離子氮化之壓力對鐵-9鋁-30錳-1.8碳合金腐蝕與機械性質影響

Abstract

本實驗由大氣熔煉而成的鐵-9鋁-30錳-1.8碳之鐵鋁錳合金，經過均質、熱軋與固溶處理後，分別在1torr、4torr及6torr之離子氮化壓力下進行450℃12小時的表面離子氮化處理，然後進行微結構觀察、機械性質測試與抗腐蝕能力測試。 研究結果顯示，不同離子氮化壓力下的鐵鋁錳合金，其氮化層厚度分別為3~4μm（1torr）、12~13μm（4torr）和7~8μm（6torr），氮化層厚度隨壓力降低而增加，但是當壓力低到一定程度（1torr），則會因為離子蝕刻增強而導致氮化層厚度銳減。在機械性質方面，離子氮化後的鐵鋁錳試片其表面硬度由未氮化前的560Hv提升到1682Hv（4torr），大約增至三倍左右，是因為氮化層主要結構為堅硬的AlN。而在抗腐蝕能力測試中，4torr的試片具有最好的抗腐蝕能力，其腐蝕電位（Ecorr）由原先的-0.715V提升到+0.095V，且離子氮化後試片的極化曲線皆有明顯的鈍化區產生，其中以4torr的試片具有最大的鈍化區（Epit-Ecorr=1.385V），代表離子氮化能有效提升鐵鋁錳合金的抗腐蝕性質，其中氮化層的厚度在合金之抗腐蝕能力中扮演重要角色。

The influence of treated pressure on the characteristic of microstructure, mechanical properties and corrosion resistance by plasma nitriding on Fe-9Al-30Mn-1.8C alloy is investigated. Plasma nitriding treatments were performed at 450℃ for 12h at working pressure in the range of 1-6torr. Morphology and microstructure of untreated and nitride samples were studied by means of microscopy techniques, energy dispersion spectroscopy and X-ray diffraction analysis; microhardness measurements and corrosion resistance tests were also performed. The nitriding treatments produce a hardened surface layer consisting mainly of the AlN. When treatments are performed at 4torr, the modified layer is about 12~13μm. When the nitriding pressure is lower or higher than 4torr, the nitride layer becomes thinner. When treatments are performed at 4torr, the surface hardness increases from 560Hv to 1682Hv, which is about three times that of the untreated alloy. In the corrosion resistance tests, the corrosion potential（Ecorr）increases from -0.715V to +0.095V when the treated pressure is 4torr. With plasma nitriding, the passive region in the polarization curve which is 1.385V at 4torr can be observed. In conclusion, the nitrided layer thickness plays an important role in improving the surface hardness and corrosion resistance.