鐵-30wt.%錳-7wt.%鋁-1.2wt.%碳經離子氮化後其機械性質與在仿人體液中之抗腐蝕性研究

Abstract

在淬火狀態下鐵-30wt.%錳-7wt.%鋁-1.2wt.%碳合金顯微結構為單一沃斯田鐵相，無任何析出物。當淬火合金在520°C離子氮化12小時後，表面生成厚度約100~120 μm 之氮化層，其組成主要為FCC AlN及少部分的FCC Fe4N。氮化層表面AlN之體積百分率為78.7%，表面氮濃度高達17 wt.% (41.9 at.%)，氮化合金表面硬度可達1716Hv。除此之外，緻密細小之κ'-碳化物亦會在離子氮化處理時於沃斯田鐵基地內析出，使得本氮化合金擁有優異的強度(降伏強度：1046MPa)和延性(伸長率：81%)組合。將氮化合金置於仿人體液(Simulted Body Fluid, SBF)中進行動態極化試驗，顯示出有明顯之鈍化區，其腐蝕電流、孔蝕電流、腐蝕電位、孔蝕電位和電位差分別為3.2×10-8A/cm2、 2.8×10-6 A/cm2、 - 124 mV,、+1497 mV和+1621 mV。本氮化合金與常用於人體內之316L不鏽鋼比較，無論是強度、延性和在仿人體液(SBF)中之抗蝕性，本氮化合金皆遠優於經最佳表面處理之316L不鏽鋼。

The as-quenched microstructure of the Fe -30 wt.% Mn -7 wt.% Al -1.21 wt.%C alloy is a single austenite(γ) phase without any precipitates. When the as-quenched alloy is plasma-nitrided at 520°C for 12 hours, resulting in a 100~120 μm-thick nitrided layer. The nitrided layer consists predominantly of FCC AlN, with a small amount of FCC Fe4N. At the surface of the nitrided alloy, the volume fraction of AlN is about 78.7%, and the nitrogen concentration is a high value of 17 wt.% (41.9 at.%). Therefore the nitrided alloy possesses a very high surface hardness 1716 Hv. Besides, a high density of fine κ'-carbide is formed within the γ matrix during plasma-nitriding treatment. Consequently, the nitrided alloy exhibits an excellent combination of strength (YS: 1046MPa) and ductility (El: 81%). The potentiodynamic polarization examination for the plasma-nitrided alloy in Simulated Body Fluid (SBF) solution appears an apparent passivation region. The corrosion current density (Icorr), pitting current density (Ipit), corrosion potential (Ecorr), pitting potential (Epit) and ΔE (Epit - Ecorr) are 3.2×10-8A/cm2, 2.8×10-6 A/cm2, - 124 mV, +1497 mV and +1621 mV, respectively. Compared to the surface-treated 316L stainless steels for implant application, the strength, ductility, and the corrosion resistance in SBF of the nitrided alloy are far superior to those obtained previously in optimally surface-treated 316L stainless steel.