms of a nickel-base single crystal superalloy at different temperatures

[J]. Mater. Sci. Eng., 2014, 598A: 154

[本文引用: 1]

[12]

Cui L Q, Su H H, Yu J J, et al.

Temperature dependence of tensile properties and deformation behaviors of nickel-base superalloy M951G

[J]. Mater. Sci. Eng., 2017, 696A: 323

[本文引用: 1]

[13]

Zhou T J, Ding H S, Ma X P, et al.

Effect of precipitates on high-temperature tensile strength of a high W-content cast Ni-based superalloy

[J]. J. Alloys Compd., 2019, 797: 486

DOIURL [本文引用: 1]

[14]

Xie J, Yu J J, Sun X F, et al.

Thermodynamics analysis and precipitation behavior of fine carbide in K416B Ni-based superalloy with high W content during creep

[J]. Trans. Nonferrous Met. Soc. China, 2015, 25(5): 1478

DOIURL [本文引用: 1]

[15]

Cormier J, Cailletaud G.

Constitutive modeling of the creep behavior of single crystal superalloys under non-isothermal conditions inducing phase transformations

[J]. Mater. Sci. Eng., 2010, 527A(23) : 6300

[本文引用: 1]

[16]

Guo X T, Zheng W W, An W R, et al.

High temperature creep behavior of a cast polycrystalline nickel-based superalloy K465 under thermal cycling conditions

[J]. Materialia, 2020, 14: 100913

DOIURL [本文引用: 1]

[17]

Li Q, Xie J, Yu J J, et al.

Solidification behavior and segregation characteristics of high W-content cast Ni-Based superalloy K416B

[J]. J. Alloys Compd., 2021, 854: 156027

DOIURL [本文引用: 1]

[18]

Hua H Y, Xie J, Shu D L, et al.

Influence of W content on the microstructure of nickel base superalloy with high W content

[J]. Acta Metall. Sin., 2020, 56(2): 161

DOI [本文引用: 1] " />

通过OM、SEM和XRD对高W镍基高温合金进行组织观察与分析，研究了W含量对镍基高温合金凝固组织的影响规律 结果表明，当W含量为14% (质量分数，下同)时，镍基合金中无α-W相析出 当W含量高于16%时，合金凝固期间可析出α-W，并且随W含量提高，合金的晶粒尺寸由1.04 mm减小至0.17 mm，共晶含量由6%增至10%；W含量对在枝晶间/枝晶干内的γ'相尺寸及形态无明显影响 由于α-W的析出温度较高，在凝固期间首先析出，并在残余液相收缩作用下，α-W向液相核心处发生转移并长大；同时α-W可作为异质形核的核心，降低枝晶形核的临界形核功，使18%W合金获得较小的晶粒尺寸 此外，在不同取向枝晶汇聚生长的作用下，残余液相中Al、Ti等元素形成较高的浓度梯度而发生共晶转变，这是18%W合金中共晶含量较高的主要原因

[19]

Xie J, Yu J J, Sun X F, et al.

Influence of temperature on tensile behaviors of K416B Ni-based superalloy with high W content

[J]. Acta Metall. Sin., 2015, 51(8): 943

[本文引用: 2]

谢 君, 于金江, 孙晓峰等 温度对高W含量K 416

B镍基合金拉伸行为的影响

[J]. 金属学报, 2015, 51(8): 943

[本文引用: 2]

[20]

Chen M K, Xie J, Shu D L, et al.

Effect of long-term thermal exposures on tensile behaviors of K416B nickel-based superalloy

[J]. Acta Metall. Sin. (Engl. Lett.), 2020, 33(12): 1699

DOIURL [本文引用: 2]

[21]

Zhou S G, Sheng N C, Sun S J, et al.

Microstructural evolution of a high W content Ni-based superalloy at γ' sub-solvus temperatures

[J]. Met. Mater Int., 2023, 29: 27

DOIURL [本文引用: 2]

[22]

Singh A R P, Nag S, Chattopadhyay S, et al.

Mechanisms related to different generations of γ' precipitation during continuous cooling of a nickel base superalloy

[J]. Acta Mater., 2013, 61(1): 280

DOIURL [本文引用: 1]

[23]

Du B N, Hu Z Y, Sheng L Y, et al.

