| 摘要: | 本論文旨在研究高熵合金FeCrNiMox (x=0.1, 0.3, 0.6, 1.0)的電化學腐蝕特性；探討Mox含量對此合金在氯鹽中之臨界孔蝕溫度(CPT)的影響。由XRD結果顯示，當-Mo含量≦0.6晶體結構為FCC單一相；當-Mo≧0.6時，則有大量之HCP相析出。本實驗以恆電位儀測量四種合金，在1M硫酸及不同濃度的氯化鈉以及硫酸鈉加氯化鈉的混合溶液的陽極極化曲線，來測定其與溫度相關之腐蝕電位、腐蝕電流、鈍態電流及可能之鈍態電位等電化學參數，並且互相比較。
四種合金會隨著溶液濃度的不同，以及溫度的變化，和三種氧溶量，有顯著的變化。經過實驗的測定，發現Mo含量的提高，並不能使該合金的一般耐腐蝕性增強，在硫酸溶液中，Mo含量較低的耐腐蝕性優於Mo含量較高的合金，而在氯化鈉溶液中，發現Mo含量越高抗孔蝕的能力就越強及臨界孔蝕溫度亦隨之上升。
四種合金經由在不同合金Mo含量及氯鹽濃度的條件下，可以在其陽極極化曲線圖中發現陽極電流大幅上升時的臨界孔蝕電位的形成及相應孔蝕的產生，溶液溫度的升高則進一步將孔蝕電位降低，利用外插法可取得較精確的臨界孔蝕溫度(CPT)。
由實驗結果顯示，合金鉬的增加可提升臨界孔蝕溫度(CPT)，而氯鹽濃度的上升則促使該合金CPT的下降，以海水氯鹽濃度(~0.6M)為例，本合金之(-Mo)CPT已超過80℃，相較316不銹鋼CPT~35℃。
The purpose of this research is to investigate the electrochemical
properties of the FeCrNiMox. The effect of Mo content on this alloy was particularly focused, including the FeCrNiMox (x=0.1, 0.3, 0.6, 1.0). The results show that the microstructure changed from FCC into HCP, as Mo contents increase above 0.6. To further understand the electrochemical properties of the HEAs, the polarization curves of those HEAs were conducted in the solution of varying concentration H2SO4, NaCl, and NaCl+ Na2SO4 mixtures, Electrochemical parameter, such as corrosion potential, corrosion current density and passive current density were all tested and measured through potential dynamic polarizations.
Results indicate that the Mo contents are important in the general corrosion of the FeCrNiMox in the H2SO4 solutions. For instance, -Mo≧
0.6 would cause the precipitation of the HCP phase ammg the FCC phase that probably enhance the galvanic corrosion of FeCrNiMox (x≧0.6). All anodic polarizations show a prominent range of passivity ~1 volt in indicating the potential for oxygen evolution and cover a range of passive current densities (~10-6-10-3 A/cm2) that also increase with the temperature. (30-90℃).
The energy barrier Q, accounting for the metal dissolution was obtained for the FeCrNiMox in various chlorides environment and temperatures; higher chlorides reduce the Q value that facilitates the alloy dissolution; lower Mo contents shows the highest Q value that prohibits the corrosion for taking place. Chloride was found significantly reducing the range of passivity and was discontinued at its breakdown potential which is dependent on the Mo contents of the FeCrNiMox as well as the chloride concentration. Critical pitting temperature(CPT), the most important kinetic factor for the alloy design, was found dependent on the Mo contents and its exposing chloride concentrations. In this study, FeCrNiMox exhibit a cpt of ~85℃, significantly higher than that of 316 stain steel ~35℃ as evaluated in a seawater of ~0.6M NaCl. |
