FeCrMn_(1.3)NiAl_(x)高熵合金显微组织演变及电化学钝化行为

Microstructure Evolution and Electrochemical Passivation Behavior of FeCrMn_(1.3)NiAl_(x)High Entropy Alloys

采用真空电磁悬浮法熔炼了4种不同Al含量的FeCrMn_(1.3)NiAl_(x)(x=0,0.25,0.5,0.75)高熵合金,通过FE-SEM、XRD、SKPFM、EPMA和动电位极化等方法研究了Al含量对铸态FeCrMn_(1.3)NiAl_(x)高熵合金显微组织及其在0.5 mol/L H_(2)SO_(4)溶液中钝化行为的影响规律及机理。结果表明:FeCrMn_(1.3)NiAl_(x)(x=0,0.25)合金试样由fcc(Fe-Mn-Ni)+bcc (Fe-Cr-Mn)结构组成,bcc结构的Fe-Cr-Mn相电化学活性较大而优先溶解,从而表现出两个明显的致钝电位和致钝电流峰;随着Al的添加,当x=0.5时,合金中fcc结构已基本消失,形成了颗粒和条带状的b2相(Al-Ni-Mn)均匀分布在具有bcc结构的Fe-Cr-Mn相上,因二者微区相电化学活性相差不大,仅呈现出一个融合的致钝电位和致钝电流峰,同时合金中新形成的硬质ρ相因具有较高的电化学活性,而呈现出低的致钝电位和较小的致钝电流密度;当x=0.75时,ρ相消失,对应的低致钝电位峰也随之消失。Al添加通过改变FeCrMn_(1.3)NiAl_(x)高熵合金中微区相组成、显微组织和电化学活性,从而影响其在0.5 mol/L H_(2)SO_(4)溶液中的电化学钝化行为,随着Al含量增加,合金致钝电流密度增加,产生的b2相钝化性能较差,使得合金的钝化性能降低。

Four high entropy alloys of FeCrMn_(1.3)NiAl_(x)(x= 0, 0.25, 0.5, 0.75) with different Al content were smelted by vacuum magnetic suspension method. The effect of Al content on the microstructure and passivation behavior of the as-cast alloys FeCrMn_(1.3)NiAl_(x)in 0.5 mol/L H_(2)SO_(4) solution was investigated by means of XRD, FE-SEM, SKPFM, EPMA and potentiodynamic polarization technique. The results show that the FeCrMn_(1.3)NiAl_(x)(x=0, 0.25) alloy presents a two-phase microstructure of fcc(Fe-Mn-Ni)+bcc(Fe-Cr-Mn). The Fe-Cr-Mn phase of bcc structure has higher electrochemical activity, and therewith is preferred to dissolve, which results in two obvious passivation-potential and-current peaks. As the Al addition reaches x=0.5, the fcc phase almost entirely disappeared in the alloy, therefore the alloy composed of the bcc Fe-Cr-Mn phase with uniformly distributed particles and strips of b2 phase(Al-Ni-Mn). Due to the difference in electrochemical activity of the above two phases is not much, so that, the alloy present only one passivation potential and passivation current peak. Meanwhile the new hard ρ-phase of higher electrochemical activity emerges in the alloy, which resulted in lower passivation potential and smaller passivation current density. The ρ-phase disappears for the alloy with x=0.75 Al, correspondingly, the low passivation potential peak also disappears. The addition of Al can affect the passivation behavior of FeCrMn_(1.3)NiAl_(x)high entropy alloys in 0.5 mol/L H_(2)SO_(4) solution by changing the microstructure, composition and distribution of phases in local-areas, so as the electrochemical activity of FeCrMn_(1.3)NiAl_(x)high entropy alloys. With the increase of Al, the passivation current density of the alloy increases due to the poor passivation performance of b2 phase, which in turn reduces the passivation performance of the alloys.