Tensile, creep behavior and microstructure evolution of an as-cast Ni-based K417G polycrystalline superalloy

[J]. J. Mater. Sci. Technol., 2018, 34(10): 1805

DOI [本文引用: 1] class="outline_tb" " />

Differential scanning calorimetry (DSC) analysis, isothermal solidification experiment and Thermo-Calc simulation were employed to investigate solidification characteristics of K417G Ni-base superalloy. Electron probe microanalysis (EPMA) was employed to analyze the segregation characteristics. Liquidus, solidus and the formation temperatures of main phases were measured. In the process of solidification, the volume fraction of liquid dropped dramatically in the initial stage, while the dropping rate became very low in the final stage due to severe segregation of positive segregation elements into the residual liquid. The solidification began with the formation of primary γ. Then with solidification proceeding, Ti and Mo were enriched in the liquid interdendrite, which resulted in the precipitation of MC carbides in the interdendrite. Al accumulated into liquid at the initial stage, but gathered to solid later due to the precipitation of γ/γ′ eutectic at the intermediate stage of solidification. However, Co tended to segregate toward the solid phase. In the case of K417G alloy, combining DSC analysis and isothermal solidification experiment is a good way to investigate the solidification characteristics. Thermo-Calc simulation can serve as reference to investigate K417G alloy.

[5]

Wang H F, Su H J, Zhang J, et al.

Investigation on solidification path of Ni-based single crystal superalloys with different Ru contents

[J]. Mater. Charact., 2017, 130: 211

[6]

MacKay R A, Gabb T P, Garg A, et al.

Influence of composition on microstructural parameters of single crystal nickel-base superalloys

[J]. Mater. Charact., 2012, 70: 83

[7]

Xie J, Yu J J, Sun X F, et al.

Carbide evolution behavior of K416B as-cast Ni-based superalloy with high W content during high temperature creep

[J]. Acta Metall. Sin., 2015, 51(4): 458

[本文引用: 2] " />

Nickel base superalloys are widely used in the preparation of hot end parts for aircraft engines because of their good comprehensive mechanical properties, oxidation resistance and structural stability. It's strengthened mainly by solid solution strengthening, γ' phase strengthening and carbide strengthening. High alloying is one of the main methods to improve the solid solution strengthening level of nickel base superalloys, where the element W is an efficient alloying element with low price. The control of the W content is extremely important for high W content nickel base superalloys. However, there are few reports on the influence of W content on the microstructure of high W alloy. According to this background, by means of OM, SEM observation and XRD analysis, the influence of W content on the solidified microstructure in nickel base superalloy have been investigated in this work. Results show that when the W content is about 14% (mass fraction, the same below), there is no α-W phase being precipitated in the alloy. While as the content of W is higher than 16%, α-W could be precipitated during the solidification. On another hand, the grain size of the alloy decreases from 1.04 mm to 0.17 mm and the volume fraction of eutectic increases from 6% to 10% with the increase of the W content. While the content of W has no obvious effect on the sizes and morphologies of γ' phase in the dendrite and inter-dendrite areas. During solidification, the α-W phase will be first precipitated due to its higher precipitation temperature, and the shrinkage of the residual liquid phase may cause the shift and growth of the α-W to the core of the liquid phase. The α-W could be as the core of the heterogeneous nucleation to reduce the critical nucleation energy, which is the main reason that the grain size of the 18%W alloy is smaller. During the growth of the dendrites with various orientations, the concentration of Al and Ti in the residual liquid phase may have a higher concentration gradient to cause the occurrence of eutectic transformation, which is the main reason that there is a higher volume fraction of eutectic in 18%W alloy.

华涵钰, 谢 君, 舒德龙 等.

W含量对一种高W镍基高温合金显微组织的影响

[J]. 金属学报, 2020, 56(2): 161



通过OM、SEM和XRD对高W镍基高温合金进行组织观察与分析，研究了W含量对镍基高温合金凝固组织的影响规律 结果表明，当W含量为14% (质量分数，下同)时，镍基合金中无α-W相析出 当W含量高于16%时，合金凝固期间可析出α-W，并且随W含量提高，合金的晶粒尺寸由1.04 mm减小至0.17 mm，共晶含量由6%增至10%；W含量对在枝晶间/枝晶干内的γ'相尺寸及形态无明显影响 由于α-W的析出温度较高，在凝固期间首先析出，并在残余液相收缩作用下，α-W向液相核心处发生转移并长大；同时α-W可作为异质形核的核心，降低枝晶形核的临界形核功，使18%W合金获得较小的晶粒尺寸 此外，在不同取向枝晶汇聚生长的作用下，残余液相中Al、Ti等元素形成较高的浓度梯度而发生共晶转变，这是18%W合金中共晶含量较高的主要原因

[19]

Xie J, Yu J J, Sun X F, et al.

