Microstructure and corrosion behavior of Ti-6Al-4V alloy using selective laser melting
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摘要:
为了揭示选区激光熔化(selective laser melting,SLM)在钛合金水下装备触水部件上的应用可行性,文中对SLM制备的Ti64合金在模拟海水环境下的耐腐蚀性能进行了研究. 结果表明,SLM制备Ti64合金主要以针状α'马氏体组织为主,β相的含量约为0.3%. 对比电化学测试发现,在质量分数为3.5%的NaCl溶液中,SLM制备Ti64合金的开路电位Eocp为−119.3 mV,远低于与锻造Ti64合金的234.12 mV. 采用外推法分析动电位极化曲线,SLM制备Ti64合金的腐蚀电位Ecorr为−237.3 mV,同样低于锻造Ti64合金的118.4 mV;采用等效电路对阻抗谱进行拟合分析,SLM制备Ti64合金钝化膜电阻 Rf 和电荷转移电阻Rct 分别为184.1 kΩ·cm2和2.76 × 105 MΩ·cm2,均低于锻造Ti64合金,钝化膜电阻 Rf 和电荷转移电阻Rct 分别为231 kΩ·cm2和4.26 × 105 MΩ·cm2. 通过对不同应变速率下的慢应变应力腐蚀结果进行分析,在应变速率为1 × 10−5 s−1,5 × 10−5 s−1和1 × 10−6 s−1下,SLM 制备Ti64合金的应力腐蚀敏感性分别为20.2%,17.2%和14.4%,均高于同等条件锻造Ti64合金的−1.4%,12.9%和10.8%.
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关键词:
- 激光选区熔化 /
- Ti-6AI-4V合金 /
- 微观组织 /
- 耐腐蚀性能
Abstract:To reveal the feasibility of applying selective laser melting (SLM) to titanium alloy-made underwater equipment components, the corrosion resistance of SLM-prepared Ti64 alloy in a simulated seawater environment was explored. The research finds that the SLM-prepared Ti64 alloy primarily consists of needle-like α' martensite, with a β-phase content of approximately 0.3%. Comparison through electrochemical tests reveals that in a NaCl solution with a mass fraction of 3.5%, the open-circuit potential of SLM-prepared Ti64 is −119.3 mV, significantly lower than that of wrought Ti64 (234.12 mV). The analysis of the potentiodynamic polarization curves using the extrapolation method shows that the corrosion potential (Ecorr) of the SLM-prepared Ti64 is −237.3 mV, also lower than that of wrought Ti64 (118.4 mV). By fitting the impedance spectra with an equivalent circuit model, the passive film resistance (Rf) and charge transfer resistance (Rct) of the SLM-prepared Ti64 alloy are 192.4 kΩ·cm2 and 2.69 MΩ·cm2, respectively, both lower than those of wrought Ti64 (235 kΩ·cm2 and 4.34 MΩ·cm2). The slow stress and strain corrosion results at different strain rates are analyzed. At strain rates of 10−5 s−1, 5 × 10–6 s−1, and 10–6 s−1, the stress corrosion susceptibility of the SLM-prepared Ti64 alloy is 20.2%, 17.2%, and 14.4%, respectively, all higher than that of wrought Ti64 under the same conditions (−1.4%, 12.9%, and 10.8%).
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图 2 SLM Ti64合金和锻造Ti64合金的EBSD
Figure 2. EBSD of SLM Ti64 alloy and wroughted Ti64 alloy. (a) orientation map of SLM Ti64 alloy; (b) phase map of SLM Ti64 alloy; (c) pole figure of SLM Ti64 alloy; (d) orientation map of wroughted Ti64 alloy; (e) phase map of wroughted Ti64 alloy; (f) pole figure of wroughted Ti64 alloy
表 1 SLM工艺参数
Table 1 SLM parameters
光斑直径
d/μm激光功率
P/W扫描速度
v/(mm·s−1)层厚
δ/mm扫描间距
h/mm150 190 1200 0.03 0.03 表 2 应力腐蚀试验参数
Table 2 Parameters of stress corrosion test
试样 成形工艺 腐蚀介质 应变速率
η/(10−5 s−1)1 SLM 空气 1.0 2 SLM NaCl溶液 1.0 3 SLM 空气 5.0 4 SLM NaCl溶液 5.0 5 SLM 空气 0.1 6 SLM NaCl溶液 0.1 7 锻造 空气 1.0 8 锻造 NaCl溶液 1.0 9 锻造 空气 5.0 10 锻造 NaCl溶液 5.0 11 锻造 空气 0.1 12 锻造 NaCl溶液 0.1 表 3 交流阻抗谱拟合结果
Table 3 Fitted results of electrochemical impedance spectroscopy
成形工艺 溶液电阻
Rs /(Ω·cm2)膜抗电阻
Rf /(kΩ·cm2)电荷转移电阻
Rct /(105MΩ·cm2)锻造 2.39 231.0 4.26 SLM 2.38 184.1 2.76 表 4 慢应变应力腐蚀性能
Table 4 slow strain rate stress corrosion properties
试样 抗拉强度 Rm /MPa 断裂时间 t/h 断后伸长率 A(%) 应力腐蚀敏感性指数 Issc(%) 1 1124.1 3.27 11.78 20.2 2 1083.2 2.72 9.80 20.2 3 1104.7 6.52 11.72 17.2 4 1102.4 6.15 11.07 17.2 5 1095.6 32.70 11.76 14.4 6 1086.3 28.60 10.28 14.4 7 978.8 4.41 15.86 − 1.4 8 915.2 4.47 16.08 − 1.4 9 963.6 7.36 13.24 12.9 10 934.8 6.52 11.72 12.9 11 970.5 41.10 14.78 10.8 12 919.8 37.10 13.34 10.8 -
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