摘要: | 本論文主要在研究FeCoNi基金屬合金之電化學性質,包括FeCoNi、Cr0.5FeCoNi、CrFeCoNi三種金屬合金來做研究,並與熱處理後之合金做比較。結果顯示,這些合金在鑄造狀態及熱處理後均為FCC結構,而含Cr的合金則有HCP結構之析出物,因此會有析出強化效應。另外,本論文以市售硫酸(98%)調配成5M的腐蝕溶液來測試合金的浸泡腐蝕速率;再以恆電流/恆電位儀測量金屬合金在1M硫酸溶液中不同溫度下的極化曲線,來測定其腐蝕電位、腐蝕電流、鈍態區間電位,並與市售304不銹鋼做比較。
六種合金浸於5M的硫酸溶液中進行靜態浸泡腐蝕實驗, FeCoNi經過熱處理後,腐蝕速率較低,而含有Cr的合金經過熱處理後,腐蝕速率卻變得較高,因為產生較多的析出物的關係。
電化學實驗結果顯示,六種金屬合金置於不同溫度下硫酸溶液中,腐蝕電流及腐蝕電位雖沒有明顯變化,但隨著硫酸的溫度的提高,鈍態區電流會向右偏移,而鈍態膜現象也會隨之減少。FeCoNi合金經過熱處理後差異性不大,而Cr0.5FeCoNi、CrFeCoNi合金經過熱處理後變得較不耐腐蝕。而合金在鑄造狀態及熱處理後之腐蝕電位以及腐蝕電流皆優於304不銹鋼 。
This thesis studied the electrochemical properties of the FeCoNi based alloys, such as FeCoNi, Cr0.5FeCoNi, and CrFeCoNi alloys under as-cast and as-annealed (1000˚C-2hr) states. The results indicated that all the matrix of these alloys were FCC structure. We also observed some HCP-structured precipitates in the matrix of the alloys contented Cr element; and these alloys had precipitation strengthening effect after annealed.Furthermore, these alloys were static immersed into 5M H2SO4 solution by measuring their corrosion rates. And,the polarization curves these alloys were tested under four different temperatures of 1 M H2SO4 solution, 30˚C, 40˚C, 50˚C, and 60˚C. After that, this experiment analyzed corrosion potentials, corrosion currents, and the passive range of potentials. All these results werealso compared with the properties of commercial 304 stainless steel.
After static immersed in the 5M H2SO4 solution, the results indicated thatthe as-annealed alloys containing Cr would be corrodedeasily than the as-cast alloys with same compositions. But the as-cast FeCoNi was worse than as-annealed one because of segregation.The corrosion potentials and currents of these alloys did not change significantly in the H2SO4 solution with different temperatures.However, the currents of passive regions would gradually increase while the temperatures increased.In addition, the passive currents and potentials of as-cast and as-annealed alloys all better than that of commercial 304 stainless steel. |