熱處理對SLM-316L不銹鋼組織結構及鈍化行為的影響機制

段智為; 滿成; 崔中雨; 董超芳; 王昕; 崔洪芝

doi:10.13374/j.issn2095-9389.2022.01.26.002

熱處理對SLM-316L不銹鋼組織結構及鈍化行為的影響機制

doi: 10.13374/j.issn2095-9389.2022.01.26.002

1.
中國海洋大學材料科學與工程學院，青島 266100
2.
北京科技大學新材料技術研究院，北京 100083

基金項目: 國家自然科學基金資助項目（51901216）

詳細信息

通訊作者:
E-mail: mancheng@ouc.edu.cn

中圖分類號: TG172.6
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出版歷程
- 收稿日期: 2022-01-26
- 網絡出版日期: 2022-04-19
- 刊出日期: 2023-04-01

Effect of heat treatment on the microstructure and passive behavior of 316L stainless steel fabricated by selective laser melting

1.
School of Materials Science and Engineering, Ocean University of China, Qingdao 266100, China
2.
Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China

More Information

Corresponding author: E-mail: mancheng@ouc.edu.cn

摘要

摘要: 對SLM-316L不銹鋼在900 ℃下進行不同時間的熱處理，結合熱處理后SLM-316L不銹鋼的組織結構和腐蝕行為研究，揭示了SLM-316L不銹鋼在900 ℃熱處理過程中組織結構的演變規律以及其對鈍化行為的作用機制。研究結果表明，900 ℃熱處理時，在組織結構方面，SLM-316L不銹鋼晶粒的基本形狀和尺寸沒有明顯變化，但是隨著保溫時間延長，SLM-316L不銹鋼中的位錯和亞晶界逐漸消失，同時伴有MnS顆粒物沿晶界析出；在耐蝕性能方面，熱處理對SLM-316L不銹鋼的耐蝕性能產生重要影響，在含有NaCl的緩沖溶液中，SLM-316L不銹鋼的點蝕電位隨著保溫時間延長逐漸降低，同時電化學阻抗逐漸減小；此外，在鈍化膜性質方面，不同熱處理時間試樣上形成的鈍化膜有明顯差異，隨著保溫時間延長，SLM-316L不銹鋼鈍化膜的厚度逐漸減小，載流子的密度以及擴散系數變大。最后，通過構建不銹鋼鈍化膜能帶結構和空間電荷層的理論模型，討論了熱處理對SLM-316L不銹鋼鈍化行為的影響機制。
- 選區激光融化 /
- 316L不銹鋼 /
- 鈍化膜 /
- 熱處理 /
- Mott-Schottky
Abstract: Selective laser melting (SLM), a rising additive manufacturing technology, has extensive application potential because of its advantage in fabricating components with individual and complex shapes. During the SLM progress, the laser molten pool cools very quickly, leading to non-equilibrium microstructure formation and high thermal residual stress in the SLM components. Therefore, a suitable heat treatment is required to reduce the residual thermal stress and obtain excellent mechanical properties after the SLM process. In this paper, the 316L stainless steel fabricated by SLM (SLM-316L SS) is first heat-treated at 900 ℃ for 0, 0.5, 1.0, 3.0, and 5.0 h. Then, the microstructures of SLM-316L SS treated at different times are investigated using SEM, TEM, and EDS, and their corrosion resistance is estimated through electrochemical measurements. Finally, the microstructure evolution of SLM-316L SS during heat treatment at 900 ℃ is discussed based on the experimental data, and the effect of the microstructure on the formation kinetics and properties of the passive film on SLM-316L SS is explained. The results of the microstructure analysis reveal that the dislocations and sub-grain boundaries in SLM-316L SS disappeared with increasing holding time, accompanied by the precipitation of MnS inclusions, carbides, and σ phases along the grain boundaries. The potentiodynamic polarization in the buffer solution with 0.1 mol·L^-1 NaCl reveals that a sample with a longer holding time shows a more negative pitting potential. According to the EIS test results, the shape of the curve in Nyquist diagram is not completely circular. The calculated film thicknesses decrease with increasing holding time. The potentiostat polarization under 0.1, 0.2, 0.3, 0.4, and 0.5 V vs SCE was used to form passive films on SLM-316L SS after heat treatments. By fitting the Mott-Schottky curves, the negative slopes demonstrate that the passive films formed on the samples are an n-type semiconductor, and the calculated point defect densities in the sample increase with the holding time. In addition, a logarithmic relationship holds between the carrier densities and the formation potentials of the passive films, and, using this relationship, the calculated diffusion coefficient of point defects across the passive film of SLM-316L SS increases with the holding time. A theoretical model related to the energy band structure and space charge layer is obtained based on the Mott-Schottky results to explain the electrochemical reaction on the passive film/solution interface.
- selective laser melting /
- 316L stainless steel /
- heat treatment /
- passive film /
- Mott-Schottky

