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LPBF制备镍基高温合金组织演化及各向异性机制

李明川, 马瑞, 常帅, 王奇舜, 李俐群

李明川, 马瑞, 常帅, 王奇舜, 李俐群. LPBF制备镍基高温合金组织演化及各向异性机制[J]. 焊接学报, 2025, 46(1): 34-40, 47. DOI: 10.12073/j.hjxb.20231108002
引用本文: 李明川, 马瑞, 常帅, 王奇舜, 李俐群. LPBF制备镍基高温合金组织演化及各向异性机制[J]. 焊接学报, 2025, 46(1): 34-40, 47. DOI: 10.12073/j.hjxb.20231108002
LI Mingchuan, MA Rui, CHANG Shuai, WANG Qishun, LI Liqun. Microstructure evolution and anisotropy of nickel-based superalloy fabricated by LPBF[J]. TRANSACTIONS OF THE CHINA WELDING INSTITUTION, 2025, 46(1): 34-40, 47. DOI: 10.12073/j.hjxb.20231108002
Citation: LI Mingchuan, MA Rui, CHANG Shuai, WANG Qishun, LI Liqun. Microstructure evolution and anisotropy of nickel-based superalloy fabricated by LPBF[J]. TRANSACTIONS OF THE CHINA WELDING INSTITUTION, 2025, 46(1): 34-40, 47. DOI: 10.12073/j.hjxb.20231108002

LPBF制备镍基高温合金组织演化及各向异性机制

详细信息
    作者简介:

    李明川,博士研究生;主要从事金属增材制造方面的科研工作;Email: 15317538065@163.com

    通讯作者:

    常帅,博士,副教授;Email: changshuai@hit.edu.cn.

  • 中图分类号: TG 456.7;TH 142.1

Microstructure evolution and anisotropy of nickel-based superalloy fabricated by LPBF

  • 摘要:

    通过改变激光粉末床熔融(laser powder bed fusion, LPBF)的扫描速度研究IN738LC合金组织演化及各向异性机制,采用光学显微镜(optical microscopy,OM)及扫描电镜(scanning electron microscopy,SEM)对组织形貌特征进行表征分析,通过X射线衍射(X-ray diffraction,XRD)对其织构性进行测试,使用显微硬度仪对显微硬度及各向异性进行评价. 结果表明,随着扫描速度从800 mm/s提高到1600 mm/s,晶粒尺寸得到显著细化,且晶粒长轴取向由低扫描速度下沿建造方向择优,转变为高扫描速度下的沿熔池边界法线方向择优. 这是因为低扫描速度下高熔池重熔率导致更多枝晶沿建造方向外延择优生长. 这种沿建造方向的强择优生长同时导致(200)面沿建造方向择优的织构性,且这种织构强度随扫描速度增加而降低. 这种(200)面沿建造方向择优织构还导致水平截面软轴居多,进而导致水平显微硬度低于侧界面显微硬度的各向异性.

    Abstract:

    The microstructure evolution and anisotropy mechanism of IN738LC alloy under varying scanning speeds in laser powder bed fusion (LPBF) were investigated. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize the microstructural features, X-ray diffraction (XRD) was employed to examine the texture, and a microhardness tester was used to evaluate microhardness and anisotropy. The results showed that as the scanning speed increased from 800 mm/s to 1600 mm/s, the grain size became significantly smaller. At low scanning speeds, the grain major axis was preferentially aligned along the build direction. However, at high scanning speeds, the grain major axis transitioned to being aligned normal to the melt pool boundary. This was attributed to the higher melt pool remelting rate at low scanning speeds, which promoted more preferential epitaxial growth of dendrites along the build direction. This strong preferential growth along the build direction also resulted in a (200) texture along the build direction. The intensity of this texture decreased as the scanning speed increased. Furthermore, the (200) preferential alignment along the build direction led to an increased presence of soft axes in the horizontal section, resulting in anisotropy where the horizontal microhardness was lower than that of the side section.

  • 作为一种先进的耐高温、抗氧化、耐辐射陶瓷基复合材料,SiCf/SiC复合材料已在航空航天及其它工业领域展现出广阔的应用前景,如超高声速飞行器热防护结构、航空涡轮发动机部件、航天热结构部件及核聚变反应堆炉第一壁结构等. 在大多数应用中,SiCf/SiC复合材料需要与高温合金等金属材料配合使用,其可靠连接成为构件成功应用的关键之一[1-4].

