Effect of element distribution on the microstructure of FeCoCrNi high entropy alloy coating
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摘要: 聚焦于激光熔覆高熵合金表面强化技术，开展了6 mm厚TC4钛合金板材表面激光熔覆FeCoCrNi高熵合金涂层的研究. 首先通过X射线衍射(XRD)对FeCoCrNi高熵合金熔覆层进行物相分析，探究其相组成. 随后，利用金相显微镜和场发射扫描电子显微镜表征手段，探究了熔覆层以及其与TC4基体结合界面处的微观组织形态及物相分布. 结果表明，Ti，Ni组合和Ti，Co组合具有最大的负混合焓(∆Hmix)，因此易造成部分物相中(Ti，Ni，Co)的富集，而其周围相中则会呈现出(Fe，Cr)的富集. 结合界面上部和下部主要由灰色的柱状晶组成，中部区域主要由白色网状组织和灰色收缩孔洞组成.Abstract: Laser cladding of FeCoCrNi high entropy alloy coating on the surface of 6 mm thick TC4 titanium plate was studied by focusing on the surface strengthening technology of laser cladding high entropy alloy. Firstly, the phase analysis of the FeCoCrNi high entropy alloy cladding layer was carried out by X-ray diffraction to explore its phase composition. Then, the microstructure and phase distribution of the cladding layer and its interface with TC4 substrate were investigated by metallographical microscope and field emission scanning electron microscope. The results show that Ti and Ni, Ti and Co have the most significant negative mixing enthalpy (∆Hmix), so it is easy to cause the enrichment of (Ti, Ni, Co) in some phases, and the enrichment of (Fe, Cr) in the surrounding phases. The upper and lower part of the bonding interface is mainly composed of gray columnar grains, and the middle part is mainly composed of white reticulum structure and gray shrinkage cavity.
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Keywords:
- TC4 titanium alloy /
- high entropy alloy /
- laser cladding /
- element distribution /
- microstructure
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图 1 高熵合金激光熔覆原理
Figure 1. Diagram of laser cladding of high entropy alloy. (a) experimental diagram；(b) three dimensional space diagram；(c) longitudinal section
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图 2 FeCoCrNi高熵合金粉体和1号试样熔覆层的XRD物相对比分析结果
Figure 2. XRD phase contrast analysis results of FeCoCrNi high entropy alloy powder and cladding layer of sample 1
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图 3 1号试样熔覆层横截面不同区域内的微观组织形态
Figure 3. Microstructure at different region of transverse section of cladding layer of sample 1. (a) overall morphology of cladding layer; (b) upper area of cladding layer; (c) middle area of cladding layer; (d) lower area of cladding layer
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图 4 3号试样和2号试样熔覆层横截面的微观组织
Figure 4. Microstructure of transverse section of cladding layer of sample 3 and sample 2. (a) transverse section of sample 3; (b) dendritic structure; (c) transverse section of sample 2; (d) equiaxed crystal structure
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图 5 EDS测试结果
Figure 5. EDS test results. (a) test location 1; (b) test location 2; (c) test location 3; (d) test location 4; (e) test location 5; (f) test location 6; (g) test location 7; (h) test location 8
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图 6 枝晶和等轴晶各物相元素含量差异对比
Figure 6. Comparison of element contents in different phases of dendritic and equiaxed crystals structure. (a) dendritic structure; (b) equiaxed crystal structure
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图 7 熔覆层与TC4基体结合界面处各元素面分布结果
Figure 7. Surface distribution results of elements at the bonding interface of cladding layer and TC4 substrate. (a) bonding area；(b) Ti；(c) Ti + Fe；(d) Ti + Cr
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图 8 熔覆层与TC4基体结合界面的微观组织
Figure 8. Microstructure at the bonding interface of cladding layer and TC4 substrate. (a) bonding interface；(b) magnification of the bonding interface；(c) columnar crystals at the upper bonding interface；(d) fine dense network structure with holes at the bonding interface
表 1 TC4基体的化学成分(质量分数，%)
Table 1 Chemical compositions of TC4 substrate
Fe Ti Al V $\leqslant $ 0.15余量 6.04 3.71 
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表 2 FeCoCrNi高熵合金粉末的化学成分(质量分数，%)
Table 2 Chemical compositions of FeCoCrNi high entropy alloy
Fe Co Cr Ni 24.44 26.18 22.43 余量
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表 3 FeCoCrNi高熵合金激光熔覆试验工艺参数
Table 3 Experimental process parameters of FeCoCrNi high entropy alloy during laser cladding
试样
编号激光功率
P/W扫描速度
V/(mm·s−1)热输入
E/(J·mm−2)预铺层厚度
D(mm)1 800 10 40 0.5 2 900 12 37.5 1 3 900 10 45 1
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表 4 熔覆层与TC4基体结合界面微观组织的元素分布(质量分数，%)
Table 4 Elements distribution of microstructure at the bonding interface of cladding layer and TC4 substrate
测试位置 Fe Co Cr Ni Ti Al V 1 11.61 11.43 10.57 9.36 50.63 3.52 2.85 2 9.09 12.59 8.49 11.86 52.44 3.06 2.46 3 13.96 10.07 20.11 6.78 43.09 2.56 3.42 4 3.68 3.20 53.88 5.31 30.29 2.18 1.95
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