Al0.5CoCrFeMo0.5Ni高熵合金與商用316不銹鋼腐蝕行為之比較

Comparative Studies of the Corrosion Behavior of the Al0.5CoCrFeMo0.5Ni High Entropy Alloy and Type 316 Stainless Steel

高熵合金首先打破傳統合金以單一元素為主要成份的觀念，藉由5種以上的主要元素相混合，各種元素之原子含量均大於5atom%，小於35atom%。其具有許多優秀的性質，如（1）易產生非晶質相與奈米級的析出、（2）高硬度與耐磨耗性、（3）良好的熱穩定性、（4）優良的耐腐蝕性。由極化掃瞄分析可以明確得知：不論在0.5M硫酸或是1M氯化鈉水溶液中，Al0.5CoCrFeMo0.5Ni皆比316不銹鋼具有較鈍態的腐蝕電位（Ecorr）與較低的腐蝕電流密度（icorr）。而由循環極化掃瞄可以發現：在含有不同濃度氯化鈉之硫酸水溶液中，當氯化鈉含量為0.1M時即呈現明顯的正遲滯現象，表示高熵合金表面已有孔蝕現象的產生，且鈍化膜不易修復；而在氯化鈉含量為0.25M時高熵合金的崩潰電位（Eb）快速下降，且電流密度急遽增加，可以瞭解Al0.5CoCrFeMo0.5Ni高熵合金對氯鹽較為敏感。

High entropy alloy is a multi-component alloy containing several major alloying elements. Each element in the alloy system is between 5 and 35 atom %. It was found that high entropy alloys possess simple solid-solution structures, ease of amorphization and nanoprecipitation in the alloy, and promising properties such as high hardness, superior resistance to temper softening, wear and corrosion. The potentiodynamic polarization curves determined that the Al0.5CoCrFeMo0.5Ni alloy is more resistant to general corrosion than 316 stainless steel (higher Ecorr, lower icorr), both in 0.5 M H2SO4 and in 1 M NaCl solutions at room temperature. The positive hysteresis of the Al0.5CoCrFeMo0.5Ni alloy in the cyclic polarization curve demonstrates that pitting can be induced in a Cl--containing (0.1 M NaCl) H2SO4 solution. However, the breakdown potential (Eb) decreases significantly and the acute increase in current density at Eb, when the chloride is higher than 0.25 M. It may conclude that resistance of the Al0.5CoCrFeMo0.5 alloy to pitting corrosion in a Cl- environment is inferior to that of the 316 stainless steel.