    针对陶瓷基复合材料与金属材料的连接技术研究,国内外主要有机械连接、胶接和钎焊3种途径[5-6]. 针对陶瓷基复合材料与异种材料的耐高温轻量化连接技术主要以钎焊为研究和应用热点. 现阶段的文献主要报道了C/C及C/SiC等复合材料的钎焊技术研究成果,如Liu 等人[7]基于C/SiC 复合材料与Nb 的高温可靠连接需求,采用一种Ti37Ni37Nb 钎料,实现了最高室温抗剪强度达149 MPa的(C/SiC)/Nb钎焊接头,其600 ℃及800 ℃的高温抗剪强度分别为120,73 MPa. 张丽霞等人[8]采用Zr-Ni钎料对C/C复合材料和Nb进行了真空钎焊,经过1 100 ℃的钎焊,接头室温抗剪强度可达到19 MPa. 冯贞伟等人[9]利用钎焊过程中Cr原子在C/C复合材料侧的偏聚及界面反应,采用BNi2钎料对C/C复合材料和GH3128高温合金进行了真空钎焊,接头室温抗剪强度可达到24MPa. 关于SiCf/SiC复合材料与高温合金耐高温钎焊研究鲜有报道.

    文中以SiCf/SiC复合材料和Ni3Al基高温合金MX246A为研究对象,选用自行研制的含Ti,Hf活性钎料,进行了两种材料的钎焊工艺试验,分析了钎焊接头的界面组织及力学性能,从而为该复合材料在飞行器设计制造领域的实际应用提供理论依据.

    图1为试验用SiCf/SiC复合材料的外观形貌及微观特征,由中国航空工业集团公司复合材料技术中心采用聚合物浸渍裂解(PIP)技术制备而成,其孔隙率为11%~13%. 复合材料中的SiC纤维呈二维编织结构. MX246A高温合金由钢铁研究总院研制,其化学成分如表1所示. MX246A高温合金的初熔温度为1 290 ℃.

    图  1  SiCf/SiC复合材料的外观形貌及微观组织
    Figure  1.  Appearance morphology and microstructure of SiCf/SiC composite. (a) appearance morphology;(b) microstructure

    MX246A高温合金的热膨胀系数为16 × 10−6−1(25~1 100 ℃),与SiCf/SiC复合材料存在较大的热膨胀差异(后者的热膨胀系数为4.5 × 10−6−1). 为缓和(SiCf/SiC)/MX246A接头在钎焊过程中的热应力,在钎焊过程中采用缓慢冷却的工艺方法. SiCf/SiC复合材料试样的尺寸为10 mm × 10 mm × 3 mm,MX246A高温合金试样的尺寸为20 mm × 10 mm × 5 mm. 试验所用钎料为含Ti,Hf活性元素的镍基钎料NiCrCoWMoTiHf,其熔化温度为1 235 ℃.

    SiCf/SiC复合材料和MX246A高温合金试样在焊接前分别采用1200号和500号砂纸进行表面研磨. 试样在丙酮中进行超声波清洗,空气干燥. 钎焊过程中,首先采用25 ℃/min的加热速度升温至1 000 ℃,然后在5 ℃/min的升温速度条件下缓慢升至钎焊温度. 经过15 min的钎焊保温过程,以10 ℃/min的冷却速度降温至400 ℃,随后炉冷. 由于MX246A高温合金的初熔温度为1 290 ℃,液相温度为1 320 ℃,因此试验中选用1 250 ℃和1 270 ℃作为钎焊温度.

    沿垂直于焊缝方向进行接头金相取样. 将制备的金相试样在S-570型扫描电子显微镜(SEM)进行微观形貌观察,采用JDX-3530M型X射线衍射仪(XRD)和JXA-8600型能谱分析(EDS)进行接头界面物相的鉴定分析. 接头的抗剪强度采用Instron 1186型力学性能试验机在1 mm/min的加载速度下进行测试,取4个相同工艺试样的性能数据数学平均值作为分析结果.