HTML全文

圖 1 900 ℃時不同熱處理時間下SLM-316L不銹鋼的TEM組織結構分析. (a)～(a1)未熱處理；(b)～(b1) 0.5 h；(c)～(c1) 5.0 h；(d) 5.0 h試樣中MnS及能譜分析

Figure 1. TEM images of SLM-316L SS with different heating treatment time at 900 ℃: (a)–(a1) as-received sample; (b)–(b1) 0.5 h; (c)–(c1) 5.0 h; (d) MnS inclusion in the sample heated for 5.0 h and EDS analysis

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圖 2 不同熱處理時間下SLM 316L不銹鋼在硼酸–硼酸鈉緩沖溶液中的動電位極化曲線.(a) 未添加NaCl；(b) 添加0.1 mol·L^–1 NaCl

Figure 2. Potentiodynamic polarization curves of the buffer solutions: (a) without NaCl; (b) with 0.1 mol·L^–1 NaCl

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圖 3 不同熱處理時間下SLM-316L不銹鋼在硼酸–硼酸鈉溶液中的電化學阻抗圖譜. (a) Nyquist圖；(b) Bode圖

Figure 3. EIS results of SLM-316L SS with different heat treatment in buffer solution: (a) Nyquist diagram; (b) Bode diagram

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圖 4 擬合EIS結果的等效電路圖

Figure 4. Equivalent circuit used for EIS fitting

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圖 5 根據擬合結果計算的電容和鈍化膜厚度

Figure 5. Capacitance and film thickness calculated using the fitting results

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圖 6 不同熱處理時間SLM-316L不銹鋼在硼酸–硼酸鈉緩沖溶液中恒電位極化1 h的lgi–lgt曲線以及鈍化因子k的擬合值.(a)~(e) 保溫時間分別為0、0.5、1.0、3.0和5.0 h；(f) 鈍化因子k

Figure 6. Double logarithmic curves of lgi–lgt during potentiostatic polarization for 1 h of SLM-316L SS with different heat treatment: (a)–(e) 0, 0.5, 1.0, 3.0, and 5.0 h; (f) fitting values of passivation factor k

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圖 7 SLM-316L不銹鋼Mott-Schottky分析結果. (a)未熱處理試樣的Mott-Schottky曲線；(b)平帶電位；(c) 載流子密度；(d) 擴散系數

Figure 7. Analysis of the Mott-Schottky curvefor SLM- 316L SS: (a) Mott-Schottky curve of the as-received SLM-316L SS; (b) flat band potentials; (c) carrier density; (d) diffusion coefficient

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圖 8 不銹鋼鈍化膜相關的理論模型. (a) 點缺陷模型，間隙陽離子（M_i^x+）、氧空位（V_O）、陽離子空位（V_M^x）；(b) 鈍化膜的能帶結構和空間電荷層

Figure 8. Models related to the passive film: (a) PDM; (b) energy band structure and space charge layer

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表 1 AISI316L不銹鋼的化學成分（質量分數）

Table 1. Composition of AISI 316L stainless steel powders %

Cr	Ni	Mo	Mn	Si	C	P	S	Fe
17.5	10.4	2.7	1.2	0.4	0.02	≤0.02	≤0.01	Bal.

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表 2 圖4中EIS數據擬合結果

Table 2. Fitting result of the EIS data in Fig.4

Heat treatment/h	R_S / （Ω·cm²）	Q₁		R_d/（Ω·cm²）	Q₂		R₂/（10⁵ Ω·cm²）
Heat treatment/h	R_S / （Ω·cm²）	Y₀ /（10^–5 Ω^–1·cm^–2·sⁿ）	n₁	R_d/（Ω·cm²）	Y₀ /（10^–5 Ω^–1·cm^–2·sⁿ）	n₂	R₂/（10⁵ Ω·cm²）
0	73.69	8.201	0.807	136.7	2.061	0.803	1.420
0.5	74.89	8.408	0.814	40.84	2.958	0.891	1.237
1.0	71.83	7.138	0.806	34.85	2.926	0.785	1.062
3.0	65.68	8.626	0.812	41.30	3.352	0.872	1.216
5.0	73.35	8.982	0.811	157.5	3.441	0.771	0.665

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表 3 Mott-Schottky曲線的擬合結果

Table 3. Fitting result of Mott-Schottky curves

Heating time/h	ω₁/(10²⁰ cm^?3)	ω₂/(10²⁰ cm^?3)	b/V^?1
0	3.60±0.13	2.95±0.09	?4.63±0.69
0.5	3.39±0.15	2.88±0.13	?4.63±0.85
1.0	3.07±0.15	2.87±0.10	?3.40±0.42
3.0	2.95±0.24	2.71±0.13	?3.84±0.10
5.0	2.32±0.40	1.54±0.33	?2.08±0.98

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