Influence of temperature on tensile behaviors of K416B Ni-based superalloy with high W content

[J]. Acta Metall. Sin., 2015, 51(8): 943

[本文引用: 2]

谢 君, 于金江, 孙晓峰等 温度对高W含量K 416

B镍基合金拉伸行为的影响

[J]. 金属学报, 2015, 51(8): 943

[本文引用: 2]

[20]

Chen M K, Xie J, Shu D L, et al.

Effect of long-term thermal exposures on tensile behaviors of K416B nickel-based superalloy

[J]. Acta Metall. Sin. (Engl. Lett.), 2020, 33(12): 1699

[本文引用: 2]

[21]

Zhou S G, Sheng N C, Sun S J, et al.

Microstructural evolution of a high W content Ni-based superalloy at γ' sub-solvus temperatures

[J]. Met. Mater Int., 2023, 29: 27

[本文引用: 2]

[22]

Singh A R P, Nag S, Chattopadhyay S, et al.

Mechanisms related to different generations of γ' precipitation during continuous cooling of a nickel base superalloy

[J]. Acta Mater., 2013, 61(1): 280

[23]

Du B N, Hu Z Y, Sheng L Y, et al.

Tensile, creep behavior and microstructure evolution of an as-cast Ni-based K417G polycrystalline superalloy

[J]. J. Mater. Sci. Technol., 2018, 34(10): 1805



The Ni-based K417G superalloy is extensively applied as aeroengine components for its low cost and good mid-temperature (600-900 °C) properties. Since used in as-cast state, the comprehensive understanding on its mechanical properties and microstructure evolution is necessary. In the present research, the tensile, creep behavior and microstructure evolution of the as-cast K417G superalloy under different conditions were investigated. The results exhibit that tensile cracks tend to initiate at MC carbide and γ/γ′ eutectic structure and then propagate along grain boundary. As the temperature for tensile tests increases from 21 °C to 700 °C, the yield strength and ultimate tensile strength of K417G superalloy decreases slightly, while the elongation to failure decreases greatly because of the intermediate temperature embrittlement. When the temperature rises to 900 °C, the yield strength and ultimate tensile strength would decrease significantly. The creep deformation mechanism varies under different testing conditions. At 760 °C/645 MPa, the creep cracks initiate at MC carbides and γ/γ′ eutectic structures, and propagate transgranularly. While at 900 °C/315 MPa and 950 °C/235 MPa, the creep cracks initiate at grain boundary and propagate intergranularly. As the creep condition changes from 760 °C/645 MPa to 900 °C/315 MPa and 950 °C/235 MPa, the γ′ phase starts to raft, which reduces the creep deformation resistance and increases the steady-state deformation rate.

[24]

Qin S Y, Hao J Q, Yan L G, et al.

Ultrafast solution treatment to improve the comprehensive mechanical properties of superalloy by pulsed electric current

[J]. Scripta Mater., 2021, 199: 113879

[25]

Raynor D, Silcock J M.

Strengthening mechanisms in γ' precipitating alloys

[J]. Met. Sci. J., 1970, 4: 121

[26]

Xia W S, Zhao X B, Yue Q Z, et al.

Formative and controlled mechanisms of nano-sized γ′ precipitates with local phase-transition within dislocation networks of nickel-based single crystal superalloys

[J]. Acta Mater., 2021, 206: 116653

[27]

Kontis P, Li Z M, Collins D M, et al.

The effect of chromium and cobalt segregation at dislocations on nickel-based superalloys

[J]. Scripta Mater., 2018, 145: 76

[28]

Xie J, Tian S G, Zhou X M, et al.

Influence of heat treatment regimes on microstructure and creep properties of FGH95 nickel base superalloy

[J]. Mater. Sci. Eng., 2012, 538A: 306

2

2006