    表  1  MX246A高温合金的化学成分(质量分数,%)
    Table  1.  Chemical compositions of MX246A high temperature alloy
    CCrAlTiWMoHf
    0.06~0.207.40~8.207.60~8.500.60~1.201.50~2.503.50~5.500.30~0.90
    FeSiMnPYBNi
    ≤ 2.00≤ 0.50≤ 0.50≤ 0.020.01≤ 0.05余量
    下载: 导出CSV 
    | 显示表格

    图2为分别在1 250,1 270 ℃保温15 min条件下钎焊(SiCf/SiC)/MX246A 接头的界面形貌. 复合材料通过钎料反应界面层与高温合金实现致密连接,界面层中有褐色斑点、灰色板条、浅灰色块状相等物相组成. 对复合材料侧的反应界面层进行能谱分析(表2),推断钎焊界面层主要由Si,TiC和HfC组成的反应层以及Ti-Al-Ni金属间化合物、W-Mo-Cr-Ni固溶体形成的扩散反应层组成[10-11]. 钎焊温度升高,可以促进接头界面各原子的扩散及反应,其中Ti,Hf与复合材料表面的SiC反应的吉布斯自由能如图3所示,较高钎焊温度能有效提高Ti,Hf与SiC的反应驱动力. 从图2b和图2d可以看出,较高钎焊温度条件下,复合材料侧的反应层呈现连续均匀分布,且合金化扩散层中的浅灰色相呈小块状弥散分布,这些有利于均匀界面结构,缓解界面应力,提高接头强度.

    图  2  SiCf/SiC复合材料钎焊接头界面形貌
    Figure  2.  Interfacial microstructure of the brazing joint of SiCf/SiC composite. (a) interfacial microstructure of the brazing joint brazed at 1 250 ℃ for 15 min;(b) high magnification SEM image of the area inside the solid line frame in Fig.2a;(c) high magnification SEM image of the area inside solid line frame in Fig.2b;(d) interfacial microstructure of the brazing joint brazed at 1 270 ℃ for 15 min
    表  2  (SiCf/SiC)/MX246A钎焊接头的化学组成(原子分数,%)
    Table  2.  Chemical compositions of the component phases at the joint interface
    位置COAlSiTiCrNiHfWMo反应相
    110.65.027.675.3768.762.58TiC, HfC, Si, (Ni,Cr)
    211.229.0124.511.4720.183.8423.696.08TiC, TiAlx, NiAlx
    39.128.342.5339.845.4829.0221.7619.86TiC, TiNix, (W,Mo)
    47.435.441.2313.0229.9828.4114.49(Ni,Cr), (W,Mo)
    510.5931.482.616.9214.7919.9313.67TiC, NiAlx, (Cr,W)
    下载: 导出CSV 
    | 显示表格
    图  3  Ti,Hf与SiC反应的吉布斯自由能曲线
    Figure  3.  Gibbs free energy of Ti, Hf reacting with SiC

    为进一步确定接头的界面物相组成,对钎焊接头的界面进行了XRD分析. 为避免高温合金对XRD检测的干扰,对SiCf/SiC复合材料试样进行表面钎涂(采用同种钎料),然后再对钎涂润湿界面层进行XRD分析,其谱图如图4所示.

    图  4  (SiCf/SiC)/MX246A钎焊接头界面及SiCf/SiC复合材料钎涂界面的XRD谱图
    Figure  4.  XRD image of (SiCf/SiC)/MX246A brazing joint interface and SiCf/SiC composite interface covered by brazing filler

    图4接头界面与钎涂界面的XRD谱图可以得出,钎焊接头的界面处有Ni2Si,NiTi,TiC,Ni31Si12反应产物生成. 根据二元合金相图及文献[10-11]可以得出,Ni-Cr,Cr-Mo及Mo-W均可钎焊加热过程中实现无限互溶,形成(Ni,Cr)、(Cr,W)和(W,Mo)固溶体. 因此,接头界面结构可以表示为:(SiCf/SiC)/TiC + NiTi + Ni2Si + Ni31Si12 + (Ni,Cr) + (Cr,W) + (W,Mo)/MX246A.

    对1250,1270 ℃不同温度钎焊接头分别在室温及1 000 ℃条件下进行剪切性能测试,其中在1 000 ℃进行性能测试时需要在保温15 min后再进行加载,以避免构件存在温度不均匀的问题. 测试结果如表3所示. 观察接头的断裂形貌看以看出,接头断于复合材料侧的基体上. 复合材料是接头的主要薄弱区域. 此外,两种钎焊温度条件下所得接头在1 000 ℃的抗剪强度均大于室温的数值. 这是由于SiCf/SiC复合材料与MX246A高温合金高温钎焊降到室温时,钎焊界面处存在一定的残余应力,残余应力会降低接头抗剪强度;在高温力学性能测试时,其热膨胀系数差引起的残余应力得到释放和缓解,因而接头抗剪强度较高. 该现象与陈杰[12]的研究结果相近,但所用钎料不同,钎焊接头强度升高的温度区间有差异. 钎焊温度越高,所得钎焊接头强度越大,这是由较高温度条件下界面的反应和扩散行为更为充分,复合材料侧的反应层呈现均匀连续的分布,钎料中的(W,Mo)相得到较充分扩散,向复合材料侧及高温合金侧均弥散分布,如图2b图2d所示. 观察接头断裂形貌,均断于复合材料侧(图5),要保障接头抗剪强度,需进一步优化接头的界面结构,实现界面应力的均匀分布,进而实现对复合材料连接界面的有效防护.

    表  3  (SiCf/SiC)/MX246A钎焊接头的室温及高温抗剪强度
    Table  3.  Shear strength of (SiCf/SiC)/MX246A brazing joints under room-temperature and high temperature
    测试温度T/℃平均抗剪强度Rτ/MPa
    1 250 ℃1 270 ℃
    室温7981
    1 0008590
    下载: 导出CSV 
    | 显示表格
    图  5  (SiCf/SiC)/MX246A钎焊接头断裂形貌
    Figure  5.  Fracture morphology of (SiCf/SiC)/MX246A brazing joint. (a) room-temperature; (b) 1 000 ℃

    (1)钎焊接头界面中有Ni2Si,NiTi,TiC,Ni31Si12化合物及(Ni,Cr),(Cr,W),(W,Mo)固溶体生成,接头界面结构可表示为(SiCf/SiC)/TiC + NiTi + Ni2Si + Ni31Si12 + (Ni,Cr) + (Cr,W) + (W,Mo)/MX246A.

    (2)在室温及1 000 ℃下,钎焊接头抗剪强度均达到70 MPa以上,接头断裂于复合材料侧基体. 复合材料侧热应力是影响接头性能的重要因素之一.

  • 图  1   IN738LC合金粉末

    Figure  1.   IN738LC alloy powder. (a) distribution of particle size; (b) SEM morphology of powder

    图  2   扫描策略及试样尺寸(mm)

    Figure  2.   Scanning strategy and sample dimension

    图  3   LPBF制备IN738LC合金OM形貌

    Figure  3.   OM morphologies of IN738LC alloy built by LPBF. (a) 800 mm/s; (b) 1100 mm/s; (c) 1600 mm/s

    图  4   LPBF制备IN738LC合金的SEM形貌

    Figure  4.   SEM morphologies of IN738LC alloy built by LPBF. (a) 800 mm/s; (b) 1600 mm/s

    图  5   不同截面XRD结果及织构系数

    Figure  5.   XRD results and texture indexes taken along different cross-sections. (a) XRD results from the side section; (b) XRD results from the horizontal section; (c) texture indexes from the side section; (d) texture indexes from the horizontal section

    图  6   扫描速度对组织形成影响的示意图

    Figure  6.   Schematic diagram of the effect of scanning speed on microstructure formation

    图  7   LBPF制备的IN738LC合金的显微硬度

    Figure  7.   Microhardness of IN738LC alloy built by LPBF. (a) horizontal cross-section; (b) vertical cross-section; (c) average microhardness

    图  8   施密特因子反极图分布图

    Figure  8.   Schmid factor distribution IPF map

    表  1   IN738LC合金粉末的名义成分 (质量分数,%)

    Table  1   Nominal compositions of IN738LC alloy powder

    含量范围NiCrCoMoWTaAlTiNbCBZr
    最小值余量15.78.01.52.41.53.23.20.60.090.070.02
    最大值余量16.39.02.02.82.03.73.71.10.130.0120.08
    下载: 导出CSV
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出版历程
  • 收稿日期:  2023-11-07
  • 网络出版日期:  2025-01-16
  • 刊出日期:  2025-01-24

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